8.2.1.2 Detailed Design Procedure

The recommended L1 = 22 µH, CBYP = 0.01 µF and low leakage CREF = 10 nF are selected. 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.

No MPPT resistors are required because VOC_SAMP can be tied to VSTOR to give 80% MPPT.

• Keeing in mind VBAT_UV < VBAT_OV ≤ 5.5 V, to size the VBAT_OV resistors, first choose RSUM_OV = R_OV1 + R_OV2 = 13 MΩ then solve Equation 2 for
Equation 11.
• R_OV2 = RSUM_OV - R_OV1 = 13 MΩ - 5.62 MΩ = 7.38 MΩ → 7.32 MΩ resulting in VBAT_OV = 4.18V due to rounding to the nearest 1% resistor.
• Keeping in mind VBAT_OV ≥ VBAT_OK_HYST > VBAT_OK ≥ VBAT_UV, to size the VBAT_OK and VBAT_OK_HYST resistors, first choose RSUM_OK = R_OK1 + R_OK2 + R_OK3 = 13 MΩ then solve Equation 3 and Equation 4 for
Equation 12.
Equation 13.
• R_OK3 = RSUM_OK - R_OK1 - R_OK2 = 13 MΩ - 5.62 MΩ - 5.479 MΩ = 1.904 MΩ → 1.87 MΩ to give VBAT_OK = 2.39 V and VBAT_OK_HYST = 2.80 V.

SLUC484 provides help on sizing and selecting the resistors.