Datasheet

Detailed Description
The MAX9939 is a general-purpose PGA with input off-
set trim capability. Its gain and input offset voltage
(V
OS
) are SPI programmable. The device also includes
an uncommitted output operational amplifier that can
be used as either a high-order active filter or to provide
a differential output. The device can be put into shut-
down through SPI.
The gain of the amplifier is programmable between
0.2V/V and 157V/V. The input offset is programmable
between ±17mV and can be used to regain output
dynamic range in high gain settings. An input offset-volt-
age measurement mode enables input offset voltage to
be calibrated out in firmware to obtain excellent DC
accuracy.
The main amplifier accepts a differential input and pro-
vides a single-ended output. The relationship between
the differential input and singled-ended output is given
by the representative equation:
V
OUTA
= V
CC
/2 - Gain x (V
INA+
- V
INA-
) + Gain x V
OS
Architecture
The MAX9939 features three internal amplifiers as
shown in the Functional Diagram . The first amplifier
(amplifier LVL) is configured as a differential amplifier
for differential to single-ended conversion with an input
offset-voltage trim network. It has extremely high
Typical Operating Characteristics (continued)
(V
CC
= 5V, V
GND
= 0V, V
IN+
= V
IN-
= 0V, Gain = 10V/V, R
OUTA
= R
OUTB
= 1kΩ to V
CC
/2, T
A
= +25°C, unless otherwise noted.)
Pin Description
PIN NAME FUNCTION
1 SCLK Serial-Clock Input
2 DIN Serial-Data Input. Data is clocked into the serial interface on the rising edge of SCLK.
3 GND Ground
4 INA- PGA Inverting Input
5 INA+ PGA Noninverting Input
6 OUTB Buffer Output
7 INB Buffer Input
8 OUTA PGA Output
9V
CC
Power Supply. Bypass to GND with 0.1µF and 1µF capacitors.
10 CS Acti ve- Low C hi p - S el ect Inp ut. D r i ve CS l ow to enab l e the ser i al i nter face. D r i ve CS hi g h to d i sab l e the ser i al i nter face.
MAX9939
SPI Programmable-Gain Amplifier
with Input V
OS
Trim and Output Op Amp
7
Maxim Integrated
200µs/div
COMMON-MODE REJECTION RESPONSE
INA+
1V/div
INA-
1V/div
MAX9939 toc19
OUTA
2V/div
V
CM
= 1V
P-P
, 1kHz
V
DM
= 25mV
P-P
, 10kHz
GAIN = 157V/V
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE
MAX9939 toc20
VOLTAGE (V)
SHUTDOWN CURRENT (µA)
3.6 4.0
16
20
8
4
12
0
2.8 3.2 4.8 5.24.4