The basic BQ51013C design is identical to the Section 9.2.2. The BQ51013C OUT pin is tied to the output of Q1 and directly to the IN pin of the BQ24040. No other changes to the BQ51013C circuitry are required.

The BQ24040 has a few parameters that need to be programmed for this charger to work properly. Ceramic decoupling capacitors are needed on the IN and OUT pins using the values shown in Figure 9-11. After evaluation during actual system operational conditions, the final values may be adjusted up or down. In high amplitude pulsed load applications, the IN and OUT capacitors will generally require larger values. The next step is setting up the fast charge current and pre-charge and termination current.

Program the Fast Charge Current, ISET: R_ISET = [K_ISET/I_OUT] = [540 AΩ / 0.8 A] = 675 Ω.

Program the Termination Current, ITERM: R_PRE-TERM = [K_TERM/%_OUT-FC] = 200 Ω/% x 10% = 2 kΩ.

TS Function: To enable the temperature sense function, a 10-kΩ NTC thermistor (103AT) from TS to VSS should be placed in the battery pack. To disable the temperature sense function, use a fixed 10-kΩ resistor between TS and VSS.

Figure 9-12 shows start-up of the wireless system with the BQ24040 charger when TX power is applied after the full RX system has been placed on the charging pad. Channel 1 (yellow) shows the initial power to the TX system. The RECT pin of the BQ51013C is shown on Channel 3 (purple). The output of the BQ24040 is shown on Channel 2 (blue). Battery current can be seen on Channel 4 (green).

Figure 9-13 shows a similar condition but in this case, the battery is not connected initially, so the battery detection routine can be observed. After the battery is connected to the charger, the charge current jumps to 800 mA and the output voltage becomes stable. Both the current out of the BQ51013C (Channel 1, yellow) and the current out of the BQ24040 (Channel 4, green) can be seen.