4 Operation Notes

In order to operate the EVM, the input voltage must increase above the UVLO threshold of the device. The UVLO threshold of the EVM is approximately 7.65 V with 200 mV of hysteresis. To adjust the UVLO threshold to a higher voltage, the values of R8 and R9 on the EVM can be adjusted as described in the product data sheet. The maximum operating input voltage for the device is 14 V. Refer to the product data sheet for further information on the input voltage range and UVLO operation.

The minimum input voltage for the TPSM84A22 is 8 V or (VOUT × 5.3), whichever is greater.

The soft-start time is a fixed value and cannot be adjusted. After application of the proper input voltage, the output voltage of the device will ramp to its final value in approximately 4.1 ms.

The power-good (PGOOD) indicator of the EVM will assert high when the output voltage is within ±5% of the programmed output voltage value. A 100-kΩ pullup resistor (R11) is populated between the PGOOD pin and the VG pin. The voltage on the VG pin is 4.8 V (typical). The VG and corresponding PGND test points are not loaded on the EVM. If driving the VG pin is required, test points can be added to the EVM.

The current limit of the device can be set to 11.25 A (typical) by placing a 47-kΩ resistor between ILIM and PGND. The EVM has a footprint for this resistor, R10, if needed.

The TPSM84A21 and TPSM84A22 nominal switching frequency is 4 MHz with a range of 3.7 MHz to 4.3 MHz when free-running. If an exact switching frequency is required, both devices can be synchronized to an external clock over the frequency range of 3.6 MHz to 4.4 MHz. Refer to the product data sheet for further information on synchronization.

The TPSM84A21 and TPSM84A22 both include input and output capacitors internal to the device. For most applications, no additional output capacitors are required. The EVM includes footprints for adding input and output capacitors to the EVM. Adding additional capacitance will improve transient response. The actual capacitance required will depend on the input and output voltage conditions of the particular application, along with the desired transient response. Refer to the product data sheet for further information on input and output capacitance and transient response.