P9235A-R Datasheet, PDF (15/23 Pages) Integrated Device Technology – Wireless Power Transmitter

Table 9. ILIM programmable thresholds
Max Power
Vout
/Max Iout
Input current Limit Voltage on ILIM
threshold
pin
1W
5 V/200 mA
0.75 A
2W
5 V/400 mA
1.25 A
3W
5 V/600 mA
2.0 A
0.48 V
0.78 V
1.23 V
P9235A-R Datasheet
Resistor Divider Values
(Input voltage: LDO18)
RTOP
[R26]
RBOTTOM
[R30]
130 kΩ,1%
47 kΩ,1%
NP
47 kΩ,1%
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
R_{BIA S}
TS
R_THM
Where:
V_TS
=
LDO33 × R_THM,TRIP
(R_THM,TRIP + R_BIAS)
=
600mV
 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:
R

R
0^exp

^{B }


1
T

1
T₀

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.
© 2016 Integrated Device Technology, Inc
15
May 17, 2016