MIC7111YM5 MICREL [Micrel Semiconductor], MIC7111YM5 Datasheet - Page 6

• Manufacturer Part Number: MIC7111YM5
• Description: 1.8V IttyBitty Rail-to-Rail Input/Output Op Amp
• Manufacturer: MICREL [Micrel Semiconductor]

MIC7111
Application Information
Input Common-Mode Voltage
The MIC7111 tolerates input overdrive by at least 300mV
beyond either rail without producing phase inversion.
If the absolute maximum input voltage is exceeded, the input
current should be limited to ±5mA maximum to prevent
reducing reliability. A 10kΩ series input resistor, used as a
current limiter, will protect the input structure from voltages as
large as 50V above the supply or below ground. See Figure
1.
Output Voltage Swing
Sink and source output resistances of the MIC7111 are
equal. Maximum output voltage swing is determined by the
load and the approximate output resistance. The output
resistance is:
V
stage. V
(output swing) portion of the appropriate Electrical Character-
istics table. I
minus V+/2 and divided by R
Electrical Characteristics DC (5V) table, the typical output
voltage drop using a 2kΩ load (connected to V+/2) is 0.015V,
which produces an I
then:
MIC7111
DROP
R
R
2.5V
OUT
OUT
is the voltage dropped within the amplifier output
Figure 1. Input Current-Limit Protection
DROP
2k
−
=
=
V
LOAD
0 015
IN
Ω
1.243mA
V
.
I
and I
LOAD
DROP
15mV
10kΩ
is equal to the typical output high voltage
V
R
LOAD
LOAD
IN
=
1.243mA
=
of:
12 1
can be determined from the V
.
LOAD
≈
1
2
. For example, using the
Ω
V
OUT
O
6
Driving Capacitive Loads
Driving a capacitive load introduces phase-lag into the output
signal, and this in turn reduces op-amp system phase margin.
The application that is least forgiving of reduced phase
margin is a unity gain amplifier. The MIC7111 can typically
drive a 500pF capacitive load connected directly to the output
when configured as a unity-gain amplifier.
Using Large-Value Feedback Resistors
A large-value feedback resistor (> 500kΩ) can reduce the
phase margin of a system. This occurs when the feedback
resistor acts in conjunction with input capacitance to create
phase lag in the fedback signal. Input capacitance is usually
a combination of input circuit components and other parasitic
capacitance, such as amplifier input capacitance and stray
printed circuit board capacitance.
Figure 2 illustrates a method of compensating phase lag
caused by using a large-value feedback resistor. Feedback
capacitor C
the phase lag caused by feedback resistor R
capacitance C
estimating C
Since a significant percentage of C
layout, it is important to note that the correct value of C
R
Figure 2. Cancelling Feedback Phase Lag
IN
V
×
IN
FB
C
IN
IN
introduces sufficient phase lead to overcome
IN
and then applying the following formula:
R
C
≤
. The value of C
IN
IN
R
FB
×
C
FB
IN
FB
C
R
FB
FB
may be caused by board
is determined by first
January 2005
FB
V
OUT
and input
FB
Micrel
may