ZN427E8 [ZARLINK]

MICROPROCESSOR COMPATIBLE 8-BIT SUCCESSIVE APPROXIMATION A-D CONVERTER; 微处理器兼容的8位逐次逼近模数转换器
ZN427E8
型号: ZN427E8
厂家: ZARLINK SEMICONDUCTOR INC    ZARLINK SEMICONDUCTOR INC
描述:

MICROPROCESSOR COMPATIBLE 8-BIT SUCCESSIVE APPROXIMATION A-D CONVERTER
微处理器兼容的8位逐次逼近模数转换器

转换器 模数转换器 微处理器
文件: 总17页 (文件大小:311K)
中文:  中文翻译
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THIS DOCUMENT IS FOR MAINTENANCE  
PURPOSES ONLY AND IS NOT  
RECOMMENDED FOR NEW DESIGNS  
DS3006 - 2.1  
ZN427E8 / ZN427J8  
MICROPROCESSOR COMPATIBLE  
8-BIT SUCCESSIVE APPROXIMATION A-D CONVERTER  
TheZN427isan8-bitsuccessiveapproximationconverter  
with three-state outputs to permit easy interfacing to a  
common data bus. The IC contains a voltage switching DAC,  
a fast comparator, successive approximation logic and a  
2.56V precision bandgap reference, the use of which is pin  
optional to retain flexibility. An external fixed or varying  
reference may therefore be substituted, thus allowing  
ratiometic operation  
BUSY (END OF CONVERSION)  
RD (OUTPUT ENABLE)  
CLOCK  
1
2
3
4
18 BIT 8 (LSB)  
17 BIT 7  
16 BIT 6  
15 BIT 5  
WR (START CONVERSION)  
Only passive external components are required for  
operation of the converter.  
R
EXT  
IN  
REF IN  
REF OUT  
5
6
7
14 BIT 4  
13 BIT 3  
12 BIT 2  
V
V
FEATURES  
Easy Interfacing to Microprocessor, or Operates as a  
V
8
9
11 BIT 1 (MSB)  
10 +VCC (+5V)  
'Stand-Alone' Converter  
GROUND  
Fast: 10 microseconds Conversion time Guaranteed  
No Missing Codes over Operating Temperature Range  
ZN427J8 (DC18)  
ZN427E8 (DP18)  
Data Outputs Three-State TTL Compatible, other  
Logic Inputs and Output TTL and CMOS Compatible  
Fig.1 Pin connection - top view  
Choice of On-Chip or External Reference Voltage  
Ratiometric Operation  
ORDERING INFORMATION  
Unipolar or Bipolar Input Ranges  
Complementary to ZN428 DAC  
Operating temperature  
Package  
Device type  
ZN427E8  
ZN427J8  
0°C to +70°C  
DP18  
DC18  
Commercial or Military Temperature Range  
-55°C to +125°C  
8
V
OUT  
REF  
D TO A OUTPUT  
R-2R LADDER  
+2.5V  
REFERENCE  
COMPARATOR  
-
9
7
GROUND  
V IN  
REF  
ANALOGUE VOLTAGE SWITCHES  
6
5
3
V
IN  
+
R
EXT  
4
1
WR (START CONVERSION)  
BUSY (END CONVERSION)  
SUCCESSIVE  
APPROXIMATION REGISTER  
CLOCK  
INPUT  
2
3-STATE BUFFERS  
RD (OUTPUT ENABLE)  
10  
V
CC  
(+5V)  
11  
MSB  
12  
13  
14  
15  
16  
17  
18  
LSB  
Fig.2 System diagram  
ZN427  
ABSOLUTE MAXIMUM RATINGS  
Supply voltage VCC  
+7.0V  
Max. voltage, logic and VREF input  
Operating temperature range  
+VCC  
0°C to +70°C (ZN427E8)  
-55°C to +125°C (ZN427J8)  
-55°C to +125°C  
Storage temperature range  
ELECTRICAL CHARACTERISTICS (at VCC = 5V, Tamb = 25°C unless otherwise specified).  
Min.  
Typ.  
Max.  
Parameter  
Units  
Conditions  
Converter  
Resolution  
Linearity error  
-
-
Bits  
LSB  
8
-
-
±0.5  
Differential non-linearity  
Linearity error T.C.  
