LT1073CS8-12#PBF_技术文档

LT1073

Micropower

DC/DC Converter

Adjustable and Fixed 5V, 12V

FEATURES

DESCRIPTION

TheLT^®1073isaversatilemicropowerDC/DCconverter.The

device requires only three external components to deliver

a fixed output of 5V or 12V. The very low minimum supply

voltage of 1V allows the use of the LT1073 in applications

wheretheprimarypowersourceisasinglecell.Anon-chip

auxiliary gain block can function as a low-battery detector

or linear post-regulator.

n

No Design Required

n

Operates at Supply Voltages from 1V to 30V

n

Consumes Only 95µA Supply Current

Works in Step-Up or Step-Down Mode

n

Only Three External Off-the-Shelf Components

Required

n

Low-Battery Detector Comparator On-Chip

n

User-Adjustable Current Limit

Internal 1A Power Switch

Average current drain of the LT1073-5 used as shown in

theTypicalApplicationcircuitbelowisjust135µAunloaded,

making it ideal for applications where long battery life is

important. The circuit shown can deliver 5V at 40mA from

an input as low as 1.25V and 5V at 10mA from a 1V input.

n

Fixed or Adjustable Output Voltage Versions

Space-Saving 8-Pin PDIP or SO-8 Package

n

APPLICATIONS

The device can easily be configured as a step-up or step-

downconverter,althoughformoststep-downapplications

or input sources greater than 3V, the LT1173 is recom-

mended. Switch current limiting is user-adjustable by

adding a single external resistor. Unique reverse-battery

protection circuitry limits reverse current to safe, non-

destructive levels at reverse supply voltages up to 1.6V.

n

Pagers

n

Cameras

n

Single-Cell to 5V Converters

n

Battery Backup Supplies

n

Laptop and Palmtop Computers

n

Cellular Telephones

Portable Instruments

n

L, LTC, and LT are registered trademarks of Linear Technology Corporation.

n

4mA to 20mA Loop Powered Instruments

n

Hand-Held Inventory Computers

n

Battery-Powered α, β, and γ Particle Detectors

TYPICAL APPLICATION

Single Alkaline “AA” Cell Operating

Hours vs DC Load Current

Single-Cell to 5V Converter

1000

CADDELL-BURNS

7300-12

1N5818

82µH

5V

40mA

100

2

1

I

V

LIM

IN

3

8

SW1

LT1073-5

L = 180µH

1.5V

AA CELL*

10

SENSE

+

100µF

SANYO

0S-CON

GND

5

SW2

4

L = 82µH

1

10

100

OPERATES WITH CELL VOLTAGE ≥1V

ADD 10µF DECOUPLING CAPACITOR IF

LOAD CURRENT (mA)

*

LT1073 TA02

BATTERY IS MORE THAN 2" AWAY FROM LT1073

1073 TA01

1

LT1073

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

ORDER PART

NUMBER

Supply Voltage, Step-Up Mode.................................15V

Supply Voltage, Step-Down Mode ............................36V

SW1 Pin Voltage.......................................................50V

TOP VIEW

LT1073CN8

I

1

2

3

4

FB (SENSE)*

8

7

6

5

LIM

SW2 Pin Voltage............................................–0.4 to V

LT1073CN8-5

LT1073CN8-12

LT1073CS8

IN

V

SET

A0

IN

Feedback Pin Voltage (LT1073)...................................5V

Switch Current.........................................................1.5A

Maximum Power Dissipation ............................. 500mW

Operating Temperature Range ..................... 0°C to 70°C

Storage Temperature Range .................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)...................300°C

SW1

SW2

GND

LT1073CS8-5

LT1073CS8-12

N8 PACKAGE

8-LEAD PDIP

S8 PACKAGE

8-LEAD PLASTIC SO

*FIXED VERSIONS

S8 PART MARKING

T

= 125°C, θ = 100°C/W (N8)

JMAX

JA

= 125°C, θ = 120°C/W (S8)

1073

JA

10735

107312

Consult factory for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_IN= 1.5V unless otherwise specified.

SYMBOL

PARAMETER

CONDITIONS

Switch Off

No Load

MIN

TYP

MAX

UNITS

l

I

Quiescent Current

95

130

µA

Q

Quiescent Current, Step-Up

Mode Configuration

LT1073-5

LT1073-12

135

250

µA

V

Input Voltage

Step-Up Mode

1.15

1.0

12.6

V

IN

l

Step-Down Mode

LT1073 (Note 2)

30

V

Comparator Trip Point Voltage

Output Sense Voltage

202

212

222

mV

l

V

OUT

LT1073-5 (Note 3)

LT1073-12 (Note 3)

4.75

11.4

5

12

5.25

12.6

V

l

Comparator Hysteresis

Output Hysteresis

LT1073

5

10

mV

l

LT1073-5

LT1073-12

125

300

250

600

mV

l

f

Oscillator Frequency

Duty Cycle

15

65

30

19

72

23

80

kHz

%

OSC

DC

Full Load (V = V

)

REF

FB

t

I

Switch ON Time

38

50

µs

nA

V

ON

FB

Feedback Pin Bias Current

Set Pin Bias Current

AO Output Low

LT1073, V = 0V

10

50

FB

V

= V

REF

60

120

0.4

SET

V

I

= –100µA

AO

0.15

AO

l

Reference Line Regulation

1V ≤ V ≤ 1.5V

0.35

0.05

1.0

0.1

%V

IN

1.5V ≤ V ≤ 12V

IN

V

Switch Saturation Voltage

Set-Up Mode

V

= 1.5V, I = 400mA

300

400

600

mV

CESAT

IN

SW

l

= 1.5V, I = 500mA

400

550

750

mV

SW

= 5V, I = 1A

700

1000

1500

mV

SW

l

A

A2 Error Amp Gain

R = 100kΩ (Note 4)

400

1000

V/V

V

L

2

LT1073

ELECTRICAL CHARACTERISTICS ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_IN= 1.5V unless otherwise specified.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

750

400

–0.3

1

MAX

UNITS

mA

I

Reverse Battery Current

Current Limit

(Note 5)

REV

LIM

220Ω Between I and V

mA

LIM

IN

Current Limit Temperature Coefficient

Switch OFF Leakage Current

Maximum Excursion Below GND

%/°C

µA

I

Measured at SW1 Pin

10

LEAK

V

I

≤ 10µA, Switch Off

SW1

–400

–350

mV

SW2

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 4: 100k resistor connected between a 5V source and the AO pin.

