AP3781

Document number: DS42518 Rev. 2 - 2

13 of 15

www.diodes.com

May 2020

© Diodes Incorporated

AP3781

Operation Principle Description (continued)

Internal Over Temperature Protection (Internal OTP)

If the IC junction temperature exceeds the threshold TOTP, the AP3781 shuts down immediately and enters the hold mode. If the junction

temperature decreases by hysteresis temperature THYS, the AP3781 can recover to normal operation. If not, the power system keeps the hold

mode.

External Over Temperature Protection (External OTP)

The AP3781 provides external over-temperature protection (OTP) by connecting a Negative-Temperature-Coefficient (NTC) resistor from OTP pin

to GND. Internally, a current source IOTP is injected to the OTP pin, which generates a voltage proportional to the NTC resistance. At high ambient

temperature, the NTC resistance gets lower and results in the OTP pin voltage decreasing. If the OTP pin voltage drops below an internally-set

threshold VOTP, then the OTP is triggered, and the AP3781 shuts down immediately and enters the fast auto-recovery mode. The power system

will keep fast auto-recovery mode until the ambient temperature decreases and OTP pin voltage increases over the voltage VOTP_REC, thus, the

AP3781 can recover to normal operation.

Brown In/ Brown Out Protection

The AP3781 detects the bus voltage at each switching cycle through FB pin during tONP period, when the VCC reaches VTH_ST after power on, the

AP3781 will output one switching pulse to check if the detected bus voltage on FB pin is higher than VFB_NEG_H. If so, the system will start up

normally, otherwise the AP3781 will stop outputting following pulses, then the VCC will drop below VOPR(MIN) and the system will repeat the process

described above until the detected FB voltage is higher than VFB_NEG_H. When the power is off or there is a ditch in bus voltage, if the detected

voltage is lower than VFB_NEG_H/3 for 3 consecutive switching cycles, the IC will shut down and enter auto-recovery mode. This function is very

useful when the bulk capacitor is open, or when the heavy load is suddenly released after power off.

Ordering Information

AP3781 X - X

Packing

Package

13 : 13" Tape & Reel

Product Name

S: SO-8

Package

Part Number

Marking ID

Packing

SO-8

AP3781S-13

3781

4000/Tape & Reel

Marking Information

SO-8

3781

(Top View)

YY WW X X

Logo

8

7

6

5

1

2

3

4

Marking ID

WW : Week : 01~52; 52

YY : Year : 19, 20, 21~

X X : Internal Code

Represents 52 and 53 Week