SLUSBC8C December 2013 – July 2018
This section discusses the pins that control the functions of the bq51003 (AD, AD_EN, EN1, EN2, and TS or CTRL).
This solution uses wireless power exclusively. The AD pin is tied low to disable wired power interaction. The output pin AD_EN is left floating.
EN1 and EN2 are tied to the system controller GPIO pins. This allows the system to control the wireless power transfer. Normal operation leaves EN1 and EN2 low or floating (GPIO low or high impedance). EN1 and EN2 have internal pulldown resistors. With both EN1 and EN2 low, wireless power is enabled and power can be transferred whenever the RX is on a suitable TX. The RX system controller can terminate power transfer and send an EPT 0x01 (Charge Complete) by setting EN1=EN2=1. The TX will terminate power when the EPT 0x01 is received. The TX will continue to test for power transfer, but will not engage until the RX requests power. For example, if the TX is the bq500212A, the TX will send digital pings approximately once per 5 seconds. During each ping, the bq51003 will resend the EPT 0x01. Between the pings, the bq500212A goes into low power Sleep mode reducing power consumption. When the RX system controller determines it is time to resume power transfer (for example, the battery voltage is below its recharge threshold) the controller simply returns EN1 and EN2 to low (or float) states. The next ping of the bq500212A will power the bq51003 which will now communicate that it is time to transfer power. The TX and RX communication resumes and power transfer is reinitiated.
The TS or CTRL pin will be used as a temperature sensor (with the NTC) and maintain the ability to terminate power transfer through the system controller. In this case, the GPIO will be in high impedance for normal NTC (Temperature Sense) control.
The CHG pin is used to indicate power transfer. A 2.1-V forward bias LED is used for D1 with a current limiting 1.5-kΩ series resistor. The LED and resistor are tied from OUT to PGND and D1 will light during power transfer.