LM12458CIVX/NOPB_技术文档

LM12454, LM12458, LM12H458

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SNAS079A –MAY 2004–REVISED FEBRUARY 2006

LM12454/LM12458/LM12H458 12-Bit + Sign Data Acquisition System with Self-Calibration

Check for Samples: LM12454, LM12458, LM12H458

1

FEATURES

DESCRIPTION

23

•

Three operating modes: 12-bit + sign, 8-bit +

sign, and “watchdog”

The LM12458, and LM12H458 are highly integrated

Data Acquisition Systems. Operating on just 5V, they

combine a fully-differential self-calibrating (correcting

linearity and zero errors) 13-bit (12-bit + sign) analog-

to-digital converter (ADC) and sample-and-hold (S/H)

with extensive analog functions and digital

functionality. Up to 32 consecutive conversions, using

two's complement format, can be stored in an internal

32-word (16-bit wide) FIFO data buffer. An internal 8-

word RAM can store the conversion sequence for up

to eight acquisitions through the LM12(H)458's eight-

input multiplexer. The obsolete LM12454 has a four-

channel multiplexer, a differential multiplexer output,

and a differential S/H input. The LM12(H)458 can

also operate with 8-bit + sign resolution and in a

supervisory “watchdog” mode that compares an input

signal against two programmable limits.

•

Single-ended or differential inputs

Built-in Sample-and-Hold and 2.5V bandgap

reference

•

Instruction RAM and event sequencer

8-channel multiplexer

32-word conversion FIFO

Programmable acquisition times and

conversion rates

•

Self-calibration and diagnostic mode

8- or 16-bit wide data bus microprocessor or

DSP interface

APPLICATIONS

Programmable acquisition times and conversion rates

are possible through the use of internal clock-driven

timers. The reference voltage input can be externally

generated for absolute or ratiometric operation or can

be derived using the internal 2.5V bandgap

reference.

•

Data Logging

Instrumentation

Process Control

Energy Management

Inertial Guidance

All registers, RAM, and FIFO are directly addressable

through the high speed microprocessor interface to

either an 8-bit or 16-bit data bus. The LM12(H)458

includes a direct memory access (DMA) interface for

high-speed conversion data transfer.

KEY SPECIFICATIONS

•

Resolution: 12-bit + sign or 8-bit + sign

13-bit conversion time: 8.8 μs, 5.5 μs (H) (max)

9-bit conversion time: 4.2 μs, 2.6 μs (H) (max)

13-bit Through-put rate:

Additional applications information can be found in

applications notes AN-906, AN-947 and AN-949.

–

88k samples/s (min)

140k samples/s (H) (min)

•

Comparison time: 2.2 μs (max)

("watchdog” mode): 1.4 μs (H) (max)

–

•

ILE: ±1 LSB (max)

V_INrange: GND to VA ⁺

Power dissipation: 30 mW, 34 mW (H) (max)

Stand-by mode: 50 μW (typ)

Single supply: 3V to 5.5V

1

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2

3

TRI-STATE is a registered trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

LM12454, LM12458, LM12H458

SNAS079A –MAY 2004–REVISED FEBRUARY 2006

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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

CONNECTION DIAGRAM

* Pin names in ( ) apply to the obsolete LM12454 and LM12H454.

Figure 1. See Package Number FN0044A

Figure 2. See Package Number PGB0044A

FUNCTIONAL DIAGRAM

LM12454

The LM12(H)454 is obsolete

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LM12(H)458

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(1) (2)

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (V_A+ and V_D+)

6.0V

−0.3V to (V⁺+ 0.3V)

− 5V to (V⁺+ 5V)

300 mV

Voltage at Input and Output Pins, except analog inputs

Voltage at Analog Inputs

|V_A+ − V_D+|

(3)

Input Current at Any Pin

±5 mA

(3)

Package Input Current

±20 mA

Power Dissipation, PQFP

(4)

(T_A= 25°C)

875 mW

Storage Temperature

Lead Temperature

−65°C to +150°C

PQFP, Infrared, 15 sec.

PLCC, Solder, 10 sec.

+300°C

+250°C

1.5 kV

(5)

ESD Susceptibility

(1) All voltages are measured with respect to GND, unless otherwise specified.

(2) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for

which the device is functional, but does not specify performance limits. For specifications and test conditions, see the Electrical

Characteristics. The specifications apply only for the test conditions listed. Some performance characteristics may degrade when the

device is not operated under the listed test conditions.

(3) When the input voltage (V_IN) at any pin exceeds the power supply rails (V_IN< GND or V_IN> (V_A+ or V_D+)), the current at that pin should

be limited to 5 mA. The 20 mA maximum package input current rating allows the voltage at any four pins, with an input current of 5 mA,

to simultaneously exceed the power supply voltages.

(4) The maximum power dissipation must be derated at elevated temperatures and is dictated by T_Jmax(maximum junction temperature),

θ_JA(package junction to ambient thermal resistance), and T_A(ambient temperature).

(5) Human body model, 100 pF discharged through a 1.5 kΩ resistor.

OPERATING RATINGS^{(1) (2)}

Temperature Range

(T_min≤ T_A≤ T_max

)

−40°C ≤ T_A≤ 85°C

Supply Voltage

V_A+, V_D+

3.0V to 5.5V

≤100 mV

|V_A+ − V_D+|

V_IN+Input Range

V_IN−Input Range

GND ≤ V_IN+≤ V_A+

GND ≤ V_IN−≤ V_A+

1V ≤ V_REF+≤ V_A+

0V ≤ V_REF−≤ V_REF+− 1V

1V ≤ V_REF≤ V_A+

V_REF+Input Voltage

V_REF−Input Voltage

V_REF+− V_REF−

(3)

+

V_REFCommon Mode Range

T_J(MAX)

0.1 V_A⁺≤ V_REFCM≤ 0.6 V_A

150°C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for

which the device is functional, but does not specify performance limits. For specifications and test conditions, see the Electrical

Characteristics. The specifications apply only for the test conditions listed. Some performance characteristics may degrade when the

device is not operated under the listed test conditions.

(2) All voltages are measured with respect to GND, unless otherwise specified.

(3) V_REFCM(Reference Voltage Common Mode Range) is defined as (V_REF++ V_REF−)/2.

4

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(1) (2) (3) (4)

CONVERTER CHARACTERISTICS

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V, V_REF+= 5V, V_REF−= 0V, 12-

bit + sign conversion mode, f_CLK= 8.0 MHz (LM12H458) or f_CLK= 5.0 MHz (LM12454/8), R_S= 25Ω, source impedance for

V_REF+and V_REF−≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless

otherwise specified. Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= 25°C.

(5)

(6)

Symbol

Parameter

Conditions

After Auto-Cal

Typical

±1/2

Limits

Units

LSB (max)

LSB

(7) (8)

ILE

Integral Linearity Error

±1

TUE

Total Unadjusted Error⁽⁷⁾

After Auto-Cal

LM12H458

±1

(7)

Resolution with No Missing Codes

Differential Non-Linearity

13

±¾

±1

Bits (max)

LSB (max)

DNL

(9) (8)

Zero Error

±1/2

±2

±1.5

±2

LSB (max)

(7) (8)

Positive Full-Scale Error

After Auto-Cal

(7) (8)

Negative Full-Scale Error

±2

(10)

DC Common Mode Error

±3.5

8-Bit + Sign and “Watchdog” Mode

Integral Linearity Error

ILE

±1/2

±3/4

9

LSB (max)

Bits (max)

LSB (max)

(7)

8-Bit + Sign and “Watchdog” Mode Total

Unadjusted Error

TUE

After Auto-Zero

±1/2

8-Bit + Sign and “Watchdog” Mode Resolution

with No Missing Codes

8-Bit + Sign and “Watchdog” Mode

Differential Non-Linearity

DNL

±3/4

8-Bit + Sign and “Watchdog” Mode Zero Error

8-Bit + Sign and “Watchdog” Full-Scale Error

±1/2

LSB (max)

8-Bit + Sign and “Watchdog” Mode

DC Common Mode Error

±1/8

LSB

Multiplexer Channel-to-Channel Matching

±0.05

GND

V_A+

V (min)

V (max)

V_IN+

V_IN−

Non-Inverting Input Range

GND

V_A+

V (min)

V (max)

Inverting Input Range

+

−V_A

V (min)

V (max)

V_IN+− V_IN−

Differential Input Voltage Range

V_A+

V (min)

V (max)

GND

V_A+

Common Mode Input Voltage Range

(1) Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above

V_A+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these

diodes are forward biased by more than 100 mV. As an example, if V_A+ is 4.5 V_DC, full-scale input voltage must be ≤4.6 V_DCto ensure

accurate conversions. See Figure 3

(2) V_A+ and V_D+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V⁺pin to

assure conversion/comparison accuracy.

(3) Accuracy is ensured when operating at f_CLK= 5 MHz for the LM12454/8 and f_CLK= 8 MHz for the LM12H458.

(4) With the test condition for V_REF(V_REF+− V_REF−) given as +5V, the 12-bit LSB is 1.22 mV and the 8-bit/“Watchdog” LSB is 19.53 mV.

(5) Typical figures are at T_A= 25°C and represent most likely parametric norm.

(6) Limits are to AOQL (Average Output Quality Level).

(7) Positive integral linearity error is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes

through positive full-scale and zero. For negative integral linearity error the straight line passes through negative full-scale and zero.

(See Figure 5 Figure 6).

(8) The LM12(H)454/8's self-calibration technique ensures linearity and offset errors as specified, but noise inherent in the self-calibration

process will result in a repeatability uncertainty of ±0.10 LSB.

(9) Zero error is a measure of the deviation from the mid-scale voltage (a code of zero), expressed in LSB. It is the worst-case value of the

code transitions between −1 to 0 and 0 to +1 (see Figure 7).

(10) The DC common-mode error is measured with both inputs shorted together and driven from 0V to 5V. The measured value is referred to

the resulting output value when the inputs are driven with a 2.5V signal.

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CONVERTER CHARACTERISTICS ^{(1) (2) (3) (4)}(continued)

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V, V_REF+= 5V, V_REF−= 0V, 12-

bit + sign conversion mode, f_CLK= 8.0 MHz (LM12H458) or f_CLK= 5.0 MHz (LM12454/8), R_S= 25Ω, source impedance for

V_REF+and V_REF−≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless

otherwise specified. Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= 25°C.

