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MIC3839 PDF даташит

Спецификация MIC3839 изготовлена ​​​​«Micrel Semiconductor» и имеет функцию, называемую «(MIC3838 / MIC3839) Flexible Push-Pull PWM Controller».

Детали детали

Номер произв MIC3839
Описание (MIC3838 / MIC3839) Flexible Push-Pull PWM Controller
Производители Micrel Semiconductor
логотип Micrel Semiconductor логотип 

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MIC3839 Даташит, Описание, Даташиты
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.
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 “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
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
1 MIC3838/3839









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MIC3839 Даташит, Описание, Даташиты
MIC3838/3839
Ordering Information
Part Number
Standard
MIC3838BMM
MIC3839BMM
Lead-Free
MIC3838YMM
MIC3839YMM
Turn On
Threshold
12.5V
4.3V
Micrel
Turn Off
Threshold
8.3V
4.1V
Temperature Range
–40°C to +85°C
–40°C to +85°C
Package
10-Pin MSOP
10-Pin MSOP
Pin Configuration
COMP 1
FB 2
ILIM 3
RAMP 4
RC 5
10 VREF
9 VDD
8 OUTA
7 OUTB
6 GND
MSOP-10 (MM)
Pin Description
Pin Number
1
2
3
4
5
6
MIC3838/3839
Pin Name
COMP
FB
ILIM
RAMP
RC
GND
Pin Function
COMP is the output of the error amplifier and the input of the PWM
comparator. The error amplifier in the MIC3838 is a true low-output imped-
ance, 4MHz operational amplifier. As such, the COMP pin can both source
and sink current. However, the error amplifier is internally current limited, so
that zero duty cycle can be externally forced by pulling COMP to GND.
The MIC3838 family features built-in full cycle soft start. Soft start is imple-
mented as a clamp on the maximum COMP voltage.
The inverting input to the error amplifier.
The input to the peak current, and overcurrent comparators. The
overcurrent comparator is only intended for fault sensing. Exceeding the
overcurrent threshold will cause a soft start cycle. An internal MOSFET
discharges the current sense filter capacitor to improve dynamic perfor-
mance of the power converter.
Input to the PWM comparator. Sawtooth ramp for PWM control. Allows for
either current-mode or voltage-mode control. An internal MOSFET dis-
charges the current sense filter capacitor.
The oscillator programming pin. Only two components are required to
program the oscillator, a resistor (tied between VDD and RC), and a capaci-
tor (tied between RC and GND). The approximate oscillator frequency is
determined by the simple formula:
FOSCILLATOR
=
1.41
R×C
The recommended range of timing resistors is between 7kand 200kand
range of timing capacitors is between 100pF and 1000pF. Timing resistors
less than 7kshould be avoided. For best performance, keep the leads
between components as short as possible. Separate ground and VDD
traces to the external timing network are encouraged.
Ground. Return path for signal and gate drive functions.
2 April 2005









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MIC3839 Даташит, Описание, Даташиты
MIC3838/3839
Pin Description
Pin Number
7, 8
9
10
Pin Name
OUTB, OUTA
VDD
VREF
Micrel
Pin Function
Alternating high current output stages. Both stages are capable of driving
the gate of a power MOSFET. Each stage is capable of 500mA peak source
current, and 1A peak sink current.
The output stages switch at half the oscillator frequency, in a push/pull
configuration. When the voltage on the RC pin is rising, one of the two
outputs is high, but during fall time, both outputs are off. This “dead time”
between the two outputs, along with a slower output rise time than fall time,
insures that the two outputs can not be on at the same time. This dead time
is typically 60ns to 200ns and depends upon the values of the timing
capacitor and resistor.
The high-current output drivers consist of MOSFET output devices, which
switch from VDD to GND. Each output stage also provides a very low
impedance to overshoot and undershoot. This means that in many cases,
external Schottky clamp diodes are not required.
The power input connection for this device. Total VDD current is the sum of
quiescent VDD current and the average gate drive (OUT) current. Knowing
the operating frequency and the MOSFET gate charge (Qg), average OUT
current can be calculated from IOUT = Qg • F, where Qg is the total gate
change of all MOSFETs (OUTA and OUTB) and F is oscillator switching
frequency. To prevent noise problems, bypass VDD to GND with a ceramic
capacitor as close to the chip as possible. A 1µF decoupling capacitor is
recommended.
Internal 3V supply. Will source 1mA maximum.
April 2005
3 MIC3838/3839










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