MIC2199BML(2004) Ver la hoja de datos (PDF) - Micrel
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MIC2199BML Datasheet PDF : 15 Pages
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MIC2199
A ramp is added to the amplified current-sense signal to
provide slope compensation, which is required to prevent
unstable operation at duty cycles greater than 50%.
A transconductance amplifier is used for the error amplifier,
which compares an attenuated sample of the output voltage
with a reference voltage. The output of the error amplifier is
Micrel
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 amplifier 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
MIC2199
Current
Sense
Amp
Error
Amp
100k
AV = 2
Gm = 0.2×10-3
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
⎛⎝1+
R1
R2
⎞
⎠
Figure 2. PWM Operation
VIN
VSW
0V
IL1
ILOAD
0A
Reset
VDD
Pulse
0V
VIN + VDD
VHSD
VLSD
0V
VDD
0V
Figure 3. PWM-Mode Timing
November 2004
7
MIC2199
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