Datasheet

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V
OUT
A Sense
V
OUT
A
AGND
V
SS
V
REF
L AB Sense
V
REF
L AB
V
REF
H AB
V
REF
H AB Sense
V
OUT
B Sense
V
OUT
B
48
47
46
45
44
43
42
41
40
39
DAC7634
R
W1
R
W2
+2.5V
+V
V
OUT
R
W1
R
W2
V
OUT
REFERENCE INPUTS
+2.5V
+V
–2.5V
–V
V
OUT
–5V
V
OUT
V
OUT
A Sense
V
OUT
A
AGND
V
SS
V
REF
L AB Sense
V
REF
L AB
V
REF
H AB
V
REF
H AB Sense
V
OUT
B Sense
V
OUT
B
48
47
46
45
44
43
42
41
40
39
DAC7634
1000pF
1000pF
2200pF
+V
OPA2234
–V
100Ω
100Ω
2200pF
DAC7634
SBAS134B – JULY 2004 – REVISED DECEMBER 2005
V
REF
L. The minimum output of each DAC is equal to
V
REF
L plus a small offset voltage (essentially, the
offset of the output operational amp). The maximum
output is equal to V
REF
H plus a similar offset voltage.
Note that V
SS
(the negative power supply) must either
be connected to ground or must be in the range of
–4.75 V to –5.25 V. The voltage on V
SS
sets several
bias points within the converter. If V
SS
is not in one of
these two configurations, the bias values may be in
error and proper operation of the device is not
specified.
The current into the V
REF
H input and out of V
REF
L
depends on the DAC output voltages, and can vary
from a few microamps to approximately 0.5 mA. The
reference input appears as a varying load to the
reference. If the reference can sink or source the
Figure 51. Analog Output Closed-Loop
required current, a reference buffer is not required.
Configuration(1/2 DAC7634)
The DAC7634 features a reference drive and sense
(R
W
Represents Wiring Resistances)
connection such that the internal errors caused by the
changing reference current and the circuit
impedances can be minimized. Figure 52 through
Figure 60 show different reference configurations,
and the effect on the linearity and differential linearity.
The reference inputs, V
REF
L and V
REF
H, can be any
voltage between VSS + 2.5 V and VCC – 2.5 V,
provided that V
REF
H is at least 1.25 V greater than
Figure 52. Dual Supply Configuration-Buffered References, Used for Dual Supply Performance
19