Silan

Microelectronics

SD670XSC_Datasheet

Boundary-conduction mode

SD670XSC works in boundary-conduction mode with strong anti-interference and high conversion efficiency. Auxiliary

winding is unnecessary to detect zero-crossing current and the peripheral circuit is simple. Due to the

boundary-conduction mode, part of harmonic oscillation energy generated by external switch is transferred to VCC.

Current detection and LEB

With the cycle-by-cycle current limit function, internal switch M1 will be turned off if CS voltage exceeds 0.45V. System

still works and internal switch M1 is turned on in the next period. There is no LEB for current limit comparator.

CS voltage and COMP voltage are compared by COMP comparator, if CS voltage is higher than COMP, internal switch

M1 is off and system keeps work. During the instant of turning on internal switch M1, 0.6

μs LEB is used for avoiding

the error operation on internal switch M1.

CS open/short circuit protection

If CS is open, open circuit protection actives and the IC stops; if CS resistor is shorted, there is no limit for inductor

current, voltage on pin CS is zero, and the short-circuit status is judged by checking drain voltage during on of internal

OUT signal. If short-circuit protection actives, output is shutdown, VCC decreases and IC restarts.

Source driver

Source drive is adopted for this IC. Gate of M2 is connected to VCC through a resistor, Source is connected to Drain of

internal switch M1. When Gate of internal switch M1 is driven by IC, the IC current can be reduced because of the low

gate capacitance of M1, and hence no auxiliary winding is needed.

Output short/open circuit protection

There is no signal which reflects the output, the IC detects the discharge time for judging over voltage. The over

voltage protection threshold value is set through pin ROVP. Please refer to application note for details.

There is no signal which reflects the output, the IC detects the discharge time for judging over voltage.

When ROVP is connected to GND via resistor, the over voltage protection threshold value is set through resistance

adjustment;

when ROVP is shorted connected to GND, the over voltage protection threshold is set by the IC. Internal Tovp is set as

4.5 us, the over voltage protection actives if Toff<Tovp, please refer to application note for details. It is recommended to

connect ROVP to GND.

Internal temperature regulatory

The output current will be reduced if the IC temperature exceeds the certain value.

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

Rev.:1.2

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