P9235A-R Datasheet

© 2016 Integrated Device Technology, Inc

12

May 17, 2016

Enable Function (EN Pin)

When voltage on the EN

¯¯ pin is greater than 2.5 V, the P9235A-R shuts down the buck regulator. It goes onto Shutdown Mode, which

disables all the analog and digital modules. Current consumption in Shutdown Mode is less than 25 µA. When EN

¯¯ is less than 1.0 V, the

P9235A-R is fully functional, and all the blocks are enabled. Figure 7 shows EN thresholds.

Figure 7. EN pin threshold

Time

VEN_L

Shutdown

Mode

Normal

Operating

mode

VEN_H

1.0V

2.5V

Normal

Operating

mode

When EN

¯¯ is less than 1.0 V and a receiver is not yet detected, the P9235A-R is in the low power Standby Mode. The P9235A-R periodically

comes out of Standby Mode to generate digital and analog pings to detect the presence of a receiver. Between these pings, the P9235A-R

continues in the Standby Mode to maintain low power consumption.

Input Current Sense

The P9235A-R monitors its input current by using an external sense resistor (R6), in series with the input voltage rail of the full bridge LC tank

driver circuit (Q2, Q3). The voltage across the sense resistor is fed into the ISNS_H and ISNS_L pin via an RC filter (R4,R5,C2). The

differential signal of ISNS_H and ISNS_L is processed by the internal ADC and associated firmware.

The current sense resistor is sensitive to noise, as well as to circuit board conditions. On the layout of PCB, it is necessary to use Kelvin

sensing when routing the ISNS_H and ISNS_L connections. Incorrect current reporting may also occur when a re-worked board has residue

(e.g. flux) around the sense resistor. More details are available in the P9235A-R layout guide, AN936.

For 2W/3W applications, use a 20mΩ sense resistor (R6). For 1W applications use a 50 mΩ sense resistor. Adjust the resistor divider (R27,

R31) value on the LED_PAT pin according to the sense resistor used.

Communication and Modulation

The wireless power system uses an in-band communication, such that the current and voltage on the transmitter’s power coil assume two

states, namely a HI state and a LO state. For a valid state, the amplitude is constant, within a certain variation Δ, for at least ts ms. If the

wireless power receiver is properly aligned to the transmitter’s power coil, and for all appropriate loads, at least one of the following two

conditions shall apply, as shown in Figure 8.

Difference of the amplitude of the transmitter current in the HI and LO state: ≥ 15 mA.

Difference of the amplitude of the transmitter voltage in the HI and LO state: ≥ 200 mV.

The minimum hold time for a valid HI or LO state: ≥ 0.15 ms

Figure 8. Modulation

Modulation

Depth

HI State

LO State

LO State

HI State

Δ

ts

ts

ts

ts

The receiver uses a 2 kHz, differential, bi-phase encoding scheme to modulate data bits onto the power signal. A logic ONE bit is encoded