TS2508

2A / 330KHz PWM Buck Converter

4/8

Version: B07

Function Descriptions (Continue)

Setting the Output Voltage

Application circuit item shows the basic application circuit with TS2508 adjustable output version. The external resistor

sets the output voltage according to the following equation:

Table 1: Resistor select for output voltage setting

R2

R1

1.3K

6.8K

5V

5.6K

30K

1.5K

4.7K

3.3V

5.6K

18K

2.2K

4.7K

2.5V

5.6K

12K

1.8V

1.2K

1.5K

1.5V

2.2K

2K

1.2V

2K

1K

1V

2K

0.5K

The R2 setting 5.6k that no load current can be reduce to under 4mA for EL CAP

Input Capacitor Selection

This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5

times the maximum input voltage. The RMS current rating requirement for the input capacitor of a buck regulator is

approximately 1⁄2 the DC load current. A low ESR input capacitor sized for maximum RMS current must be used. A

220µF low ESR capacitor for most applications is sufficient

Output Capacitor Selection

The output capacitor is required to filter the output and provide regulator loop stability. The important capacitor

parameters are; the 100KHz Equivalent Series Resistance (ESR), the RMS ripples current rating, voltage rating, and

capacitance value. For the output capacitor, the ESR value is the most important parameter. The ESR can be

calculated from the following formula.

An aluminum electrolytic capacitor's ESR value is related to the capacitance and its voltage rating. In most case, higher

voltage electrolytic capacitors have lower ESR values. Most of the time, capacitors with much higher voltage ratings

may be needed to provide the low ESR values required for low output ripple voltage. It is recommended to replace this

low ESR capacitor by using a 330µF low ESR values < 130mΩ

Inductor Selection

For most designs, the operate with inductors of 12µH to 33µH. The inductor value can be derived from the following

equation:

Where is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high

ripple currents. Choose inductor ripple current approximately 15% of the maximum load current 2A, ∆IL=0.3A. The DC

current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to

prevent core saturation (2A+0.15A).