MIC2184 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – Low Voltage Buck PWM Control IC Final Information

MIC2184
Functional Diagram
EN/UVLO 7
VDD 10
SYNC 11
FREQ/2 15
FreqOut 2
÷2
SS 3
COMP 4
VREF 13
C_DECOUP
VINA 1
VREF
1.245V
OVERCURRENT
COMPARATOR
0.1V
9 CSH
BIAS
VDD
ON
fs/4
CONTROL
GAIN
3.7
8 CSL
CURRENT
SENSE
AMP
16 VINP
14 OUTP
OSC
RESET
SLOPE
COMPENSATION
∑
12 PGND
PWM
COMPARATOR
gm = 0.0002
gain = 20
V_REF
100k
ERROR
AMP 6 FB
V_REF
0.3V
fs/4
FREQUENCY
FOLDBACK
5 SGND
V_IN
C_IN
R_SENSE
Q1
L1
D1
Micrel
C_OUT
V_OUT
Figure 1. MIC2184 Block Diagram
Functional Characteristics
Controller Overview and Functional Description
The MIC2184 is a BiCMOS, switched mode, synchronous,
step down (buck) converter controller. It uses a P-Channel
MOSFET, 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 corrective 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 MIC2184 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 MIC2184 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.
At the beginning of the next switching cycle, the P-channel
MOSFET is turned on which turns off the diode, D1.
MIC2184
8
December 10, 2001