SC310 Datasheet, PDF (8/12 Pages) Semtech Corporation – High-Side Current-Sense Amplifier with Low Impedance Voltage Output

POWER MANAGEMENT
Block Diagram
SC310
VCC
CS+
CS-
SHDN
R4
Gain = A1
Gain = A2
+
Gain = A3
1k
A
Q1
R5
-
Gain = B
+
B
1k
-
R3
R1 _20k
10k
R2 5k
Disable
OUT
GND
Detailed Description
SC310 is a unidirectional high-side current sense ampli-
fier for precision current monitoring. It has a wide com-
mon-mode range of 2.7 to 25V and allows high-side cur-
rent-sensing at voltages greater than supply voltage (V_CC).
The SC310 operates as follows: Current from source (as
shown in the typical applications circuit on page. 1), flows
through RSENSE to the load. Since the inverting input of
amplifier A has a high input impedance, negligible cur-
rent flows through R5 (neglecting the input bias current).
Amplifier A has an inverting input voltage which equals
V(CS+) - I_LOAD*R_SENSE. The amplifier’s high open-loop gain
forces the non-inverting input voltage to the same volt-
age as the inverting input. The drop across R4 equals
I_LOAD*R_SENSE. Since I_R4 flows through R4, IR4 =
(I_LOAD*R_SENSE)/R4. Resistor R3 then sets the overall gain
for amplifier A, A1, A2 or A3 (neglecting the input bias
currents for non-inverting inputs for amplifiers A and B).
The second amplifier, B, is a fixed gain stage (gain = B)
and the final output includes the gain obtained from this
stage.
The SC310 has three gain versions as follows:
Version
Gain Expression
Gain Value
SC310A
A1*B
20
SC310B
A2*B
50
SC310C
A3*B
100
 2005 Semtech Corp.
8
www.semtech.com