AP64352

Document number: DS41978 Rev. 5 - 2

14 of 21

www.diodes.com

August 2019

© Diodes Incorporated

AP64352

Application Information (cont.)

10

Setting the Output Voltage

The AP64352 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 AP64352 referencing Figure 1.

Table 1. Recommended Components Selections, fsw = 500kHz

AP64352

Output Voltage

(V)

R1

(k

Ω)

R2

(k

Ω)

L

(µH)

C1

(µF)

C2

(µF)

C3

(nF)

C4

(pF)

1.2

11.0

22.1

3.3

10

2 x 22

100

OPEN

1.5

19.6

22.1

3.3

10

2 x 22

100

OPEN

1.8

27.4

22.1

3.3

10

2 x 22

100

OPEN

2.5

47.5

22.1

4.7

10

2 x 22

100

OPEN

3.3

69.8

22.1

4.7

10

2 x 22

100

OPEN

5.0

115.8

22.1

5.5

10

2 x 22

100

OPEN

12.0

309.0

22.1

10.0

10

2 x 22

100

OPEN

11

Programming Soft-Start Time

The AP64352 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. AP64352 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 2ms