Differential non-linearity T.C.  
Full-scale (gain) T.C.  
Zero T.C.  
±0.5  
±3  
±6  
±2.5  
±8  
15  
LSB  
-
-
-
-
-
-
-
-
-
-
ppm/°C  
ppm/°C  
ppm/°C  
µV/°C  
mV  
External Ref. 2.5V  
Zero transition  
00000000  
to 00000001  
11111110  
12  
10  
2.545  
18  
16  
2.555  
DC Package  
DP Package  
13  
2.550  
mV  
V
F.S. transition  
VREF IN = 2.560V  
to 11111111  
Conversion time  
-
-
-
µs  
V
V
mA  
mW  
-
1.5  
4.5  
-
10  
3.0  
5.5  
40  
-
See note 1  
External reference voltage  
Supply voltage (VCC)  
Supply current  
25  
125  
Power consumption  
-
Comparator  
Input current  
1
100  
-
-
-
µA  
kΩ  
µA  
V
-
-
-
-
15  
-30.0  
3.5  
VIN = +3V, REXT = 82kΩ  
V - = -5V  
Input resistance  
Tail current, IEXT  
Negative supply, V–  
Input voltage  
25  
-3.0  
-0.5  
See comparator (page x-xx)  
V
Internal voltagee reference  
Output voltage  
Slope resistance  
2.475  
-
-
2.560  
0.5  
50  
2.625  
2
-
V
RREF = 390, CREF = 4µ7  
VREF temperature coefficient  
ppm/°C  
mA  
Reference current  
4
-
15  
See reference (page x-xx)  
Logic (over operating temperature range)  
High level input voltage VIH  
Low level input voltage VIL  
High level input current,  
WR and RD inputs IIH  
2.0  
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0.8  
50  
15  
100  
30  
-5  
-100  
1.6  
-
0.4  
2
-1.5  
250  
250  
-
V
V
µA  
µA  
µA  
µA  
µA  
µA  
mA  
V
V
µA  
V
ns  
ns  
ns  
ns  
ns  
kHz  
VIN = 5.5V, VCC = max.  
VIN = 2.4V, VCC = max.  
VIN = 5.5V, VCC = max.  
VIN = 2.4V, VCC = max.  
VIN = 0.4V, VCC = max.  
High level input current,  
Clock input IIH  
Low level input current IIL  
High level output current IOH  
Low level output current IOL  
High level output voltage VOH  
Low level output voltage VOL  
Disable output leakage  
Input clamp diode voltage  
Read input to data output  
Enable/disable delay time tRD  
Start pulse width tWR  
-
2.4  
-
-
-
-
IOH = max., VCC = min.  
IOL = max., VCC = min.  
VO = 2.4V  
See Fig.9  
See Fig.9  
-
180  
160  
-
250  
-
500  
900  
WR to BUSY propagation delay tBD  
Clock pulse width  
Maximum clock frequency  
250  
-
-
-
1000  
See note 1  
Note 1: A 900kHz clock gives a conversion time of 10µs (9 clock periods).  
2
ZN427  
GENERAL CIRCUIT OPERATION  
to 1. This procedure is repeated for all eight bits. On the ninth  
negative clock edge BUSY goes high indicating that the  
conversion is complete.  
The ZN427 utilises the successive approximation technique.  
Upon receipt of a negative-going pulse at the WR input the  
BUSY output goes low, the MSB is set to 1 and all other bits  
aresetto0,whichproducesanoutputvoltageofVREF/2 fromthe  
DAC. This is compared to the input voltage VIN; a decision is  
made on the next negative clock edge to reset the  
During a conversion the RD input will normally be held high to  
keep the three-state buffers in their high impedance state.  
Data can be read out by taking RD high, thus enabling the  
three-state output. Readout is non-destructive. The BUSY  
output may be tied to the RD input to automatically enable the  
outputs when the data is valid.  
VREF  
2
VREF  
2
MSB to 0 if  
> VIN or leave it set to 1 if  
< VIN.  
