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PDF SD4872R Data sheet ( Hoja de datos )
| Número de pieza | SD4872R | |
| Descripción | CURRENT MODE PWM + PFM CONTROLLER | |
| Fabricantes | Silan Microelectronics | |
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Silan
Microelectronics
SD4872X_Datasheet
CURRENT MODE PWM＋PFM CONTROLLER
DESCRIPTION
SD4872X is a current mode PWM controller IC for high
performance, low standby power offline flyback converter
application.
In no load or light load condition, the IC operates in Light Load
Mode to reduce switching loss and improve efficiency.
Large startup resistor could be used in the startup circuit to
minimize the standby current because of low startup current.
SD4872X offers complete protection functions including cycle-
by-cycle over current protection, over load protection, over
voltage and under voltage protections for VDD voltage, etc.
Excellent EMI performance is achieved with frequency shuffling
technique and soft switching control at the totem pole gate
driver output.
FEATURES
APPLICATIONS
* Adapters
* Frequency shuffling to improve EMI performance
* Set-Top Box Power Supplies
* Light Load Mode for minimum standby power
* 65kHz switching frequency
* 10µA low startup current
* Internal LEB circuit
* VDD over-voltage and under-voltage protection
* External programmable over-temperature protection
* Brown-out protection
* External programmable output over-voltage protection
* Over-power compensation
* Gate output voltage clamp
* Cycle-by-cycle current limiting
* Over load protection
* SOP8 package
ORDERING INFORMATION
Part No.
SD4872
SD4872TR
SD4872R
SD4872RTR
Package
SOP-8-225-1.27
SOP-8-225-1.27
SOP-8-225-1.27
SOP-8-225-1.27
Marking
SD4872
SD4872
SD4872R
SD4872R
Material
Pb free
Pb free
Pb free
Pb free
Packing
Tube
Tape & Reel
Tube
Tape & Reel
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.1 2012.09.07
Page 1 of 10
1 page  
Silan
Microelectronics
SD4872X_Datasheet
FUNCTION DESCRIPTIONS
SD4872X is a current mode PWM+PFM controller used in applications for offline flyback converter. The
description of functions is as follows.
Startup Control
Startup current of SD4872X is very low so that IC could start up quickly. A large startup resistor can be
used in startup circuit to minimize standby power loss yet provides reliable startup in application.
Frequency Shuffling Control
Frequency shuffling is used in SD4872X to improve EMI performance.
The oscillation frequency is modulated randomly so that the tone energy is spread out. The spread
spectrum minimizes the conduction band EMI and the system design can be easier. The entire application
system design can become simpler.
Light Load Mode
In no load or light load condition, major power loss of total power consumption is from switching loss on the
MOSFET transistor switching loss, the core loss of the transformer and the loss on the external snubber
circuit, which become the majority in total power loss. The value of those power losses is proportional to
switching actions within a fixed period of time. So reducing number of switching actions can reduce the
power loss.
SD4872X enters Light Load Mode in no load or light load condition. The gate drive output switches only
when output DC voltage drops below a preset level and the switching frequency reduces. Otherwise the
gate drive remains at off state.
Current Sense and LEB
At switching leading edge time, the current spike due to snubber diode reverse recovery should be
chopped off for it will affect the error of PWM comparator. And this is available through internal LEB
(Leading Edge Blanking) circuit. So that the external RC filter circuit on SENSE input is no longer required.
During the blanking period, the PWM comparator and OC comparator are disabled and MOSFET transistor
keeps turn-on state. The minimum on time of MOSFET is LEB time.
Gate Driver
GATE pin is connected to external MOSFET’s gate for switch control. Too weak the gate drive ability
results in more switch loss of MOSFET while too strong gate drive compromises the EMI performance.
A good tradeoff is achieved through the totem pole gate drive design with appropriate output ability and
dead time control.
The output high voltage of GATE is clamped at 13V to protect the external MOSFET.
Over Load Protection
When FB input voltage is higher than over load threshold voltage 3.8V and lasts for more than 50ms, the
circuit enters into over-load protection status. The MOSFET is off and the circuit restarts. The waveform is
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.1 2012.09.07
Page 5 of 10
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| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet SD4872R.PDF ] | |
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