SGM8534 Shengbang Microelectronics, SGM8534 Datasheet - Page 7

• Manufacturer Part Number: SGM8534
• Description: (SGM8531 - SGM8534) Rail-to-Rail Output CMOS Operational Amplifier
• Manufacturer: Shengbang Microelectronics

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APPLICATION NOTES
Driving Capacitive Loads
The SGM853X can directly drive 250pF in unity-gain without
oscillation. The unity-gain follower (buffer) is the most sensitive
configuration to capacitive loading. Direct capacitive loading
reduces the phase margin of amplifiers and this results in
ringing or even oscillation. Applications that require greater
capacitive drive capability should use an isolation resistor
between the output and the capacitive load like the circuit in
Figure 1. The isolation resistor R
form a zero to increase stability. The bigger the R
value, the more stable V
results in a loss of gain accuracy because R
divider with the R
An improvement circuit is shown in Figure 2, It provides DC
accuracy as well as AC stability. R
by connecting the inverting signal with the output, C
serve to counteract the loss of phase margin by feeding the
high frequency component of the output signal back to the
amplifier’s inverting input, thereby preserving phase margin in
the overall feedback loop.
Figure 2. Indirectly Driving Heavy Capacitive Load with DC
Accuracy
For no-buffer configuration, there are two others ways to
increase the phase margin: (a) by increasing the amplifier’s
gain or (b) by placing a capacitor in parallel with the feedback
resistor to counteract the parasitic capacitance associated with
inverting node.
Figure 1. Indirectly Driving Heavy Capacitive Load
V
V
IN
IN
SGM8531
SGM8531
C
LOAD
F
.
OUT
will be. Note that this method
R
R
ISO
ISO
ISO
F
C
provides the DC accuracy
L
and the load capacitor C
R
C
F
ISO
L
V
forms a voltage
R
OUT
L
ISO
F
V
and R
OUT
resistor
Iso
L
７
Power-Supply Bypassing and Layout
The SGM853X family operates from either a single +2.5V to
+5.5V supply or dual ±1.25V to ±2.75V supplies. For
single-supply operation, bypass the power supply V
0.1µF ceramic capacitor which should be placed close to the
V
supplies should be bypassed to ground with separate 0.1µF
ceramic capacitors. 2.2µF tantalum capacitor can be added for
better performance.
Vn
Vp
DD
pin. For dual-supply operation, both the V
V
SGM8531
Figure 3. Amplifier with Bypass Capacitors
V
DD
SS
(GND)
0.1µF
10µF
SGM8531/8532/8534
V
OUT
Vn
Vp
V
SGM8531
DD
V
SS
DD
0.1µF
0.1µF
and the V
10µF
10µF
DD
with a
V
OUT
SS