Bit 2 is set to 1 on the same clock edge, producing an output  
V
VREF  
2
V
from the DAC of REF or  
4
+
REF depending on the state  
4
For reliable operation of the converter the start pulse applied  
to the WR input must meet certain timing criteria with respect  
to the converter clock. These are detailed in the timing  
diagram of Fig.3.  
of the MSB. This voltage is compared to VIN and on the next  
clock edge a decision is made regarding bit 2, whilst bit 3 is set  
Fig.3 Timing diagram  
NOTES ON TIMING DIAGRAM  
2. The BUSY output goes low during a conversion. When  
BUSY goes high at the end of a conversion the output data is  
valid. In a microprocessor system the BUSY output can be  
used to generate an interrupt request when the conversion is  
complete.  
1. A conversion sequence is shown for the digital word  
01100110. For clarity the three-state outputs are shown as  
being enabled during the conversion, but normal practice  
would be to disable them until the conversion was complete.  
3
ZN427  
3. In the timing diagram cross hatching indicates a 'don't  
care' condition.  
PRACTICAL CLOCK AND SYNCHRONISING  
CIRCUITS  
4. The start pulse operates as an asynchronous  
(independent of clock) reset that sets the MSB output to 1 and  
sets all other outputs and the end of conversion flag to 0. This  
resetting occurs on the low-going edge of the start pulse and  
as long as WR is low the converter is inhibited. Conversion  
commences on the first active (negative going) clock edge  
after the WR input has gone high again, when the MSB  
decision is made. A number of timing constraints thus supply  
to the start pulse.  
The actual method of generating the clock signal and  
synchronising it to the start conversion system in which the  
ZN427 is incorporated.  
When used with a microprocessor the ZN427 can be treated  
as RAM and can be assigned a memory address using an  
address decoder. If the µP clock is used to drive the ZN427  
and the µP write pulse meets the ZN427 timing criteria with  
respect to the µP clock then generating the start pulse is  
simply a matter of gating the decoded address with the  
microprocessor write pulse. Whilst the conversion is being  
performed the microprocesor can perform other instructions  
or No operation (NOP). when the conversion is complete the  
outputs can be enabled onto the bus by gating the decoded  
address with the read pulse. A timing diagram for this  
sequence of operation is given in Fig.4.  
(a) The minimum duration of the start pulse is 250ns, to allow  
reliable resetting of the converter logic circuits.  
(b) Thereisnolimittothemaximumdurationofthestartpulse.  
(c) To allow the MSB to settle at least 1.5µs must elapse  
betweenthenegativegoingedgeofthestartpulseandthefirst  
active clock edge that indicates the MSB desicion.  
An advantage of using the microprocessor clock is that the  
conversion time is known precisely in terms of machine  
cycles. the data outputs may therefore be read after a fixed  
delay of at least nine clock cycles after the end of the WR  
pulse, when the conversion will be complete.  
(d) To ensure relaible clocking the positive-going edge of the  
start pulse should not occur within 200ns of an active  
(negative-going) clock edge. The ideal place for the positive-  
goingedgeofthestartpulseiscoincidentwithapositive-going  
clock edge. As a special case of the above conditions that  
start pulse may be synchronous with a negative-going clock  
pulse.  
Alternatively the read operation may be initiated by using the  
BUSY output to generate interrupt request.  
Fig.4 Typical timing diagram using µP clock and write pulse  
(a) The MPU clock is not available externally.  
(b) The clock frequency is too high.  
In some systems, for example single-chip microcomputers  
such as the 8048, this simple method may not be feasible for  
one or more of the following reasons:  
4
ZN427  
(c) The write pulse timing criteria make it unsuitable for direct  
use as a start conversion pulse.  
If any of these conditions apply then the self-synchronising  
clock circuit of Fig.5a is recommended.  
Fig.5a Self-synchronising clock circuit  
Fig.5b Timing diagram for circuit of Fig.5a  
5
ZN427  
N1 is connected as an astable multivibrator which, when the  
BUSY output is high, is inhibited by the output of N2 holding  
one of its inputs low. The start conversion pulse resets the  
BUSY flag and N1 begins to oscillate. When the conversion  
is complete BUSY goes high and the clock is inhibited.  
C1 starts from a fully charged condition whereas on  
subsequent cycles it changes between the upper and lower  
threshold (VT+ and VT) of the Schmitt trigger.  
LOGIC INPUTS AND OUTPUTS  
Since the start pulse starts the clock it may occur at any time.  