Note 5: The LT1073 is guaranteed to withstand continuous application of

Note 2: This specification guarantees that both the high and low trip point

of the comparator fall within the 202mV to 222mV range.

1.6V applied to the GND and SW2 pins while V , I and SW1 pins are

grounded.

IN LIM

Note 3: This specification guarantees that the output voltage of the fixed

versions will always fall within the specified range. The waveform at the

SENSE pin will exhibit a sawtooth shape due to the comparator hysteresis.

TYPICAL PERFORMANCE CHARACTERISTICS

Saturation Voltage Step-Up Mode

(SW2 Pin Grounded)

Switch ON Voltage Step-Down Mode

(SW1 Pin Connected to V_IN)

Maximum Switch Current vs R_LIM

1.2

1.0

0.8

0.6

0.4

0.2

0

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

1200

1100

1000

900

800

700

600

500

400

300

200

100

V

= 1.5V

L = 82µH

IN

V

= 3V

IN

V

= 1.25V

IN

V

= 1V

IN

V

= 5V

IN

V

IN

= 1.5V

V

= 3V

IN

V

= 2V

IN

0

0.4

0.6

0.8

1.0

1.2

0

0.1 0.2 0.3 0.4 0.5

(A)

0.6

0.7 0.8

10

100

(Ω)

1000

0.2

R

I

(A)

I

LIM

SWITCH

1073 G03

1073 G01

1073 G02

FB Pin Bias Current vs

Temperature

SET Pin Bias Current vs

Temperature

“Gain Block” Gain

20

18

16

14

12

10

8

200

175

150

125

100

75

1800

1600

1400

1200

1000

800

600

400

200

0

V

= 1.5V

= 100k

IN

L

R

50

6

25

4

0

–25

0

25

50

75

125

–25

0

25

50

75

125

–25

0

25

50

75

125

–50

100

–50

100

–50

100

TEMPERATURE (°C)

1073 G04

1073 G05

1073 G06

3

LT1073

TYPICAL PERFORMANCE CHARACTERISTICS

Recommended Minimum

Inductance Value

Guaranteed Minimum Output

Current at 5V vs V_IN

Supply Current vs Temperature

150

140

130

120

110

100

90

1000

100

10

300

250

200

150

100

50

V

= 1.5V

IN

R

LIM

= 0V

80

FOR V > 1.6V A

IN

70

68Ω RESISTOR

MUST BE CONNECTED

60

BETWEEN I

AND V

LIM

IN

50

0

–25

0

25

50

75

100

125

1.0

1.5

2.0

V

2.5

(V)

3.0

3.5

–50

1.0

3.0

4.0 4.5

1.5 2.0 2.5

3.5

5.0

INPUT VOLTAGE (V)

TEMPERATURE (°C)

IN

1073 G09

1073 G07

1073 G08

PIN FUNCTIONS

I

(Pin 1): Connect this pin to V for normal use. Where

GND (Pin 5): Ground.

LIM

IN

lower current limit is desired, connect a resistor between

and V . A 220Ω resistor will limit the switch current

AO (Pin 6): Auxiliary Gain Block (GB) Output. Open col-

I

LIM

IN

lector, can sink 100µA.

to approximately 400mA.

SET (Pin 7): GB Input. GB is an op amp with positive

input connected to SET pin and negative input connected

to 212mV reference.

V (Pin 2): Input Supply Voltage

IN

SW1 (Pin 3): Collector of Power Transistor. For step-up

mode connect to inductor/diode. For step-down mode

FB/SENSE(Pin8):OntheLT1073(adjustable)thispingoes

tothecomparatorinput. OntheLT1073-5andLT1073-12,

this pin goes to the internal application resistor that sets

output voltage.

connect to V .

IN

SW2 (Pin 4): Emitter of Power Transistor. For step-up

mode connect to ground. For step-down mode connect

to inductor/diode. This pin must never be allowed to go

more than a Schottky diode drop below ground.

BLOCK DIAGRAMS

LT1073-5 and LT1073-12

SET

+

–

LT1073

A2

A0

SET

+

–

A2

A0

GAIN BLOCK/ERROR AMP

V

IN

I

SW1

GAIN BLOCK/ERROR AMP

LIM

V

IN

212mV

REFERENCE

I

SW1

Q1

LIM

A1

OSCILLATOR

Q1

212mV

REFERENCE

DRIVER

A1

OSCILLATOR

SW2

COMPARATOR

GND

DRIVER

R2

940k

SW2

COMPARATOR

R1

LT1073-5: R1 = 40k

LT1073-12: R2 = 16.3k

FB

1073 BD01

SENSE

1073 BD02

GND

4

LT1073

OPERATION

LT1073

The LT1073 is gated oscillator switcher. This type archi-

tecture has very low supply current because the switch is

cycledonlywhenthefeedbackpinvoltagedropsbelowthe

referencevoltage.Circuitoperationcanbestbeunderstood

by referring to the LT1073 Block Diagram. Comparator A1

compares the FB pin voltage with the 212mV reference

signal. When FB drops below 212mV, A1 switches on the

19kHz oscillator. The driver amplifier boosts the signal

level to drive the output NPN power switch Q1. An adap-

tive base drive circuit senses switch current and provides

justenoughbasedrivetoensureswitchsaturationwithout

overdriving the switch, resulting in higher efficiency. The

switch cycling action raises the output voltage and FB pin

voltage. When the FB voltage is sufficient to trip A1, the

oscillator is gated off. A small amount of hysteresis built

into A1 ensures loop stability without external frequency

compensation. When the comparator is low the oscillator

and all high current circuitry is turned off, lowering device

quiescentcurrenttojust95µAforthereference,A1andA2.