(5)

(6)

Symbol

Parameter

Zero Error

Conditions

Typical

Limits

±1.75

Units

V_A+ = V_D+ = 5V ±10%

±0.2

LSB (max)

Power Supply Sensitivity

V_REF+= 4.5V, V_REF−

GND

=

PSS

Full-Scale Error

Linearity Error

±0.4

±2

LSB (max)

(11)

±0.2

85

LSB

pF

C_REF

C_IN

V_REF+/V_REF−Input Capacitance

Selected Multiplexer Channel Input Capacitance

75

pF

(11) Power Supply Sensitivity is measured after Auto-Zero and/or Auto-Calibration cycle has been completed with V_A+ and V_D+ at the

specified extremes.

6

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(1) (2) (3) (4)

CONVERTER AC CHARACTERISTICS

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V, V_REF+= 5V, V_REF−= 0V, 12-

bit + sign conversion mode, f_CLK= 8.0 MHz (LM12H458) or f_CLK= 5.0 MHz (LM12454/8), R_S= 25Ω, source impedance for

V_REF+and V_REF−≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless

otherwise specified. Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= 25°C.

(5)

(6)

Symbol

Parameter

Conditions

Typical

Limits

Units

%

Clock Duty Cycle

50

40

60

% (min)

% (max)

13-Bit Resolution, Sequencer State

S5 (Figure 45)

44 (t_CLK

21 (t_CLK

)

44 (t_CLK) + 50 ns

21 (t_CLK) + 50 ns

9 (t_CLK) + 50 ns

(max)

t_C

Conversion Time

Acquisition Time

9-Bit Resolution, Sequencer State S5

(Figure 45)

Sequencer State S7 (Figure 45) Built-

in minimum for 13-Bits

9 (t_CLK

2 (t_CLK

)

t_A

Built-in minimum for 9-Bits and

“Watchdog” mode

)

2 (t_CLK) + 50 ns

76 (t_CLK) + 50 ns

(max)

t_Z

Auto-Zero Time

Sequencer State S2 (Figure 45)

76 (t_CLK)

t_CAL

4944 (t_CLK) + 50

ns

Full Calibration Time

Sequencer State S2 (Figure 45)

4944 (t_CLK)

89

88

kHz (min)

(7)

Throughput Rate

LM12H458

142

140

“Watchdog” Mode Comparison Time

Sequencer States S6, S4, and S5

(Figure 45)

t_WD

11 (t_CLK

)

11 (t_CLK) + 50 ns

(max)

V_IN= ±5V

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

V_IN= 5 V_p-p

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

V_IN= ±5V

77.5

75.2

74.7

dB

DSNR

Differential Signal-to-Noise Ratio

69.8

69.2

66.6

dB

SESNR

Single-Ended Signal-to-Noise Ratio

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

V_IN= 5 V_p-p

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

76.9

73.9

70.7

dB

Differential Signal-to-Noise +

Distortion Ratio

DSINAD

SESINAD

69.4

68.3

65.7

dB

Single-Ended Signal-to-Noise +

Distortion Ratio

(1) Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above

V_A+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these

diodes are forward biased by more than 100 mV. As an example, if V_A+ is 4.5 V_DC, full-scale input voltage must be ≤4.6 V_DCto ensure

accurate conversions. See Figure 3

(2) V_A+ and V_D+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V⁺pin to

assure conversion/comparison accuracy.

(3) Accuracy is ensured when operating at f_CLK= 5 MHz for the LM12454/8 and f_CLK= 8 MHz for the LM12H458.

(4) With the test condition for V_REF(V_REF+− V_REF−) given as +5V, the 12-bit LSB is 1.22 mV and the 8-bit/“Watchdog” LSB is 19.53 mV.

(5) Typical figures are at T_A= 25°C and represent most likely parametric norm.

(6) Limits are to AOQL (Average Output Quality Level).

(7) The Throughput Rate is for a single instruction repeated continuously. Sequencer states 0 (1 clock cycle), 1 (1 clock cycle), 7 (9 clock

cycles) and 5 (44 clock cycles) are used (see Figure 45). One additional clock cycle is used to read the conversion result stored in the

FIFO, for a total of 56 clock cycles per conversion. The Throughput Rate is f_CLK(MHz)/N, where N is the number of clock

cycles/conversion.

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CONVERTER AC CHARACTERISTICS ^{(1) (2) (3) (4)}(continued)

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V, V_REF+= 5V, V_REF−= 0V, 12-

bit + sign conversion mode, f_CLK= 8.0 MHz (LM12H458) or f_CLK= 5.0 MHz (LM12454/8), R_S= 25Ω, source impedance for

V_REF+and V_REF−≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless

otherwise specified. Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= 25°C.

(5)

(6)

Symbol

Parameter

Conditions

Typical

Limits

Units

V_IN= ±5V

f_IN= 1 kHz

−85.8

−79.9

−72.9

dB

DTHD

Differential Total Harmonic Distortion

f_IN= 20 kHz

f_IN= 40 kHz

V_IN= 5 V_p-p

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

V_IN= ±5V

−80.3

−75.6

−72.8

dB

Single-Ended Total Harmonic

Distortion

SETHD

DENOB

SEENOB

DSFDR

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

V_IN= 5 V_p-p

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

V_IN= ±5V

12.6

12.2

12.1

Bits

Differential Effective Number of Bits

Single-Ended Effective Number of Bits

11.3

11.2

10.8

Bits

f_IN= 1 kHz

f_IN= 20 kHz

f_IN= 40 kHz

87.2

78.9

72.8

dB

Differential Spurious Free Dynamic

Range

V_IN= 5 V_P-P, f_IN= 40 kHz,

LM12454 MUXOUT Only

−76

−78

dB

Multiplexer Channel-to-Channel

Crosstalk

V_IN= 5 V_P-P, f_IN= 40 kHz,

LM12(H)458 MUX plus Converter

t_PU

Power-Up Time

Wake-Up Time

10

ms

t_WU

8

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(1) (2) (3)

DC CHARACTERISTICS

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V, V_REF+= 5V, V_REF−= 0V,

f_CLK= 8.0 MHz (LM12H454/8) or f_CLK= 5.0 MHz (LM12458), and minimum acquisition time unless otherwise specified.

Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= 25°C.

(4)

(5)

Symbol

Parameter

Conditions

Typical

Limits

Units

CS = “1”

LM12454/8

LM12H458

I_D+

V_D+ Supply Current

0.55

1.0

1.2

mA (max)

CS = “1”

I_A+

I_ST

V_A+ Supply Current

LM12454/8

LM12H458

3.1

5.0

5.5

mA (max)

Stand-By Supply Current (I_D+) + (I_A+)

[Power-Down Mode Selected]

Clock Stopped

8 MHz Clock

10

40

μA (max)

V_A+ = 5.5V

ON-Channel = 5.5V,

OFF-Channel = 0V

0.1

0.3

μA (max)

Multiplexer ON-Channel Leakage

Current

ON-Channel = 0V

OFF-Channel = 5.5V

V_A+ = 5.5V

ON-Channel = 5.5V

OFF-Channel = 0V

0.3

Multiplexer OFF-Channel Leakage

Current

ON-Channel = 0V

OFF-Channel = 5.5V

LM12454

V_IN= 5V

V_IN= 2.5V

V_IN= 0V

LM12454

V_IN= 5V

V_IN= 2.5V

V_IN= 0V

800

850

760

1500

Ω(max)

R_ON

Multiplexer ON-Resistance

±1.0%

±3.0%

(max)

Multiplexer Channel-to-Channel

R_ONmatching

(1) Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above

V_A+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these

diodes are forward biased by more than 100 mV. As an example, if V_A+ is 4.5 V_DC, full-scale input voltage must be ≤4.6 V_DCto ensure

accurate conversions. See Figure 3

(2) V_A+ and V_D+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V⁺pin to

assure conversion/comparison accuracy.

(3) Accuracy is ensured when operating at f_CLK= 5 MHz for the LM12454/8 and f_CLK= 8 MHz for the LM12H458.

(4) Typical figures are at T_A= 25°C and represent most likely parametric norm.

(5) Limits are to AOQL (Average Output Quality Level).

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(1) (2)

INTERNAL REFERENCE CHARACTERISTICS

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V unless otherwise specified.

Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= 25°C.

Typical

Limits

Symbol

V_REFOUT

Parameter

Conditions

Units

V (max)

ppm/°C

(3)

(4)

Internal Reference Output Voltage

2.5

40

2.5 ±4%

Internal Reference Temperature

Coefficient

ΔV_REF/ΔT

Sourcing (0 < I_L≤ +4 mA)

Sinking (−1 ≤ I_IL< 0 mA)

4.5V ≤ V_A+ ≤ 5.5V

0.2

1.2

20

%/mA (max)

mV (max)

mA (max)

ppm/kHr

Δ_REF/ΔI_L

Internal Reference Load Regulation

Line Regulation

ΔV_REF

I_SC

3

Internal Reference Short Circuit Current V_REFOUT= 0V

Long Term Stability

13

25

ΔV_REF/Δt

200

V_A+ = V_D+ = 0V →

5V, C_L= 100 μF

t_SU

Internal Reference Start-Up Time

10

ms

(1) Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above

V_A+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these

diodes are forward biased by more than 100 mV. As an example, if V_A+ is 4.5 V_DC, full-scale input voltage must be ≤4.6 V_DCto ensure

accurate conversions. See Figure 3

(2) V_A+ and V_D+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V⁺pin to

assure conversion/comparison accuracy.

(3) Typical figures are at T_A= 25°C and represent most likely parametric norm.

(4) Limits are to AOQL (Average Output Quality Level).

DIGITAL CHARACTERISTICS^{(1) (2)}

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V, unless otherwise specified.

Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= 25°C.

