MIC2194_05 Datasheet, PDF (6/10 Pages) Micrel Semiconductor – 400kHz SO-8 Buck Control IC

MIC2194
Functional Diagram
C_DECOUP
V_IN
C_IN
EN/UVLO 3
VDD 5
VIN 8
VREF
1.245V
OVERCURRENT
COMPARATOR
BIAS
VDD
ON
0.1V
Threshold
9 CSH
GAIN
3
CURRENT
SENSE VIN
AMP
4 CSL
R_SENSE
fs/4
CONTROL
7 OUTP
Q1
L1
D1
OSC
RESET
SLOPE
COMPENSATION
∑
COMP 1
PWM
COMPARATOR
gm = 0.0002
gain = 20
V_REF
100k
ERROR
AMP 2 FB
0.3V
fs/4
FREQUENCY
FOLDBACK
6 GND
Micrel
C_OUT
V_OUT
Figure 1. MIC2194 Block Diagram
Functional Characteristics
Controller Overview and Functional Description
The MIC2194 is a BiCMOS, switched-mode, 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 MIC2194 configured as a
buck converter. At the beginning of the switching 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 MIC2194 and combined with
an internal ramp for stability. This signal is compared 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.
MIC2194
6
April 2005