GAIN TRIM
+15V
16
V
(–10V)
REF
2KΩ
17
4
D
(MSB)
V
V
18
1
11
REF
DD
R
FB
1KΩ
I
O1
–
+
V
INPUT
DATA
OUT
HS7541A
10KΩ
390Ω
15
2
I
10KΩ
D
(LSB)
O2
0
GND
3
–
+
10KΩ
500Ω
Figure 5. Bipolar Operation
As shown in the figure, the output current of the
HS7541A is typically connected to an external
op amp, with its non-inverting input tied to
ground. The amplifier should be selected for
low input bias current and low drift over tem-
perature. Tomaintainthespecifiedlinearity, the
amplifier’sinputoffsetvoltageshouldbemulled
to less than ±200µV (0.1 LSB).
minal, may be anywhere between 10kΩ (the
feedback resistor alone when all digital inputs
are LOW) and 7.5kΩ (the feedback resistor in
parallel with approximately 30kΩ of the R-2R
ladder network resistance when any single bit is
HIGH). Static accuracy and dynamic perfor-
mance will be affected by these variations.
UNIPOLAR OPERATION
BIPOLAR OPERATION
Figure 4 shows the connections to implement
digital unipolar operation of the HS7541A. The
reference voltage applied to VREF (pin17) may be
positive or negative. The 2KΩ potentiometer
tied to VREF, and the 1KΩ resistor in the feed-
back loop are both optional; they are needed
only when gain error must be trimmed to less
than 0.3% FSR. They should track each other to
better than 0.1%. It is not necessary that they
track the resistors internal to the HS7541A.
Figure 5 shows the connections for bipolar
operation of the HS7541A. The digital input
coding is offset binary as shown in Table 2. As
is the case for unipolar operation, the gain trim
resistors can be omitted if minimum gain error
is not required. The op amp selection criteria
and offset nulling are the same as for unipolar
operation.
DIGITAL INPUT
1111 1111 1111
1000 0000 0001
1000 0000 0000
0100 0000 0000
0000 0000 0000
I0UT
DIGITAL INPUT
1111 1111 1111
1000 0000 0000
0111 1111 1111
0000 0000 0000
I0UT
-0.99951 x VREF
-0.00049 x VREF
0V
-0.99975 x VREF
-0.50000 x VREF
-0.49975 x VREF
0V
+0.50000 x VREF
+1.00000 x VREF
Table 1. Unipolar Input Coding
Table 2. Bipolar Input Coding
HS7541A
12-Bit CMOS Multiplying DAC
© Copyright 2000 Sipex Corporation
6
SIPEX [ SIPEX CORPORATION ]
