The NTC input pin allows for user programmable thermal protection. See the Electrical Characteristics for NTC pin thresholds. The NTC input pin threshold is ratiometric with V_CC. The external resistor divider setting V_NTC must be connected to the TPS25831-Q1 V_CC pin to achieve accurate results, see Figure 10-28 and Figure 10-29. When V_NTC = 0.5 × V_CC (approximately 2.5-V typically), the TPS25831-Q1 performs two actions:

1. If operating with 3-A Type-C advertisement, the CC1 and CC2 pin automatically reduces advertisement to the 1.5-A level.
2. The THERM_WARN flag is asserted to provide an indication of the over-temperature condition. FAULT is NOT asserted at this time.

Figure 10-28 NTC Input Pin

Figure 10-29 TPS25831-Q1 Behavior When Trigger NTC Threshold

If the overtemprature condition persists causing V_NTC = V_CC × 0.65 (3.25-V typical), the TPS25831-Q1 turns off the buck regulator and pulls the LS_GD pin low. The THERM_WARN flag remains asserted; however, the FAULT pin is NOT asserted for this condition.

Tuning the V_NTC theshold levels of V_{WARN_HIGH} and V_{SD_HIGH} is achieved by adding R_SER, R_PARA, or both R_SER and R_PARA in conjunction with R_NTC. Figure 10-30 is an example illustrating how to set the THERM_WARN threshold between 75°C and 90°C with a ΔT between THERM_WARN assertion and device shutdown of 17°C to 28°C. Consult the chosen NTC manufacturer's specification for the value of β. It may take some iteration to establish the desired warning and shutdown thresholds.

Below is NTC spec and resistor value used in Figure 10-30 example.

• R₀ = 470 kΩ. β = 4750. R_NTC=R₀ × exp β × (1/T-1/T₀)
• R_PARA = 100 kΩ.
• R_SER = 5 kΩ.
• R_B = R_NTC(at T_ THERM_WARN) = 32 kΩ

Figure 10-30 V_NTC Threshold Examples

The NTC resistor should be placed near the hottest point on the PCB. In most cases, this will be close to the SW node of the TPS25831-Q1, near the buck inductor, R_SNS sense resistor and external MOSFETs (if used).

Figure 10-31 NTC Placement Example