JAJSF16D march 2013 – september 2020 BQ51013B
PRODUCTION DATA
The components chosen for the Section 9.2.1 system are identical. Adding a blocking FET while using the BQ51013B for control is the only addition to the circuitry.The AD pin will be tied to the DC input as a threshold detector. The AD_EN pin will be used to enable or disable the blocking FET. The blocking FET must be chosen to handle the appropriate current level and the DC voltage level supplied from the input. In this example, the expectation is that the DC input will be 5 V with a maximum current of 1 A (same configuration as the wireless power supply). The CSD75207W15 is a good fit because it is a P-Channel, –20-V, 3.9-A FET pair in a 1.5-mm2 WCSP.
The following scope plots show behavior under different conditions.
Figure 9-7 shows the transition from wireless power to wired power when power is added to the AD pin. VRECT drops and there is a short time (IOUT drops to zero) when neither source is providing power. When Q1 is enabled (through AD_EN) the output current turns back on. Note the RECT voltage after about 500 ms. This is the TX sending a ping to check to see if power is required. RECT returns to low after the BQ51013B informs the TX it does not need power (without enabling the OUT pin). This timing is based on the TX (BQ500212A used here).
Figure 9-8 shows the transition to wireless power when the AD voltage is removed. Note that after wired power is removed, the next ping from the (BQ500212A) will energize the BQ51013B. Once the rectifier voltage is stable the output will turn on.
Figure 9-9 shows a system placed onto the transmitter with AD already powered. The TX sends a ping which the RX responds to and informs the TX that no power is needed. The ping will continue with the timing based on the TX used.
Figure 9-10 shows the AD added when the RX is not on a TX. This indicates normal start-up without requirement of the TX.