XC9248 Series
■OPERATIONAL EXPLANATION (Continued)
<CL high-speed discharge function>
When L level is input into the EN pin and the IC enters the standby state, the charge on the output capacitor CL can be
discharged at high speed with the Nch MOS switch Tr. incorporated between LX and GND. This enables the prevention of
application malfunctioning due to CL charge remaining when the IC stops.
The CL discharge time can be calculated from the equation below. Note that the equation varies depending on the set voltage
VOUT(E)
.
(1) Equation when the set voltage VOUT(E) is 1V to 4V.
The CL discharge time is determined by CL and RDCHG. If the time constant of CL and RDCHG is τ(τ= CL×RDCHG), the output
voltage discharge time can be calculated by using the following equation:
V = VOUT(E) × e -t / τ or t = τln ( VOUT(E) / V )
V : Output voltage after discharge
VOUT(E) : Output voltage
t : Discharge time
τ: CL×RDCHG
(2) Equation when the set voltage VOUT(E) is 4.1V to 12V.
The CL discharge time is determined by constant current until VOUT(E) is 4 V. When 4V or less, it is determined by CL and RDCHG
as in (1). If τ(τ= CL×RDCHG) is the time constant of CL and RDCHG and the CL discharge current is IDCHG, the discharge time of
the output voltage can be calculated by using the following equation:
t = τln ( 4 / V ) + CL × (VOUT(E) - 4) / IDCHG
V : Output voltage after discharge
VOUT(E) : Output voltage,
t: Discharge time
τ: CL×RDCHG
IDCHG : CL : Discharge time
12/21
TOREX [ Torex Semiconductor ]
