Datasheet

C1
R
SENSE
POWER
SWITCH
INDUCTIVE
LOAD
24V
-+
+IN
-IN
+
-
Preamplifier
Output Buffer
Gain = K2
A1
A2
Gain = 10
OFFSET
Internal
Resistor
100 k:
OUT
Level
shift
1
5
3 4
7
8
LMP8601/
LMP8601Q
ADC
LMP8601, LMP8601-Q1
SNOSAR2E –SEPTEMBER 2008–REVISED MARCH 2013 www.ti.com
Figure 40. Reduce Error When Driving ADCs
The external capacitor absorbs the charge that flows when the ADC sampling capacitor is connected. The
external capacitor should be much larger than the sample and hold capacitor at the input of the ADC and the RC
time constant of the external filter should be such that the speed of the system is not affected.
LOW SIDE CURRENT SENSING APPLICATION
Figure 41 illustrates a low side current sensing application with a low side driver. The power transistor is pulse
width modulated to control the average current flowing through the inductive load which is connected to a
relatively high battery voltage. The current through the load is measured across a shunt resistor R
SENSE
in series
with the load. When the power transistor is on, current flows from the battery through the inductive load, the
shunt resistor and the power transistor to ground. In this case, the common mode voltage on the shunt is close
to ground. When the power transistor is off, current flows through the inductive load, through the shunt resistor
and through the freewheeling diode. In this case the common mode voltage on the shunt is at least one diode
voltage drop above the battery voltage. Therefore, in this application the common mode voltage on the shunt is
varying between a large positive voltage and a relatively low voltage. Because the large common mode voltage
range of the LMP8601/LMP8601Q and because of the high AC common mode rejection ratio, the
LMP8601/LMP8601Q is very well suited for this application.
R
SENSE
= 0.01Ω, K2 = 2, V
OUT
= 0.2 V/A
Figure 41. Low Side Current Sensing Application
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