MCP6001/2/4
4.0
APPLICATION INFORMATION
–
The MCP6001/2/4 family of op amps is manufactured
using Microchip’s state-of-the-art CMOS process and
is specifically designed for low-cost, low-power and
general-purpose applications. The low supply voltage,
low quiescent current and wide bandwidth makes the
MCP6001/2/4 ideal for battery-powered applications.
This device has high phase margin, which makes it
stable for larger capacitive load applications.
VOUT
RIN
MCP600X
+
VIN
(Maximum expected VIN) – VDD
------------------------------------------------------------------------------
2 mA
RIN
≥
VSS – (Minimum expected VIN
)
4.1
Rail-to-Rail Input
---------------------------------------------------------------------------
RIN
≥
2 mA
The MCP6001/2/4 op amps are designed to prevent
phase reversal when the input pins exceed the supply
voltages. Figure 4-1 shows the input voltage exceeding
the supply voltage without any phase reversal.
FIGURE 4-2:
Resistor (RIN).
Input Current Limiting
4.2
Rail-to-Rail Output
6
The output voltage range of the MCP6001/2/4 op amps
is VDD – 25 mV (min.) and VSS + 25 mV (max.) when
RL = 10 kΩ is connected to VDD/2 and VDD = 5.5V.
Refer to Figure 2-14 for more information.
VIN
VDD = 5.0V
G = +2 V/V
5
4
VOUT
3
4.3
Capacitive Loads
2
Driving large capacitive loads can cause stability prob-
lems for voltage feedback op amps. As the load capac-
itance increases, the feedback loop’s phase margin
decreases and the closed-loop bandwidth is reduced.
This produces gain peaking in the frequency response,
with overshoot and ringing in the step response. While
a unity-gain buffer (G = +1) is the most sensitive to
capacitive loads, all gains show the same general
behavior.
1
0
0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
6.E-05
7.E-05
8.E-05
9.E-05
1.E-04
-1
Time (10 µs/div)
FIGURE 4-1:
Phase Reversal.
The MCP6001/2/4 Show No
The input stage of the MCP6001/2/4 op amps use two
differential input stages in parallel. One operates at a
low common mode input voltage (VCM), while the other
operates at a high VCM. With this topology, the device
operates with a VCM up to 300 mV above VDD and
300 mV below VSS. The input offset voltage is
measured at VCM = VSS – 300 mV and VDD + 300 mV
to ensure proper operation.
When driving large capacitive loads with these op
amps (e.g., > 100 pF when G = +1), a small series
resistor at the output (RISO in Figure 4-3) improves the
feedback loop’s phase margin (stability) by making the
output load resistive at higher frequencies. The band-
width will be generally lower than the bandwidth with no
capacitance load.
Input voltages that exceed the input voltage range
(VSS – 0.3V to VDD + 0.3V at 25°C) can cause
excessive current to flow into or out of the input pins,
while current beyond ±2 mA can cause reliability
problems. Applications that exceed this rating must be
externally limited with a resistor, as shown in Figure 4-2.
–
RISO
VOUT
MCP600X
+
VIN
CL
FIGURE 4-3:
Output resistor, RISO
stabilizes large capacitive loads.
DS21733F-page 8
© 2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
