ADP2302ARDZ-5.0-R7 datasheet(17/28 Pages) AD

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Data Sheet

ADP2302/ADP2303

Rev. A | Page 17 of 28

2468

VOUT (V)

MAXIMUM INPUT VOLTAGE

MINIMUM INPUT VOLTAGE

Figure 47. Voltage Conversion Limitations

LOW INPUT VOLTAGE CONSIDERATIONS

For low input voltage between 3 V and 5 V, the internal boot

regulator cannot provide enough bootstrap voltage due to the

internal dropout voltage. As a result, the increased MOSFET

RDS(ON) reduces the available load current. To prevent this, add

an external small-signal Schottky diode from a 5.0 V external

bootstrap bias voltage. Because the absolute maximum rating

between the BST and SW pins is 6.0 V, the bias voltage should

be less than 5.5 V. Figure 48 shows the application diagram for

the external bootstrap circuit.

VIN

3.0V ~ 5.0V

ADP2302/

ADP2303

GND

OFF

BST

SCHOTTKY

DIODE

5V BIAS VOLTAGE

Figure 48. External Bootstrap Circuit for Low Input Voltage Application

PROGRAMMING THE PRECISION ENABLE

Generally, the EN pin can connect to the VIN pin so that the

device automatically starts up when the input power is applied.

However, the precision enabling feature allows the ADP2302/

ADP2303 to be used as a programmable UVLO by connecting

a resistive voltage divider to VIN, as shown in Figure 49. This

configuration prevents the start-up problems that can occur

when VIN ramps up slowly in soft start with a relatively high

load current.

VIN

REN1

REN2

ADP2302/

ADP2303

Figure 49. Precision Enable Used as a Programmable UVLO

The precision enable feature also allows the ADP2302/ADP2303 to

be sequenced precisely by using a resistive voltage divider from

another dc-to-dc power supply, as shown in Figure 50.

REN1

REN2

ADP2302/

ADP2303

ANOTHER

DC/DC

SUPPLIER

Figure 50. Precision Enable Used as a Sequencing Control

from Another DC-to-DC Power Supply

With a 1.2 μA pull-down current on the EN pin, the equation for

the start-up voltage in Figure 49 and Figure 50 is

μA





















EN1

EN2

STARTUP

where:

VSTARTUP is the start-up voltage to enable the chip.

REN1 is the resistor from the dc source to EN.

REN2 is the resistor from EN to GND.

INDUCTOR

The high switching frequency of the ADP2302/ADP2303 allows

the use of small inductors. For best performance, use inductor

values between 1 μH and 15 μH.

The peak-to-peak inductor ripple current is calculated using the

following equation:























OUT

RIPPLE

)

(

where:

fSW is the switching frequency.

L is the inductor value.

VD is the diode forward drop.

VIN is the input voltage.

VOUT is the output voltage.

Inductors of smaller values are usually smaller in size but

increase the ripple current and the output ripple voltage. As a

guideline, the inductor peak-to-peak ripple current is typically

set to 30% of the maximum load current for optimal transient

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