NCP81147

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8

VSEN

VTH

LG

BUFFER

VPU

Figure 4. PreOVP circuit

Vin Detection

UV protection will be enabled; If a UV fault is triggered in

the softstart, it will restart SS after a fixed delay. The UV

protection is to avoid IC to startup without Vin or with

insufficient Vin voltage.

Overcurrent Protection

NCP81147 measures the differential current sensing

signal through CSP and CSN/VO pin. There are two current

protection levels: OCP1 and OCP2. If the differential

voltage across pin CSP and CSN/VO is over 20 mV (but

below 30 mV) for four consecutive cycles, OCP1 will be

tripped. Both UG and LG will be forced to low to turn off the

high side and low side FETs, it is a latched condition; If the

differential voltage across pin CSP and CSN is over 30 mV,

OCP2 will be tripped, the UG and LG will be pulled low and

latched immediately. Toggling VCC power or EN will reset

the Overcurrent protection.

The current sensing R/C network should be selected to

match the inductor time constant as below,

(RCS1

RCS2)

@ C + L

DCR

(Notes: the actual RC network time constant may be

slightly higher)

Thus, OCP1 and OCP2 levels can be configured as,

OCP1

+

20 mV

DCR

@ RCS1 ) RCS2

RCS2

OCP2

+

30 mV

DCR

@ RCS1 ) RCS2

RCS2