AMC7836 Datasheet, PDF (73/88 Pages) Texas Instruments – AMC7836 High-Density, 12-Bit Analog Monitor and Control Solution With Multichannel ADC, Bipolar DACs, Temperature Sensor, and GPIO Ports

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AMC7836
SLAS986C – NOVEMBER 2014 – REVISED APRIL 2016
Application Information (continued)
8.1.2 Current Sensing Applications
In applications that require current sensing of the power amplifier, an external high-side current sense amplifier
can be added and configured to the unipolar ADC inputs. Figure 116 shows this design.
The LMP8480 device is a precision current sense device that amplifies the small differential voltage developed
across a current-sense resistor in the presence of high input common-mode voltages. The LMP8480 device
accepts input signals with a common-mode voltage range from 4 V to 76 V with a bandwidth of 270 kHz. The
LMP8480 device offers different fixed gain settings. The optimal gain setting is dependent on the accuracy
requirement of the application. To maintain precision over temperature, the output of the LMP8480 device should
be directly connected to the AMC7836 unipolar ADC inputs. If the output range of the LMP8480 device is scaled
by a voltage divider, as shown in Figure 116, an output amplifier may be required to drive the ADC unipolar input
to ensure a low impedance source. If the series resistance, in this case R4, is low enough then the buffer may
not be required because the LMP8480 device is capable of driving the input of the AMC7836 unipolar ADC
channel.
NOTE
The external resistors will cause some small error because of temperature drift and the
input bias current of the operation amplifier.
Figure 116 also shows a simple method to ensure proper power sequencing of the power amplifier by adding a
series PMOS transistor to the PA drain terminal. The activation of the PMOS transistor connects the PAV_DD
voltage supply to the drain pin of the power amplifier. The PMOS transistor is driven with a voltage divider that
swings from the PAV_DD voltage to PAV_DD × (R2 / (R1 + R2)). The NMOS shown in Figure 116 is connected to a
microcontroller output that controls the state of the PMOS transistor.
PAV_DD
R1
R_(SENSE)
V_CC
RSP
VOUT
NC
RSN
GND
+
R4
R3
ADC Input
LMP8480
PC GPIO
R2
Gate
DAC Voltage
Drain
PA
Source
Figure 116. Current-Sense Application With PMOS ON and OFF
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