220.127.116.11 Detailed Design Procedure
The recommended L1 = 22 µH, CBYP = 0.01 µF and low leakage CREF = 10 nF are selected. The rectifier diodes are Panasonic DB3X316F0L. In order to ensure the fastest recovery of the harvester output voltage to the MPPT level following power extraction, the minimum recommended CIN = 4.7 µF is selected. Because no large system load transients are expected and to ensure fast charge time during cold start, the minimum recommended CSTOR = 4.7 µF.
- Keeping in mind that VREF_SAMP stores the MPP voltage for the harvester, first choose RSUMOC = ROC1 + ROC2 = 20 MΩ then solve Equation 1 for
- ROC2 = RSUMOC x (1 - VREF_SAMP / VIN_DC(OC) = 20 MΩ x (1 - 0.4 V / 1 V ) = 12 MΩ → series 10 MΩ and
2 MΩ easy to obtain 1% resistors.
- Referring back to the procedure in Detailed Design Procedure or using using the spreadsheet calculator at SLUC484 gives the following values
- ROV1 = 7.15 MΩ, ROV2 = 5.90 MΩ resulting in VBAT_OV = 3.31V due to rounding to the nearest 1% resistor.
- ROK1 = 4.99 MΩ, ROK2 = 6.65 MΩ, ROK3 = 1.24 MΩ resulting in VBAT_OK = 2.82 V and VBAT_OK_HYST =
3.12 V after rounding to the nearest 1% resistor value.
- ROUT1 = 8.66 MΩ and ROUT2 = 4.22 MΩ resulting in VOUT = 1.8V.