DS1650 Datasheet, PDF (17/26 Pages) National Semiconductor (TI) – Quad Differential Line Receivers

Thermal Management
The RT1650 provides an external device thermal
management function with an external NTC thermistor
and a resistor connected between TS pin and GND pin
shown as Figure 5. User can use this function to control
the temperature of the coil, battery or other device.
An internal current source (60A) is provided to the
external NTC thermistor and generates a voltage at the
TS pin. The TS voltage is detected and sent to the ADC
converter for external device thermal manage control.
RT1650
I_TS
ADC
TS
GND
R1 R_NTC
Figure 5. NTC Circuit for Device Temperature
Detection and Thermoregulation
The thermal management function is shown as Figure
6. If the temperature is higher than Hot_temp or lower
than Cold_temp threshold, the RT1650 will send the
EPT to disable the power transfer. When the detected
temperature increases and reaches the desired
Regulation_temp, RT1650 will decrease the current
limit to reduce the output current to regulate the
temperature. When the detected temperature is lower
than the Regulation_temp, the current limit will increase
to the default value. This function is shown as Figure 7.
Temperature
Hot_temp
Regulation_temp
Send EPT
Periodically reduce current limit to regulate temperature.
Thermal regulation is active.
Cold_temp
Send EPT
Figure 6. Thermal Management Function
RT1650
Temperature,
Current
Regulation_temp
Temperature
Thermal regulation is active
Current-limit
Loading
Output Current
Time
Figure 7. Thermoregulation Control
The NTC thermistor should be placed as close as possible
to the device such as battery or mobile device. The
recommended NTC thermistor is NCP15WF104F03RC
(tolerance ±1%, β = 4250k). The typical resistance of the
NTC is 100k at 25C. The recommended resistance for
R1 is 33k(±1%).The value of the NTC thermistor at the
desired temperature can be estimated by the following
equation.
R_{NTC_Reg} =
R_Oe^{β}
1
T_Reg
-
1
T₀


R_eq
=
R₁ R_{NTC_Reg}
R₁+R_{NTC_Reg}
where TReg is the desired regulation temperature in
degree Kelvin. RO is the nominal resistance at
temperature T0 and β is the temperature coefficient of
the NTC thermistor. Req is the equivalent resistor of
NTC thermistor in parallel with R1.
Figure 8 shows the equivalent resistance of the
thermistor in parallel with R1 resistor varies with
operating temperature. Figure 9 shows the VTS voltage
with operating temperature. Customer can select the
desire temperature and calculate the mapping data by
the following equation.
Data = (VTS/2 x 1024)
If the thermal management function is not used (RNTC
= open), the resistor R1 = 24k must be connected
between the TS and GND pins
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS1650-00 July 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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