A resistor connected between the I pin and V adjusts

LIM

IN

maximumswitchcurrent.Whentheswitchcurrentexceeds

the set value, the switch is turned off. This feature is espe-

cially useful when small inductance values are used with

high input voltages. If the internal current limit of 1.5A is

desired, I

should be tied directly to V . Propagation

LIM

IN

delay through the current-limit circuitry is about 2µs.

In step-up mode, SW2 is connected to ground and SW1

drivestheinductor.Instep-downmode,SW1isconnected

to V and SW2 drives the inductor. Output voltage is set

IN

by the following equation in either step-up or step-down

modes where R1 is connected from FB to GND and R2 is

connected from V

to FB.

OUT









R2

R1

V_OUT= 212mV

+1





(

)

LT1073-5 and LT1073-12

TheLT1073-5andLT1073-12fixedoutputvoltageversions

have the gain-setting resistor on-chip. Only three external

components are required to construct a fixed-output con-

verter. 5µA flows through R1 and R2 in the LT1073-5, and

12.3µA flows in the LT1073-12. This current represents

a load and the converter must cycle from time to time to

maintain the proper output voltage. Output ripple, inher-

ently present in gated-oscillator designs, will typically

run around 150mV for the LT1073-5 and 350mV for the

LT1073-12 with the proper inductor/capacitor selection.

This output ripple can be reduced considerably by using

the gain block amp as a preamplifier in front of the FB

pin. See the Applications Information section for details.

The oscillator is set internally for 38µs ON time and 15µs

OFF time, optimizing the device for step-up circuits where

V

≈ 3V , e.g., 1.5V to 5V. Other step-up ratios as well

OUT

IN

as step-down (buck) converters are possible at slight

losses in maximum achievable power output.

A2 is a versatile gain block that can serve as a low-battery

detector, a linear post-regulator, or drive an undervolt-

age lockout circuit. The negative input of A2 is internally

connected to the 212mV reference. An external resistor

divider from V to GND provides the trip point for A2. The

IN

AO output can sink 100µA (use a 56k resistor pull-up to

5V). This line can signal a microcontroller that the battery

voltage has dropped below the preset level.

5

LT1073

APPLICATIONS INFORMATION

Table 1. Component Selection for Step-Up Converters

INPUT

VOLTAGE (V)

BATTERY

TYPE

OUTPUT

VOLTAGE (V)

OUTPUT

CURRENT (MIN)

INDUCTOR

VALUE (µH)

INDUCTOR

PART NUMBER

CAPACITOR

VALUE (µF)

NOTES

1.55-1.25

1.30-1.05

1.55-1.25

1.30-1.05

3.1-2.1

Single Alkaline

Single Ni-Cad

Single Alkaline

Single Ni-Cad

Two Alkaline

Lithium

3

60mA

20mA

30mA

10mA

80mA

25mA

100mA

25mA

5mA

82

180

82

G GA10-822K, CB 7300-12

G GA10-183K, CB 7300-16

G GA10-822K, CB 7300-12

G GA10-183K, CB 7300-16

G GA10-123K, CB 7300-14

G GA10-473K, CB 7300-21

G GA40-153K, CB 6860-15

G GA10-123K, CB 7300-14

G GA10-473K, CB 7300-21

G GA10-153K, CB 7300-15

G GA40-223K, CB 6860-17

G GA10-104K, CB 7300-25

G GA40-223K, CB 6860-17

150

47

5

100

22

5

180

120

470

150

120

470

150

220

1000

220

5

470

150

470

220

100

220

470

100

150

*

3.1-2.1

5

3.3-2.5

5

3.1-2.1

Two Alkaline

Lithium

12

24

3.1-2.1

3.3-2.5

30mA

90mA

22mA

35mA

4.5-5.5

TTL Supply

*

4.5-5.5

G = GOWANDA

CB = CADDELL-BURNS

*Add 68Ω from I to V

LIM IN

Measuring Input Current at Zero or Light Load

LT1073. The circuit must be “booted” by shorting V2 to

. After the LT1073 output voltage has settled, dis-

V

SET

Obtaining meaningful numbers for quiescent current and

efficiency at low output current involves understanding

howtheLT1073operates. Atveryloworzeroloadcurrent,

the device is idling for seconds at a time. When the output

voltage falls enough to trip the comparator, the power

switch comes on for a few cycles until the output voltage

rises sufficiently to overcome the comparator hysteresis.

When the power switch is on, inductor current builds up

to hundreds of milliamperes. Ordinary digital multimeters

are not capable of measuring average current because

of bandwidth and dynamic range limitations. A different

approach is required to measure the 100µA off-state and

500mA on-state currents of the circuit.

connect the short. Input voltage is V2 and average input

current can be calculated by this formula:

V2– V1

100Ω

I =

IN

Inductor Selection

ADC/DCconverteroperatesbystoringenergyasmagnetic

flux, in an inductor core and then switching this energy

into the load. Since it is flux, not charge, that is stored,

the output voltage can be higher, lower, or opposite in

polarity to the input voltage by choosing an appropriate

switching topology. To operate as an efficient energy

transfer element, the inductor must fulfill three require-

ments. First, the inductance must be low enough for the

inductor to store adequate energy under the worst-case

condition of minimum input voltage and switch ON time.

