MB39A214APFT-G-JNERE1 Datasheet, PDF (20/56 Pages) Fujitsu Component Limited. – 2ch DC/DC converter IC with PFM/ PWM synchronous rectification

MB39A214A
(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.
y PWM-fixed mode
IOUTx
ILXx
VLXx
y Automatic PFM/PWM selection mode
IOUTx
0A
Inductor current in the opposite
direction
ILXx
0A
VLXx
X : Each channel number
Switching frequency reduced
20
DS405-00007-1v0-E