MAX532 Maxim, MAX532 Datasheet - Page 13

• Manufacturer Part Number: MAX532
• Description: Dual / Serial-Input / Voltage-Output / 12-Bit MDAC
• Manufacturer: Maxim

Figure 12. Programmable-Gain Amplifer
V
IN
1
RFBA
MAX532
AGNDA
R/2
______________________________________________________________________________________
4
R
2
DACA
CODE
4096
VREFA
VOUTA
V
V
OUT
IN
3
2
=
Voltage-Output, 12-Bit MDAC
-4096
CODE
V
OUT
The DAC/amplifier combination, along with access to
the feedback resistors, makes the MAX532 ideal as a
programmable-gain amplifier. In this application, the
DAC functions as a programmable resistor in the feed-
back loop. This type of configuration is shown in Figure
12, and is suitable for AC gain control. The DAC code
controls the gain for the PGA. As the code decreases,
the effective DAC resistance increases, and so the gain
also increases. The transfer function is given by:
where RFBA is the value of the feedback resistor (R/2),
and REQA is the effective DAC resistance controlled
by the digital input code:
where CODE is the DAC code in decimal.
The transfer function is thus:
The code may be programmed between 1 and (2
The zero code is not allowed, as it results in an open-
loop amplifier response.
On power-up, the internal DAC latches are set to
00 . . . . .00.
Programmable-Gain Amplifier (PGA)
Dual, Serial-Input,
V
REQA = —— (————) ,
OUT
/V
——— =
IN
V
V
OUT
IN
= -REQA/RFBA,
R
2
CODE
———
CODE
-4096
4096
Power-On Reset
12
-1).
13