DAC8811_15 Datasheet, PDF (14/29 Pages) Texas Instruments – DAC8811 16-Bit, Serial Input Multiplying Digital-to-Analog Converter

DAC8811
SLAS411C – NOVEMBER 2004 – REVISED OCTOBER 2015
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Feature Description (continued)
R1'R3 R1 R2
Z_{O R1(R2' R3') R1'(R2 R3)}
(4)
As shown in Equation 4, with matched resistors, Z_O is infinite and the circuit is optimum for use as a current
source. However, if unmatched resistors are used, Z_O 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.
R2’
15 kW
C1 10 pF
V_REF
V_DD
V_DD R_FB
V_REF
U1
DAC8811
GND
U2
OPA277
I_OUT
−
+
R1’
150 kW
U2
OPA277
−
+
R2
15 kW
R3’
50 W
V_OUT
R3
50 W
R1
150 kW
I_L
LOAD
Figure 23. Programmable Bidirectional Current Source Circuit
8.4 Device Functional Mode
Table 1. Control Logic Truth Table⁽¹⁾
CLK
CS
Serial Shift Register
DAC Register
X
H
No effect
Latched
↑+
L
Shift register data advanced one bit
Latched
X
H
No effect
Latched
X
↑+
Shift register data transferred to DAC register New data loaded from serial register
(1) ↑+ Positive logic transition; X = Don't care
14
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