The inductance must also be high enough so that maxi-

mum current ratings of the LT1073 and inductor are not

exceeded at the other worst-case condition of maximum

input voltage and ON time. Additionally, the inductor

core must be able to store the required flux, i.e., it must

not saturate. At power levels generally encountered

with LT1073-based designs, small axial-lead units with

1MΩ

12V

1µF*

–

100Ω

LT1073

LTC1050

CIRCUIT

V1

V2

+

1000µF

*NONPOLARIZED

V

SET

1073 F01

Figure 1. Test Circuit Measures No-Load

Quiescent Current of LT1073 Converter

Quiescent current can be accurately measured using the

circuit in Figure 1. V

is set to the input voltage of the

SET

6

LT1073

APPLICATIONS INFORMATION

1200

1000

800

600

400

200

0

saturation current ratings in the 300mA to 1A range (de-

pending on application) are adequate. Lastly, the inductor

must have sufficiently low DC resistance so that excessive

power is not lost as heat in the windings. An additional

consideration is electro-magnetic interference (EMI).

Toroid and pot core type inductors are recommended in

applications where EMI must be kept to a minimum; for

example, where there are sensitive analog circuitry or

transducers nearby. Rod core types are a less expensive

choice where EMI is not a problem.

0

1

2

3

4

5

V

(V)

Specifying a proper inductor for an application requires

first establishing minimum and maximum input voltage,

output voltage and output current. In a step-up converter,

the inductive events add to the input voltage to produce

the output voltage. Power required from the inductor is

determined by:

IN

1073 F02

Figure 2. Maximum Switch Current vs Input Voltage

Capacitor Selection

Selecting the right output capacitor is almost as important

as selecting the right inductor. A poor choice for a filter

capacitor can result in poor efficiency and/or high output

ripple.Ordinaryaluminumelectrolytics,whileinexpensive

andreadilyavailable, mayhaveunacceptablypoorequiva-

lent series resistance (ESR) and ESL (inductance). There

arelow-ESRaluminumcapacitorsonthemarketspecifically

designed for switch-mode DC/DC converters which work

much better than general purpose units. Tantalum capaci-

tors provide still better performance at more expense. We

recommend OS-CON capacitors from Sanyo Corporation

(SanDiego,CA).Theseunitsarephysicallyquitesmalland

have extremely low ESR. To illustrate, Figures 3, 4, and 5

showtheoutputvoltageofanLT1073basedconverterwith

three 100µF capacitors. The peakswitch current is 500mA

in all cases. Figure 3 shows a Sprague 501D aluminum

P = (V

+ V – V )(I

)

L

OUT

D

IN OUT

where V is the diode drop (0.5V for a 1N5818 Schottky).

D

Maximum power in the inductor is

P_L=E_L•f_OSC

1

= L i_PEAK²•f_OSC

2

where















^ON



V_IN

R

–Rt

L

i_PEAK

=

1–e

R = Switch equivalent resistance (1Ω maximum)

added to the DC resistance of the inductor and t = ON

ON

capacitor. V

jumps by over 150mV when the switch

OUT

time of the switch.

turns off, followed by a drop in voltage as the inductor

dumps into the capacitor. This works out to be an ESR of

over 300mΩ. Figure 4 shows the same circuit, but with a

Sprague150Dtantalumcapacitorreplacingthealuminum

unit. Output jump is now about 30mV, corresponding to

an ESR of 60mΩ. Figure 5 shows the circuit with an OS-

CON unit. ESR is now only 30mΩ.

At maximum V and ON time, i

should not be al-

PEAK

IN

lowed to exceed the maximum switch current shown in

Figure 2. Some input/output voltage combinations will

1

cause continuous mode operation. In these cases a

resistor is needed between I

(Pin 1) and V (Pin 2)

LIM

IN

to keep switch current under control. See the “Using the

I

Pin” section for details.

LIM

In very low power applications where every microampere

is important, leakage current of the capacitor must be

considered. The OS-CON units do have leakage cur-

rent in the 5µA to 10µA range. If the load is also in the

NOTE 1: i.e., inductor current does not go to zero when the switch is off.

7

LT1073

APPLICATIONS INFORMATION

50mV/DIV

20µs/DIV

Figure 3. Aluminum

Figure 4. Tantalum

Figure 5. OS-CON

microampere range, a leaky capacitor will noticeably

decrease efficiency. In this type application tantalum ca-

pacitors are the best choice, with typical leakage currents

in the 1µA to 5µA range.

not short-circuit protected since there is a DC path from

input to output.

The usual step-up configuration for the LT1073 is shown

in Figure 6. The LT1073 first pulls SW1 low causing V -

IN

V

to appear across L1. A current then builds up in

CESAT

Diode Selection

2

L1. At the end of the switch ON time the current in L1 is :

Speed, forward drop and leakage current are the three

main considerations in selecting a catch diode for LT1073

converters. “General-purpose” rectifiers such as the

1N4001 are unsuitable for use in any switching regulator

application. Although they are rated at 1A, the switching

time of a 1N4001 is in the 10µs to 50µs range. At best,

efficiency will be severely compromised when these

diodes are used and at worst, the circuit may not work at

all. Most LT1073 circuits will be well served by a 1N5818

Schottky diode. The combination of 500mV forward drop

at 1A current, fast turn-on and turn-off time and 4µA to

10µA leakage current fit nicely with LT1073 requirements.

Atpeakswitchcurrentsof100mAorless, a1N4148signal

diode may be used. This diode has leakage current in the

1nA to 5nA range at 25°C and lower cost than a 1N5818.

(You can also use them to get your circuit up and running,

but beware of destroying the diode at 1A switch currents.)

