MAX512 Maxim, MAX512 Datasheet - Page 13

• Manufacturer Part Number: MAX512
• Description: Low-Cost / Triple / 8-Bit Voltage-Output DACs with Serial Interface
• Manufacturer: Maxim

Table 3. Unipolar Code Table
1LSB
Using Figure 4’s circuit, the MAX512/MAX13 can be con-
figured for bipolar outputs. Table 4 lists the bipolar codes
and corresponding output voltages. There are two ways to
achieve
MAX512/MAX513 with a single supply and positive refer-
ence voltages or 2) Use dual supplies with a positive or
negative voltage at REFAB and a positive voltage at REFC.
In either case, the op amps need dual supplies. When
using the dual-supply mode, possible errors associated
with the divide-by-two attenuator and gain-of-two buffer are
eliminated (see the Output Buffer Amplifier section). For
maximum output swing of all outputs in dual-supply mode,
connect REFAB to V
mode, connect REFAB, REFC, and V
With dual supplies, DACs A and B can perform four-
quadrant multiplication. Please note that in dual-supply
mode, the REFAB input ranges from V
1.5V). Because REFC accepts only positive inputs,
DAC C performs two-quadrant multiplication.
Figure 4 shows Maxim’s ICL7612A with rail-to-rail input
common-mode range and rail-to-rail output voltage
swing—ideal for a high output voltage swing from low
supply voltages.
Note :
ANALOG OUTPUT
B7 B6 B5 B4 B3 B2 B1 B0
1
1
1
0
0
0
1
0
0
1
0
0
DAC CONTENTS
1
0
0
1
0
0
REF_
Low-Cost, Triple, 8-Bit Voltage-Output DACs
rail-to-rail
1
0
0
1
0
0
1
0
0
1
0
0
2
______________________________________________________________________________________
8
1
0
0
1
0
0
SS
REF_
and REFC to V
1
0
0
1
0
0
REF_
outputs:
1
1
0
1
1
0
256
D
0V
REF_
REF_
REF_
REF_
REF_
256
1
DD
1)
DD
Bipolar Output
together.
ANALOG
OUTPUT
. In single-supply
255
256
129
256
128
256
127
256
256
Operate
1
SS
to (V
REF_
DD
2
the
-
Table 4. Bipolar Code Table
1LSB
Both the MAX512 and MAX513 can bias GaAs FETs,
where the gate of the FETs must be negatively biased
to ensure that there is no drain current. In a typical
application, power to the RF amplifiers should not be
turned on until the bias voltages provided by DAC A
and DAC B are fully established; likewise, the supply
should be turned off before the bias voltage is switched
off. Figure 5 shows how DAC B supplies the negative
bias V
negative bias V
The DAC A and DAC B outputs are also ideal for con-
trolling VCOs in mobile radios or cellular phones. Other
applications include varactor and PIN diode circuits.
The unbuffered DAC C provides a span within GND
and V
cally adjusts offset and gain in the system.
1 [John Wachsmann. “A High-Efficiency GaAs MMIC Power Amplifier for
1.9GHz PCS Applications,” Proceedings of the First Annual Wireless
Symposium, pp. 375, Penton Publishing, Jan. 1993.]
Note :
ANALOG OUTPUT
B7 B6 B5 B4 B3 B2 B1 B0
1
1
1
0
0
0
1
0
0
1
0
0
with Serial Interface
DD
GG1
DAC CONTENTS
1
0
0
1
0
0
REF_
and is individually set at REF C. DAC C typi-
for the driver stage and DAC A provides the
1
0
0
1
0
0
GG2
1
0
0
1
0
0
2
(
8 - 1)
1
0
0
1
0
0
for the output stage [1].
REF_
1
0
0
1
0
0
1
1
0
1
1
0
REF_
128
D
0V
REF_
REF_
REF_
REF_
REF_
1
RF Applications
128
1
ANALOG
OUTPUT
127
128
128
128
127
128
128
128
1
1
=
REF_
13