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MIC2198_05 Datasheet, PDF (6/14 Pages) Micrel Semiconductor – 500kHz 4mm × 4mm Synchronous Buck Controller | |||
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MIC2198
A ramp is added to the ampliï¬ed current-sense signal to
provide slope compensation, which is required to prevent
unstable operation at duty cycles greater than 50%.
A transconductance ampliï¬er is used for the error ampliï¬er,
which compares an attenuated sample of the output voltage
with a reference voltage. The output of the error ampliï¬er is
Micrel, Inc.
the COMP (compensation) pin, which is compared to the
current-sense waveform in the PWM block. When the current
signal becomes greater than the error signal, the comparator
turns off the high-side drive. The COMP pin (pin 1) provides
access to the output of the error ampliï¬er and allows the use
of external components to stabilize the voltage loop.
VIN
CONTROL LOGIC AND
PULSE-WIDTH MODULATOR
VDD
Reference VIN
Q
RS
PWM
COMPARATOR
COMP
1
CCOMP
RCOMP
RESET
CORRECTIVE
RAMP
Oscillator
MIC2198
Current
Sense
Amp
Error
Amp
100k
AV = 2
Gm = 0.2Ã10-3
CIN
VDD
7
VIN
D2
6
BST
10
HSD
CBST
12
Q2
VSW
L1
11
LSD
8
D1
Q1
4.7µF
RCS
VOUT
COUT
PGND
9
CSH
4
VOUT
5
R1
FB
3
R2
VOUT = 0.8V
ï£1+
R1
R2


Figure 2. PWM Operation
VIN
VSW
0V
IL1
Reset
Pulse
VHSD
ILOAD
0A
VDD
0V
VIN + VDD
VLSD
0V
VDD
0V
Figure 3. PWM-Mode Timing
MIC2198
6
October 2005
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