MIC2186_05 Datasheet, PDF (7/15 Pages) Micrel Semiconductor – Low Voltage PWM Control IC

MIC2186
Functional Diagram
V_IN
C_DECOUP
V_INA ₁
EN/UVLO
7
Bias
SKIP
2
fs/4
On
Control
Overcurrent Reset
Freq/2
15
Sync
Osc
11
HiDC
V_DD
13
Corrective
Ramp
Soft Start
3
PWM
Comparator
V_REF
V_DD
C_IN
L1
V_INP
16
D1
P_GND
OutN
14
C_OUT
0.1V
Overcurrent
Comparator
CSH
9
COMP
4
Error
Amplifier
gm = 0.0002
Gain = 20
100k
Gain = 3.7
V_REF
P_GND
0.3V
R_SENSE
P_GND
12
Micrel, Inc.
V_OUT
V_REF
8
V_DD
10
V_REF
V_DD
fs/4
R1
V_fb
6
Frequency
R2
Foldback
S_GND
S_GND 5
Figure 1. MIC2186 PWM Block Diagram
Functional Description
The MIC2186 is a BiCMOS, switched mode multi-topology
controller. It will operate most low side drive topologies
including boost, SEPIC, flyback and forward. The controller
has a low impedance driver capable of switching large N-
channel MOSFETs. It features multiple frequency and duty
cycle settings. 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 shows a block diagram of the MIC2186 configured
as a PWM boost converter.
The switching cycle starts when OutN goes high and turns on
the low side, N-channel MOSFET, Q1. The Vgs of the
MOSFET is equal to V_INP. This forces current to ramp up in
the inductor. The inductor current flows through the current
sense resistor, Rsense. The voltage across the resistor is
amplified and combined with an internal ramp for stability.
This signal is compared with the error voltage signal from the
error amplifier. When the current signal equals the error
voltage signal, the low side MOSFET is turned off. The
inductor current then flows through the diode, D1, to the
output. The MOSFET remains off until the beginning of the
next switching cycle.
April 2005
7
M9999-042205