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
• On-chip V
DD
clamping
• 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
Typical Application
V
OUT
12V 100W
V
IN
36V to 75V
Start-Up
Circuitry
MIC3808
RC
VDD
GND OUTA
COMP OUTB
FB
CS
Slope
Comp
Reference
& Isolation
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2005
1
MIC3808/3809
MIC [ MIC GROUP RECTIFIERS ]
