L9611 datasheet(6/12 Pages) STMICROELECTRONICS

6 / 12 page

Figure 2 : The Typical Waveforms for the Power Limitation Function.

SHORT CIRCUIT CURRENT REGULATION

The maximum load current in the short circuit con-

dition can be chosen by the value of the current

sensing resistor RS according to :

ISC =VSI/RS

Two identical VS compatible comparators are pro-

vided to realize the short circuit protection.

After reaching the lower threshold voltage (typical

value VSI-10 mV), the first comparator enables the

timer and the gate is driven with the full continuous

pump voltage : when the upper threshold voltage

value is reached the second comparator maintains

the chosen ISC driving the NMOS gate in continuous

mode.

This function - showed in fig. 3 - speeds up the

switch on phase for a lamp as a load.

BANDGAP VOLTAGE REFERENCE

The circuit provides a reference voltage which may

be used as control input voltage through a resistive

divider. This reference is protected against the short

circuit current.

CHARGE PUMP

The charge pump circuit holds the N-MOS gate

above the supply voltage during the ON phase. This

circuit consists of an RC astable which drives a com-

parator with a push-pull output stage. The external

charge pump capacitor CP must be at least equal to

the NMOS parasitic input capacitance.

For fast gate voltage variation CP must be increased

or the bootstrap function can be used. The bootstrap

capacitor should be at least 10 times greater than

the powerMOS parasitic capacitance.

The charge pump voltage VPUMP can reach to :

VPUMP =2 VS -VBE -VCESAT

The circuit is disabled if the supply voltage is higher

than VSH.

L9610C - L9611C

6/12

L9611 bảng dữ liệu(PDF) 6 Page - STMicroelectronics