Datasheet

V
IN
+V
ADC
-
+
V
REF
LMP7701 ADC122S021
SDO
LM7705
+V
C
OUT
C
RES
C
FLY
B
A
-V
LM7705
www.ti.com SNVS420B –NOVEMBER 2008–REVISED MARCH 2013
Figure 32. Typical True Zero Output Voltage Application with/without LM7705
The output voltage of the LMP7701 is converted to the digital domain using an ADC122S021. This is an 12 bit
analog to digital converter with a serial data output. Data processing and graphical displaying is done with a
computer. The negative power supply pin of the op amp can be connected to ground level or to the output of the
negative bias generator, to demonstrate the effect at the output voltage range of the op amp.
The key specifications of the used components are given in the next part of the section.
Supply Voltage/Reference Voltage
Supply voltage +5V
ADC Voltage Reference +5V
LMP7701
V
DSAT
(typical) 18 mV
V
DSAT
(over temperature) 50 mV
LM7705
Output voltage ripple 4 mV
PP
Output voltage noise 10 mV
PP
ADC
Type ADC122S021
Resolution 12 bit
Quantization level 5V/4096 = 1.2mV
Measurement Results
The output voltage range of the LMP7701 has been measured, especially the range to ground level. A small DC
signal, with a voltage swing of 50 mV
PP
is applied to the input. The digitized output voltage of the op amp is
measured over a given time period, when its negative supply pin is connected to ground level or connected to
the output of the LM7705.
Figure 33A and Figure 33B show the digitized output voltage of the LMP7701 op amp.
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