Typical

Limits

Symbol

Parameter

Conditions

Units

(3)

(4)

V_IN(1)

Logical “1” Input Voltage

Logical “0” Input Voltage

Logical “1” Input Current

Logical “0” Input Current

D0–D15 Input Capacitance

V_A+ = V_D+ = 5.5V

2.0

0.8

V (min)

V (max)

μA (max)

pF

V_IN(0)

I_IN(1)

I_IN(0)

C_IN

V_A+ = V_D+ = 4.5V

V_IN= 5V

0.005

−0.005

6

1.0

V_IN= 0V

−1.0

V_A+ = V_D+ = 4.5V

I_OUT= −360 μA

I_OUT= −10 μA

V_OUT(1)

Logical “1” Output Voltage

2.4

V (min)

4.25

V_A+ = V_D+ = 4.5V

I_OUT= 1.6 mA

V_OUT(0)

I_OUT

Logical “0” Output Voltage

0.4

V (max)

V_OUT= 0V

V_OUT= 5V

−0.01

−3.0

μA (max)

TRI-STATE^®Output Leakage Current

0.01

3.0

(1) Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above

V_A+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these

diodes are forward biased by more than 100 mV. As an example, if V_A+ is 4.5 V_DC, full-scale input voltage must be ≤4.6 V_DCto ensure

accurate conversions. See Figure 3

(2) V_A+ and V_D+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V⁺pin to

assure conversion/comparison accuracy.

(3) Typical figures are at T_A= 25°C and represent most likely parametric norm.

(4) Limits are to AOQL (Average Output Quality Level).

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(1) (2) (3)

DIGITAL TIMING CHARACTERISTICS

The following specifications apply to the LM12454, LM12458, and LM12H458 for V_A+ = V_D+ = 5V, t_r= t_f= 3 ns, and C_L= 100

pF on data I/O, INT and DMARQ lines unless otherwise specified. Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other

limits T_A= T_J= 25°C.

Symbol (See

Figure 7

Figure 40

Figure 42)

(4)

(5)

Parameter

Conditions

Typical

Limits

Units

1, 3

2, 4

5

CS or Address Valid to ALE Low Set-Up Time

CS or Address Valid to ALE Low Hold Time

ALE Pulse Width

40

20

45

35

20

100

20

60

75

140

40

30

10

70

10

110

10

80

20

10

60

10

60

ns (min)

ns (max)

ns (min)

ns (max)

ns (min)

ns (max)

ns (min)

ns (max)

ns (min)

ns (max)

6

RD High to Next ALE High

ALE Low to RD Low

7

8

RD Pulse Width

9

RD High to Next RD or WR Low

ALE Low to WR Low

10

11

12

13

14

15

WR Pulse Width

WR High to Next ALE High

WR High to Next RD or WR Low

Data Valid to WR High Set-Up Time

Data Valid to WR High Hold Time

16

17

18

RD Low to Data Bus Out of TRI-STATE

RD High to TRI-STATE

40

30

R_L= 1 kΩ

RD Low to Data Valid (Access Time)

20

21

19

Address Valid or CS Low to RD Low

Address Valid or CS Low to WR Low

Address Invalid from RD or WR High

22

23

INT High from RD Low

30

DMARQ Low from RD Low

(1) Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above

V_A+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these

diodes are forward biased by more than 100 mV. As an example, if V_A+ is 4.5 V_DC, full-scale input voltage must be ≤4.6 V_DCto ensure

accurate conversions. See Figure 3

(2) V_A+ and V_D+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V⁺pin to

assure conversion/comparison accuracy.

(3) Accuracy is ensured when operating at f_CLK= 5 MHz for the LM12454/8 and f_CLK= 8 MHz for the LM12H458.

(4) Typical figures are at T_A= 25°C and represent most likely parametric norm.

(5) Limits are to AOQL (Average Output Quality Level).

Figure 3.

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V_REF= V_REF+− V_REF−

V_IN= V_IN+− V_IN−

GND ≤ V_IN+≤V_A+

GND ≤ V_IN−≤V_A+

V_REF+− V_REF−= 4.096V

V_IN= V_IN+− V_IN−

GND ≤ V_IN+≤V_A+

GND ≤ V_IN−≤V_A+

V_REF= V_REF+− V_REF−

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V_REF= V_REF+− V_REF−

V_A+ = 5V

Figure 4. Transfer Characteristic

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Figure 5. Simplified Error Curve vs. Output Code without Auto-Calibration or Auto-Zero Cycles

Figure 6. Simplified Error Curve vs. Output Code after Auto-Calibration Cycle

Figure 7. Offset or Zero Error Voltage

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TYPICAL PERFORMANCE CHARACTERISTICS

⁽¹⁾The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. The performance for 8-

bit + sign and “watchdog” modes is equal to or better than shown.

Linearity Error Change

vs. Clock Frequency

Linearity Error Change

vs. Temperature

Figure 8.

Figure 9.

Linearity Error Change

vs. Reference Voltage

Linearity Error Change

vs. Supply Voltage

Figure 10.

Figure 11.

Full-Scale Error Change

vs. Clock Frequency

Full-Scale Error Change

vs. Temperature

Figure 12.

Figure 13.

(1) With the test condition for V_REF(V_REF+− V_REF−) given as +5V, the 12-bit LSB is 1.22 mV and the 8-bit/“Watchdog” LSB is 19.53 mV.

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

⁽¹⁾The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. The performance for 8-

bit + sign and “watchdog” modes is equal to or better than shown.

Full-Scale Error Change

vs. Reference Voltage

Full-Scale Error

vs. Supply Voltage

Figure 14.

Figure 15.

Zero Error Change

vs. Clock Frequency

Zero Error Change

vs. Temperature

Figure 16.

Figure 17.

Zero Error Change

vs. Reference Voltage

Zero Error Change

vs. Supply Voltage

Figure 18.

Figure 19.

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

⁽¹⁾The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. The performance for 8-

bit + sign and “watchdog” modes is equal to or better than shown.

Analog Supply Current

Digital Supply Current

vs. Clock Frequency

vs. Temperature

Figure 20.

Figure 21.

Digital Supply Current

vs. Temperature

V_REFOUTLoad Regulation

Figure 22.

Figure 23.

V_REFOUTLine Regulation

Figure 24.

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TYPICAL DYNAMIC PERFORMANCE CHARACTERISTICS

The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified.

Bipolar Signal-to-Noise

Bipolar Signal-to-Noise Ratio

vs. Input Frequency

+ Distortion Ratio

vs. Input Frequency

Figure 25.

Figure 26.

Bipolar Signal-to-Noise

+ Distortion Ratio

vs. Input Signal Level

Bipolar Spectral Response

with 1.028 kHz Sine Wave Input

Figure 27.

Figure 28.

Bipolar Spectral Response

with 10 kHz Sine Wave Input

Bipolar Spectral Response

with 20 kHz Sine Wave Input

Figure 29.

Figure 30.

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TYPICAL DYNAMIC PERFORMANCE CHARACTERISTICS (continued)

The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified.

Bipolar Spectral Response

with 40 kHz Sine Wave Input

Bipolar Spurious Free

Dynamic Range

Figure 31.

Figure 32.

Unipolar Signal-to-Noise

+ Distortion Ratio

vs. Input Frequency

Unipolar Signal-to-Noise Ratio

vs. Input Frequency

Figure 33.

Figure 34.

Unipolar Signal-to-Noise

+ Distortion Ratio

vs. Input Signal Level

Unipolar Spectral Response

with 1.028 kHz Sine Wave Input

Figure 35.

Figure 36.

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TYPICAL DYNAMIC PERFORMANCE CHARACTERISTICS (continued)

The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified.

Unipolar Spectral Response

with 10 kHz Sine Wave Input

Unipolar Spectral Response

with 20 kHz Sine Wave Input

Figure 37.

Figure 38.

Unipolar Spectral Response

with 40 kHz Sine Wave Input

Figure 39.

TEST CIRCUITS and WAVEFORMS

Figure 40. TRI-STATE Test Circuits and Waveforms

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Figure 41. TRI-STATE Test Circuits and Waveforms

TIMING DIAGRAMS

V_A+ = V_D+ = +5V, t_R= t_F= 3 ns, C_L= 100 pF for the INT, DMARQ, D0–D15 outputs.

Figure 42. Multiplexed Data Bus

1, 3: CS or Address valid to ALE low set-up time.

2, 4: CS or Address valid to ALE low hold time.

5: ALE pulse width

6: RD high to next ALE high

7: ALE low to RD low

8: RD pulse width

9: RD high to next RD or WR low

10: ALE low to WR low

11: WR pulse width

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12: WR high to next ALE high

13: WR high to next WR or RD low

14: Data valid to WR high set-up time

15: Data valid to WR high hold time

16: RD low to data bus out of TRI-STATE

17: RD high to TRI-STATE

18: RD low to data valid (access time)

Figure 43. Non-Multiplexed Data Bus (ALE = 1)

8: RD pulse width

9: RD high to next RD or WR low

11: WR pulse width

13: WR high to next WR or RD low

14: Data valid to WR high set-up time

15: Data valid to WR high hold time

16: RD low to data bus out of TRI-STATE

17: RD high to TRI-STATE

18: RD low to data valid (access time)

19: Address invalid from RD or WR high (hold time)

20: CS low or address valid to RD low

21: CS low or address valid to WR low

V_A+ = V_D+ = +5V, t_R= t_F= 3 ns, C_L= 100 pF for the INT, DMARQ, D0–D15 outputs.

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Figure 44. Interrupt and DMARQ

22: INT high from RD low

23: DMARQ low from RD low

Pin Descriptions

Analog and digital supply voltage pins. The LM12(H)454/8's supply voltage operating range is +3.0V to +5.5V.

Accuracy is ensured only if V_A+ and V_D+ are connected to the same power supply. Each pin should have a

parallel combination of 10 µF (electrolytic or tantalum) and 0.1 µF (ceramic) bypass capacitors connected

between it and ground.

V_A+ V_D+

D0–D15

The internal data input/output TRI-STATE buffers are connected to these pins. These buffers are designed to

drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances.

These pins allows the user a means of instruction input and data output. With a logic high applied to the BW

pin, data lines D8–D15 are placed in a high impedance state and data lines D0–D7 are used for instruction

input and data output when the LM12(H)454/8 is connected to an 8-bit wide data bus. A logic low on the BW

pin allows the LM12(H)454/8 to exchange information over a 16-bit wide data bus.

Input for the active low READ bus control signal. The data input/output TRI-STATE buffers, as selected by the

logic signal applied to the BW pin, are enabled when RD and CS are both low. This allows the LM12(H)454/8

to transmit information onto the data bus.

RD

WR

CS

Input for the active low WRITE bus control signal. The data input/output TRI-STATE buffers, as selected by the

logic signal applied to the BW pin, are enabled when WR and CS are both low. This allows the LM12(H)454/8

to receive information from the data bus.

Input for the active low Chip Select control signal. A logic low should be applied to this pin only during a READ

or WRITE access to the LM12(H)454/8. The internal clocking is halted and conversion stops while Chip Select

is low. Conversion resumes when the Chip Select input signal returns high.

