MIC2186

Micrel

MIC2186

8

July 2002

Control Loop

PWM and SKIP modes of operation

The MIC2186 can operate in either PWM (pulse width modu-

lated) or SKIP mode. The efficiency of the boost converter

can be improved at lower output loads by manually selecting

the skip mode of operation. The potential disadvantage of

skip mode is the variable switching frequency that accompa-

nies this mode of operation. The occurrence of switching

pulses depends on component values as well as line and load

conditions. PWM mode is the best choice of operation at

higher output loads. PWM mode has the advantages of lower

output ripple voltage and higher efficiencies at higher output

loads. Pulling the SKIP pin (pin 3) low will force the controller

to operate in PWM mode for all load conditions. Pulling the

SKIP pin high will force the controller to operate in SKIP

mode.

The description of the MIC2186 controller is broken

down into 6 basic functions.

• Control Loop

• PWM Operation

• SKIP Mode Operation

• Current Limit

• MOSFET gate drive

• Reference, enable & UVLO

• Oscillator & Sync

• Soft start

Osc

D1

Q1

L1

Control

Bias

Skip Current

Limit Comparator

Hysteresis

Comparator

±1%

Current

Reset

On

P

GND

12

CSH

9

OutN

14

V

V

16

1

V

fb

5

S

GND

6

V

DD

10

V

REF

8

COMP

4

Soft Start

3

HiDC

13

Sync

11

Freq/2

15

SKIP

2

EN/UVLO

7

50mV

1.245V

R2

R1

Figure 2. MIC2186 SKIP Mode Block Diagram