MIC2169BYMM Micrel Inc, MIC2169BYMM Datasheet - Page 14

• Manufacturer Part Number: MIC2169BYMM
• Description: IC CTLR PWM BUCK SYNC 10MSOP
• Manufacturer: Micrel Inc

Specifications of MIC2169BYMM

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 550kHz
• Duty Cycle: 92%
• Voltage - Supply: 3 V ~ 14.5 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Frequency-max: 550kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-3641-5; MIC2169BYMM

Depending on the circuit components and operating
conditions, an external Schottky diode will give a ½% to
1% improvement in efficiency.
Feedback Loop Compensation
The MIC2169B controller comes with an internal
transconductance error amplifier used for compensating
the voltage feedback loop by placing a capacitor (C1) in
series with a resistor (R1) and another capacitor C2 in
parallel from the COMP pin to ground. See “Functional
Block Diagram.”
Power Stage
The power stage of a voltage mode controller has an
inductor,
connected to the output capacitor, C
electrical series resistance (ESR) as shown in Figure 7.
The transfer function G(s), for such a system is:
Plotting this transfer function with the following assumed
values
ESR=0.025Ω) gives lot of insight as to why one needs to
compensate the loop by adding resistor and capacitors
on the COMP pin. Figures 8 and 9 show the gain curve
and phase curve for the above transfer function.
Micrel, Inc.
April 2010
Figure 7. The Output LC Filter in a Voltage-Mode Buck
G
(
) s
=
L1,
⎛
⎜ ⎜
⎝
(L=1μH,
Figure 8. The Gain Curve for G(s)
DCR
with
×
s
×
L
C
its
Converter
(
+
DCR=0.009Ω,
1
s
+
2
winding
ESR
×
DCR
L
×
×
C
s
ESR
+
×
C
1
C
resistance
OUT
+
)
ESR
V
O
OUT
C
×
OUT
, with its
s
×
=660μF,
C
(DCR)
⎞
⎟ ⎟
⎠
14
It can be seen from the transfer function G(s) and the
gain curve that the output inductor and capacitor create
a two pole system with a break frequency at:
Therefore, f
By looking at the phase curve, it can be seen that the
output capacitor ESR (0.025Ω) cancels one of the two
poles (LC
Therefore, F
From the point of view of compensating the voltage loop,
it is recommended to use higher ESR output capacitors
since they provide a 90° phase gain in the power path.
For comparison purposes, Figure 10, shows the same
phase curve with an ESR value of 0.002Ω.
f
f
LC
ZERO
Figure 10. The Phase Curve with ESR = 0.002 Ω
=
OUT
2
=
LC
×
ZERO
) system by introducing a zero at:
2
π
Figure 9. Phase Curve for G(s)
= 6.2kHz
×
L
π
= 9.6kHz.
1
×
×
C
ESR
OUT
1
×
C
OUT
M9999-041210-B
MIC2169B