Address Latch Enable input. It is used in systems containing a multiplexed data bus. When ALE is asserted

high, the LM12(H)454/8 accepts information on the data bus as a valid address. A high-to-low transition will

latch the address data on A0–A4 while the CS is low. Any changes on A0–A4 and CS while ALE is low will not

affect the LM12(H)454/8. See Figure 42. When a non-multiplexed bus is used, ALE is continuously asserted

high. See Figure 43.

ALE

External clock input pin. The LM12(H)454/8 operates with an input clock frequency in the range of 0.05 MHz to

10.0 MHz.

CLK

The LM12(H)454/8's address lines. They are used to access all internal registers, Conversion FIFO, and

A0–A4

Instruction RAM.

Synchronization input/output. When used as an output, it is designed to drive capacitive loads of 100 pF or

less. External buffers are necessary for driving higher load capacitances. SYNC is an input if the Configuration

register's “I/O Select” bit is low. A rising edge on this pin causes the internal S/H to hold the input signal. The

next rising clock edge either starts a conversion or makes a comparison to a programmable limit depending on

which function is requested by a programming instruction. This pin will be an output if “I/O Select” is set high.

The SYNC output goes high when a conversion or a comparison is started and low when completed. (See

Section 2.2). An internal reset after power is first applied to the LM12(H)454/8 automatically sets this pin as an

input.

SYNC

Bus Width input pin. This input allows the LM12(H)454/8 to interface directly with either an 8- or 16-bit data

bus. A logic high sets the width to 8 bits and places D8–D15 in a high impedance state. A logic low sets the

width to 16 bits.

BW

INT

Active low interrupt output. This output is designed to drive capacitive loads of 100 pF or less. External buffers

are necessary for driving higher load capacitances. An interrupt signal is generated any time a non-masked

interrupt condition takes place. There are eight different conditions that can cause an interrupt. Any interrupt is

reset by reading the Interrupt Status register. (See Section 2.3.)

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Pin Descriptions (continued)

Active high Direct Memory Access Request output. This output is designed to drive capacitive loads of 100 pF

or less. External buffers are necessary for driving higher load capacitances. It goes high whenever the number

of conversion results in the conversion FIFO equals a programmable value stored in the Interrupt Enable

register. It returns to a logic low when the FIFO is empty.

DMARQ

GND

LM12(H)454/8 ground connection. It should be connected to a low resistance and inductance analog ground

return that connects directly to the system power supply ground.

The eight (LM12(H)458) or four (LM12454) analog inputs. A given channel is selected through the instruction

RAM. Any of the channels can be configured as an independent single-ended input. Any pair of channels,

whether adjacent or non-adjacent, can operate as a fully differential pair.

IN0–IN7 (IN0–IN3

LM12H454 LM12454)

S/H IN+ S/H IN-

The LM12454's non-inverting and inverting inputs to the internal S/H.

MUXOUT+ MUXOUT-

The LM12454's non-inverting and inverting outputs from the internal multiplexer.

The negative reference input. The LM12(H)454/8 operate with 0V = V_REF-= V_REF+. This pin should be bypassed

to ground with a parallel combination of 10 µF and 0.1 µF (ceramic) capacitors.

V_REF-

The positive reference input. The LM12(H)454/8 operate with 0V = V_REF+= V_A+. This pin should be bypassed

to ground with a parallel combination of 10 µF and 0.1 µF (ceramic) capacitors.

V_REF+

V_REFOUT

The internal 2.5V bandgap's output pin. This pin should be bypassed to ground with a 100 µF capacitor.

FUNCTIONAL DESCRIPTION

The LM12454 and LM12(H)458 are multi-functional Data Acquisition Systems that include a fully differential 12-

bit-plus-sign self-calibrating analog-to-digital converter (ADC) with a two's-complement output format, an 8-

channel (LM12(H)458) or a 4-channel (LM12454) analog multiplexer, an internal 2.5V reference, a first-in-first-out

(FIFO) register that can store 32 conversion results, and an Instruction RAM that can store as many as eight

instructions to be sequentially executed. The LM12454 also has a differential multiplexer output and a differential

S/H input. All of this circuitry operates on only a single +5V power supply.

The LM12(H)454/8 have three modes of operation:

12-bit + sign with correction

8-bit + sign without correction

8-bit + sign comparison mode (“watchdog” mode)

The fully differential 12-bit-plus-sign ADC uses a charge redistribution topology that includes calibration

capabilities. Charge re-distribution ADCs use a capacitor ladder in place of a resistor ladder to form an internal

DAC. The DAC is used by a successive approximation register to generate intermediate voltages between the

voltages applied to V_REF−and V_REF+. These intermediate voltages are compared against the sampled analog

input voltage as each bit is generated. The number of intermediate voltages and comparisons equals the ADC's

resolution. The correction of each bit's accuracy is accomplished by calibrating the capacitor ladder used in the

ADC.

Two different calibration modes are available; one compensates for offset voltage, or zero error, while the other

corrects both offset error and the ADC's linearity error.

When correcting offset only, the offset error is measured once and a correction coefficient is created. During the

full calibration, the offset error is measured eight times, averaged, and a correction coefficient is created. After

completion of either calibration mode, the offset correction coefficient is stored in an internal offset correction

register.

The LM12(H)454/8's overall linearity correction is achieved by correcting the internal DAC's capacitor mismatch.

Each capacitor is compared eight times against all remaining smaller value capacitors and any errors are

averaged. A correction coefficient is then created and stored in one of the thirteen internal linearity correction

registers. An internal state machine, using patterns stored in an internal 16 x 8-bit ROM, executes each

calibration algorithm.

Once calibrated, an internal arithmetic logic unit (ALU) uses the offset correction coefficient and the 13 linearity

correction coefficients to reduce the conversion's offset error and linearity error, in the background, during the 12-

bit + sign conversion. The 8-bit + sign conversion and comparison modes use only the offset coefficient. The 8-

bit + sign mode performs a conversion in less than half the time used by the 12-bit + sign conversion mode.

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The LM12(H)454/8's “watchdog” mode is used to monitor a single-ended or differential signal's amplitude. Each

sampled signal has two limits. An interrupt can be generated if the input signal is above or below either of the

two limits. This allows interrupts to be generated when analog voltage inputs are “inside the window” or,

alternatively, “outside the window”. After a “watchdog” mode interrupt, the processor can then request a

conversion on the input signal and read the signal's magnitude.

The analog input multiplexer can be configured for any combination of single-ended or fully differential operation.

Each input is referenced to ground when a multiplexer channel operates in the single-ended mode. Fully

differential analog input channels are formed by pairing any two channels together.

The LM12454's multiplexer outputs and S/H inputs (MUXOUT+, MUXOUT− and S/H IN+, S/H IN−) provide the

option for additional analog signal processing. Fixed-gain amplifiers, programmable-gain amplifiers, filters, and

other processing circuits can operate on the signal applied to the selected multiplexer channel(s). If external

processing is not used, connect MUXOUT+ to S/H IN+ and MUXOUT− to S/H IN−.

The LM12(H)454/8's internal S/H is designed to operate at its minimum acquisition time (1.13 μs, 12 bits) when

the source impedance, R_S, is ≤ 60Ω (f_CLK≤ 8 MHz). When 60Ω < R_S≤ 4.17 kΩ, the internal S/H's acquisition

time can be increased to a maximum of 4.88 μs (12 bits, f_CLK= 8 MHz). See Section 2.1 (Instruction RAM “00”)

Bits 12–15 for more information.

An internal 2.5V bandgap reference output is available at pin 44. This voltage can be used as the ADC reference

for ratiometric conversion or as a virtual ground for front-end analog conditioning circuits. The V_REFOUTpin should

be bypassed to ground with a 100 μF capacitor.

Microprocessor overhead is reduced through the use of the internal conversion FIFO. Thirty-two consecutive

conversions can be completed and stored in the FIFO without any microprocessor intervention. The

microprocessor can, at any time, interrogate the FIFO and retrieve its contents. It can also wait for the

LM12(H)454/8 to issue an interrupt when the FIFO is full or after any number (≤32) of conversions have been

stored.

Conversion sequencing, internal timer interval, multiplexer configuration, and many other operations are

programmed and set in the Instruction RAM.

A diagnostic mode is available that allows verification of the LM12(H)458's operation. The diagnostic mode is

disabled in the LM12454. This mode internally connects the voltages present at the V_REFOUT, V_REF+, V_REF−, and

GND pins to the internal V_IN+and V_IN−S/H inputs. This mode is activated by setting the Diagnostic bit (Bit 11) in

the Configuration register to a “1”. More information concerning this mode of operation can be found in Section

2.2.

Internal User-Programmable Registers

INSTRUCTION RAM

The instruction RAM holds up to eight sequentially executable instructions. Each 48-bit long instruction is divided

into three 16-bit sections. READ and WRITE operations can be issued to each 16-bit section using the

instruction's address and the 2-bit “RAM pointer” in the Configuration register. The eight instructions are located

at addresses 0000 through 0111 (A4–A1, BW = 0) when using a 16-bit wide data bus or at addresses 00000

through 01111 (A4–A0, BW = 1) when using an 8-bit wide data bus. They can be accessed and programmed in

random order.

Any Instruction RAM READ or WRITE can affect the sequencer's operation:

The Sequencer should be stopped by setting the RESET bit to a “1” or by resetting the START bit in the

Configuration Register and waiting for the current instruction to finish execution before any Instruction

RAM READ or WRITE is initiated. Bit 0 of the Configuration Register indicates the Sequencer Status. See

paragraph 2.2 for information on the Configuration Register.

A soft RESET should be issued by writing a “1” to the Configuration Register's RESET bit after any READ

or WRITE to the Instruction RAM.

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The three sections in the Instruction RAM are selected by the Configuration Register's 2-bit “RAM Pointer”, bits

D8 and D9. The first 16-bit Instruction RAM section is selected with the RAM Pointer equal to “00”. This section

provides multiplexer channel selection, as well as resolution, acquisition time, etc. The second 16-bit section

holds “watchdog” limit #1, its sign, and an indicator that shows that an interrupt can be generated if the input

signal is greater or less than the programmed limit. The third 16-bit section holds “watchdog” limit #2, its sign,

and an indicator that shows that an interrupt can be generated if the input signal is greater or less than the

programmed limit.

