MCP6004-I/SN Microchip Technology, MCP6004-I/SN Datasheet - Page 9

• Manufacturer Part Number: MCP6004-I/SN
• Description: 1 MHz Bandwidth Low Power Op Amp
• Manufacturer: Microchip Technology

3.6.3
The MCP6001/2/4 op amp has a high input impedance,
rail-to-rail input and output and low input bias current,
which makes this device suitable for a peak detector
applications. Figure 3-7 shows a peak detector circuit
with clear and sample switches. The peak-detection
cycle uses a clock (CLK), as shown in Figure 3-7.
At the rising edge of CLK, Sample Switch closes to
begin sampling. The peak voltage stored on C
pled to C
end of the sample time (falling edge of Sample Signal),
Clear Signal goes high and closes the Clear Switch.
When the Clear Switch closes, C
R
time (falling edge of Clear Signal), op amp A begins to
store the peak value of V
t
In order to define the t
to determine the capacitor charging and discharging
period. The capacitor charging time is limited by the
amplifier source current, while the discharging time ( )
is defined using R
the input signal is sampled on C
the input voltage change frequency.
The op amp output current limit, and the size of the
storage capacitors (both C
ing limitations as the input voltage (V
rent through a capacitor is dependent on the size of the
capacitor and the rate of voltage change. From this
relationship, the rate of voltage change or the slew rate
FIGURE 3-7:
DETECT
V
1
2003 Microchip Technology Inc.
IN
for a time defined by t
.
MCP6002
+
–
2
1/2
for a sample time defined by t
PEAK DETECTOR
A
1
( = R
D
SAMP
Peak Detector with Clear and Sample CMOS Analog Switches.
1
CLEAR
IN
1
*C
1
on C
and t
and C
1
R
). t
ISO
. At the end of the clear
1
1
DETECT
CLEAR
, and is dependent on
1
2
for a time defined by
Switch
), could create slew-
Clear
V
discharges through
IN
C1
) increases. Cur-
C
, it is necessary
is the time that
1
Sample Signal
SAMP
Clear Signal
1
R
. At the
is sam-
1
CLK
MCP6002
+
–
1/2
t
SAMP
t
CLEAR
B
can be determined. For example, with op amp short-cir-
cuit current of I
C
EQUATION
This voltage change rate is less than the MCP6001/2/4
slew rate of 600 mV/µs. When the input voltage swings
below the voltage across C
biased, which opens the feedback loop and rails the
amplifier. When the input voltage increases, the ampli-
fier recovers at its slew rate. Based on the rate of volt-
age change shown in the above equation, it takes an
extended period of time to charge a 0.1 µF capacitor.
The capacitors need to be selected so that the circuit is
not limited by the amplifier slew rate. Therefore, the
capacitors should be less than 40 µF and a stabilizing
resistor (R
Section 3.3, “Capacitive Load and Stability”, for op amp
stability.
t
DETECT
1
= 0.1 µF, then:
Sample
Switch
ISO
) needs to be properly selected. Refer to
SC
R
dV
------------ -
dV
------------ -
ISO
dt
dt
I
MCP6001/2/4
SC
C1
C1
= 25 mA and load capacitor of
V
=
=
=
=
C2
C
I
------- -
-------------- -
0.1 F
250mV
---------------- -
25mA
C
SC
C
1
1
2
1
s
, D
dV
------------ -
dt
1
MCP6001
+
–
C1
becomes reverse-
DS21733D-page 9
C
V
OUT