MS1003SH datasheet(15/41 Pages) SHINDENGEN

15 / 41 page

MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

15/41

This current limit protection function incorporates a function to correct dependence on input voltage. The

function changes the OCL threshold on the IC from the VTH (OCL start) of approximately 0.35 V to the

VTH (OCL) clamp of approximately 0.55 V linearly with time. Since the slope (di/dt) of the drain current

of the main switching device is proportional to the input voltage, when the input voltage increases, the

current reaches the OCL threshold with smaller IDP, and the droop is corrected.

3.4.3 Overload protection (timer latch function)

The overload timer latch function is a protection

function that latches the IC when the F/B pin

voltage stays at the VF/B (latch count) = 4.6 V or

more for more than Tlatch count = 2 seconds.

The power limit for protection is activated if power

exceeds the droop power set as the overcurrent

limit VTH (OCL), and the output voltage begins to

fall. The feedback voltage increases beyond the

control limit, and the VF/B voltage increases to the

VF/B (latch count) = 4.6 V or more. The timer

detects this voltage and begins counting.

When the increase in voltage is detected

continuously for Tlatch count = 2 seconds, the IC

is latched to prevent a persisting overload. The

timer is set for 2 seconds to avoid false detection.

The timer is reset if the F/B pin voltage drops below the VF/B (latch count) = 4.6 V or if the VCC voltage

drops below the VUL as the timer counts. After the IC is latched, the bias assist function of the startup

circuit turns off to reduce heat buildup in the IC.

VOCL level

VGS

大

小

Vin

VTH(OCL start)

VTH(OCL)clamp

TOCL

出力電流 Io

大

小

Vin

出力電流 Io(A)

VTH(OCL)垂下電力制限以上に

負荷を取ると、出力電圧が降下し

Tlatch count=2秒(TYP)経過でﾗｯﾁ停止

ﾗｯﾁ停止

Small

Large

Output current Io

Small

Large

If the load exceeds the VTH (OCL) droop

power limit, the output voltage falls; after

Tlatch count = 2 s (TYP) has elapsed, the

IC is latched.

Latched

Output current Io (A)

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