Instruction RAM “00”

Bit 0 is the LOOP bit. It indicates the last instruction to be executed in any instruction sequence when it is set to

a “1”. The next instruction to be executed will be instruction 0.

Bit 1 is the PAUSE bit. This controls the Sequencer's operation. When the PAUSE bit is set (“1”), the Sequencer

will stop after reading the current instruction and before executing it, and the start bit in the Configuration register

is automatically reset to a “0”. Setting the PAUSE also causes an interrupt to be issued. The Sequencer is

restarted by placing a “1” in the Configuration register's Bit 0 (Start bit).

After the Instruction RAM has been programmed and the RESET bit is set to “1”, the Sequencer retrieves

Instruction 000, decodes it, and waits for a “1” to be placed in the Configuration's START bit. The START bit

value of “0” “overrides” the action of Instruction 000's PAUSE bit when the Sequencer is started. Once started,

the Sequencer executes Instruction 000 and retrieves, decodes, and executes each of the remaining instructions.

No PAUSE Interrupt (INT 5) is generated the first time the Sequencer executes Instruction 000 having a PAUSE

bit set to “1”. When the Sequencer encounters a LOOP bit or completes all eight instructions, Instruction 000 is

retrieved and decoded. A set PAUSE bit in Instruction 000 now halts the Sequencer before the instruction is

executed.

Bits 2–4 select which of the eight input channels (“000” to “111” for IN0–IN7) will be configured as non-inverting

inputs to the LM12(H)458's ADC. (See Table 3.) They select which of the four input channels (“000” to “011” for

IN0–IN4) will be configured as non-inverting inputs to the LM12454's ADC. (See Table 4.)

Bits 5–7 select which of the seven input channels (“001” to “111” for IN1 to IN7) will be configured as inverting

inputs to the LM12(H)458's ADC. (See Table 3.) They select which of the three input channels (“001” to “011” for

IN1–IN4) will be configured as inverting inputs to the LM12454's ADC. (See Table 4.) Fully differential operation

is created by selecting two multiplexer channels, one operating in the non-inverting mode and the other operating

in the inverting mode. A code of “000” selects ground as the inverting input for single ended operation.

Bit 8 is the SYNC bit. Setting Bit 8 to “1” causes the Sequencer to suspend operation at the end of the internal

S/H's acquisition cycle and to wait until a rising edge appears at the SYNC pin. When a rising edge appears, the

S/H acquires the input signal magnitude and the ADC performs a conversion on the clock's next rising edge.

When the SYNC pin is used as an input, the Configuration register's “I/O Select” bit (Bit 7) must be set to a “0”.

With SYNC configured as an input, it is possible to synchronize the start of a conversion to an external event.

This is useful in applications such as digital signal processing (DSP) where the exact timing of conversions is

important.

When the LM12(H)454/8 are used in the “watchdog” mode with external synchronization, two rising edges on the

SYNC input are required to initiate two comparisons. The first rising edge initiates the comparison of the selected

analog input signal with Limit #1 (found in Instruction RAM “01”) and the second rising edge initiates the

comparison of the same analog input signal with Limit #2 (found in Instruction RAM “10”).

Bit 9 is the TIMER bit. When Bit 9 is set to “1”, the Sequencer will halt until the internal 16-bit Timer counts down

to zero. During this time interval, no “watchdog” comparisons or analog-to-digital conversions will be performed.

Bit 10 selects the ADC conversion resolution. Setting Bit 10 to “1” selects 8-bit + sign and when reset to “0”

selects 12-bit + sign.

Bit 11 is the “watchdog” comparison mode enable bit. When operating in the “watchdog” comparison mode, the

selected analog input signal is compared with the programmable values stored in Limit #1 and Limit #2 (see

Instruction RAM “01” and Instruction RAM “10”). Setting Bit 11 to “1” causes two comparisons of the selected

analog input signal with the two stored limits. When Bit 11 is reset to “0”, an 8-bit + sign or 12-bit + sign

(depending on the state of Bit 10 of Instruction RAM “00”) conversion of the input signal can take place.

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Bits 12–15 are used to store the user-programmable acquisition time. The Sequencer keeps the internal S/H in

the acquisition mode for a fixed number of clock cycles (nine clock cycles, for 12-bit + sign conversions and two

clock cycles for 8-bit + sign conversions or “watchdog” comparisons) plus a variable number of clock cycles

equal to twice the value stored in Bits 12–15. Thus, the S/H's acquisition time is (9 + 2D) clock cycles for 12-bit +

sign conversions and (2 + 2D) clock cycles for 8-bit + sign conversions or “watchdog” comparisons, where D is

the value stored in Bits 12–15. The minimum acquisition time compensates for the typical internal multiplexer

series resistance of 2 kΩ, and any additional delay created by Bits 12–15 compensates for source resistances

greater than 60Ω (100Ω). (For this acquisition time discussion, numbers in ( ) are shown for the LM12(H)454/8

operating at 5 MHz.) The necessary acquisition time is determined by the source impedance at the multiplexer

input. If the source resistance (R_S) < 60Ω (100Ω) and the clock frequency is 8 MHz, the value stored in bits

12–15 (D) can be 0000. If R_S> 60Ω (100Ω), the following equations determine the value that should be stored in

bits 12–15.

D = 0.45 x R_Sx f_CLK

(1)

for 12-bits + sign

D = 0.36 x R_Sx f_CLK

(2)

for 8-bits + sign and “watchdog”

R_Sis in kΩ and f_CLKis in MHz. Round the result to the next higher integer value. If D is greater than 15, it is

advisable to lower the source impedance by using an analog buffer between the signal source and the

LM12(H)458's multiplexer inputs. The value of D can also be used to compensate for the settling or response

time of external processing circuits connected between the LM12454's MUXOUT and S/H IN pins.

Instruction RAM “01”

The second Instruction RAM section is selected by placing a “01” in Bits 8 and 9 of the Configuration register.

Bits 0–7 hold “watchdog” limit #1. When Bit 11 of Instruction RAM “00” is set to a “1”, the LM12(H)454/8

performs a “watchdog” comparison of the sampled analog input signal with the limit #1 value first, followed by a

comparison of the same sampled analog input signal with the value found in limit #2 (Instruction RAM “10”).

Bit 8 holds limit #1's sign.

Bit 9's state determines the limit condition that generates a “watchdog” interrupt. A “1” causes a voltage greater

than limit #1 to generate an interrupt, while a “0” causes a voltage less than limit #1 to generate an interrupt.

Bits 10–15 are not used.

Instruction RAM “10”

The third Instruction RAM section is selected by placing a “10” in Bits 8 and 9 of the Configuration register.

Bits 0–7 hold “watchdog” limit #2. When Bit 11 of Instruction RAM “00” is set to a “1”, the LM12(H)454/8

performs a “watchdog” comparison of the sampled analog input signal with the limit #1 value first (Instruction

RAM “01”), followed by a comparison of the same sampled analog input signal with the value found in limit #2.

Bit 8 holds limit #2's sign.

Bit 9 's state determines the limit condition that generates a “watchdog” interrupt. A “1” causes a voltage greater

than limit #2 to generate an interrupt, while a “0” causes a voltage less than limit #2 to generate an interrupt.

Bits 10–15 are not used.

CONFIGURATION REGISTER

The Configuration register, 1000 (A4–A1, BW = 0) or 1000x (A4–A0, BW = 1) is a 16-bit control register with

read/write capability. It acts as the LM12454's and LM12(H)458's “control panel” holding global information as

well as start/stop, reset, self-calibration, and stand-by commands.

Bit 0 is the START/STOP bit. Reading Bit 0 returns an indication of the Sequencer's status. A “0” indicates that

the Sequencer is stopped and waiting to execute the next instruction. A “1” shows that the Sequencer is running.

Writing a “0” halts the Sequencer when the current instruction has finished execution. The next instruction to be

executed is pointed to by the instruction pointer found in the status register. A “1” restarts the Sequencer with the

instruction currently pointed to by the instruction pointer. (See Bits 8–10 in the Interrupt Status register.)

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Bit 1 is the LM12(H)454/8's system RESET bit. Writing a “1” to Bit 1 stops the Sequencer (resetting the

Configuration register's START/STOP bit), resets the Instruction pointer to “000” (found in the Interrupt Status

register), clears the Conversion FIFO, and resets all interrupt flags. The RESET bit will return to “0” after two

clock cycles unless it is forced high by writing a “1” into the Configuration register's Standby bit. A reset signal is

internally generated when power is first applied to the part. No operation should be started until the RESET bit is

“0”.

Writing a “1” to Bit 2 initiates an auto-zero offset voltage calibration. Unlike the eight-sample auto-zero calibration

performed during the full calibration procedure, Bit 2 initiates a “short” auto-zero by sampling the offset once and

creating a correction coefficient (full calibration averages eight samples of the converter offset voltage when

creating a correction coefficient). If the Sequencer is running when Bit 2 is set to “1”, an auto-zero starts

immediately after the conclusion of the currently running instruction. Bit 2 is reset automatically to a “0” and an

interrupt flag (Bit 3, in the Interrupt Status register) is set at the end of the auto-zero (76 clock cycles). After

completion of an auto-zero calibration, the Sequencer fetches the next instruction as pointed to by the Instruction

RAM's pointer and resumes execution. If the Sequencer is stopped, an auto-zero is performed immediately at the

time requested.

Writing a “1” to Bit 3 initiates a complete calibration process that includes a “long” auto-zero offset voltage

correction (this calibration averages eight samples of the comparator offset voltage when creating a correction

coefficient) followed by an ADC linearity calibration. This complete calibration is started after the currently

running instruction is completed if the Sequencer is running when Bit 3 is set to “1”. Bit 3 is reset automatically to

a “0” and an interrupt flag (Bit 4, in the Interrupt Status register) will be generated at the end of the calibration

procedure (4944 clock cycles). After completion of a full auto-zero and linearity calibration, the Sequencer

fetches the next instruction as pointed to by the Instruction RAM's pointer and resumes execution. If the

Sequencer is stopped, a full calibration is performed immediately at the time requested.

