ZHCSPJ0C april 2022 – august 2023 TPSI3050
PRODUCTION DATA
The selection of RPXFR allows for a tradeoff between power consumed and power delivered, as described in the Three-wire Mode section. For this design, one must choose an appropriate RPXFR selection that ensures enough power is transferred to support the amount of load being driven at the specified switching frequency.
During switching of the load, QLOAD of charge on VDDH is transferred to the load and VDDH supply voltage droops. After each switching cycle, this charge must be replenished before the next switching cycle occurs. This action ensures that the charge residing on VDDH does not deplete over time due to subsequent switching cycles of the load. The time it takes to recover this charge, tRECOVER, can be estimated as follows:
where
For this design, QLOAD = 100 nC and fMAX = 10 kHz are known, so IOUT required can be estimated as
IOUT represents the minimum average current required to meet the design requirements. Using the TPSI3050 calculator tool, one can easily find the RPXFR necessary by referring to the IOUT or fMAX columns directly. Table 9-2 shows the results from the tool, assuming VDDP = 4.75 V, to account for the supply tolerance specified in the design requirements. The TPSI3050 Calculator tool can be found at Design Calculator.
| RPXFR, k? | Power Converter Duty Cycle, % | IVDDP, mA | PIN, mW | POUT, mW | IOUT, mA | tSTART, μs | tRECOVER, μs | fEN_MAX, kHz | IAUX_MAX, mA |
|---|---|---|---|---|---|---|---|---|---|
| 9.09 | 21.1 | 6.82 | 32.0 | 10.8 | 1.05 | 1944.3 | 93.13 | 10.74 | 0.15 |
| 11 | 40.0 | 14.09 | 66.6 | 23.7 | 2.32 | 976.0 | 42.68 | 23.43 | 2.66 |
| 12.7 | 53.3 | 19.22 | 90.9 | 32.5 | 3.19 | 754.1 | 31.11 | 32.14 | 4.38 |
| 14.7 | 66.7 | 24.38 | 115.4 | 41.3 | 4.07 | 626.1 | 24.44 | 40.91 | 6.12 |
| 16.5 | 80.0 | 29.50 | 139.8 | 50.7 | 4.99 | 539.5 | 19.93 | 50.17 | 7.96 |
| 20 | 93.3 | 34.62 | 164.1 | 59.6 | 5.87 | 482.4 | 16.96 | 58.98 | 9.70 |
Table 9-3 summarizes the various output parameters of the calculator tool.
| Parameter | Description |
|---|---|
| RPXFR | External resistor setting that controls the amount of power transferred to the load by adjusting the duty cycle. Higher RPXFR settings lead to increased power transfer and power consumption. |
| Power Converter Duty Cycle | Nominal duty cycle of the power converter. Higher RPXFR settings leads to higher duty cycles of the power converter and higher power transfer. |
| IVDDP | Average current consumed from the VDDP supply |
| PIN | Average power consumed from the VDDP supply |
| POUT | Average power delivered to the VDDH supply |
| IOUT | Average current delivered to the VDDH supply |
| tSTART | Start-up time from VDDP rising until VDDH supply rail is fully charged. This parameter assumes VDDH and VDDM supply rails are fully discharged initially. |
| tRECOVER | Represents the time for the VDDH rail to recover after switching the load present on VDRV |
| fMAX | Maximum switching frequency possible for a given RPXFR setting for the applied loading conditions |
| IAUX_MAX | Maximum auxiliary current available at current user input settings. There is an inverse relationship between fMAX and IAUX_MAX. |
For this design example, RPXFR must be configured to the 9.09-kΩ setting or higher to transfer enough power to support switching the specified load at the required 10-kHz frequency.