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PDF SD4871 Data sheet ( Hoja de datos )

Número de pieza SD4871
Descripción CURRENT MODE PWM CONTROLLER
Fabricantes Silan Microelectronics 
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SD4871_Datasheet
CURRENT MODE PWM CONTROLLER
DESCRIPTION
SD4871 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.
SD4871 offers complete protection functions including cycle-by-
cycle over current protection, over load protection, over voltage
SOT-23-6L
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.
APPLICATIONS
FEATURES
* Battery Chargers
* Frequency shuffling to improve EMI performance
* Adapters
* Light Load Mode for minimum standby power
* Set-Top Box Power Supplies
* External programmable switching frequency
* 3μA low startup current
* Internal LEB circuit
* VDD over voltage and under voltage protection
* Gate output maximum voltage clamp
* Current limiting
* Over load protection
* SOT-23-6L package
ORDERING INFORMATION
Part No.
SD4871TR
Package
SOT-23-6L
Marking
4871
Material
Pb free
Packing
Tape & Reel
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:0.2 2011.06.21
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SD4871 pdf
SD4871_Datasheet
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.
Soft Start
SD4871 features an internal 4ms soft start during startupwhen the switching frequency is set to 65kHz.
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.
Protections control
SD4871 offers complete protection functions including cycle-by-cycle over current protection, over load
protection, over voltage and under voltage protection for VDD input voltage, etc.
Constant output power limit over universal input voltage range is achieved with over current protection
threshold line voltage compensation to over current protection threshold.
VDD is supplies by auxiliary winding output of the transformer. It is clamped when VDD is higher than clamp
threshold value. The MOSFET is shut down when VDD drops below shut-down voltage and IC enters power
on startup sequence thereafter.
When FB input voltage is higher than over load threshold voltage for more than TD_OL, the MOSFET is shut
down and VDD voltage drops. IC restarts when VDD is lower than shut-down voltage.
TYPICAL APPLICATION CIRCUIT
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:0.2 2011.06.21
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