AME5269 Datasheet, PDF(9/18 Page) Analog Microelectronics – 2A, 28V, 340KHz Synchronous Rectified Step-Down Converter

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AME5269 Datasheet, PDF (9/18 Pages) Analog Microelectronics – 2A, 28V, 340KHz Synchronous Rectified Step-Down Converter

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AME

AME5269

2A, 28V, 340KHz Synchronous

Rectified Step-Down Converter

n Detailed Description

Over-Voltage Protection

Oscillator Frequency

The internal free running oscillator sets the PWM fre-

quency at 340KHz.

Enable and Soft start

The EN Pin provides electrical on/off control of the regu-

lator. Once the EN pin voltage exceeds the lockout thresh-

old voltage, the regulator starts operation and the soft start

begins to ramp. If the EN pin voltage is pulled below the

lockout threshold voltage, the regulator stops switching

and the soft start resets. Connecting the pin to ground or

to any voltage less than 1.1V will disable the regulator and

activate the shutdown mode. To limit the start-up inrush

current, a soft-start circuit is used to ramp up the refer-

ence voltage from 0V to its final value, linearly. The soft-

start time is 15 ms typically.

Under Voltage Lockout (UVLO)

The AME5269 has an over-voltage protection (OVP) cir-

cuit to minimize voltage overshoot when recovering from

output fault conditions. The OVP circuit include an over-

voltage comparator to compare the FB pin voltage and a

threshold of 120% x VFB. Once the FB pin voltage is higher

than the threshold, the COMP pin and the SS pin are dis-

charged to GND, forcing the high-side MOSFET off. When

the FB pin voltage drops lower than the threshold, the high-

side MOSFET will be enabled again.

Thermal Shutdown

The AME5269 protects itself from overheating with an

internal thermal shutdown circuit. If the junction tempera-

ture exceeds the thermal shutdown trip point, the voltage

reference is grounded and the high-side MOSFET is turned

off. The part is restarted under control of the soft start

circuit automatically when the junction temperature drops

30OC below the thermal shutdown trip point.

The AME5269 incorporates an under voltage lockout cir- Component Selection

cuit to keep the device disabled when VIN (the input volt-

age) is below the UVLO start threshold voltage. During

Setting the Output Voltage

power up, internal circuits are held inactive and the soft

start is grounded until VIN exceeds the UVLO start thresh-

old voltage. Once the UVLO start threshold voltage is

The output voltage is using a resistive voltage divider con-

nected from the output voltage to FB. It divides the output

reached, the soft start is released and device start-up be- voltage down to the feedback voltage by the ratio:

gins. The device operates until VIN falls below the UVLO

stop threshold voltage. The typical hysteresis in the UVLO i e

comparator is 210mV.

VFB = VOUT R2

R1+ R2

Over Current Protection

Overcurrent limiting is implemented by monitoring the

current through the high side MOSFET. If this current ex-

ceeds the over-current threshold limit, the overcurrent in-

dicator is set true. The system will ignore the over-current

indicator for the leading edge blanking time at the begin-

ning of each cycle to avoid any turn-on noise glitches.

the output voltage is:

VOUT = 0.925 Ã R1 + R2

Once overcurrent indicator is set true. The high-side

MOSFET is turned off for the rest of the cycle after a propa-

gation delay. This over-current limiting mode is called

cycle-by-cycle current limiting.

Rev. B.01

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