Datasheet

_______________Detailed Description
The MAX4372 high-side current-sense amplifier fea-
tures a 0 to +28V input common-mode range that is
independent of supply voltage. This feature allows the
monitoring of current flow out of a battery in deep dis-
charge, and also enables high-side current sensing at
voltages far in excess of the supply voltage (V
CC
).
Current flows through the sense resistor, generating a
sense voltage (Figure 1). Since A1’s inverting input is
high impedance, the voltage on the negative terminal
equals V
IN
- V
SENSE
. A1 forces its positive terminal to
match its negative terminal; therefore, the voltage
across R
G1
(V
IN
- V1-) equals V
SENSE
. This creates a
current to flow through R
G1
equal to V
SENSE
/ R
G1
. The
transistor and current mirror amplify the current by a
factor of β. This makes the current flowing out of the
current mirror equal to:
I
M
= β V
SENSE
/ R
G1
A2’s positive terminal presents high impedance, so this
current flows through R
GD
, with the following result:
V
2+
= R
GD
β · V
SENSE
/ R
G1
R1 and R2 set the closed-loop gain for A2, which
amplifies V
2+
, yielding:
V
OUT
= R
GD
· β · V
SENSE
/ R
G1
(1 + R2 / R1)
The gain of the device equals:
V
OUT
= R
GD
· β (1 + R2 / R1) / R
G1
V
SENSE
__________Applications Information
Recommended Component Values
The MAX4372 operates over a wide variety of current
ranges with different sense resistors. Table 1 lists com-
mon resistor values for typical operation of the
MAX4372.
Choosing R
SENSE
Given the gain and maximum load current, select
R
SENSE
such that V
CC
- V
OUT
does not exceed +0.25V
and V
OUT
does not exceed +10V. To measure lower
currents more accurately, use a high value for R
SENSE
.
A higher value develops a higher sense voltage, which
overcomes offset voltage errors of the internal current
amplifier.
In applications monitoring very high current, ensure
R
SENSE
is able to dissipate its own I
2
R losses. If the
resistor’s rated power dissipation is exceeded, its value
may drift or it may fail altogether, causing a differential
voltage across the terminals in excess of the absolute
maximum ratings.
MAX4372T/F/H
Low-Cost, SOT23, Micropower, High-Side
Current-Sense Amplifier with Voltage Output
6 _______________________________________________________________________________________
MAX4372T/F/H
GND
TO
LOAD
V
IN
0 TO +28V
+2.7V
TO
+28V
R1
R
GD
R
G2
RS+
RS-
R
G1
R2
OUT
V2+
V1+
V1-
V2-
V
CC
R
SENSE
I
LOAD
I
M
V
SENSE
CURRENT
MIRROR
A1
A2
Pin Description
1 3 Ground
2 4 Output Voltage. V
OUT
is proportional to the magnitude of V
SENSE
(V
RS+
- V
RS-
).
PIN
GND
OUT
SO
FUNCTION
SOT23-5
NAME
3 1 Supply Voltage
4 8 Power Connection to the External Sense Resistor
V
CC
RS+
5 6 Load-Side Connection to the External Sense Resistor
— 2, 5, 7 No Connection. Not internally connected.
RS-
N.C.
Figure 1. Functional Diagram