AME5297 Datasheet, PDF(7/14 Page) Analog Microelectronics

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AME5297 Datasheet, PDF (7/14 Pages) Analog Microelectronics – Step-Down DC/DC Converter

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AME

AME5297

3A, 18V, 500KHz Synchronous

Step-Down DC/DC Converter

n Detailed Descriptiion

Internal VCC Regulator

The internal VCC regulator is adjusted 5.0V to provide

power to the internal circuits from input voltage VIN. In

order to maintain the VCC voltage stably, a 0.1Âµ F-to-1ÂµF

ceramic capacitor is recommended.

Enable and Soft Start

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

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

old voltage, the regulator starts to operate and the soft

start begins to charge the external capacitor. If the EN pin

voltage is pulled below the lockout threshold voltage, the

regulator stops switching and the soft start resets. Con-

necting the EN pin to ground or to any voltage less than

1.2V 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 reference voltage from 0V to

its final value linearly. The soft start time can be calcu-

lated as follows:

t SS

0.8Ã CSS

ISS

Under Voltage Lockout (UVLO)

The AME5297 incorporates an under voltage lockout cir-

cuit to keep the device disabled when the input voltage

VIN is below the UVLO start threshold voltage. During

powering up, the internal circuits are held inactive and the

soft start is grounded until the input voltage VIN exceeds

the UVLO start threshold voltage. Once the UVLO start

threshold voltage is reached, the soft start is activated and

the device begins to operate. The device operates until

the input voltage VIN falls below the UVLO stop threshold

voltage. The typical hysteresis in the UVLO comparator

is 650mV.

Rev. A.05

Thermal Shutdown

The AME5297 protects itself from overheating with an

internal thermal shutdown circuit. If the junction tempera-

ture exceeds the thermal shutdown threshold, the voltage

reference is grounded and the shutdown mode is activated.

The AME5297 is restarted under control of the soft start

automatically when the junction temperature drops 20oC

below the thermal shutdown threshold.

Over-Current Protection and Hiccup Mode

The over-current limiting is implemented by cycle-by-

cycle monitoring the current through the high side MOSFET.

If the peak current exceeds the over-current limit thresh-

old, the high side MOSFET is turned off. When the feed-

back voltage VFB drops below 0.4V, the oscillator frequency

is reduced to about 1/4 of the normal frequency to ensure

that the inductor current has more time to decay, thereby

preventing runaway. Meanwhile, the AME5297 enters hic-

cup mode, the average short circuit current is greatly re-

duced to alleviate the thermal issue and to protect the

regulator.

Enternal Bootstrap Circuit

The external bootstrap circuit contains a capacitor and a

resistor. A bootstrap capacitor provides power for the high

side MOSFET driver. In order to supply the AC current and

maintain the BST-SW voltage stably at the switching con-

dition of the high side MOSFET, a 0.1ÂµF low ESR ceramic

capacitor is recommended. The bootstrap resistor which

suggests placing 10â¦ is utilized to reduce switching spike

voltage and noise.

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