The only constraints on the start pulse are that it must be  
longerthan250nsbutatleast200nsshorterthanthefirstclock  
pulse. The first clock pulse is in fact longer than the rest since  
The logic inputs of the ZN427 utilise the emitter-follower  
configuration shown in Fig.6. This gives extremely low input  
currents for CMOS as well as TTL compatibility.  
Fig.6 Equivalent circuit of all inputs  
The BUSY output, shown in Fig.7, utilises a passive pullup for CMOS/TTL compatibility.  
Fig.7  
impedance state. When RD is high the data output will  
assume the appropriate logic state (0 or 1).  
The data outputs have three-state buffers, an equivalent  
circuit of which is shown in Fig.8. Whilst the RD input is low  
bothoutputtransistorsareturnedoffandtheoutputisinahigh  
6
ZN427  
V
CC  
500  
20k  
BITS 1-8  
(PINS 11-18)  
10k  
RD  
(PIN 2)  
GROUND  
Fig.8 Equivalent circuit of data outputs  
A test circuit and timing diagram for the output enable/disable delays are given in Fig.9.  
Fig.9 Output enable/disable waveforms  
7
ZN427  
ANALOG CIRCUITS  
D-A converter  
IThe converter is of the voltage switching type and uses an R-  
2R ladder network as shown in Fig.10. Each element is  
connectedtoeither0VorVREFINbytransistorvoltageswitches  
specially designed for low offset voltage (<1mV).  
VOS is a small offset voltage that is produced by the device  
supply current flowing in the package lead resistance. The  
value of VOS is typically 2mV for the ZN427E8 and 4mV for the  
ZN427J8.  
A binary weighted voltage is produced at the output of the R-  
2R ladder.  
This offset will normally be removed by the setting up  
procedure and since the offset temperature coefficient is low  
(8µV/°C), the effect on accuaracy will be negligible.  
D to A output = n (VREF IN -VOS) + VOS  
256  
The D-A output range can be considered to be 0 - VREF IN  
through an output resistance R (4k).  
where n is the digital input to the D-A from successive  
approximation register.  
R(4k)  
2R  
R
R
R
D TO A OUTPUT  
2R  
2R  
2R  
2R  
V
IN  
REF  
(PIN 7)  
VOLTAGE  
SWITCHES  
0 VOLTS  
(PIN 9)  
V
BIT 8  
BIT 7  
BIT 2  
BIT 1  
MSB  
OS  
Fig.10 R-2R ladder network  
REFERENCE  
(a) Internal reference  
The internal reference is an active bandgap circuit which is  
equivalent to a 2.5V Zener diode with a very low slope  
impedance (Fig.11). A Resistor (RREF) should be connected  
between pins 8 and 10. The recommended value of 390will  
supply a nominal reference current of (5.0 - 2.5)/0.39=6.4mA.  
A stabilising/decoupling capacitor, CREF (4µ7), is required  
between pins 8 and 9. For internal reference operation VREF  
OUT (pin 8) is connected to VREF IN (pin 7).  
UP to five ZN427's may be driven from one internal reference,  
there being no need to reduce RREF. This useful feature saves  
power and gives excellent gain tracking between the  
converters.  
Alternatively the internal reference can be used as the  
reference voltage for other external circuits and can source or  
sink up to 3mA.  
8
ZN427  
V
+5V  
CC  
(PIN 10)  
R
REF  
(390)  
V
OUT  
REF  
(PIN 8)  
C
REF  
(4.7µ)  
GROUND  
(PIN 9)  
Fig.11 Internal voltage reference  
(b) External reference  
same supply. The external reference can vary from +1.5 to  
+3.0V. The ZN448/9 will operate if VREF IN is less than +1.5V  
but reduced overdrive to the comparator will increase its delay  
and so the conversion time will need to be increased.  
If required an external reference in the range +1.5 to +3.0V  
may be connected to VREF IN. The slope resistance of such a  
reference source should be less than 2.5, where n is the  
n
number of converters supplied.  
COMPARATOR  
The ZN427 contains a fast comparator, the equivalent input  
circuit of which is shown in Fig.12.  
