AP3984 datasheet(11/15 Pages) DIODES

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AP3984

Document number: DS37655 Rev. 3 - 2

11 of 15

www.diodes.com

December 2016

AP3984

Operation Description (Cont.)

condition is removed before VCC is still higher than VOPR(MIN), the device will enter normal operating mode. If not, the AP3984 will remain off and

wait for another tOFF(MAX). When VCC drops to VOPR(MIN), the AP3984 will enter the restart process, and VCC voltage changes between VTH(ST)

and VOPR(MIN) until VFB(OVP) condition is removed.

When over temperature protection is activated, the device enters the hold mode. Once the hold mode is triggered, the AP3984 doesn

’t signal

any pulse until the fault condition is removed, and VCC Voltage is hold not lower than LVCC voltage.

When other fault protections are triggered, the device enters the auto-recovery mode. Once the AP3984 enters the auto-recovery mode, the

device shuts down immediately and

doesn’t signal any pulse, the VCC current is decreased from operating current (mean: 550μA) to standby

current (mean: 17.5

μA). Until VCC voltage drops to VOPR(MIN), the AP3984 will enter the restart process, and VCC voltage changes between

VTH(ST) and VOPR(MIN) until the fault condition is removed. The slope of VCC voltage to discharge is very small, and the time to drop to VOPR(MIN)

is very long. It can decrease the average power dissipation at a fault condition.

Short Circuit Protection (SCP)

Short Circuit Protection (SCP) detection principle is similar to the normal output voltage feedback detection by sensing FB pin voltage. When the

detected FB pin voltage is below VFB(SCP) for a duration of about tSCP, the SCP is triggered. Then the AP3984 enters hiccup mode that the IC

immediately shuts down and then restarts, so that the VCC voltage changes between VTH_ST and UVLO threshold until VFB(SCP) condition is

removed.

As to the normal system startup, the time duration of FB pin voltage below VFB(SCP) should be less than tSCP to avoid entering SCP mode. But for

the output short condition or the output voltage below a certain level, the SCP mode should happen.

Figure 8 is the AP3984 normal start-up waveform that the voltage of FB pin is above VFB(SCP) during tSCP after VCC gets to the VTH_ST, which

doesn

’t enter the SCP mode. As shown in Figure 9, VOUT is short and the voltage of FB pin is lower than VFB(SCP) during tSCP, the AP3984

triggers the SCP and enters hiccup mode.

VTH_ST

VFB(SCP)

tSCP

VCC

VFB

VOUT

VOUT(SCP)

Figure 8. Normal Start-up

VTH_ST

VOPR(MIN)

VFB(SCP)

tSCP

VCC

VFB

VOUT

Figure 9. Short Circuit Protection (SCP) and Hiccup Mode

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