P9235A-R Datasheet

© 2016 Integrated Device Technology, Inc

15

May 17, 2016

Table 9. ILIM programmable thresholds

Max Power

Vout

/Max Iout

Input current Limit

threshold

Voltage on ILIM

pin

Resistor Divider Values

(Input voltage: LDO18)

RTOP

[R26]

RBOTTOM

[R30]

1W

5 V/200 mA

0.75 A

0.48 V

130 kΩ,1%

47 kΩ,1%

2W

5 V/400 mA

1.25 A

0.78 V

NP

47 kΩ,1%

3W

5 V/600 mA

2.0 A

1.23 V

22 kΩ,1%

47 kΩ,1%

Remote Temperature Sensing and Over Temperature Protection

The P9235A-R uses a NTC thermistor connected to the TS pin to monitor the remote temperature during the power transfer phase. Connect

the NTC thermistor to a voltage divider as shown in Figure 15. If the voltage on the TS pin decreases below 0.6 V, the transmitter shuts off

the power, and will resume the wireless power transfer once the TS pin voltage rises above 0.8 V.

Figure 12. NTC connection

LDO33

TS

RBIAS

RTHM

VTS =

LDO33 × RTHM,TRIP

(RTHM,TRIP + RBIAS)

= 600mV

Where:



VTS (V) = Trip voltage at the desired trip temperature



RTHM,TRIP (kΩ) = Resistance of the thermistor at the desired trip temperature

Given LDO33 = 3.3V and RBIAS=10kΩ, then RTHM,TRIP = 2.22 kΩ at the trip temperature

The basic characteristic of an NTC thermistor is:































0

0

T

1

T

1

B

exp

R

R

Where:



T (Kelvin) = The trip temperature.



R0 (kΩ) = The known resistance at calibration temperature T0 (Kelvin).



B (beta, Kelvin) = The material constant .

With RBIAS=10kΩ, RTHM =2.2kΩ, and VTS=600mV at a trip temperature T, the desired R0 and B can be calculated, and the appropriate

thermistor chosen.