SLVSF07 July 2021 TPS7H5001-SP
There are several methods for enabling the TPS7H5001-SP through the EN pin. The pin can be tied directly to VLDO, which would allow for the device to be enabled as soon as the voltage on VLDO surpasses the rising edge voltage threshold of the EN pin. The pin can also be driven with an externally generated signal or a compatible PGOOD signal for instances in which sequencing is desired. Lastly, two resistors can be used to program the controller to enable when VIN surpasses a user determined threshold, as shown in Figure 7-1 . The two resistors are configured as a divider, with one between VIN and EN and the other between EN and AVSS.
Using Equation 1, the user can calculate the value for RUVLO_TOP for a chosen value of RUVLO_BOT based on the desired maximum startup voltage for the device. With these selected resistors Equation 2 can be used to determine the minimum startup voltage.
In the two-resistor configuration of Figure 7-1, the controller will also shut down due to undervoltage lockout when the input voltage falls below a particular threshold. This is due to the hysteresis of the EN pin. In order to determine the voltages at which shutdown is expected to occur, use Equation 3 and Equation 4.
It is important to note that the user should take care when selecting the values for RUVLO_TOP and RUVLO_BOT. It is recommended to optimize the selection of these resistors for startup in order to ensure proper operation. The UVLO value must be approximately 75% or less of the input voltage in order to ensure that the device turns on as expected under all circumstances. Setting the UVLO any higher may cause issues with the turn-on of the device. Figure 7-2 shows the expected startup and UVLO voltages on a 12 V rail where the maximum startup voltage is 90% of the nominal input voltage. In this instance, turn-off will occur when the input voltage falls to between 75% and 67% of its nominal value.