FREQ datasheet(20/56 Pages) FUJITSU

20 / 56 page

MB39A214A

Limitation : development tool vendor use only

FUJITSU SEMICONDUCTOR CONFIDENTIAL

DS405-00007-1v0-E

(10) Over Temperature Protection (OTP)

The over-temperature protection circuit block (OTP) provides a function that prevents the IC from a thermal

destruction. If the junction temperature reaches + 150

°C, the DRVH1 pin (pin 24) and DRVH2 pin (pin 13)

are set to the “L” level, and the DRVL1 pin (pin 22 ) and DRVL2 pin (pin 15) are set to the “L” level. This

fixes the high-side and low-side FETs to the off-state, of both channels in the DC/DC converter, causing

switching to be stopped. The discharge operation is then carried out to discharge the output capacitor (The

discharge operation continues until the state of the over-temperature protection is released). If the junction

temperature drops to + 125

°C, the soft start is reactivated. (Restored automatically.)

(11) Operation mode

In the PWM-fixed mode, the system acts by the switching frequency specified with the FREQ pin

regardless of the load.

In the automatic PFM/PWM selection mode, the switching frequency is reduced at low load, for enhancing

the conversion efficiency characteristics. This function detects 0 A of the inductor current from the

electromotive force of the low-side FET ON resistance when the low-side FET ON state, and places the

low-side FET into the off state. This idle period continued until the output voltage decreased, this results the

switching frequency being reduced automatically depending on the load current when the inductor current

is below the critical current. The system acts by the switching frequency specified with the FREQ pin, when

the inductor current exceeds the critical current.

For Automatic PFM/PWM selection mode with PAF function, the switching frequency at low load is held to

30 kHz (Min) or more.

The operation mode can be switched by setting the MODE pin (pin 17) to any one of GND connection,

OPEN, and VB connection.

PWM-fixed mode

IOUTx

ILXx

VLXx

0 A

Automatic PFM/PWM selection mode

IOUTx

ILXx

VLXx

0 A

Switching frequency reduced

Inductor current in the opposite

direction

X : Each channel number

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