InsituationswheretheloadisintermittentandtheLT1073

is idling most of the time, battery life can sometimes be

extended by using a silicon diode such as the 1N4933,

which can handle 1A but has leakage current of less than

1µA. Efficiency will decrease somewhat compared to a

1N5818 while delivering power, but the lower idle current

may be more important.

V_IN

L

i_PEAK

=

t_ON

NOTE 2: This simple expression neglects the effect of switch and coil resistance. These are

taken into account in the “Inductor Selection” section.

D1

L1

V

IN

OUT

R3*

I

V

IN

LIM

R2

R1

SW1

LT1073

+

C1

FB

GND

SW2

1073 F06

*= OPTIONAL

Figure 6. Step-Up Mode Hookup.

(Refer to Table 1 for Component Values)

Immediately after switch turn-off, the SW1 voltage pin

starts to rise because current cannot instantaneously

stop flowing in L1. When the voltage reaches V

+ V ,

OUT

D

the inductor current flows through D1 into C1, increasing

V

. This action is repeated as needed by the LT1073 to

OUT

keep V at the internal reference voltage of 212mV. R1

FB

and R2 set the output voltage according to the formula:

Step-Up (Boost Mode) Operation











R2

R1

A step-up DC/DC converter delivers an output voltage

higher than the input voltage. Step-up converters are

V_OUT= 1+

212mV



(

)

8

LT1073

APPLICATIONS INFORMATION

Step-Down (Buck Mode) Operation

saturating the inductor. The 220Ω resistor programs the

switch to turn off when the current reaches approximately

400mA.WhenusingtheLT1073instep-downmode,output

voltage should be limited to 6.2V or less.

A step-down DC/DC converter converts a higher voltage

to a lower voltage. It is short-circuit protected because the

switch is in series with the output. Step-down converters

are characterized by low output voltage ripple but high in-

put current ripple. The usual hookup for an LT1073-based

step-down converter is shown in Figure 7.

Inverting Configurations

The LT1073 can be configured as a positive-to-negative

converter (Figure 8), or a negative-to-positive converter

(Figure 9). In Figure 8, the arrangement is very similar to

a step-down, except that the high side of the feedback is

referred to ground. This level shifts the output negative.

As in the step-down mode, D1 must be a Schottky diode,

V

IN

R3

220Ω

I

V

SW1

FB

LIM IN

LT1073

SW2

and V  should be less than 6.2V.

L1

OUT

+

V

OUT

C2

InFigure9,theinputisnegativewhiletheoutputispositive.

In this configuration, the magnitude of the input voltage

canbehigherorlowerthantheoutputvoltage.Alevelshift,

provided by the PNP transistor, supplies proper polarity

feedback information to the regulator.

R2

GND

+

D1

1N5818

C1

R1

1073 FO7

Figure 7. Step-Down Mode Hookup

+V

IN

+

C2 R3

When the switch turns on, SW2 pulls up to V – V

.

,

IN

SW

This puts a voltage across L1 equal to V – V – V

I

V

SW1

FB

LIM IN

IN

SW

OUT

causing a current to build up in L1. At the end of the

switch ON time, the current in L1 is equal to

LT1073

SW2

L1

V – V_SW– V_OUT

IN

GND

R1

R2

i_PEAK

=

t_ON

L

+

D1

C1

When the switch turns off the SW2 pin falls rapidly and

actually goes below ground. D1 turns on when SW2

reaches 0.4V below ground. D1 MUST BE A SCHOTTKY

DIODE. The voltage at SW2 must never be allowed to go

below –0.5V. A silicon diode such as the 1N4933 will al-

low SW2 to go to –0.8V, causing potentially destructive

power dissipation inside the LT1073. Output voltage is

determined by

1N5818

–V

OUT

1073 FO8

Figure 8. Positive-to-Negative Converter

D1

L1

+V

OUT

+

C1

R1

I

V

IN

LIM











R2

R1

SW1

LT1073

2N3906

+

V_OUT= 1+

212mV



(

)

C2

AO

FB

R3 programs switch current limit. This is especially im-

portant in applications where the input varies over a wide

range.WithoutR3,theswitchstaysonforafixedtimeeach

cycle. Under certain conditions the current in L1 can build

up to excessive levels, exceeding the switch rating and/or

GND

SW2

R2

–V

IN

R1

V

=

(_R2)212mV + 0.6V

OUT

1073 F09

Figure 9. Negative-to-Positive Converter

9

LT1073

APPLICATIONS INFORMATION

Figure 10, the inductor current increases to a high level

before the comparator turns off the oscillator. This high

current can cause excessive output ripple and requires

oversizing the output capacitor and inductor. With the

Using the I Pin

LIM

The LT1073 switch can be programmed to turn off at a set

switch current, a feature not found on competing devices.

This enables the input to vary over a wide range without

exceeding the maximum switch rating or saturating the

inductor. Consider the case where analysis shows the

LT1073 must operate at an 800mA peak switch current

I

feature, however, the switch current turns off at a

LIM

programmed level as shown in Figure 11, keeping output

ripple to a minimum.

with a 2V input. If V rises to 4V, the peak switch current

will rise to 1.6A, exceeding the maximum switch current

IN

Using the Gain Block

The gain block (GB) on the LT1073 can be used as an er-

ror amplifier, low-battery detector or linear post-regulator.

The gain block itself is a very simple PNP input op amp

with an open-collector NPN output. The (–) input of the

gain block is tied internally to the 212mV reference. The

(+) input comes out on the SET pin.

rating.Withtheproperresistor(seethe“MaximumSwitch

Current vs R ” characteristic) selected, the switch cur-

LIM

rent will be limited to 800mA, even if the input voltage

increases. The LT1073 does this by sampling a small

fraction of the switch current and passing this current

through the external resistor. When the voltage on the I

LIM

Arrangement of the gain block as a low battery detector

is straightforward. Figure 12 shows hookup. R1 and R2

need only be low enough in value so that the bias current

of the SET input does not cause large errors. 100kΩ for

R2 is adequate.

pin drops a V below V , the oscillator terminates the

cycle. Propagation delay through this loop is about 2µs.

