SLASFC6 August 2024 TAS2120
ADVANCE INFORMATION
The boost converter requires multiple passive devices that are labeled L1, C7, C8, C12 in Section 7.2 and whose specifications are provided in Table 7-1. These specifications are based on the design of the TAS2120 and are necessary to meet the performance targets of the device. In particular, L1 should not be allowed to enter in the current saturation region. The saturation current (ISAT) for L1 should be > (ILIM + 5%) to deliver Class-D peak power. ISAT and ILIM values should be selected based on peak output power required in the application.
Additionally, the ratio of L1/C (the derated value of C7,C8,C12) has to be less than 1/3 for boost stability. This ratio is relaxed to 1/2 in 2S battery mode of operation. This ratio should be maintained including the worst case variation of boost inductor and output capacitors.
To satisfy sufficient energy transfer, L1 needs to be ≥ 0.47μH at the boost switching frequency (100kHz to 4MHz). Using a 0.47μH will help in reducing the capacitor requirements and save board space, but comes at the cost of increased voltage ripple on VBAT and reduces average input current and hence max POUT of the device. High PSRR of TAS2120 should minimize the effect from the additional ripple on VBAT supply.
The L1 inductor series resistance (ESR) is another critical parameter to be selected in the application. Lower ESR reduces power loss and helps in improving overall system efficiency. Based on available board space, smallest ESR inductors which meet the application needs will give better efficiency performance.