RATIOMETRIC OPERATION  
If the output from a transducer varies with its supply then an  
external reference for the ZN427 should be derived from the  
+5V PIN 10  
6k  
6k  
-
TO LOGIC  
HIGH = 'RETAIN BIT'  
+
R
IN  
A
V
IN  
IN  
D TO A OUTPUT  
(O - V  
IN)  
REF  
PIN 6  
4k  
4k  
PIN 5  
R
EXT  
I
EXT  
V -  
Fig.12 Comparator equivalent circuit  
9
ZN427  
The output from the D-A converter is connected through the  
4kladder resistance to one side of the comparator. The  
analoginputtobeconvertedcouldbeconnecteddirectlytothe  
other comparator input (VIN, pin 6) but for optimum stability  
with temperature the analog input should be applied through  
a source resistance (RIN = 4k) to match the ladder  
resistance).  
The comparator derives the tail current, IEXT, for its first stage  
from an external resistor, REXT, which is taken to a negative  
supply V–.  
This arrangement allows the ZN427 to work with any negative  
supply in the range -3 to -30 volts. the ZN427 is designed to  
be insensitive to changes in IEXT from 25µA to 150µA. The  
suggested nominal value of IEXT is 65µA and a suitable value  
for REXT is given by REXT = |V_|15k.  
ANALOG INPUT RANGES  
The basic connection of the ZN427 shown in Fig.13 has an  
analog input range 0 to VREF IN which, in some applications,  
may be made available from previous signal conditioning/  
scaling circuits. Input voltage ranges greater than this are  
accommodated by providing an attenuator on the comparator  
input, whilst for smaller input ranges the signal must be  
amplified to a suitable level.  
V(volts)  
REXT (±10%)  
-3  
-5  
47kΩ  
82kΩ  
-10  
-12  
-15  
-20  
-25  
-30  
150kΩ  
180kΩ  
220kΩ  
330kΩ  
390kΩ  
470kΩ  
Bipolar input ranges are accommodated by off-setting the  
analog input input range so that the comparator always sees  
a positive input voltage.  
DIGITAL OUTPUTS  
LSB  
BIT 8  
MSB  
BIT 1  
V
CC  
(+5V)  
7
6
5
4
3
2
18  
17  
16  
15  
14  
13  
12  
11  
10  
R
REF  
(390)  
1
2
3
4
5
6
7
8
9
V
IN  
R
EXT  
(82k)  
R
(4k)  
IN  
C
REF  
(4µ7)  
BUSY  
RD  
CK  
WR  
V-  
(-5V)  
A
V
INV  
REF  
OUT GND  
(0V)  
IN  
REF  
NOMINAL A RANGE = 0 TO V  
IN  
IN  
REF  
Fig.13 External components for basic operation  
10  
ZN427  
UNIPOLAR OPERATION  
The general connection for unipolar operation is shown in  
To match the ladder resistance R1/R2 (RIN) = 4k.  
Fig.14.  
The required nominal values of R1 and R2 are given by  
R1 = 4Gk, R2 = 4G kΩ  
The values of R1 and R2 are chosen so that VIN = VREF IN when  
the analogue input (AIN) is at full-scale.  
G-1  
The resulting full-scale range is given by:  
R1  
AINFS = 1 +  
, VREF IN = G.VREF IN.  
R2  
A
V
IN  
IN  
REF  
1M  
ZERO  
ADJUST  
R1  
680k  
7
9
V
IN  
6
ZN427  
GROUND  
R2  
Fig.14 Unipolar operation - general connection  
Zero adjustment  
Using these relationships a table of nominal values of R1 and  
R2 can be constructed for VREF IN = 2.5V.  
Due to offsets in the DAC and comparator the zero (0 to 1)  
code transition would occur with typically 15mV applied to the  
comparator input, which correpsonds to 1.5LSB with a 2.56V  
reference.  
Input range  
R1  
R2  
G
+5V  
+10V  
8kΩ  
16kΩ  
8kΩ  
5.33kΩ  
2
4
Zero adjustment must therefore be provided to set the zero  
transition to its correct value of +0.5LSB or 5mV with a 2.56V  
reference. Thisisachievedbyapplyinganadjustablepositive  
offset to the comparator input via P2 and R3. The values  
shown are suitable for all input ranges greater than 1.5 times  
VREF IN.  
Gain adjustment  
Due to tolerance in R1 and R2, tolerance in VREF and the gain  
(full-scale) error of the DAC, some adjustment should be  
incorporated into R1 to calibrate the full-scale of the converter.  
