MIC2186 MICREL [Micrel Semiconductor], MIC2186 Datasheet - Page 7

• Manufacturer Part Number: MIC2186
• Description: Low Voltage PWM Control IC
• Manufacturer: MICREL [Micrel Semiconductor]

Functional 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.
July 2002
MIC2186
V
V
IN
DD
EN/UVLO
Soft Start
COMP
Freq/2
HiDC
SKIP
Sync
V
V
REF
15
11
13
10
DD
7
2
3
4
8
fs/4
Osc
Corrective
Ramp
V
V
REF
DD
Control
Figure 1. MIC2186 PWM Block Diagram
100k
Amplifier
C
Error
DECOUP
gm = 0.0002
Overcurrent Reset
PWM
Comparator
On
Gain = 20
S
GND
S
GND
V
5
IN
Bias
A
fs/4
1
V
REF
7
Gain = 3.7
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
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.
Frequency
Foldback
V
V
REF
DD
Overcurrent
Comparator
0.1V
0.3V
P
GND
P
GND
C
IN
V
16
OutN
14
CSH
9
P
12
V
6
IN
IN
GND
fb
P
P. This forces current to ramp up in
L1
R
SENSE
D1
C
OUT
R1
R2
V
OUT
MIC2186
Micrel