MIC2183_05 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – Low Voltage Synchronous Buck PWM Control IC

MIC2183
Functional Diagram
EN/UVLO 7
VDD 10
SYNC 11
FREQ/2 15
FreqOut 2
÷2
SS 3
COMP 4
C_DECOUP
VINA 1
VREF
1.245V
OVERCURRENT
COMPARATOR
0.1V
9 CSH
BIAS
VDD
ON
fs/4
CONTROL
OSC
RESET
SLOPE
COMPENSATION
GAIN
3.7
8 CSL
CURRENT
SENSE
AMP
16 VINP
14 OUTP
PGND
13 OUTN
12 PGND
∑
PWM
COMPARATOR
gm = 0.0002
gain = 20
V_REF
100k
ERROR
AMP 6 FB
0.3V
fs/4
FREQUENCY
FOLDBACK
5 SGND
V_IN
C_IN
R_SENSE
Q1
L1
Q2
D1
Micrel, Inc.
C_OUT
V_OUT
Figure 1. MIC2183 Block Diagram
Functional Characteristics
Controller Overview and Functional Description
The MIC2183 is a BiCMOS, switched mode, synchronous,
step down (buck) converter controller. It uses both N and P-
Channel MOSFETs, which allows the controller to operate at
100% duty cycle and eliminates the need for a high side drive
bootstrap circuit. Current mode control is used to achieve
superior transient line and load regulation. An internal correc-
tive ramp provides slope compensation for stable operation
above a 50% duty cycle. The controller is optimized for high
efficiency, high performance DC-DC converter applications.
Figure 1 is a block diagram of the MIC2183 configured as a
synchronous buck converter. At the beginning of the switch-
ing cycle, the OUTP pin pulls low and turns on the high-side
P-Channel MOSFET, Q1. Current flows from the input to the
output through the current sense resistor, MOSFET and
inductor. The current amplitude increases, controlled by the
inductor. The voltage developed across the current sense
resistor, R_SENSE, is amplified inside the MIC2183 and com-
bined with an internal ramp for stability. This signal is com-
pared to the output of the error amplifier. When the current
signal equals the error voltage signal, the P-channel MOSFET
is turned off. The inductor current flows through the diode, D1,
until the synchronous, N-Channel MOSFET turns on. The
voltage drop across the MOSFET is less than the forward
voltage drop of the diode, which improves the converter
efficiency. At the end of the switching period, the synchro-
nous MOSFET is turned off and the switching cycle repeats.
M9999-042205
8
April 2005