MIC3808/3809
Micrel
MIC3808/3809
Push-Pull PWM Controller
General Description
Features
The MIC3808 and MIC3809 are a family of complementary
outputpush-pullPWMcontrolICsthatfeaturehighspeedand
lowpowerconsumption.TheMIC3808/9areidealfortelecom
level (36V to 75V) isolated step down dc/dc conversion
applications where high output current, small size, and high
efficiency are required.
• 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
The dual-ended push-pull architecture of the MIC3808/9
allowsmoreefficientutilizationofthetransformerthansingle-
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,limitingthedutycycleofeachoutputstagetolessthan
50%.
• On-chip V clamping
DD
• 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
TheMIC3808/9arebuiltonalow-power,high-speedBiCMOS
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.
• Push-pull converters
• Voltage-fed push-pull converters
• Telecom equipment and power supplies
• Networking power supplies
• Industrial power supplies
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.
• 42V automotive power supplies
• Base stations
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Typical Application
VOUT
12V 100W
VIN
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
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MIC3808/3809