AD7538 查看數據表（PDF） - Analog Devices

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AD7538

LC2MOS Microprocessor-Compatible 14-Bit DAC

Analog Devices 

AD7538

BIPOLAR OPERATION (4-QUADRANT

MULTIPLICATION)

The recommended circuit diagram for bipolar operation is

shown in Figure 8. Offset binary coding is used. The code table

for Figure 8 is given in Table 7.

With the DAC loaded to 10 0000 0000 0000, adjust R1 for VO =

0 V. Alternatively, one can omit R1 and R2 and adjust the ratio

of R5 and R6 for VO = 0 V. Full-scale trimming can be accom-

plished by adjusting the amplitude of VIN or by varying the

value of R7.

The values given for R1, R2 are the minimum necessary to

calibrate the system for Resistors R5, R6, R7 ratio matched to

0.1%. System linearity error is independent of resistor ratio

matching and is affected by DAC linearity error only.

When operating over a wide temperature range, it is important

that the resistors be of the same type so that their temperature

coefficients match.

LOW LEAKAGE CONFIGURATION

For CMOS multiplying DAC, as the device is operated at higher

temperatures, the output leakage current increases. For a 14-bit

resolution system, this can be a significant source of error. The

AD7538 features a leakage reduction configuration to keep the

leakage current low over an extended temperature range. One

may operate the device with or without this configuration. If VSS

(Pin 24) is tied to AGND then the DAC exhibits normal output

leakage currents at high temperatures. To use the low leakage

facility, VSS should be tied to a voltage of approximately −0.3 V

as in Figure 6 and Figure 8. A simple resistor divider (R3, R4)

produces approximately −300 mV from −15 V. The C2

capacitor in parallel with R3 is an integral part of the low

leakage configuration and must be 4.7 μF or greater. Figure 7

is a plot of leakage current vs. temperature for both conditions.

It clearly shows the improvement gained by using the low

leakage configuration.

Table 7. Bipolar Code Table for the Offset Binary Circuit

of Figure 8

Binary Number In

DAC Register

MSB

LSB

11 1111 1111 1111

10 0000 0000 0001

10 0000 0000 0000

01 1111 1111 1111

00 0000 0000 0000

Analog Output VOUT

+VIN(8191/8192)

+VIN(1/8192)

0V

−VIN(1/8192)

−VIN(8191/8192)

VDD = 15V

60

VREF = 10V

50

40

30

20

10

0

VSS = 0V

VSS = –0.3V

30 40 50 60 70 80 90 100 110 120

TEMPERATURE (°C)

Figure 7. Graph of Typical Leakage Current vs. Temperature for AD7538

VIN

R1

VDD

50Ω

R2

22Ω

R6

20kΩ

LDAC

CS

WR

1

VREF

20 LDAC

21 CS

22 WR

23

VDD

2

RFB

AD7538

IOUT 3

AGND 4

C1

33pF

R5

10kΩ

A1

AD711

DB13 TO DB0 DGND VSS

6

19

5

24

DIGITAL

INPUT DATA GND

C2

4.7µF

+

R3

1kΩ

R4

47kΩ

R8

5kΩ, 10%

ANALOG

GND

–15V

Figure 8. Bipolar Operation

R7

20kΩ

A2

AD711

VO

Rev. B | Page 11 of 16

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