AP3984 datasheet(10/15 Pages) DIODES

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AP3984

Document number: DS37655 Rev. 3 - 2

10 of 15

www.diodes.com

December 2016

AP3984

Operation Description (Cont.)

LINE

AUX















………(15)

So, the AP3984 can change the line compensation capability by adjusting the upper resistor at FB pin (RFB1). Higher resistance means lower line

compensation capability.

Adjustable Cable Compensation

To meet the voltage drop of different output cables, the AP3984 can realize the adjustable cable compensation.

As shown in Figure 7, VCBC follows the VLOAD that reflects the power system loading percentage.

VLOAD

RFB1

RFB2

VAUX

VCBC

RCBC

ICBC

Figure 7. Adjustable Cable Compensation Circuit

If the CBC resistance (RCBC) and RFB1 are fixed, the current (ICBC) flowing through the CBC resistance (RCBC) also follows the changing of the

VLOAD:

CBC

LOAD

CBC



…………………………(16)

The voltage change (

VAUX) of auxiliary winding (VAUX) is varied with the VLOAD:

LOAD

CBC

AUX











………… (17)

The VO changing (VO) which △VAUX reflects is also changed with VLOAD:

LOAD

CBC

aux

AUX













……(18)

So, we can achieve the right cable compensation by adjusting RCBC. The 90kΩ resistance can ensure about 350mV cable compensation from no

load to full load.

Protection

The AP3984 has various built-in single-point fault protection features: FB over voltage protection, VCC over voltage protection, output short

circuit protection, FB open circuit protection, transformer saturation protection and current sense resistor fault (short or open) protection, over

temperature protection. The fault conditions to trigger these protections are different and protection modes to enter after the protections are

triggered are different.

Protection Mode

The AP3984 has three protection modes: DMIN, auto-recovery and hold. The Operation Principles are different.

When FB over voltage protection and FB open circuit protection are triggered, the AP3984 enters the DMIN mode whereby the AP3984

immediately shuts down and signals a pulse to turn on the primary switch after tOFF(MAX), that detects if the fault condition is removed. If the fault

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