TSM9634
PIN FUNCTIONS
PIN
SOT23
5
4
1, 2
3
LABEL
RS+
RS-
GND
OUT
FUNCTION
External Sense Resistor Power-Side Connection
External Sense Resistor Load-Side Connection
Ground. Connect these pins to analog ground.
Output Voltage. V
OUT
is proportional to V
SENSE
= V
RS+
- V
RS-
BLOCK DIAGRAMS
DESCRIPTION OF OPERATION
The internal configuration of the TSM9634 – a
unidirectional high-side, current-sense amplifier - is
based on a commonly-used operational amplifier (op
amp) circuit for measuring load currents (in one
direction) in the presence of high-common-mode
voltages. In the general case, a current-sense
amplifier monitors the voltage caused by a load
current through an external sense resistor and
generates an output voltage as a function of that load
current. Referring to the typical application circuit on
Page 1, the inputs of the op-amp-based circuit are
connected across an external RSENSE resistor that
is used to measure load current. At the non-inverting
input of the TSM9634 (the RS+ terminal), the applied
voltage is I
LOAD
x RSENSE. Since the RS- terminal is
the non-inverting input of the internal op amp, op-amp
feedback action forces the inverting input of the
internal op amp to the same potential
(I
LOAD
x RSENSE). Therefore, the voltage drop across
TSM9634DS r1p0
RSENSE (V
SENSE
) and the voltage drop across R1 (at
the RS+ terminal) are equal. To minimize any
additional error because of op-amp input bias current
mismatch, both R1s are the same value.
Since the internal p-channel FET’s source is
connected to the inverting input of the internal op
amp and since the voltage drop across R1 is the
same as the external V
SENSE
, op amp feedback action
drives the gate of the FET such that the FET’s drain-
source current is equal to:
S
V
SENSE
R1
Page 7
RTFDS
TOUCHSTONE [ TOUCHSTONE SEMICONDUCTOR INC ]