Bit 4 is the Standby bit. Writing a “1” to Bit 4 immediately places the LM12(H)454/8 in Standby mode. Normal

operation returns when Bit 4 is reset to a “0”. The Standby command (“1”) disconnects the external clock from

the internal circuitry, decreases the LM12(H)454/8's internal analog circuitry power supply current, and preserves

all internal RAM contents. After writing a “0” to the Standby bit, the LM12(H)454/8 returns to an operating state

identical to that caused by exercising the RESET bit. A Standby completion interrupt is issued after a power-up

completion delay that allows the analog circuitry to settle. The Sequencer should be restarted only after the

Standby completion is issued. The Instruction RAM can still be accessed through read and write operations while

the LM12(H)454/8 are in Standby Mode.

Bit 5 is the Channel Address Mask. If Bit 5 is set to a “1”, Bits 13–15 in the conversion FIFO will be equal to the

sign bit (Bit 12) of the conversion data. Resetting Bit 5 to a “0” causes conversion data Bits 13 through 15 to hold

the instruction pointer value of the instruction to which the conversion data belongs.

Bit 6 is used to select a “short” auto-zero correction for every conversion. The Sequencer automatically inserts

an auto-zero before every conversion or “watchdog” comparison if Bit 6 is set to “1”. No automatic correction will

be performed if Bit 6 is reset to “0”.

The LM12(H)454/8's offset voltage, after calibration, has a typical drift of 0.1 LSB over a temperature range of

−40°C to +85°C. This small drift is less than the variability of the change in offset that can occur when using the

auto-zero correction with each conversion. This variability is the result of using only one sample of the offset

voltage to create a correction value. This variability decreases when using the full calibration mode because eight

samples of the offset voltage are taken, averaged, and used to create a correction value.

Bit 7 is used to program the SYNC pin (29) to operate as either an input or an output. The SYNC pin becomes

an output when Bit 7 is a “1” and an input when Bit 7 is a “0”. With SYNC programmed as an input, the rising

edge of any logic signal applied to pin 29 will start a conversion or “watchdog” comparison. Programmed as an

output, the logic level at pin 29 will go high at the start of a conversion or “watchdog” comparison and remain

high until either have finished. See Instruction RAM “00”, Bit 8.

Bits 8 and 9 form the RAM Pointer that is used to select each of a 48-bit instruction's three 16-bit sections during

read or write actions. A “00” selects Instruction RAM section one, “01” selects section two, and “10” selects

section three.

Bit 10 activates the Test mode that is used only during production testing. Leave this bit reset to “0”.

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Bit 11 is the Diagnostic bit and is available only in the LM12(H)458. It can be activated by setting it to a “1” (the

Test bit must be reset to a “0”). The Diagnostic mode, along with a correctly chosen instruction, allows

verification that the LM12(H)458's ADC is performing correctly. When activated, the inverting and non-inverting

inputs are connected as shown in Table 3. As an example, an instruction with “001” for both V_IN+and V_IN−while

using the Diagnostic mode typically results in a full-scale output.

INTERRUPTS

The LM12454 and LM12(H)458 have eight possible interrupts, all with the same priority. Any of these interrupts

will cause a hardware interrupt to appear on the INT pin (31) if they are not masked (by the Interrupt Enable

register). The Interrupt Status register is then read to determine which of the eight interrupts has been issued.

Table 3. LM12(H)458 Input Multiplexer

Channel Configuration Showing Normal

Mode and Diagnostic Mode

Channel

Selection

Data

Normal Mode

Diagnostic Mode

V_IN+

V_IN−

V_IN+

V_IN−

000

001

010

011

100

101

110

111

IN0

IN1

IN2

IN3

IN4

IN5

IN6

IN7

GND

IN1

IN2

IN3

IN4

IN5

IN6

IN7

V_REFOUT

V_REF+

IN2

GND

V_REF−

IN2

IN3

IN4

IN5

IN6

IN7

Table 4. LM12454 Input Multiplexer

Channel Configuration

Channel Selection Data

MUX+

IN0

MUX−

GND

IN1

000

001

010

011

1XX

IN1

IN2

IN3

OPEN

NOTE: The LM12(H)454 is no longer available. Information shown for reference only.

The Interrupt Status register, 1010 (A4–A1, BW = 0) or 1010x (A4–A0, BW = 1) must be cleared by reading it

after writing to the Interrupt Enable register. This removes any spurious interrupts on the INT pin generated

during an Interrupt Enable register access.

Interrupt 0 is generated whenever the analog input voltage on a selected multiplexer channel crosses a limit

while the LM12(H)454/8 are operating in the “watchdog” comparison mode. Two sequential comparisons are

made when the LM12(H)454/8 are executing a “watchdog” instruction. Depending on the logic state of Bit 9 in

the Instruction RAM's second and third sections, an interrupt will be generated either when the input signal's

magnitude is greater than or less than the programmable limits. (See the Instruction RAM, Bit 9 description.) The

Limit Status register will indicate which preprogrammed limit, #1 or #2 and which instruction was executing when

the limit was crossed.

Interrupt 1 is generated when the Sequencer reaches the instruction counter value specified in the Interrupt

Enable register's bits 8–10. This flag appears before the instruction's execution.

Interrupt 2 is activated when the Conversion FIFO holds a number of conversions equal to the programmable

value stored in the Interrupt Enable register's Bits 11–15. This value ranges from 0001 to 1111, representing 1 to

31 conversions stored in the FIFO. A user-programmed value of 0000 has no meaning. See Section 3.0 for more

FIFO information.

The completion of the short, single-sample auto-zero calibration generates Interrupt 3.

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The completion of a full auto-zero and linearity self-calibration generates Interrupt 4.

Interrupt 5 is generated when the Sequencer encounters an instruction that has its Pause bit (Bit 1 in Instruction

RAM “00”) set to “1”.

The LM12(H)454/8 issues Interrupt 6 whenever it senses that its power supply voltage is dropping below 4V

(typ). This interrupt indicates the potential corruption of data returned by the LM12(H)454/8.

Interrupt 7 is issued after a short delay (10 ms typ) while the LM12(H)454/8 returns from Standby mode to active

operation using the Configuration register's Bit 4. This short delay allows the internal analog circuitry to settle

sufficiently, ensuring accurate conversion results.

INTERRUPT ENABLE REGISTER

The Interrupt Enable register at address location 1001 (A4–A1, BW = 0) or 1001x (A4–A0, BW = 1) has

READ/WRITE capability. An individual interrupt's ability to produce an external interrupt at pin 31 (INT) is

accomplished by placing a “1” in the appropriate bit location. Any of the internal interrupt-producing operations

will set their corresponding bits to “1” in the Interrupt Status register regardless of the state of the associated bit

in the Interrupt Enable register. See Section 2.3 for more information about each of the eight internal interrupts.

Bit 0 enables an external interrupt when an internal “watchdog” comparison limit interrupt has taken place.

Bit 1 enables an external interrupt when the Sequencer has reached the address stored in Bits 8–10 of the

Interrupt Enable register.

Bit 2 enables an external interrupt when the Conversion FIFO's limit, stored in Bits 11–15 of the Interrupt Enable

register, has been reached.

Bit 3 enables an external interrupt when the single-sample auto-zero calibration has been completed.

Bit 4 enables an external interrupt when a full auto-zero and linearity self-calibration has been completed.

Bit 5 enables an external interrupt when an internal Pause interrupt has been generated.

Bit 6 enables an external interrupt when a low power supply condition (V_A+ < 4V) has generated an internal

interrupt.

Bit 7 enables an external interrupt when the LM12(H)454/8 return from power-down to active mode.

Bits 8 – 10 form the storage location of the user-programmable value against which the Sequencer's address is

compared. When the Sequencer reaches an address that is equal to the value stored in Bits 8–10, an internal

interrupt is generated and appears in Bit 1 of the Interrupt Status register. If Bit 1 of the Interrupt Enable register

is set to “1”, an external interrupt will appear at pin 31 (INT).

The value stored in bits 8–10 ranges from 000 to 111, representing 0 to 7 instructions stored in the Instruction

RAM. After the Instruction RAM has been programmed and the RESET bit is set to “1”, the Sequencer is started

by placing a “1” in the Configuration register's START bit. Setting the INT 1 trigger value to 000 does not

generate an INT 1 the first time the Sequencer retrieves and decodes Instruction 000. The Sequencer

generates INT 1 (by placing a “1” in the Interrupt Status register's Bit 1) the second time and after the

Sequencer encounters Instruction 000. It is important to remember that the Sequencer continues to operate even

if an Instruction interrupt (INT 1) is internally or externally generated. The only mechanisms that stop the

Sequencer are an instruction with the PAUSE bit set to “1” (halts before instruction execution), placing a “0” in

the Configuration register's START bit, or placing a “1” in the Configuration register's RESET bit.

Bits 11–15 hold the number of conversions that must be stored in the Conversion FIFO in order to generate an

internal interrupt. This internal interrupt appears in Bit 2 of the Interrupt Status register. If Bit 2 of the Interrupt

Enable register is set to “1”, an external interrupt will appear at pin 31 (INT).

Other Registers and Functions

INTERRUPT STATUS REGISTER

This read-only register is located at address 1010 (A4–A1, BW = 0) or 1010x (A4–A0, BW = 1). The

corresponding flag in the Interrupt Status register goes high (“1”) any time that an interrupt condition takes place,

whether an interrupt is enabled or disabled in the Interrupt Enable register. Any of the active (“1”) Interrupt Status

register flags are reset to “0” whenever this register is read or a device reset is issued (see Bit 1 in the

Configuration Register).

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Bit 0 is set to “1” when a “watchdog” comparison limit interrupt has taken place.

Bit 1 is set to “1” when the Sequencer has reached the address stored in Bits 8–10 of the Interrupt Enable

register.

Bit 2 is set to “1” when the Conversion FIFO's limit, stored in Bits 11–15 of the Interrupt Enable register, has

been reached.

Bit 3 is set to “1” when the single-sample auto-zero has been completed.

Bit 4 is set to “1” when an auto-zero and full linearity self-calibration has been completed.

Bit 5 is set to “1” when a Pause interrupt has been generated.

Bit 6 is set to “1” when a low-supply voltage condition (V_A+ < 4V) has taken place.

Bit 7 is set to “1” when the LM12(H)454/8 return from power-down to active mode.

Bits 8–10 hold the Sequencer's actual instruction address while it is running.

Bits 11–15 hold the actual number of conversions stored in the Conversion FIFO while the Sequencer is running.

