P9038 DATASHEET
©2016 Integrated Device Technology, Inc. 10 P9038 August 1, 2016
Description of the Wireless Power Charging System
A wireless charging system is comprised of a base station
(transmitter) and a secondary coil (receiver) positioned
against each other allowing power to be transferred
magnetically. A WPC1 transmitter may be a free-positioning or
magnetically-guided type. A free-positioning type of
transmitter has an array of coils that gives limited spatial
freedom to the end-user, whereas a magnetically-guided type
of transmitter helps the end-user align the receiver to the
transmitter with a magnetic attraction.
The amount of power transferred to the Wireless charging
device is controlled by the receiver. The receiver sends
communication packets to the transmitter to increase power,
decrease power, or maintain the power level. The
communication is digital, and communication of 1's and 0's is
achieved by the Rx modulating the amount of load on the
receiver coil.
To conserve power, the transmitter places itself in a
very-low-power sleep mode unless it detects the presence of
a receiver. Once a receiver is detected, the transmitter exits
sleep mode and begins the power transfer per the WPC
specification.
Input Capacitors
Improper selection of the decoupling capacitor will degrade
the electrical performance of the P9038. The REG_IN and
IN_A to IN_D are the supply rails with nominal operating range
of 4.5V to 6.9V powering the internal drivers and the full bridge
inverter, respectively. At full load, the current through these
pins are both high and fast switching.
Typically, three 10µF and one 0.1µF ceramic capacitor across
the IN_A to IN_D pins are recommended. Similarly, for
REG_IN, a 1µF in parallel with 0.1µF capacitors are sufficient.
Prior to selecting the capacitor, always examine the
capacitor's DC voltage coefficient characteristics as the value
of the capacitors will decrease due to capacitance-to-applied
voltage characteristics of the commonly-used ceramic
dielectrics. For example, a 22µF X7R 6.3V capacitor's value
can actually be 6µF when operating at 5V, depending on the
manufacturer. Typically, 10V- or 16V-rated capacitors are
required. It is typically best to select these capacitors with a
voltage rating from two to two and half times the expected
applied voltage.
For optimum device performance, the decoupling capacitors
must be mounted on the component side of the PCB, and
also, located as physically close as possible to the related
power pins and power ground (PGND).
LDO5V & LDO2P5V
The LDO5V and LDO2P5V are 5V and 2.5V linear regulators
designed to power the internal circuitry. They can support
maximum of 10mA and 5mA of load current, respectively. To
stabilize the regulators, a 1µF capacitor from the output pin to
GND must be connected.
The GATE pin and associated MOSFET shown in Figure 2
below provide protection to the P9038 from input over-voltage
events and control current inrush. Both of these features are
described in subsequent sections of this document.
Figure 2. Input Voltage Support Range (UVLO)
Full-bridge MOSFET Drive and MOSFET
Current Sense
The P9038 incorporates an integrated full-bridge inverter.
Each half-bridge contains a high-side current sense block that
is used for control and for peak current protection. For EMI
reduction purposes, the switching rising and falling rates of the
internal MOSFETs are controlled.
Input Over-voltage Protection and In-rush
Control
The P9038 offers additional protection in the event of input
voltage transients and the programmable soft start time to
minimize the inrush currents. The P9038 is powered from a
VBUS input which may be subjected to voltages above 5.5V
under normal operation. The P9038 is designed to support
voltages as high as 27 V on this input. An external OVP
MOSFET is used to isolate pins that would be damaged by a
27 V transient on the V
BUS
input. The OVP MOSFET has a
second function: limiting inrush current from the V
BUS
line
during startup. This is necessary due to the USB inrush
specification and the large total effective capacitance (~40µF)
on the REG_IN and IN pins of the IC.
P9038
REG_IN
C
REG_IN
LDO5V
C
LDO5V
GATE
VBUS_SNS
ADAPTOR
4.5 V Min
25 m
To Inverter
IDC = 1.5 A
4.5 V - 25 m
* 1.5 A =
4.46 V
5
To IC
IDC = 45 mA
For Demonstration Purposes Only
Not All Connections Shown
Not To Scale
4.46 V – 5 * 45 mA = 4.23 V
LDO2P5V_IN
LDO2P5V
LDO2P5V
UVLO
BAND
GAP
LDO5V
INVERTER
& MCU
