APL5934 datasheet(14/24 Pages) ANPEC

14 / 24 page

Rev. A.1 - Mar., 2016

www.anpec.com.tw

APL5934

Function Description

Power-On-Reset

Internal Soft-Start

Output Voltage Regulation

Current-Limit Protection

Short Current-Limit Protection

Thermal Shutdown

Enable Control

Power-OK and Delay

A Power-On-Reset (POR) circuit monitors both of supply

voltages on VCNTL and VIN pins to prevent wrong logic

controls. The POR function initiates a soft-start process

after both of the supply voltages exceed their rising POR

voltage thresholds during powering on. The POR func-

tion also pulls low the POK voltage regardless the output

status when one of the supply voltages falls below its

falling POR voltage threshold.

An internal soft-start function controls rise rate of the out-

put voltage to limit the current surge during start-up. The

typical soft-start interval is about 0.6 ms.

An error amplifier works with a temperature-com-

pensated 0.8V reference and an output NMOS regulates

output to the preset voltage. The error amplifier is de-

signed with high bandwidth and DC gain provides very

fast transient response and less load regulation. It com-

pares the reference with the feedback voltage and ampli-

fies the difference to drive the output NMOS which pro-

vides load current from VIN to VOUT.

The APL5934 monitors the current flowing through the

output NMOS and limits the maximum current to prevent

load and APL5934 from damages during current over-

load conditions.

The short current-limit function reduces the current-limit

level down to 1.1A (typical) when the voltage on FB pin

falls below 0.2V (typical) during current overload or short-

circuit conditions.

The short current-limit function is disabled for success-

ful start-up during soft-start interval.

A thermal shutdown circuit limits the junction tempera-

ture of APL5934. When the junction temperature exceeds

+170oC, a thermal sensor turns off the output NMOS, al-

lowing the device to cool down. The regulator regulates

the output again through initiation of a new soft-start pro-

cess after the junction temperature cools by 50oC, result-

ing in a pulsed output during continuous thermal over-

load conditions. The thermal shutdown is designed with

a 50oC hysteresis to lower the average junction tempera-

ture during continuous thermal overload conditions, ex-

tending lifetime of the device.

For normal operation, the device power dissipation should

be externally limited so that junction temperatures will

not exceed +125oC.

The APL5934/C has a dedicated enable pin (EN). A logic

low signal applied to this pin shuts down the output. Fol-

lowing a shutdown, a logic high signal re-enables the

output through initiation of a new soft-start cycle. When

left open, this pin is pulled up/low by an internal current

source (3

µA typical) to enable/shutdown normal

operation. It

’s not necessary to use an external transistor

to save cost.

The APL5934 indicates the status of the output voltage by

monitoring the feedback voltage (V

FB) on FB pin. As the

FB rises and reaches the rising Power-OK voltage thresh-

old (V

THPOK), an internal delay function starts to work. At

the end of the delay time, the IC turns off the internal

NMOS of the POK to indicate that the output is ok. As the

FB fal ls an d r ea che s t he fa lli ng Po we r -OK vol t age

threshold, the IC turns on the NMOS of the POK (after a

debounce time of 10

µs typical).

The APL5934B/D has a dedicated enable pin (ENB). A

logic high signal applied to this pin shuts down the output.

Following a shutdown, a logic low signal re-enables the

output through initiation of a new soft-start cycle. When

left open, this pin is pulled up/low by an internal current

source (3

µA typical) to shutdown/enable normal

operation. It

’s not necessary to use an external transistor

to save cost.

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