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SMP04 View Datasheet(PDF) - Analog Devices

Part Name
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SMP04 Datasheet PDF : 15 Pages
First Prev 11 12 13 14 15
VIN
(؎3.5V)
RESET
PD/H
POSITIVE
PD/H
NEGATIVE
AMPLIFIER A
+5V
1/2 OP221
–5V
AMPLIFIER B
1/2 OP221
R1
20k
D1
1N914
D2
G
SD214
R2
100
D
S Q1
R3
20k
D3
1N914 D4
G
SD214
R4
100
D
S Q2
+5V
VDD
–5V
VSS
VSS
1/2 SMP04
VSS
DGND
Figure 21. Positive and Negative Peak Detector with Hold Control
SMP04
VOUT
POSITIVE
VOUT
NEGATIVE
POSITIVE AND NEGATIVE PEAK DETECTOR WITH
HOLD CONTROL (Figure 21)
In this application the top amplifier (Amplifier A) is the positive
peak detector and the bottom amplifier (Amplifier B) is the
negative peak detector. Operation can be analyzed as follows:
Assume that the S/H switch is closed. As a positive increasing
voltage is applied to VIN, D2 turns on, and D1 turns off, closing
the feedback loop around Amplifier A and the SMP04, causing
the output to track the input. Conversely, in the negative peak
detector circuit at the bottom, D4 turns off and D3 turns on,
holding the last most negative input voltage on the SMP04.
This voltage is buffered to the VO(NEG) output.
As VIN falls in voltage the above conditions reverse, causing the
most positive peak voltage to be held at VO(POS) output. This
voltage will be held until the input has a more positive voltage
than the previously held peak voltage, or a reset condition is
applied.
An optional HOLD control can be used by applying a logic HIGH
to the PD/H inputs. This HOLD mode further reduces leakage
current through the reverse-biased diodes (D2 and D4) during
peak hold.
GAIN OF 10 SAMPLE-AND-HOLD (Figure 22)
This application places the SMP04 in a feedback loop of an
amplifier. Because the SMP04 has no sign inversion and the
amplifier has very high open-loop gain, the gain of the circuit is set
by the ratio of the sum of the source and feedback resistances
1k
VIN
0V TO
1.0V
8.66k
+12V
340
1N914
+12V
1/4 SMP04
1/4 OP490
100k
VSS
VOUT
0V TO
10V
S/H
Figure 22. Gain of 10 Sample-and-Hold Amplifier
to the source resistance. When a logic LOW is applied to the
S/H control input, the loop is closed around the OP490,
yielding a gain of 10 (in the example shown) amplifier. When
the S/H control goes HIGH, the loop opens and the SMP04
holds the last sampled voltage. The loop remains open and the
output is unaffected by the input until a logic LOW is reapplied
to the S/H control. The pair of back-to-back diodes from the
output of the op amp to the output of the track-and-hold pre-
vents the op amp from saturating when the track-and-hold is in
the hold mode and the loop is open.
REV. D
–11–
 

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