9.2.2 Detailed Design Procedure

9.2.2.1 Maximum Junction Temperature Check

For a 200 mA current limit:

• Choose driver output current limit, IO(LIM) = 250 mA (allowing for current limit tolerance); RSET = 27 kΩ

• The maximum voltage drop across the high-side switch at 250 mA current is VDS(ON) = 1.1 V.

This causes a power consumption of:

PDOP=VDSON × IOLIM =1.1 V ×250 mA=275 mW

(1)

For a 5 mA LDO current output,

PDLDO= VL+−VVCCOUT × IVCC_OUT= 30−5V ×5 mA=125 mW

(2)

Total power dissipation,

PD= PDLDO+PDOP=275 mW+125 mW=400 mW 

(3)

Multiply this value with the Junction-to-ambient thermal resistance of θJA = 45.9 °C/W (taken from the Thermal

Information table) to receive the difference between junction temperature, TJ, and ambient temperature, TA:

∆T=TJ−TA=PD 

× θJA=400 mW × 45.9 ℃W=18.36 ℃

(4)

Add this value to the maximum ambient temperature of TA = 105°C to receive the final junction temperature:

TJ=TA+ ∆T=TA+ PD 

× θJA=105 ℃+ 400 mW × 45.9 ℃W=105 ℃+18.36 ℃= 123.36 ℃ (5)

As long as TJ is below the recommended maximum value of 150°C, no thermal shutdown will occur. However,

the junction temperature is closer to TWRN and thermal warning may be generated if the junction temperature

rises above TWRN.

Note that the modeling of the complete system may be necessary to predict junction temperature in smaller

PCBs and/or enclosures without air flow.

9.2.2.2 Driving Capacitive Loads

These devices are capable of driving capacitive loads on the OUT output. Assuming a pure capacitive load

without series/parallel resistance, the maximum capacitance that can be charged without triggering current fault

can be calculated as:

SC

O LIM

LOAD

VCC

I

x t

C

V

[

]

(6)

To drive higher capacitive loads and avoid overcurrent condition disabling the driver, it is recommended to leave

ILIM_ADJ pin floating. With ILIM_ADJ floating, TIOS102(x) indicates overcurrent fault without blanking time

delay (tSC) but does not disable the driver. Another approach is to drive high capacitive loads with a series

resistor between the output and the load to avoid overcurrent condition. Capacitive loads can be connected to

GND or VCC

TIOS102, TIOS1023, TIOS1025

SLLSFL4A – FEBRUARY 2022 – REVISED DECEMBER 2022

www.ti.com

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