LTC1590 查看數據表（PDF） - Linear Technology

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LTC1590

Dual Serial 12-Bit Multiplying DAC

Linear Technology 

LTC1590

APPLICATIONS INFORMATION

Unipolar 2-Quadrant Multiplying Mode

(VOUT = 0V to – VREF)

The LTC1590 can be used with a dual op amp to provide

a dual 2-quadrant multiplying DAC as shown in Figure 2.

The unipolar DAC transfer function is shown in Table 1.

The 33pF feedback capacitor is recommended to compen-

sate for the pole caused by the internal feedback resistor

and the OUT1 output capacitance. For high speed op amps

this feedback capacitor is required for stability, and a

smaller value, 8pF to 15pF, may be desired to get the

fastest transient response and shortest settling time. A

larger feedback capacitor can be used to reduce wideband

noise, glitch impulse and distortion for lower frequency

signals. A pole is introduced in the DAC transfer function

at approximately (CFB)(RFB). For example, a 100pF feed-

back capacitor will typically give a pole at:

( )( ) 145kHz =

1

2π 100pF 11kΩ

Table 1. Unipolar Binary Code Table

DIGITAL INPUT

BINARY NUMBER

IN DAC REGISTER

MSB

LSB

ANALOG OUTPUT

VOUT

1111 1111 1111

1000 0000 0000

0000 0000 0001

0000 0000 0000

– VREF (4095/4096)

– VREF (2048/4096) = – VREF/2

– VREF (1/4096)

0V

Bipolar 4-Quadrant Multiplying Mode

(VOUT = – VREF to +VREF)

The circuit of Figure 3 can be used to provide a dual

4-quadrant multiplying DAC. This circuit starts with the

unipolar application circuit and adds three resistors and an

op amp. These extra devices provide a gain of – 2 from the

unipolar output to the bipolar output, plus an offset of

(–1)(VREF) to produce the transfer function shown in Table

2. A pack of matched 20k resistors, with two resistors in

parallel forming the 10k resistor, is recommended.

5V

VREF

–10V TO 10V

0.1µF

VCC VREF RFB

OUT1

LTC1590

DAC A OR DAC B

OUT2

DGND AGND

33pF

15V

–

1/2

+ LT1112

–15V

VOUT

0V TO –VREF

1590 F02

Table 2. Bipolar Offset Binary Code Table

DIGITAL INPUT

BINARY NUMBER

IN DAC REGISTER

MSB

LSB

ANALOG OUTPUT

VOUT

1111 1111 1111

1000 0000 0001

1000 0000 0000

0111 1111 1111

0000 0000 0000

+VREF (2047/2048)

+VREF (1/2048)

0V

– VREF (1/2048)

– VREF (2048/2048) = – VREF

Figure 2. Unipolar Operation (2-Quadrant Multiplication)

8

VREF

–10V TO 10V

5V

0.1µF

VCC VREF RFB

OUT1

LTC1590

DAC A OR DAC B

OUT2

DGND AGND

R2

20k

33pF

15V

–

1/2

+ LT1112

–15V

R3

20k

R1

15V

10k

–

1/2

+ LT1112

–15V

Figure 3. Bipolar Operation (4-Quadrant Multiplication)

VOUT

–VREF TO VREF

1590 F03

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