The TPS40040 and TPS40041 dc-to-dc controllers are designed to operate from a 2.25-V to 5.5-V input source. To reduce the number of external components, several operating parameters are fixed internally; namely, frequency, soft start time, and short circuit protection (SCP) levels. For example, the operating frequencies of TPS40040/1 are 300 kHz/600 kHz, respectively.
One of three short circuit threshold levels may be selected by the addition of an external resistor from the COMP pin to circuit ground. During power on, and before the internal soft start commands the output voltage to rise, the TPS40040/1 enters a calibration cycle, measures the current out of the COMP pin, and selects an internal SCP threshold voltage. At the end of the 1.6-ms calibration time, the output voltage is allowed to rise for a 4-ms soft start. During operation, the selected SCP threshold voltage is compared to the upper MOSFETs voltage drop during its ON time to determine whether there is an overload condition.
The packaging of the TPS40040/1 is unique in that the PowerPAD is used as an electrical ground connection as well as a thermal connection.