XC9101
Series
GFunctional
Settings
1. Soft Start
CE and soft start (SS) functions are commonly assigned to the CE/SS pin. The soft start function is effective until the voltage at the CE pin
reaches approximately 1.55 V rising from 0 V. Soft start time is approximated by the equation below according to values of Vcont, Rss, and
Css.
T = -Css
×
Rss
×
ln((Vcont - 1.55)/Vcont)
Example: When C
SS
= 0.1
µF,
R
SS
= 470 kΩ, and Vcont = 5 V, T = -0.1 e
-6
×
470 e
3
×
ln ((5 - 1.55)/5) = 17.44 ms.
CE/SS pin
Rss
Vcont
Css
[Inside the IC]
CE,
UVLO
Vref
circuit
To Verr amplifier
Set the soft start time to a value sufficiently longer than the period of a clock pulse.
4
> Circuit example 1: N-ch open drain
Vcont
Rss
CE/SS pin
ON/OFF signal
Css
[Inside the IC]
> Circuit example 2: CMOS logic (low current dissipation)
Vcont
Rss
ON/OFF signal
Css
CE/SS pin
[Inside the IC]
> Circuit example 3: CMOS logic (low current dissipation), quick off
Vcont
Rss
ON/OFF signal
Css
CE/SS pin
[Inside the IC]
397
TOREX [ TOREX SEMICONDUCTOR ]
