T8302 Ver la hoja de datos (PDF) - Taiwan Memory Technology

Número de pieza

componentes Descripción

Fabricante

T8302

PWM Control 1A Step-Down Converter

Taiwan Memory Technology 

tm TE

CH

T8302

Capacitor selection

A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in

series with the supply source impedance and lowers overall efficiency. This capacitor has to supply

the relatively high peak current to the coil and smooth the current ripple on the input supply. A

minimum value of 47uF is acceptable if the input source is close to the device, but higher values

will improve performance at lower input voltages, especially when the source impedance is high. In

order to avoid high frequency noise influence and improve circuit stability, it is recommended to

shunt a value of 0.22uF Capacitor. The input capacitor should be placed as close as possible to the

IC. For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better

dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this

application and should not be used.

Inductor selection

Recommended inductor values for the T8302 are in the range 33uH to 100uH. Higher values of

inductance are recommended at higher supply voltages in order to minimize errors due to switching

delays, which result in increased ripple and lower efficiency. Higher values of inductance also result

in a smaller change in output current over the supply voltage range. The inductor should be mounted

as close to the device as possible with low resistance connections to the LX and VIN pins. The

chosen coil should have a saturation current higher than the peak output current and a continuous

current rating above the required mean output current.

The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times

within the specified limits over the supply voltage and load current range.

LX switch on time : ton = L∆I / (VIN – VLED - Iavg (RS+rL+RLX)) , note: tonmin > 100ns

LX switch off time : toff = L∆I / (VLED + VD + Iavg (RS+rL)) , note: toffmin > 60ns

Where:

“L” is the coil inductance (H)

“∆I” is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg}

“rL” is the coil resistance (ohm)

“RS” is the current sense resistance

“Iavg” is the required LED current (A)

“VIN” is the supply voltage (V)

“VLED” is the total LED forward voltage (V)

“RLX” is the switch resistance (ohm) {=0.3 ohm nominal}

“VD” is the diode forward voltage at the required load current (V)

TM Technology, Inc. reserves the right

P. 8

to change products or specifications without notice.

Publication Date:April 2014

Revision: E

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