Dropout Operation (Cont.)
An important detail to remember is that on resistance of P-FET switch will increase at low input supply voltage.
Therefore, the user should calculate the power dissipa-tion when the JTMA7290 is used at 100% duty cycle with
low input voltage.
 
Over-Temperature Protection (OTP)
The over-temperature circuit limits the junction tempera-ture of the JTMA7290. When the junction temperature ex-
ceeds 150oC, a thermal sensor turns off the both power MOSFETs, allowing the devices to cool. The thermal sen-
sor allows the converters to start a soft-start process and regulate the output voltage again after the junction tem-
perature cools by 30oC. The OTP designed with a 30oC hysteresis lowers the average Junction Temperature (TJ)
during continuous thermal overload conditions, increas-ing the life time of the device.
 
Short-Circuit Protection
When the output is shorted to ground, the frequency of the oscillator is reduced to about 210 kHz, 1/7 of the nomi-
nal frequency. This frequency fold back ensures that the inductor current has more time to decay, thereby prevent-
ing runaway. The oscillator’s frequency will progressively increase to 1.5MHz when VFB or VOUT rises above 0V.

Low Battery Detection
The low battery detection is used to monitor the battery voltage and to generate a signal. This function includes
two pins, LBI is the inverting input of the comparator and LBO is an open drain output (See Block Diagram). When
the LBI voltage drops below the threshold voltage 0.6V,the open drain device will turn on and LBO becomes low.
The Low battery threshold voltage can be programmed with a resistive divider from battery to LBI pin to the round.
Since the LBO is an open drain output, it usually requires an external pull-up resistor.