MIC2198 Datasheet, PDF (7/15 Pages) Micrel Semiconductor – 500kHz 4mm × 4mm Synchronous Buck Controller

MIC2198
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.
V_IN
CONTROL LOGIC AND
PULSE-WIDTH MODULATOR
V_DD
Reference _VIN
Q
RS
PWM
COMPARATOR
COMP
1
C_COMP
R_COMP
RESET
CORRECTIVE
RAMP
Oscillator
MIC2198
Current
Sense
Amp
Error
Amp
100k
A_V = 2
G_m = 0.2×10^-3
C_IN
VDD
7
VIN
D2
6
BST
10
HSD
C_BST
12
Q2
VSW
L1
11
LSD
8
D1
Q1
4.7µF
R_CS
V_OUT
C_OUT
PGND
9
CSH
4
VOUT
5
R1
FB
3
R2
V_OUT = 0.8V
⎛⎝₁₊
R1
R2
⎞
⎠
Figure 2. PWM Operation
V_IN
V_SW
0V
I_L1
I_LOAD
0A
Reset
V_DD
Pulse
0V
V_IN + V_DD
V_HSD
V_LSD
0V
V_DD
0V
Figure 3. PWM-Mode Timing
November 2004
7
MIC2198