AP64501

Document number: DS41980 Rev. 4 - 2

14 of 26

www.diodes.com

August 2019

© Diodes Incorporated

AP64501

Application Information (cont.)

10

Setting the Output Voltage

The AP64501 has adjustable output voltages starting from 0.8V using an external resistive divider. An optional external capacitor, C4 in Figure 1,

of 10pF to 220pF improves the transient response. The resistor values of the feedback network are selected based on a design trade-off between

efficiency and output voltage accuracy. There is less current consumption in the feedback network for high resistor values, which improves

efficiency at light loads. However, values too high cause the device to be more susceptible to noise affecting its output voltage accuracy. R1 can

be determined by the following equation:

(

)

Eq. 6

Table 1 shows a list of recommended component selections for common output voltages for AP64501 referencing Figure 1.

Table 1. Recommended Components Selections

AP64501

Output Voltage

(V)

R1

(k

Ω)

R2

(k

Ω)

L

(µH)

C1

(µF)

C2

(µF)

C3

(nF)

C4

(pF)

R5

(k

Ω)

C5

(nF)

C6

(pF)

(Optional)

1.2

11.0

22.1

1.5

10

3 x 22

100

OPEN

3.74

2.7

150

1.5

19.6

22.1

2.2

10

3 x 22

100

OPEN

4.75

2.7

120

1.8

27.4

22.1

2.2

10

3 x 22

100

OPEN

5.62

2.7

100

2.5

47.5

22.1

3.3

10

3 x 22

100

OPEN

7.87

2.7

68

3.3

69.8

22.1

3.3

10

3 x 22

100

OPEN

10.50

2.7

56

5.0

115.8

22.1

3.6

10

3 x 22

100

OPEN

15.80

2.7

33

12.0

309.0

22.1

10.0

10

3 x 22

100

OPEN

37.40

2.7

15

11

Programming Soft-Start Time

The AP64501 features a programmable soft-start time to prevent inrush current during the start-up sequence. Connect an external soft-start

capacitor, Css, from the SS pin to ground.

The SS pin sources an internal 4µA current to charge Css when the EN pin exceeds the device’s turn-on threshold. AP64501 uses the lower

voltage between the SS pin voltage and the internal 0.8V reference voltage as the input reference voltage for the error amplifier to regulate the

output. Soft-start finishes when the SS pin voltage exceeds the 0.8V internal reference. The Css capacitance required for a given soft-start time is

calculated by:

Eq. 7

Where:



Css is the capacitance in nF and is at least 10nF



tss is the soft-start time in ms and is at least 4ms