BE

IN

Another situation where the I feature is useful is when

LIM

the device goes into continuous mode operation. This

occurs in step-up mode when

Output ripple of the LT1073, normally 150mV at 5V

,

OUT

V_OUT+V_DIODE

1

can be reduced significantly by placing the gain block in

front of the FB input as shown in Figure 13. This effectively

reduces the comparator hysteresis by the gain of the gain

block. Output ripple can be reduced to just a few millivolts

using this technique. Ripple reduction works with step-

down or inverting modes as well.

<

V – V

1–DC

IN

SW

When the input and output voltages satisfy this relation-

ship, inductor current does not go to zero during the

switch OFF time. When the switch turns on again, the

current ramp starts from the nonzero current level in

the inductor just prior to switch turn-on. As shown in

PROGRAMMED CURRENT LIMIT

I

L

I

L

ON

SWITCH

OFF

1073 F10

1073 F11

Figure 10. No Current Limit Causes

Large Inductor Current Build-Up

Figure 11. Current Limit Keeps Inductor Current Under Control

10

LT1073

APPLICATIONS INFORMATION

D1

L1

5V

V

OUT

V

IN

LT1073

R3

680k

100k

212mV

REF

–

+

I

V

R1

R2

LIM

IN

SW1

LT1073

R2

V

A0

TO

BAT

AO

+

PROCESSOR

SET

C1

FB

SET

GND

V

BAT

LB

GND

SW2

R1 = R2

(

–1

)

R1

212mV

= BATTERY TRIP POINT

1073 F12

V

LB

1073 F13

R2

R1

V

=

+ 1 212mV

(

)

