DAC80504 datasheet(37/50 Pages) TI2

37 / 50 page

VOUT

LOAD

OPA277

VDD

REF

DACx0504

GND

R1'

150 k

15 k

R2'

15 k

10 pF

R3'

VREF

VDAC

R3 R1 R2

R1 R2

R1 R2 R3

REF

R2 R3 / R1

CODE

DAC80504, DAC70504, DAC60504

www.ti.com

SBAS871C – AUGUST 2017 – REVISED JANUARY 2019

Product Folder Links: DAC80504 DAC70504 DAC60504

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Application Information (continued)

9.1.2 Programmable Current Source Circuit

The DACx0504 can be integrated into the circuit in Figure 75 to implement an improved Howland current pump

for precise voltage to current conversions. Bidirectional current flow and high voltage compliance are two

features of the circuit. With a matched resistor network, the load current of the circuit is shown by Equation 2.

(2)

The value of R3 in Equation 2 can be reduced to increase the output current drive of U3. U3 can drive ±20 mV in

both directions with voltage compliance limited up to 15 V by the U3 voltage supply. Elimination of the circuit

compensation capacitor C1 in the circuit is not suggested as a result of the change in the output impedance ZO,

according to Equation 3.

(3)

As shown in Equation 3, with matched resistors, ZO is infinite and the circuit is optimum for use as a current

source. However, if unmatched resistors are used, ZO is positive or negative with negative output impedance

being a potential cause of oscillation. Therefore, by incorporating C1 into the circuit, possible oscillation problems

are eliminated. The value of C1 can be determined for critical applications; for most applications, however, a

value of several pF is suggested.

Figure 75. Programmable Bidirectional Current Source Circuit

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