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MIC3838_11 Datasheet, PDF (1/11 Pages) MIC GROUP RECTIFIERS – Flexible Push-Pull PWM Controller | |||
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MIC3838/3839
Micrel
MIC3838/3839
Flexible Push-Pull PWM Controller
General Description
The MIC3838 and MIC3839 are a family of complementary
output push-pull PWM control ICs that feature high speed and
low power consumption. The MIC3838/9 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 MIC3838/9 are designed for high flexibility with minimum
pin-count. The devices are easily configurable for either
voltage-mode or current-mode control. Additionally, the
MIC3838/9 can easily implement a volt-second clamp that
automatically limits the duty cycle during input transients,
allowing designers to use the smallest possible transformers
and power components. A 3V reference output is also avail-
able that eliminates the need for an external reference.
The dual-ended push-pull architecture of the MIC3838/9
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 MIC3838 has a turn-on threshold of 12.5V whereas the
MIC3839 has a lower turn-on threshold of 4.3V. Both devices
are available in a small size MSOP-10 package with an
operating range of â40°C to +85°C.
Data sheets and support documentation can be found on
Micrelâs web site at www.micrel.com.
Typical Application
VIN
36V to 75V
Start-Up
Circuitry
Features
⢠Dual output drive stages in push-pull configuration
⢠Configurable for current-mode or voltage-mode control
⢠Easily implements volt-second clamp
⢠Leading edge current-sense blanking
⢠3V reference output available
⢠130µA typical start-up current
⢠1mA typical run current
⢠Operation to 1MHz
⢠On-chip error amplifier with 4MHz gain bandwidth
product
⢠Internal soft start
⢠On-chip VDD clamping
⢠Output drive stages capable of 500mA peak source
current, 1A peak sink current
Applications
⢠High efficiency âbrickâ power supply modules
⢠Half bridge converters
⢠Full bridge converters
⢠Push-pull converters
⢠Voltage-fed push-pull converters
⢠Telecom equipment and power supplies
⢠Industrial power supplies
⢠42V automotive power supplies
⢠Base stations
⢠Networking power supplies
VOUT
12V 100W
MIC3838x-x
VREF VDD
RC
OUTA
GND OUTB
COMP RAMP
FB
ILIM
Feed Forward
Ramp/
Volt Sec Clamp
Reference
& Isolation
Voltage-Mode Half-Bridge Converter CIrcuit
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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MIC3838/3839
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