BD9532EKN_08 Datasheet, PDF (10/21 Pages) Rohm – Switching Regulators for DDR-SDRAM Cores

●Timing Chart
• Soft Start Function
EN
TSS
SS
VOUT
IIN
・Timer Latch Type Short Circuit Protection
VOUT
REF×0.7
TSCP
SCP
EN/UVLO
・Over current protection circuit
tON
tON
HG
TMAX
LG
ILIMIT
IL
Soft start is exercised with the EN pin set high. Current
control takes effect at startup, enabling a moderate
output voltage “ramping start.” Soft start timing and
incoming current are calculated with formulas (2) and
(3) below.
Soft start time
Tss= ^REF×Css [sec] ・・・(2)
2μA(typ)
Incoming current
IIN= ^Co×VOUT
Tss
[A] ・・・(3)
(Css: Soft start capacitor; Co: Output capacitor)
Short protection kicks in when output falls to or below
REF X 0.7. When the programmed time period elapses,
output is latched OFF to prevent destruction of the IC.
Output voltage can be restored either by reconnecting
the EN pin or disabling UVLO. Short circuit protection
time is programmed using formula (4) below.
Short protection time setting
Tscp= ^{1.25(V)×CSCP}
2μA(typ)
[sec] ・・・(4)
During the normal operation, when VOUT becomes less
than REF Voltage, HG becomes High during the time
TON. However, when inductor current exceeds I_LIMIT
threshold, HG becomes OFF.
After MAX ON TIME, HG becomes ON again if the
output voltage is lower than the specific voltage level
and I_L is lower than I_LIMIT level.
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