SC46166

current mode PWM operation,SC46166 automatically detects the output, if the output load current falls below an

internally programmed threshold (The threshold has an dependence on the input voltage, output voltage and also

the value of the external inductor.), it shifts to Power Saving Mode operation, in which the IC consumes only 20

μA,

the efficiency is increased. However, the output ripple typically increases. Power Saving Mode ripple can be

and FB pins.

Operating at heavy loads for a long time, the die temperature will rise, if the die temperature continues to rise and

reaches 150

°C, the device shuts off entirely, the part will be enabled again when the die temperature drops by about

20

°C.

APPLICATIONS INFORMATION

Output Voltage Setting

)X1.23V

R2

R1

(1

+

=

Feedback Loop Design

Referring to Application Circuit of figure1, the selection of R1 and R2 are based on the trade-off between

quiescent current consumption and interference immunity. Higher R reduces the quiescent current (Path current =

1.23V/R2), however resistors beyond 5M

Ω , are not recommended. Lower R gives better noise immunity, and is

less sensitive to interference, layout parasitics, FB node leakage, and improper probing to FB pins. A proper value

of feed-forward capacitor C1 parallel with R1 can improve the noise immunity of the feedback loops, especially in

an improper layout. An empirical suggestion is around 100pF~1nF for feedback resistors of M

Ω, and 10nF~100nF

for feedback resistors of hundreds k

Ω.

COMPONENT SELECTION

Inductor Selection

The SC46166 can utilize small surface mount and chip inductors due to its fast 500kHz switching frequency.

Typically, a 4.7

μH inductor is recommended for most applications. Larger values of inductance will allow greater

output current capability by reducing the inductor ripple current. Increasing the inductance above will also increase

size .

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

REV:1.2

2008.07.04

Http://www.silan.com.cn

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