Sailesh Chittipeddi - EEWeb

M1 OFF when M2 is conducting current. The disabled
FET does not contribute to the resultant output voltage
in either case.
For both types of uni-directional or bi-directional CSAs,
gain error accuracy is a measure of how well-controlled
is the ratio of ROUT to RGAIN, especially over
temperature. Gain error accuracy can be
100μV or more.
The CSA’s SIGN Output Comparator
The bi-directional CSA incorporated one additional
feature as was shown in Figure 2 – an analog comparator
the inputs of which monitor the internal amplifier’s
differential output voltage. The SIGN comparator
output indicates the load current’s direction while the
voltage at its OUT terminal indicates the magnitude of
the load current. The SIGN output is a logic high when
M1 is conducting current (VRS+ > VRS). Alternatively,
the SIGN output is a logic low when M2 is conducting
current (VRS+ < VRS-).
Note that the SIGN comparator exhibits no “dead zone”
at ILOAD switchover, unlike other bi-directional CSAs
where hysteresis was purposely introduced to prevent
comparator output voltage chatter. The load current
transition band is less than ±0.2mA with respect to a
50-mΩ external sense resistor. Other types of CSAs
OUT
VDD
LOAD
SIGN
0.1µF
0.047µF
To AC Wall Cube
OR Charger
+3.3V
Figure 2: A Typical Application for a Bi-directional High-precision Current Sense Amplifier
(Touchstone Semiconductor’s TS1101).
V DD
Microcontroller
ADC Input
Digital Input
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