TS2508A_12 Datasheet, PDF (4/8 Pages) Taiwan Semiconductor Company, Ltd – 3A / 330KHz PWM Buck Converter

TS2508A
3A / 330KHz PWM Buck Converter
Function Descriptions (Continue)
Setting the Output Voltage
Application circuit item shows the basic application circuit with TS2508A adjustable output version. The external
resistor sets the output voltage according to the following equation:
Table 1: Resistor select for output voltage setting
V_OUT
5V
R2
1.3K
5.6K
R1
6.8K
30K
3.3V
1.5K
5.6K
4.7K
18K
2.5V
2.2K
5.6K
4.7K
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.
V_RIPPLE = ∆I_L x ESR = 0.33A x 130mΩ = 43mV
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, 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 3A, ∆IL=0.4A. 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 (3A+0.2A).
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Version: C12