OUT

(

Figure 12. Settling Low Battery Detector Trip Point

Table 2. Inductor Manufacturers

Figure 13. Output Ripple Reduction Using Gain Block

Table 3. Capacitor Manufacturers

MANUFACTURER

PART NUMBERS

MANUFACTURER

PART NUMBERS

Gowanda Electronics Corporation

1 Industrial Place

Gowanda, NY 14070

716-532-2234

GA10 Series

GA40 Series

Sanyo Video Components

1201 Sanyo Avenue

San Diego, CA 92073

619-661-6322

OS-CON Series

Caddell-Burns

7300 Series

6860 Series

Nichicon America Corporation

927 East State Parkway

Schaumberg, IL 60173

708-843-7500

PL Series

258 East Second Street

Mineola, NY 11501

516-746-2310

Coiltronics International

984 S.W. 13th Court

Pompano Beach, FL 33069

305-781-8900

Custom Toroids

Surface Mount

Sprague Electric Company

Lower Main Street

Stanford, ME 04073

207-324-4140

150D Solid Tantalums

550D Tantalex

Toko America Incorporated

1250 Feehanville Drive

Mount Prospect, IL 60056

312-297-0070

Type 8RBS

Renco Electronics Incorporated

60 Jefryn Boulevard, East

Deer Park, NY 11729

800-645-5828

RL1283

RL1284

TYPICAL APPLICATIONS

1.5V to 3V Step-Up Converter

1.5V to 9V Step-Up Converter

L1^†

120µH

L1^†

1N5818

120µH

9V OUTPUT

3V OUTPUT

7mA AT V

= 1V

= 1.5V

20mA AT

BATTERY

16mA AT V

V

= 1V

BATTERY

220Ω

I

V

I

V

LIM

IN

SW1

LT1073

LIM

IN

SW1

LT1073

1M*

536k*

+

1.5V

CELL

1.5V

CELL

47µF

100µF

FB

GND

SW2

GND

SW2

24.3k*

40.2k*

* 1% METAL FILM

L1 = GOWANDA GA10-123k

OR CADDELL-BURNS 7300-14

* 1% METAL FILM

L1 = GOWANDA GA10-123k

OR CADDELL-BURNS 7300-14

†

1073 TA04

1073 TA03

11

LT1073

TYPICAL APPLICATIONS

1.5V to 12V Step-Up Converter

3V to 5V Step-Up Converter

L1^†

120µH

L1^†

1N5818

68µH

12V OUTPUT

5mA AT V

5V OUTPUT

100mA AT

= 1V

= 1.5V

BATTERY

16mA AT V

V

= 2V

BATTERY

100Ω

I

V

I

V

IN

LIM

IN

LIM

SW1

LT1073-12

SW1

LT1073-5

+

TWO

1.5V

CELLS

1.5V

CELL

47µF

100µF

SENSE

SW2

SENSE

SW2

GND

†

L1 = GOWANDA GA10-123k

OR CADDELL-BURNS 7300-14

L1 = GOWANDA GA10-682k

OR CADDELL-BURNS 7300-11

1073 TA06

1073 TA05

3V to 12V Step-Up Converter

3V to 15V Step-Up Converter

L1^†

1N5818

68µH

1N5818

68µH

12V OUTPUT

35mA AT

BATTERY

15V OUTPUT

27mA AT

V

= 2V

V

= 2V

BATTERY

100Ω

1M*

I

V

I

V

IN

LIM

IN

LIM

SW1

LT1073-12

SW1

LT1073

+

TWO

1.5V

CELLS

TWO

1.5V

CELLS

47µF

SENSE

SW2

FB

GND

SW2

14.3k*

†

L1 = GOWANDA GA10-682k

OR CADDELL-BURNS 7300-11

* 1% METAL FILM

L1 = GOWANDA GA10-682k

OR CADDELL-BURNS 7300-11

†

1073 TA07

1073 TA08

5V to 12V Step-Up Converter

5V to 15V Step-Up Converter

L1^†

1N5818

150µH

1N5818

150µH

12V OUTPUT

130mA AT 4.5V

15V OUTPUT

100mA AT 4.5V

5V

IN

50Ω

1M*

I

V

I

V

IN

LIM

IN

LIM

SW1

LT1073-12

SW1

LT1073

+

100µF

SENSE

SW2

FB

GND

SW2

14.3k*

†

L1 = GOWANDA GA20-153k

OR CADDELL-BURNS 7200-15

* 1% METAL FILM

1073 TA09

1073 TA10

† L1 = GOWANDA GA20-153k

OR CADDELL-BURNS 7200-15

12

LT1073

TYPICAL APPLICATIONS

1.5V to 5V Step-Up Converter with Logic Shutdown

1.5V to 5V Step-Up Converter with Low-Battery Detector

L1^†

82µH

1N5818

82µH

1N5818

5V OUTPUT

100k

909k*

442k*

100k*

I

V

I

V

IN

LIM

IN

SW1

LT1073

LIM

1.5V

CELL

SET

SW1

+

1.5V

CELL

100µF

LT1073-5

FB

AO

SENSE

SW2

GND

SW2

GND

LO BAT

1N4148

74C04

40.2k*

GOES LOW

AT V

BATTERY

= 1.15V

* 1% METAL FILM

L1 = GOWANDA GA10-822k

OR CADDELL-BURNS 7300-12

†

1073 TA11

1073 TA12

SHUTDOWN

* 1% METAL FILM

L1 = GOWANDA GA10-822k

OR CADDELL-BURNS 7300-12

OPERATE

†

9V to 5V Step-Down Converter

9V to 3V Step-Down Converter

3V OUTPUT

220Ω

I

V

I

V

LIM

IN

SW1

LT1073-5

LIM

IN

SW1

LT1073

536k*

9V

BATTERY

9V

BATTERY

5V OUTPUT

SENSE

SW2

FB

L1^†

100µH

L1^†

100µH

GND

SW2

40.2k*

+

1N5818

100µF

1N5818

100µF

†

L1 = GOWANDA GA10-103k

OR CADDELL-BURNS 7300-13

* 1% METAL FILM

L1 = GOWANDA GA10-103k

OR CADDELL-BURNS 7300-13

1073 TA14

†

1073 TA13

1.5V to 5V Bootstrapped Step-Up Converter

Memory Backup Supply

L1^†

5V TO MEMORY,

4.5V WHEN MAIN

SUPPLY OPEN

5V MAIN

SUPPLY

1N5818

47µH

5V OUTPUT

50mA

L1^†

2N3906

56Ω

1N5818

82µH

2.2k

+

I

V

LIM

IN

SW1

LT1073

I

V

1.5V

CELL

LIM

IN

SW1

LT1073-5

806k*

100µF

+

1.5V

CELL

100µF**

FB

SENSE

SW2

GND

SW2

GND

40.2k*

* 1% METAL FILM

†

L1 = GOWANDA GA10-123k

OR CADDELL-BURNS 7300-14

1073 TA16

**OPTIONAL

1073 TA15

†

L1 = GOWANDA GA10-822k

OR CADDELL-BURNS 7300-12

MINIMUM START-UP VOLTAGE = 1.1V

13

LT1073

TYPICAL APPLICATIONS

3V to 5V Step-Up Converter with Undervoltage Lockout

1.5V to 5V Low Noise Step-Up Converter

L1^†

1N5818

82µH

5V OUTPUT

100mA

1N5818

68µH

5V OUTPUT

LOCKOUT

AT 1.8V

20mV RIPPLE

P-P

100k

100Ω

680k

1.5V

909k*

I

V

IN

I

V

IN

LIM

909k*

1M*

100k

2.2M

SW1

LT1073

AO

SW1

LT1073

FB

2N3906

+

100µF

OS-CON

100µF

3V

AO

SET

FB

GND

SW2

GND

SW2

40.2k*

100k*

40.3k*

* 1% METAL FILM

L1 = GOWANDA GA10-682k

OR CADDELL-BURNS 7300-11

* 1% METAL FILM

†

1073 TA17

L1 = GOWANDA GA10-822k

OR CADDELL-BURNS 7300-12

1073 TA18

1.5V to 5V Very Low Noise Step-Up Converter

9V to 5V Reduced Noise Step-Down Converter

L1^†

1N5818

470µH

47µH

+V

5V

5V OUTPUT

5mA AT V

IN

OUT

6.5V TO 12V

90mA AT 6.5V

= 1V

IN

BATTERY

10mV RIPPLE

P-P

680k

220Ω

I

680k

1.5V

909k*

1N5818

I

V

SW1

LIM

IN

LIM IN

909k*

+

100µF

OS-CON

SW1

LT1073

FB

+

100µF

OS-CON

LT1073

AO

SET

AO

GND

SET

GND

SW2

40.2k*

1073 TA20

* 1% METAL FILM

L1 = GOWANDA GA10-472k

OR CADDELL-BURNS 7300-09

EFFICIENCY ≈ 80%

I ≈ 130µA

Q

OUTPUT NOISE ≈ 100mV

†

L1 = GOWANDA GA10-473k

OR CADDELL-BURNS 7300-21

EFFICIENCY = 83% AT 5mA LOAD

1073 TA19

†

P-P

3V to 6V at 1A Step-Up Converter

1.5V Powered 350ps Risetime Pulse Generator

INPUT

3V TO 6V

(2 LITHIUM CELLS)

