Datasheet

(V+ = +12V, V
RS+
= 12V, R
OUT
= 1kΩ, T
A
= +25°C, unless otherwise noted.)
Detailed Description
The MAX4172 is a unidirectional, high-side current-
sense amplifier with an input common-mode range that is
independent of supply voltage. This feature not only
allows the monitoring of current flow into a battery in deep
discharge, but also enables high-side current sensing at
voltages far in excess of the supply voltage (V+).
The MAX4172 current-sense amplifier’s unique topology
simplifies current monitoring and control. The MAX4172’s
amplifier operates as shown in Figure 1. The battery/
load current flows through the external sense resistor
(R
SENSE
), from the RS+ node to the RSnode. Current
flows through R
G1
and Q1, and into the current mirror,
where it is multiplied by a factor of 50 before appearing
at OUT.
To analyze the circuit of Figure 1, assume that current
flows from RS+ to RS-, and that OUT is connected to
GND through a resistor. Since A1’s inverting input is high
impedance, no current flows though R
G2
(neglecting the
input bias current), so A1’s negative input is equal to
V
SOURCE
- (I
LOAD
x R
SENSE
). A1’s open-loop gain forces
its positive input to essentially the same voltage level as
the negative input. Therefore, the drop across R
G1
equals
Pin Description
Typical Operating Characteristics (continued)
5µs/div
STARTUP DELAY
GND
V
OUT
500mV/div
V+
2V/div
GND
V
SENSE
= 100mV
MAX4172-10
10ms/div
V+ to PG POWER-UP DELAY
GND
PG
2V/div
V+
2V/div
GND
100kW PULLUP RESISTOR FROM PG TO +4V
MAX4172-11
PIN NAME FUNCTION
1 RS+ Power connection to the external sense resistor. The “+” indicates the direction of current ow.
2 RS- Load-side connection for the external sense resistor. The “-” indicates the direction of current ow.
3, 4 N.C. No Connect. No internal connection. Leave open or connect to GND.
5 GND Ground
6 OUT
Current Output. OUT is proportional to the magnitude of the sense voltage (V
RS+
- V
RS-
). A 1kΩ
resistor from OUT to ground will result in a voltage equal to 10V/V of sense voltage.
7 PG
Power Good Open-Collector Logic Output. A low level indicates that V+ is su󰀩cient to power the
MAX4172, and adequate time has passed for power-on transients to settle out.
8 V+ Supply Voltage Input for the MAX4172
MAX4172 Low-Cost, Precision, High-Side
Current-Sense Amplier
www.maximintegrated.com
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