Datasheet

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DRIVING A/D CONVERTERS
10 toW
20W
OPAx340
V+
V
IN
V
OUT
R
S
R
L
C
L
ADS7816
12-BitA/D
DCLOCK
D
OUT
CS/SHDN
OPA340
+5V
V
IN
V+
2
+In
3
-In
V
REF
8
4GND
Serial
Interface
1
0.1mF 0.1mF
7
6
5
NOTE:A/DInput=0toV
REF
V =0Vto5Vfor
IN
0Vto5Voutput.
RCnetworkfiltershighfrequencynoise.
500W
3300pF
OPA340
OPA2340
OPA4340
SBOS073B – SEPTEMBER 1997 – REVISED NOVEMBER 2007
One method of improving capacitive load drive in the
unity gain configuration is to insert a 10 Ω to 20 Ω
OPA340 series op amps are optimized for driving
resistor in series with the output, as shown in
medium speed (up to 100kHz) sampling A/D
Figure 26 . This significantly reduces ringing with large
converters. However, they also offer excellent
capacitive loads. However, if there is a resistive load
performance for higher speed converters. The
in parallel with the capacitive load, it creates a
OPA340 series provides an effective means of
voltage divider introducing a dc error at the output
buffering the A/D ’ s input capacitance and resulting
and slightly reduces output swing. This error may be
charge injection while providing signal gain. Figure 27
insignificant. For instance, with R
L
= 10k Ω and R
S
=
and Figure 28 show the OPA340 driving an
20 Ω , there is only about a 0.2% error at the output.
ADS7816 . The ADS7816 is a 12-bit, micro-power
sampling converter in the tiny MSOP-8 package.
When used with the miniature package options of the
OPA340 series, the combination is ideal for
space-limited and low-power applications. For further
information consult the ADS7816 data sheet . With the
OPA340 in a noninverting configuration, an RC
network at the amplifier ’ s output can be used to filter
high-frequency noise in the signal (see Figure 27 ). In
the inverting configuration, filtering may be
accomplished with a capacitor across the feedback
Figure 26. Series Resistor in Unity-Gain
resistor (see Figure 28 ).
Configuration Improves Capacitive Load Drive
Figure 27. OPA340 in Noninverting Configuration Driving ADS7816
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Product Folder Link(s): OPA340 OPA2340 OPA4340