When used with the internal reference and 2% resistors a  
preset capable of adjusting R1 by at least ±5% of its nominal  
value is suggested.  
Practical circuit values for +5 and +10V input ranges are given  
in Fig.15, which incorporates both zero and gain adjustments.  
11  
ZN427  
A
V
IN  
A
V
IN  
REF  
IN  
REF  
IN  
P2  
P2  
P1 5k  
GAIN  
1M  
ZERO  
P1 10k  
GAIN  
1M  
ZERO  
ADJUST  
ADJUST  
ADJUST  
ADJUST  
R1 5k6  
680k  
R1 11k  
R2 5k6  
680k  
R3  
R3  
TO PIN 6  
TO PIN 6  
± 2% RESISTORS  
R2 8k2  
±20% POTENTIOMETERS  
+5V FULL-SCALE  
+10V FULL-SCALE  
Fig.15 Unipolar operation - component values  
Unipolar adjustment prodedure  
(iii) Apply 0.5LSB) to AIN and adjust zero until 8 bit just flickers  
between 0 and 1 with all other bits at 1.  
(i) Apply continuous convert pulses at intervals long enough  
to allow a complete conversion and monitor the digital  
outputs.  
(ii) Applyfull-scaleminus1.5LSB toAIN andadjustoff-setuntil  
the 8 bit (LSB) output just flickers between 0 and 1 with all  
other bits at 0.  
Unipolar setting up points  
FS - 1.5LSB  
0.5LSB  
Input range, +FS  
1LSB = FS  
256  
4.9707V  
9.9414V  
9.8mV  
19.5mV  
+5V  
+10V  
Unipolar logic coding  
Output code  
Analogue input (AIN)  
(offset binary)  
(Nominal code centre value)  
11111111  
11111110  
11000000  
10000001  
10000000  
01111111  
01000000  
00000001  
00000000  
FS - 1LSB  
FS - 2LSB  
0.75FS  
0.5FS + 1LSB  
0.5FS  
0.5FS - 1LSB  
0.25FS  
1LSB  
0
12  
ZN427  
BIPOLAR OPERATION  
For bipolar operation the input to the ZN427 is offset by half  
full-scale by connecting a resistor R3 between VREF IN and VIN  
(Fig.16).  
A
V
IN  
REF  
IN  
R1  
R3  
7
9
V
IN  
6
ZN427  
GROUND  
R2  
Fig.16 Bipolar operation - general connection  
When AIN = -FS, VIN needs to be equal to zero.  
When AIN = +FS, VIN needs to be equal to VREF IN.  
Thus the nominal values of R1, R2, R3 are given by R1 = 8 Gk,  
R2 = 8G/(G - 1)k, R3 = 8k.  
A bipolar range of ±VREF IN (which corresponds to the basic  
If the full-scale range is ± G. VREF IN then R1 = (G - 1). R2 and  
R1 = G. R3 fulfil the required conditions.  
unipolar range 0 to +VREF IN) results if R1 = R3 = 8kand R2 =  
.  
To match the ladder resistance, R1/R2/R3 (=RIN) = 4k.  
Assuming the VREF IN = 2.5V the nominal values of resistors for  
±5 and ±10V input ranges are given in the following table.  
R3  
Input range  
R1  
R2  
G
8kΩ  
8kΩ  
+5V  
+10V  
16kΩ  
32kΩ  
16kΩ  
10.66kΩ  
2
4
Minusfull-scale(offset)issetbyadjustingR1 aboutitsnominal  
value relative to R3. Plus full-scale (gain) is set by adjusting R2  
relative to R1.  
Note that in the±5V case R3 has been chosen as 7.5k (instead  
of 8.2k) to obtain a more symmetrical range of adjustment  
using standard potentiometers.  
Practical circuit realisations are given in Fig.17.  
13  
ZN427  
A
V
A
V
IN  
REF  
IN  
REF  
5k  
OFFSET  
ADJUST  
10k  
OFFSET  
ADJUST  
7k5  
8k2  
13k  
27k  
TO PIN 6  
TO PIN 6  
5k  
5k  
GAIN  
GAIN  
ADJUST  
ADJUST  
± 2% RESISTORS  
±20% POTENTIOMETERS  
13  
8k2  
±5VOLTS FULL SCALE  
±10VOLTS FULL SCALE  
Fig.17 Bipolar operation - component values  
Bipolar adjustment prodedure  
(iii) Apply +(FS -1.5LSB) to AIN and adjust gain until the 8 bit  
just flickers between 0 and 1 with all other bits at 1.  
