TS3552

2A/350kHz Synchronous Buck DC/DC Converter

5/11

Version: B11

Application Information

Setting Output Voltage

The output voltage is set using a resistive divider from the output to FB. The FB pin regulated voltage is 0.925V.

Thus the output voltage is:

Recommended Component Selection

R1 (K )

R2 (K )

R3 (K )

C3 (nF)

L1 (µH)

12

5

44.1

10

2.2

3.3

15

22 X 1

5 or 12

3.3

25.7

10

2.2

3.3

10

22 X 1

5 or 12

1.8

9.5

10

2.2

3.3

4.7

22 X 1

5 or 12

1.2

3

10

2.2

3.3

3.3

22 X 1

5 or 12

1

0.81

10

2.2

3.3

2.2

22 X 1

Selecting Inductor

The inductor selection depends on the current ripple of inductor, the input voltage and the output voltage.

Accepting a large current ripple of inductor allows the use of a smaller inductance. However, higher current ripple

of inductor can cause higher output ripple voltage and large core loss. By setting an acceptable current ripple of

inductor, a suitable inductance can be obtained from above formula.

In addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor current in

application to prevent core saturation. The peak value of inductor current can be calculated according to the

following formula.

Soft-Start

The TS3552 provides the soft-start function. Initially, the voltage at SS pin is 0V. Then an internal current source of

6

A (typ.) charges an external soft



-start capacitor. During the soft-start period, the voltage at SS pin will limit the

feedback threshold voltage at FB pin. When the voltage at SS pin is higher than 0.925V, the feedback threshold

voltage at FB pin reaches the desired value. The soft-start time can be calculated in accordance with the following

formula:

The soft-start capacitor is discharged to GND when the EN pin is connected to GND