MUR120

90V BIAS

6V OUTPUT

1A AT

IN

L1^†

25µH

L1^†

150µH

0.1µF

1.5V

V

= 3V

MUR120

1M

C1

2pF TO 4pF

220Ω

I

V

IN

560k

549k*

LIM

1N5820

10M

SW1

LT1073

FB

I

V

IN

LIM

MUR120

0.1µF

Q1

2N2369

+

SW1

LT1073

2200µF

1000µF

AO

SET

OUTPUT

5V INTO

50Ω PULSE

WIDTH ≈ 1ns

GND

SW2

FB

GND

SW2

1N5818

51Ω

24k 10k

50Ω

20k*

MTP3055EL

^†L1 = TOKO 262LYF-0095K

SELECT Q1 AND C1 FOR OPTIMUM RISE AND FALL

1073 TA22

2N3906

5.1k

* 1% METAL FILM

†

L1 = COILTRONICS CTX25-5-52

1073 TA21

LOW I (<250µA)

Q

14

LT1073

PACKAGE DESCRIPTION ^{Dimensions in inches (millimeters) unless otherwise noted.}

N8 Package

8-Lead PDIP (Narrow 0.300)

(LTC DWG # 05-08-1510)

0.400*

(10.160)

MAX

0.130 0.005

0.300 – 0.325

0.045 – 0.065

(3.302 0.127)

(1.143 – 1.651)

(7.620 – 8.255)

8

1

7

6

5

0.065

(1.651)

TYP

0.255 0.015*

(6.477 0.381)

0.009 – 0.015

(0.229 – 0.381)

0.125

0.020

(0.508)

MIN

(3.175)

MIN

+0.035

–0.015

2

4

3

0.325

0.018 0.003

0.100

(2.54)

BSC

+0.889

8.255

(0.457 0.076)

(

)

N8 1098

–0.381

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

0.189 – 0.197*

(4.801 – 5.004)

0.010 – 0.020

(0.254 – 0.508)

7

5

8

6

× 45°

0.053 – 0.069

(1.346 – 1.752)

0.004 – 0.010

(0.101 – 0.254)

0.008 – 0.010

(0.203 – 0.254)

0°– 8° TYP

0.150 – 0.157**

(3.810 – 3.988)

0.228 – 0.244

(5.791 – 6.197)

0.016 – 0.050

(0.406 – 1.270)

0.050

(1.270)

BSC

0.014 – 0.019

(0.355 – 0.483)

TYP

*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

SO8 1298

**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD

FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

1

3

4

2

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

15

LT1073

TYPICAL APPLICATION

1.5V Powered Temperature Compensated Crystal Oscillator

L1^†

820µH

1.5V

30.1k* 27.4k*

150k*

+

–

I

V

LIM

IN

SW1

LT1073

SET

FB

LT1017

150k

1.5V

2N3906

1k

6.81K*

LM134-3

1.5V

47µF

2N3906

100k

A0

SW2

1N4148

1.5V

150k*

73.2k*

+

39.2k*

47µF

100Ω

100k

10M*

2N3904

OUTPUT

1MHz

0.05ppm/°C

100k

1MHz

560k

510pF

0.02µF

MV209

* 1% METAL FILM

2k

†

L1 = J.W. MILLER #100267

= AT CUT –35° 20' ANGLE

1073 TA23

1.5V Powered α, β, γ Particle Detector

0.01µF

T1

3

4

10

1N976

D1

D2

D3

1M

3M

330Ω

1N4148

NC

I

V

2N3906

LIM

IN

SW1

LT1073

X1

0.01µF

5

7

FB

2N3904

NC

1

2

0.01µF

1M

1.5V

10k

AO

SET

500V

REGULATED

GND

SW2

10M

68pF

600V

1N5818

T1 = COILTRONICS CTX10052-1

X1 = PROJECTS UNLIMITED AT-

11k OR 8Ω SPEAKER

1073 TA24

R1

500M

210k

0.01µF

U1

D1, D2, D3 = MUR1100

R1 = VICTOREEN MOX-300

U1 = LND-712 CORP., OCEANSIDE, NY

RELATED PARTS

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DESCRIPTION

Single Cell Micropower 600kHz PWM DC/DC Converter

COMMENTS

3.3V at 75mA from One Cell, MSOP Package

LT1316

Burst Mode™ Operation DC/DC with Programmable Current Limit

2-Cell Micropower DC/DC with Low-Battery Detector

Single Cell Micropower DC/DC Converter

1.5V Minimum, Precise Control of Peak Current Limit

3.3V at 200mA from Two Cells, 600kHz Fixed Frequency

3V at 30mA from 1V, 1.7MHz Fixed Frequency

–5V at 150mA from 5V Input, Tiny SOT-23 Package

5V at 200mA from 3.3V Input, Tiny SOT-23 Package

20V at 12mA from 2.5V, Tiny SOT-23 Package

–15V at 12mA from 2.5V, Tiny SOT-23 Package

5V at 450mA from 3.3V Input, Tiny SOT-23 Package

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Inverting 1.4MHz Switching Regulator in 5-Lead SOT-23

1.4MHz Switching Regulator in 5-Lead SOT-23

LT1613

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Micropower Constant Off-Time DC/DC Converter in 5-Lead SOT-23

Micropower Inverting DC/DC Converter in 5-Lead SOT-23

LT1617

LT1930/LT1930A 1.2MHz/2.2MHz, 1A Switching Regulator in 5-Lead SOT-23

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Burst Mode operation is a trademark of Linear Technology Corporation.

1073fa LT/TP 0301 2K REV A • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

16

●

 LINEAR TECHNOLOGY CORPORATION 2000

(408)432-1900 FAX: (408) 434-0507 www.linear-tech.com


型号：	LT1073CS8-12#PBF
厂家：	Linear
描述：	LT1073 - Micropower DC-DC Converter Adjustable and Fixed 5V, 12V; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C 开关光电二极管
文件：	总16页 (文件大小：270K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT1073CS8-12#PBF [Linear]

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