MIC5191YML TR Micrel Inc, MIC5191YML TR Datasheet - Page 9

• Manufacturer Part Number: MIC5191YML TR
• Description: IC FILTER/LDO CTRLR HS 10-MLF
• Manufacturer: Micrel Inc
• Type: Positive Adjustabler

Specifications of MIC5191YML TR

• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Supply: 15mA
• Voltage - Input: 1 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 10-MLF®, QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-2722-2; MIC5191YML TR; MIC5191YMLTR; MIC5191YMLTR

Compensation
The
controlling the gain and bandwidth. This allows the
MIC5191 design to be tailored to each individual design.
In designing the MIC5191, it is important to maintain
adequate phase margin. This is generally achieved by
having the gain cross the 0dB point with a single pole
20dB/decad roll-off. The compensation pin is configured
as Figure 3 demonstrates.
This places a pole at 2.3 kHz at 80dB and calculates as
follows.
There is single pole roll off. For most applications, an
output capacitor is required. The output capacitor and
load resistance create another pole. This causes a two-
pole system and can potentially cause design instability
with inadequate phase margin. What should we do?
Answer : we compensate it externally. By providing a
dominant pole and zero–allowing the output capacitor
and load to provide the final pole–a net single pole roll
off is created, with the zero canceling the dominant pole.
Figure 5 demonstrates:
Micrel, Inc.
December 2006
MIC5191
F
F
P
P
100
-20
80
60
40
20
0
= 2.32kHz
0.01
=
Figure 3. Internal Compensation
Figure 4. Internal Compensation
2
Error Amplifier
π
0.1
×
allows
Frequency Response
External
3.42MΩ
20pF
1
1
Frequency (KHz)
Internal
10
the
×
20pF
100
Comp
flexibility
Driver
1000
10000 100000
of
225
180
135
90
45
0
-45
externally
9
Placing an external capacitor (C
(R
the dominant pole can be calculated as follows:
And the zero can be calculated as follows:
This allows for high DC gain, and high bandwidth with
the output capacitor and the load providing the final pole.
It is recommended that the gain bandwidth should be
designed to be less than 1 MHz. This is because most
capacitors lose capacitance at high frequency and
becoming resistive or inductive. This can be difficult to
compensate for and can create high frequency ringing or
worse, oscillations.
By increasing the amount of output capacitance,
transient response can be improved in multiple ways.
First, the rate of voltage drop vs. time is decreased.
Also, by increasing the output capacitor, the pole formed
by the load and the output capacitor decreases in
frequency. This allows for the increasing of the
COMP
) for the external pole-zero combination. Where
F
F
P
100
Z
-20
80
60
40
20
0
0.01
=
=
Figure 5. External Compensation
Figure 6. External Compensation
2
2
Error Amplifier
π
π
0.1
×
×
Fp
Frequency Response
External
3.42MΩ
R
Fz
20pF
COMP
The Dominant Pole
2
1
×
2
C
1
. 3
External Zero
Frequency (KHz)
Internal
R
1
×
COMP
42
Rcomp
COMP
10
×
M
×
1
C
×
1
C
COMP
Ccomp
100
×
COMP
Comp
Ccomp
Driver
R
1000
load
COMP
x C
10000 100000
out
Pole
) and resistor
M9999-122206
225
180
135
90
45
0
-45
MIC5191