P9221-R_17 Datasheet, PDF (16/35 Pages) Integrated Device Technology – Wireless Power Receiver for 15W Applications

P9221-R Datasheet
8. Theory of Operation
The P9221-R is a highly-integrated, wireless power receiver targeted for 15W applications. The device integrates a full-wave synchronous
rectifier, low-dropout (LDO) linear regulator, and a 32-bit ARM®-based M0 processor to manage all the digital control required to comply with
the WPC-1.2.2 communication protocol.
The rectifier voltage and the output current are sampled periodically and digitized by the analog-to-digital converter (ADC). The digital
equivalents of the voltage and current are supplied to the internal control logic, which determines whether the loading conditions on the VRECT
pin indicate that a change in the operating point is required. If the load is heavy enough and brings the voltage at VRECT below its target, the
transmitter is set to a lower frequency that is closer to resonance and to a higher output power. If the voltage at VRECT is higher than its target,
the transmitter is instructed to increase its frequency. To maximize efficiency, the voltage at VRECT is programmed to decrease as the LDO’s
load current increases. The internal temperature is continuously monitored to ensure proper operation.
In the event that the VRECT voltage increases above 13.5V, the control loop disables the LDO and sends error packets to the transmitter in an
attempt to bring the rectifier voltage back to a safe operating voltage level while simultaneously clamping the incoming energy using the
open-drain SINK pin for VRECT linear clamping. The clamp is released when the VRECT voltage falls below the V_OVP-DC minus V_OVP-HYS. See
Figure 17.
The receiver utilizes IDT’s proprietary voltage clamping scheme, which limits the maximum voltage at the rectifier pin to 13.5V, reducing the
voltage rating on the output capacitors while eliminating the need for over-voltage protection (OVP) capacitors. As a result, it provides a small
application area, making it an industry-leading wireless power receiver for high power density applications. Combined with the P9242-R
transmitter, the P9221-R is a complete wireless power system solution.
8.1 LDO – Low Dropout Regulators
The P9221-R has three low-dropout linear regulators. The main regulator is used to provide the power required by the battery charger where
the output voltage can be set to either 9V or 12V. For more information about setting the output voltage, see section 8.2. It is important to
connect a minimum of 30µF ceramic capacitance to the OUT pin.
The other two regulators, VDD5V and VDD18, are to bias the internal circuitry of the receiver. The LDOs must have local 1µF ceramic capacitors
placed as close as possible to the pins.
8.2 Setting the Output Voltage – VOSET
The output voltage on the P9221-R is programmed by connecting the center tap of the external resistors R34 and R33 to the VOSET pin as
shown in the application schematic in Figure 24. There are only two voltages available: 9.0V or 12V. The recommended settings for R33 and
R34 are summarized in Table 6.
The default output voltage is set to 12V in the P9221-R Evaluation Board. For applications where the transmitter is capable of delivering only
5W, the P9221-R will automatically switch to 5V to ensure 5W power delivery. The 5W option can be disabled by adding R33 as described in
Table 6.
Table 6. Setting the Output Voltage
R34 (kΩ)
R33 (kΩ)
Output Voltage (V)
5V Output Option
10
OPEN
12
Enable
10
30
12
Disable
OPEN
10
9
Enable
10
3.3
9
Disable
© 2017 Integrated Device Technology, Inc.
16
April 4, 2017