(i) Apply continuous SC pulses at intervals long enough to  
allow a complete conversion and monitor the digital  
outputs.  
(iv) Repeat step (ii).  
(ii) Apply -(FS -0.5LSB) to AIN and adjust off-set until the 8 bit  
(LSB)outputjustflickersbetween0and1withallotherbits  
at 0.  
Bipolar setting up points  
+(FS -1.5LSB)  
-(FS -0.5LSB)  
Input range, ±FS  
1LSB =2FS  
265  
+4.9414V  
+9.8828V  
-4.9805V  
-9.9609V  
+5V  
+10V  
Bipolar logic coding  
Output code  
Analogue input (AIN)  
(offset binary)  
(Nominal code centre value)  
11111111  
11111110  
11000000  
10000001  
10000000  
01111111  
01000000  
00000001  
00000000  
+(FS - 1LSB)  
+(FS - 2LSB)  
+0.5FS  
+1LSB  
0
-1LSB  
-0.5FS  
-(FS - 1LSB)  
-FS  
14  
ZN427  
SINGLE 5 V SUPPLY RAIL OPERATION  
any clock frequency from 10kHz to 1MHz and can supply up  
to five ZN427's.  
TheZN427takesverylittlepowerfromthenegativerailandso  
a suitable negative supply can be generated very easily using  
a 'diode pump' circuit. The circuit shown in Fig.18 works with  
Fig.18 single 5V supply operation  
15  
ZN427  
CUSTOMER SERVICE CENTRES  
HEADQUARTERS OPERATIONS  
GEC PLESSEY SEMICONDUCTORS  
Cheney Manor, Swindon,  
Wiltshire SN2 2QW, United Kingdom.  
Tel: (0793) 518000  
• FRANCE & BENELUX Les Ulis Cedex Tel: (1) 64 46 23 45 Fax : (1) 64 46 06 07  
• GERMANY Munich Tel: (089) 3609 06-0 Fax : (089) 3609 06-55  
• ITALY Milan Tel: (02) 66040867 Fax: (02) 66040993  
• JAPAN Tokyo Tel: (03) 5276-5501 Fax: (03) 5276-5510  
• NORTH AMERICA Integrated Circuits and Microwave Products Scotts Valley, USA  
Tel (408) 438 2900 Fax: (408) 438 7023.  
Fax: (0793) 518411  
Hybrid Products, Farmingdale, USA Tel (516) 293 8686 Fax: (516) 293 0061.  
• SOUTH EAST ASIA Singapore Tel: (65) 3827708 Fax: (65) 3828872  
SWEDEN Stockholm, Tel: 46 8 702 97 70 Fax: 46 8 640 47 36  
• UK, EIRE, DENMARK, FINLAND & NORWAY  
Swindon Tel: (0793) 518510 Fax : (0793) 518582  
These are supported by Agents and Distributors in major countries world-wide.  
GEC PLESSEY SEMICONDUCTORS  
P.O. Box 660017  
1500 Green Hills Road,  
Scotts Valley, California 95067-0017,  
United States of America.  
Tel: (408) 438 2900  
Fax: (408) 438 5576  
© GEC Plessey Semiconductors 1994 Publication No. DS3006 Issue No. 2.1 May 1994  
This publication is issued to provide information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose nor form part of any order or contract nor to be regarded  
as a representation relating to the products or services concerned. No warranty or guarantee express or implied is made regarding the capability, performance or suitability of any product or service. The Company  
reserves the right to alter without prior knowledge the specification, design or price of any product or service. Information concerning possible methods of use is provided as a guide only and does not constitute  
any guarantee that such methods of use will be satisfactory in a specific piece of equipment. It is the user's responsibility to fully determine the performance and suitability of any equipment using such information  
and to ensure that any publication or data used is up to date and has not been superseded. These products are not suitable for use in any medical products whose failure to perform may result in significant injury  
or death to the user. All products and materials are sold and services provided subject to the Company's conditions of sale, which are available on request.  

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