April 2005

1

MIC3808/3809

MIC3808/3809

Micrel

MIC3808/3809

Push-Pull PWM Controller

General Description

The MIC3808 and MIC3809 are a family of complementary

output push-pull PWM control ICs that feature high speed and

low power consumption. The MIC3808/9 are ideal for telecom

level (36V to 75V) isolated step down dc/dc conversion

applications where high output current, small size, and high

efficiency are required.

The dual-ended push-pull architecture of the MIC3808/9

allows more efficient utilization of the transformer than single-

ended topologies, allowing smaller size dc/dc solutions.

Additionally, the out-of-phase push-pull topology allows a

higher effective duty cycle, reducing input and output ripple

as well as stress on the external components. The dead-time

between the two outputs is adjustable between 60ns to

200ns, limiting the duty cycle of each output stage to less than

50%.

The MIC3808/9 are built on a low-power, high-speed BiCMOS

process. The 130µA start-up current and 1mA run-current

reduce the size of the start-up circuitry and allow high

efficiency even at light loads. The high-speed internal 4MHz

error amplifier allows MIC3808/9 operation up to 1MHz.

The MIC3808 has a turn-on threshold of 12.5V whereas the

MIC3809 has a lower turn-on threshold of 4.3V. Both devices

are available in SOP-8 and MSOP-8 package options with an

operating range of –40°C to +85°C.

Data sheets and support documentation can be found on

Micrel’s web site at: www.micrel.com.

Features

• Dual output drive stages in push-pull configuration

• Leading edge current-sense blanking

• 130µA typical start-up current

• 1mA typical run current

• Operation to 1MHz

• Internal soft start

• On-chip error amplifier with 4MHz gain bandwidth

product

• Output drive stages capable of 500mA peak source

current, 1A peak sink current

Applications

• High efficiency “brick” power supply modules

• Half bridge converters

• Full bridge converters

• Push-pull converters

• Voltage-fed push-pull converters

• Telecom equipment and power supplies

• Networking power supplies

• Industrial power supplies

• 42V automotive power supplies

• Base stations

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

Typical Application

36V to 75V

MIC3808

12V 100W

RC

GND

VDD

OUTA

FB

COMP OUTB

CS

Start-Up

Circuitry

Slope

Comp

Reference

& Isolation