XCL201 datasheet(9/21 Pages) TOREX

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XCL201/XCL202

Series

■

OPERATIONAL DESCRIPTION (Continued)

In PFM control operation, until coil current reaches to a specified level (IPFM), the IC keeps the P-ch MOSFET on. In this case, on-time (tON) that

the P-ch MOSFET is kept on can be given by the following formula.

tON = L

×IPFM / (VIN−VOUT) →IPFM①

In the PFM control operation, the PFM Duty Limit (DTYLIMIT_PFM) is set to 200% (TYP.). Therefore, under the condition that the duty increases (e.g.

the condition that the step-down ratio is small), it’s possible for P-ch MOSFET to be turned off even when coil current doesn’t reach to IPFM. →IPFM②

The XCL201/XCL202 series can quickly discharge the electric charge at the output capacitor (CL) when a low signal to the CE pin which enables

a whole IC circuit put into OFF state, is inputted via the N-channel transistor located between the LX pin and the VSS pin. When the IC is disabled,

electric charge at the output capacitor (CL) is quickly discharged so that it may avoid application malfunction. Discharge time of the output

capacitor (CL) is set by the CL auto-discharge resistance (R) and the output capacitor (CL). By setting time constant of a CL auto-discharge

resistance value [R] and an output capacitor value (CL) as τ(τ=C x R), discharge time of the output voltage after discharge via the N channel

transistor is calculated by the following formula.

V = VOUT(T) x e

–t/τ or t=τln (V

OUT(T) / V)

V : Output voltage after discharge

VOUT(T) : Output voltage

t: Discharge time,

τ: C x R

C=Capacitance of output capacitor (CL)

R=CL auto-discharge resistance

100

Discharge Time ｔ(ms)

CL=10μF

CL=20μF

CL=50μF

tON

IPFM

0mA

IPFM①

IPFM②

0mA

fOSC

最大 IPFM 制限

Output Voltage Discharge Characteristics

RDCHG=300Ω(TYP.)

ILx

IPFM

DTY LIMIT_PFM

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