ADP2302/ADP2303

Rev. 0 | Page 16 of 28

APPLICATIONS INFORMATION

PROGRAMMING OUTPUT VOLTAGE

ADP2302/ADP2303 have an adjustable version where the output

voltage is programmed through an external resistive divider, as

shown in Figure 45. Suggested resistor values for the typical

output voltage setting are listed in Table 6. The output voltages

are calculated using the following equation:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

+

×

=

BOT

TOP

OUT

R

R

V

1

V

800

.

0

where:

ADP2302/

ADP2303

FB

Figure 45. Programming the Output Voltage Using a Resistive Voltage Divider

Table 6. Suggested Values for Resistive Voltage Divider

1.2

10

20

1.5

10

11.3

1.8

12.7

10.2

2.5

21.5

10.2

3.3

31.6

10.2

5.0

52.3

10

VOLTAGE CONVERSION LIMITATIONS

There are both lower and upper output voltage limitations for a

given input voltage due to the minimum on time, the minimum

off time, and the bootstrap dropout voltage.

The lower limit of the output voltage is constrained by the

controllable minimum on time, which can be as high as 170 ns

for the worst case. By considering the variation of both the switch-

ing frequency and the input voltage, the equation for the lower

limit of the output voltage is

where:

The upper limit of the output voltage is constrained by the mini-

mum controllable off time, which can be as high as 280 ns in

ADP2302/ADP2303 for the worst case. By considering the

variation of both the switching frequency and the input voltage,

the equation for the upper limit of the output voltage is

where:

In addition, the bootstrap circuit limits the minimum input voltage

for the desired output due to the internal dropout voltage. To

attain stable operation at light loads and ensure proper startup for

the prebiased condition, the ADP2302/ADP2303 require the

voltage difference between the input voltage and the regulated

output voltage (or between the input voltage and the prebias

voltage) to be greater than 2.1 V for the worst case. If the voltage

difference is smaller, the bootstrap circuit relies on some minimum

load current to charge the boost capacitor for startup. Figure 46

shows the typical required minimum input voltage vs. load current

for the 3.3 V output voltage.

3.5

3.7

3.9

4.1

4.3

4.5

4.7

4.9

5.1

5.3

1

10

100

1000

OUPTUT CURRENT (mA)

FOR START UP

WHILE IN

OPERATION

Figure 46. Minimum Input Voltage vs. Load Current

Based on three conversion limitations (the minimum on time,

the minimum off time, and the bootstrap dropout voltage),

Figure 47 shows the voltage conversion limitations.