LIMIT STATUS REGISTER

The read-only register is located at address 1101 (A4–A1, BW = 0) or 1101x (A4–A0, BW = 1). This register is

used in tandem with the Limit #1 and Limit #2 registers in the Instruction RAM. Whenever a given instruction's

input voltage exceeds the limit set in its corresponding Limit register (#1 or #2), a bit, corresponding to the

instruction number, is set in the Limit Status register. Any of the active (“1”) Limit Status flags are reset to “0”

whenever this register is read or a device reset is issued (see Bit 1 in the Configuration register). This register

holds the status of limits #1 and #2 for each of the eight instructions.

Bits 0–7 show the Limit #1 status. Each bit will be set high (“1”) when the corresponding instruction's input

voltage exceeds the threshold stored in the instruction's Limit #1 register. When, for example, instruction 3 is a

“watchdog” operation (Bit 11 is set high) and the input for instruction 3 meets the magnitude and/or polarity data

stored in instruction 3's Limit #1 register, Bit 3 in the Limit Status register will be set to a “1”.

Bits 8–15 show the Limit #2 status. Each bit will be set high (“1”) when the corresponding instruction's input

voltage exceeds the threshold stored in the instruction's Limit #2 register. When, for example, the input to

instruction 6 meets the value stored in instruction 6's Limit #2 register, Bit 14 in the Limit Status register will be

set to a “1”.

TIMER

The LM12(H)454/8 have an on-board 16-bit timer that includes a 5-bit pre-scaler. It uses the clock signal applied

to pin 23 as its input. It can generate time intervals of 0 through 2²¹clock cycles in steps of 2⁵. This time interval

can be used to delay the execution of instructions. It can also be used to slow the conversion rate when

converting slowly changing signals. This can reduce the amount of redundant data stored in the FIFO and

retrieved by the controller.

The user-defined timing value used by the Timer is stored in the 16-bit READ/WRITE Timer register at location

1011 (A4–A1, BW = 0) or 1011x (A4–A0, BW = 1) and is pre-loaded automatically. Bits 0–7 hold the preset

value's low byte and Bits 8–15 hold the high byte. The Timer is activated by the Sequencer only if the current

instruction's Bit 9 is set (“1”). If the equivalent decimal value “N” (0 ≤ N ≤ 2¹⁶− 1) is written inside the 16-bit Timer

register and the Timer is enabled by setting an instruction's bit 9 to a “1”, the Sequencer will delay the same

instruction's execution by halting at state 3 (S3), as shown in Figure 45, for 32 × N + 2 clock cycles.

DMA

The DMA works in tandem with Interrupt 2. An active DMA Request on pin 32 (DMARQ) requires that the FIFO

interrupt be enabled. The voltage on the DMARQ pin goes high when the number of conversions in the FIFO

equals the 5-bit value stored in the Interrupt Enable register (bits 11–15). The voltage on the INT pin goes low at

the same time as the voltage on the DMARQ pin goes high. The voltage on the DMARQ pin goes low when the

FIFO is emptied. The Interrupt Status register must be read to clear the FIFO interrupt flag in order to enable the

next DMA request.

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DMA operation is optimized through the use of the 16-bit data bus connection (a logic “0” applied to the BW pin).

Using this bus width allows DMA controllers that have single address Read/Write capability to easily unload the

FIFO. Using DMA on an 8-bit data bus is more difficult. Two read operations (low byte, high byte) are needed to

retrieve each conversion result from the FIFO. Therefore, the DMA controller must be able to repeatedly access

two constant addresses when transferring data from the LM12(H)454/8 to the host system.

FIFO

The result of each conversion stored in an internal read-only FIFO (First-In, First-Out) register. It is located at

1100 (A4–A1, BW = 0) or 1100x (A4–A0, BW = 1). This register has 32 16-bit wide locations. Each location holds

13-bit data. Bits 0–3 hold the four LSB's in the 12 bits + sign mode or “1110” in the 8 bits + sign mode. Bits 4–11

hold the eight MSB's and Bit 12 holds the sign bit. Bits 13–15 can hold either the sign bit, extending the register's

two's complement data format to a full sixteen bits or the instruction address that generated the conversion and

the resulting data. These modes are selected according to the logic state of the Configuration register's Bit 5.

The FIFO status should be read in the Interrupt Status register (Bits 11–15) to determine the number of

conversion results that are held in the FIFO before retrieving them. This will help prevent conversion data

corruption that may take place if the number of reads are greater than the number of conversion results

contained in the FIFO. Trying to read the FIFO when it is empty may corrupt new data being written into the

FIFO. Writing more than 32 conversion data into the FIFO by the ADC results in loss of the first conversion data.

Therefore, to prevent data loss, it is recommended that the LM12(H)454/8's interrupt capability be used to inform

the system controller that the FIFO is full.

The lower portion (A0 = 0) of the data word (Bits 0–7) should be read first followed by a read of the upper portion

(A0 = 1) when using the 8-bit bus width (BW = 1). Reading the upper portion first causes the data to shift down,

which results in loss of the lower byte.

Bits 0–12 hold 12-bit + sign conversion data. Bits 0–3 will be 1110 (LSB) when using 8-bit plus sign resolution.

Bits 13–15 hold either the instruction responsible for the associated conversion data or the sign bit. Either mode

is selected with Bit 5 in the Configuration register.

Using the FIFO's full depth is achieved as follows. Set the value of the Interrupt Enable register's Bits 11–15 to

11111 and the Interrupt Enable register's Bit 2 to a “1”. This generates an external interrupt when the 31st

conversion is stored in the FIFO. This gives the host processor a chance to send a “0” to the LM12(H)454/8's

Start bit (Configuration register) and halt the ADC before it completes the 32nd conversion. The Sequencer halts

after the current (32) conversion is completed. The conversion data is then transferred to the FIFO and occupies

the 32nd location. FIFO overflow is avoided if the Sequencer is halted before the start of the 32nd conversion by

placing a “0” in the Start bit (Configuration register). It is important to remember that the Sequencer continues to

operate even if a FIFO interrupt (INT 2) is internally or externally generated. The only mechanisms that stop

the Sequencer are an instruction with the PAUSE bit set to “1” (halts before instruction execution), placing a “0”

in the Configuration register's START bit, or placing a “1” in the Configuration register's RESET bit.

Sequencer

The Sequencer uses a 3-bit counter (Instruction Pointer, or IP, in Figure 40) to retrieve the programmable

conversion instructions stored in the Instruction RAM. The 3-bit counter is reset to 000 during chip reset or if the

current executed instruction has its Loop bit (Bit 1 in any Instruction RAM “00”) set high (“1”). It increments at the

end of the currently executed instruction and points to the next instruction. It will continue to increment up to 111

unless an instruction's Loop bit is set. If this bit is set, the counter resets to “000” and execution begins again with

the first instruction. If all instructions have their Loop bit reset to “0”, the Sequencer will execute all eight

instructions continuously. Therefore, it is important to realize that if less than eight instructions are programmed,

the Loop bit on the last instruction must be set. Leaving this bit reset to “0” allows the Sequencer to execute

“unprogrammed” instructions, the results of which may be unpredictable.

The Sequencer's Instruction Pointer value is readable at any time and is found in the Status register at Bits 8–10.

The Sequencer can go through eight states during instruction execution:

State 0: The current instruction's first 16 bits are read from the Instruction RAM “00”. This state is one clock

cycle long.

State 1: Checks the state of the Calibration and Start bits. This is the “rest” state whenever the Sequencer is

stopped using the reset, a Pause command, or the Start bit is reset low (“0”). When the Start bit is set to a “1”,

this state is one clock cycle long.

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State 2: Perform calibration. If bit 2 or bit 6 of the Configuration register is set to a “1”, state 2 is 76 clock

cycles long. If the Configuration register's bit 3 is set to a “1”, state 2 is 4944 clock cycles long.

State 3: Run the internal 16-bit Timer. The number of clock cycles for this state varies according to the value

stored in the Timer register. The number of clock cycles is found by using the expression below

32T + 2

(3)

where 0 ≤ T ≤ 2¹⁶−1.

State 7: Run the acquisition delay and read Limit #1's value if needed. The number of clock cycles for 12-bit +

sign mode varies according to

9 + 2D

(4)

where D is the user-programmable 4-bit value stored in bits 12–15 of Instruction RAM “00” and is limited to 0 ≤ D

≤ 15.

The number of clock cycles for 8-bit + sign or “watchdog” mode varies according to

2 + 2D

(5)

where D is the user-programmable 4-bit value stored in bits 12–15 of Instruction RAM “00” and is limited to 0 ≤ D

≤ 15.

State 6: Perform first comparison. This state is 5 clock cycles long.

State 4: Read Limit #2. This state is 1 clock cycle long.

State 5: Perform a conversion or second comparison. This state takes 44 clock cycles when using the 12-bit +

sign mode or 21 clock cycles when using the 8-bit + sign mode. The “watchdog” mode takes 5 clock cycles.

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Figure 45. Sequencer Logic Flow Chart (IP = Instruction Pointer)

36

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DESIGN CONSIDERATIONS

REFERENCE VOLTAGE

The difference in the voltages applied to the V_REF+and V_REF−defines the analog input voltage span (the

difference between the voltages applied between two multiplexer inputs or the voltage applied to one of the

multiplexer inputs and analog ground), over which 4095 positive and 4096 negative codes exist. The voltage

sources driving V_REF+or V_REF−must have very low output impedance and noise.

The ADC can be used in either ratiometric or absolute reference applications. In ratiometric systems, the analog

input voltage is proportional to the voltage used for the ADC's reference voltage. When this voltage is the system

power supply, the V_REF+pin is connected to V_A+ and V_REF−is connected to GND. This technique relaxes the

system reference stability requirements because the analog input voltage and the ADC reference voltage move

together. This maintains the same output code for given input conditions.

For absolute accuracy, where the analog input voltage varies between very specific voltage limits, a time and

temperature stable voltage source can be connected to the reference inputs. Typically, the reference voltage's

magnitude will require an initial adjustment to null reference voltage induced full-scale errors.

When using the LM12(H)454/8's internal 2.5V bandgap reference, a parallel combination of a 100 μF capacitor

and a 0.1 μF capacitor connected to the V_REFOUTpin is recommended for low noise operation. When left

unconnected, the reference remains stable without a bypass capacitor. However, ensure that stray capacitance

at the V_REFOUTpin remains below 50 pF.

INPUT RANGE

The LM12(H)454/8's fully differential ADC and reference voltage inputs generate a two's-complement output that

is found by using the equation below.

