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 –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
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 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
• Industrial power supplies
• 42V automotive power supplies
• Base stations
• Networking power supplies
Typical Application
V
IN
36V to 75V
V
OUT
12V 100W
Start-Up
Circuitry
MIC3838x-x
VREF
VDD
GND
OUTB
COMP
FB
RAMP
ILIM
Driver
Feed Forward
Ramp/
Volt Sec Clamp
Reference
& Isolation
RC
OUTA
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
1
MIC3838/3839
MIC [ MIC GROUP RECTIFIERS ]
