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Table 9-1. Design Parameters (continued)

PARAMETERS

Design Requirement

TIOS102(x) Specification

Maximum Ambient Temperature,

105°C

TIOS102(x) can support up to TA

of 125 °C if TJ < T(SDN)

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.

10 Power Supply Recommendations

The TIOS102 and TIOS102x are designed to operate from a 24-V nominal supply at VCC, which can vary by

+12 V and -17 V from the nominal value to remain within the device's recommended supply voltage range of 7 V

to 36 V. This supply should be buffered with at least a 100-nF/100-V capacitor.

TIOS102, TIOS1023, TIOS1025

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