(6)

Round up to the next integer value between −4096 to 4095 for 12-bit resolution and between −256 to 255 for 8-

bit resolution if the result of the above equation is not a whole number. As an example, V_REF+= 2.5V, V_REF−= 1V,

V_IN+= 1.5V and V_IN−= GND. The 12-bit + sign output code is positive full-scale, or 0,1111,1111,1111. If V_REF+

5V, V_REF−= 1V, V_IN+= 3V, and V_IN−= GND, the 12-bit + sign output code is 0,1100,0000,0000.

=

INPUT CURRENT

A charging current flows into or out of (depending on the input voltage polarity) the analog input pins, IN0–IN7 at

the start of the analog input acquisition time (t_ACQ). This current's peak value will depend on the actual input

voltage applied. This charging current causes voltage spikes at the inputs. This voltage spikes will not corrupt the

conversion results.

INPUT SOURCE RESISTANCE

For low impedance voltage sources (<100Ω for 5 MHz operation and <60Ω for 8 MHz operation), the input

charging current will decay, before the end of the S/H's acquisition time, to a value that will not introduce any

conversion errors. For higher source impedances, the S/H's acquisition time can be increased. As an example,

operating with a 5 MHz clock frequency and maximum acquisition time, the LM12(H)454/8's analog inputs can

handle source impedance as high as 6.67 kΩ. When operating at 8 MHz and maximum acquisition time, the

LM12H454/8's analog inputs can handle source impedance as high as 4.17 kΩ. Refer to Section 2.1, Instruction

RAM “00”, Bits 12–15 for further information.

INPUT BYPASS CAPACITANCE

External capacitors (0.01 μF to 0.1 μF) can be connected between the analog input pins, IN0–IN7, and analog

ground to filter any noise caused by inductive pickup associated with long input leads. It will not degrade the

conversion accuracy.

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NOISE

The leads to each of the analog multiplexer input pins should be kept as short as possible. This will minimize

input noise and clock frequency coupling that can cause conversion errors. Input filtering can be used to reduce

the effects of the noise sources.

POWER SUPPLIES

Noise spikes on the V_A+ and V_D+ supply lines can cause conversion errors; the comparator will respond to the

noise. The ADC is especially sensitive to any power supply spikes that occur during the auto-zero or linearity

correction. Low inductance tantalum capacitors of 10 μF or greater paralleled with 0.1 μF monolithic ceramic

capacitors are recommended for supply bypassing. Separate bypass capacitors should be used for the V_A+ and

V_D+ supplies and placed as close as possible to these pins.

GROUNDING

The LM12(H)454/8's nominal performance can be maximized through proper grounding techniques. These

include the use of a single ground plane and meticulously separating analog and digital areas of the board. The

use of separate analog and digital digital planes within the same board area generally provides best

performance. All components that handle digital signals should be placed within the digital area of the board, as

defined by the digital power plane, while all analog components should be placed in the analog area of the

board. Such placement and the routing of analog and digital signal lines within their own respective board areas

greatly reduces the occurrence of ground loops and noise. This will also minimize EMI/RFI radiation and

susceptibility.

It is recommended that stray capacitance between the analog inputs or outputs, including the reference pins, be

kept to a minimum by increasing the clearance (+1/16th inch) between the analog signal and reference pins and

the ground plane.

CLOCK SIGNAL CONSIDERATIONS

The LM12(H)458's performance is optimized by routing the analog input/output and reference signal conductors

(pins 34–44) as far as possible from the conductor that carries the clock signal to pin 23.

Avoid overshoot and undershoot on the clock line by treating this line as a transmission line (use proper

termination techniques). Failure to do so can result in erratic operation. Generally, a series 30Ω to 50Ω resistor in

the clock line, located as close to the clock source as possible, will prevent most problems. The clock source

should drive ONLY the LM12(H)458 clock pin.

Common Application Problems

Driving the analog inputs with op-amp(s) powered from supplies other than the supply used for the

LM12(H)458. This practice allows for the possibility of the amplifier output (LM12(H)458 input) to reach potentials

outside of the 0V to V_A+ range. This could happen in normal operation if the amplifier use supply voltages

outside of the range of the LM12(H)458 supply rails. This could also happen upon power up if the amplifier

supply or supplies ramp up faster than the supply of the LM12(H)458. If any pin experiences a potential more

than 100 mV below ground or above the supply voltage, even on a fast transient basis, the result could be erratic

operation, missing codes, one channel interacting with one or more of the others, skipping channels or a

complete malfunction, depending upon how far the input is driven beyond the supply rails.

Not performing a full calibration at power up. This can result in missing codes. The device needs to have a

full calibration run and completed after power up and BEFORE attempting to perform even a single conversion or

watchdog operation. The only way to recover if this is violated is to interrupt the power to the device.

Not waiting for the calibration process to complete before trying to write to the device. Once a calibration

is requested, the ONLY read of the LM12(H)458 should be if the Interrupt Status Register to check for a

completed calibration. Attempting a write or any other read during calibration would cause a corruption of the

calibration process, resulting in missing codes. The only way to recover would be to interrupt the power.

38

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Improper termination of digital lines. Improper termination can result in energy reflections that build up to

cause overshoot that goes above the supply potential and undershoot that goes below ground. It is never good

to drive a device beyond the supply rails, unless the device is specifically designed to handle this situation, but

the LM12(H)458 is more sensitive to this condition that most devices. Again, if any pin experiences a potential

more than 100 mV below ground or above the supply voltage, even on a fast transient basis, the result could be

erratic operation, missing codes, or a complete malfunction, depending upon how far the input is driven beyond

the supply rails. The clock input is the most sensitive digital one. Generally, a 50Ω series resistor, located very

close to the signal source, will keep digital lines "clean".

Excessive output capacitance on the digital lines. The current required to charge the capacitance on the

digital outputs can cause noise on the supply bus within the LM12(H)458, causing internal supply "bounce" even

when the external supply pin is pretty stable. The current required to discharge the output capacitance can cause

die ground "bounce". Either of these can cause noise to be induced at the analog inputs, resulting in conversion

errors.

Output capacitance should be limited as much as possible. A series 100Ω resistor in each digital output line,

located very close to the output pin, will limit the charge and discharge current, minimizing the extent of the

conversion errors.

Improper CS decoding. If address decoder is used, care must be exercised to ensure that no "runt" (very

narrow) pulse is produced on theCS line when trying to address another device or memory. Even sub-

nanosecond spikes on the CS line can cause the chip to be reprogrammed in accordance with what happens to

be on the data lines at the time. The result is unexpected operation. The worst case result is that the device is

put into the "Test" mode and the on-board EEPROM that corrects linearity is corrupted. If this happens, the only

recourse is to replace the device.

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PACKAGE OUTLINE

FN0044A

PLCC - 4.57 mm max height

SCALE 0.800

PLASTIC CHIP CARRIER

.180 MAX

[4.57]

B

.650-.656

[16.51-16.66]

NOTE 3

.020 MIN

[0.51]

A

(.008)

[0.2]

6

1 44

40

7

39

PIN 1 ID

(OPTIONAL)

.650-.656

[16.51-16.66]

NOTE 3

.582-.638

[14.79-16.20]

17

29

18

28

.090-.120 TYP

[2.29-3.04]

44X .026-.032

[0.66-0.81]

C

SEATING PLANE

.004 [0.1] C

44X .013-.021

[0.33-0.53]

40X .050

[1.27]

.007 [0.18]

C A B

.685-.695

[17.40-17.65]

TYP

4215154/A 04/2017

NOTES:

1. All linear dimensions are in inches. Any dimensions in brackets are in millimeters. Any dimensions in parenthesis are for reference only.

Controlling dimensions are in inches. Dimensioning and tolerancing per ASME Y14.5M.

2. This drawing is subject to change without notice.

3. Dimension does not include mold protrusion. Maximum allowable mold protrusion .01 in [0.25 mm] per side.

4. Reference JEDEC registration MS-018.

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EXAMPLE BOARD LAYOUT

FN0044A

PLCC - 4.57 mm max height

PLASTIC CHIP CARRIER

SYMM

44X (.093 )

[2.35]

44

40

6

1

7

39

44X (.030 )

[0.75]

SYMM

(.64

)

[16.2]

40X (.050 )

[1.27]

29

17

(R.002 ) TYP

[0.05]

18

28

(.64

)

[16.2]

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE:4X

.002 MIN

[0.05]

ALL AROUND

.002 MAX

[0.05]

ALL AROUND

EXPOSED METAL

METAL UNDER

SOLDER MASK

OPENING

METAL

SOLDER MASK

OPENING

NON SOLDER MASK

DEFINED

SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK DETAILS

4215154/A 04/2017

NOTES: (continued)

5. Publication IPC-7351 may have alternate designs.

6. Solder mask tolerances between and around signal pads can vary based on board fabrication site.

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EXAMPLE STENCIL DESIGN

FN0044A

PLCC - 4.57 mm max height

PLASTIC CHIP CARRIER

SYMM

44X (.093 )

[2.35]

6

44

40

1

7

39

44X (.030 )

[0.75]

SYMM

(.64

)

[16.2]

40X (.050 )

[1.27]

29

17

(R.002 ) TYP

[0.05]

18

28

(.64

)

[16.2]

SOLDER PASTE EXAMPLE

BASED ON 0.125 mm THICK STENCIL

SCALE:4X

4215154/A 04/2017

NOTES: (continued)

7. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate

design recommendations.

8. Board assembly site may have different recommendations for stencil design.

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IMPORTANT NOTICE AND DISCLAIMER

TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATA SHEETS), DESIGN RESOURCES (INCLUDING REFERENCE

DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”

AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY

IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD

PARTY INTELLECTUAL PROPERTY RIGHTS.

These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate

TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable

standards, and any other safety, security, regulatory or other requirements.

These resources are subject to change without notice. TI grants you permission to use these resources only for development of an

application that uses the TI products described in the resource. Other reproduction and display of these resources is prohibited. No license

is granted to any other TI intellectual property right or to any third party intellectual property right. TI disclaims responsibility for, and you

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TI objects to and rejects any additional or different terms you may have proposed. IMPORTANT NOTICE

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265


型号：	LM12458CIVX/NOPB
厂家：	TEXAS INSTRUMENTS
描述：	具有自校准功能的 88kSPS、12 位 + 符号数据采集系统 \| FN \| 44 \| -40 to 85
文件：	总47页 (文件大小：1867K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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