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LM3102-Q1

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SNVSB33 – MAY 2018

Product Folder Links: LM3102-Q1

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Feature Description (continued)

An internal switch grounds the SS pin if any of the following three cases happens: (i) VCC is below the UVLO

threshold; (ii) a thermal shutdown occurs; or (iii) the EN pin is grounded. Alternatively, the output voltage can be

shut off by connecting the SS pin to ground using an external switch. Releasing the switch allows the SS pin to

ramp up and the output voltage to return to normal. The shutdown configuration is shown in Figure 20.

Figure 20. Alternate Shutdown Implementation

7.3.9 Thermal Protection

The junction temperature of the LM3102-Q1 should not exceed the maximum limit. Thermal protection is

implemented by an internal Thermal Shutdown circuit, which activates (typically) at 165°C to make the controller

enter a low power reset state by disabling the main MOSFET, disabling the ON-timer, and grounding the SS pin.

Thermal protection helps prevent catastrophic failures from accidental device overheating. When the junction

temperature falls back below 145°C (typical hysteresis = 20°C), the SS pin is released and normal operation

resumes.

7.3.10 Thermal Derating

The LM3102-Q1 can supply 2.5 A below an ambient temperature of 100°C. Under worst-case operation, with

either input voltage up to 42 V, operating frequency up to 1 MHz, or voltage of the RON pin below the absolute

maximum of 7 V, the LM3102-Q1 can deliver a minimum of 1.9-A output current without thermal shutdown with a

PCB ground plane copper area of 40 cm2, 2 oz/Cu. Figure 21 shows a thermal derating curve for the minimum

output current without thermal shutdown against ambient temperature up to 125°C. Obtaining 2.5-A output

current is possible by increasing the PCB ground plane area, or reducing the input voltage or operating

frequency.

Figure 21. Thermal Derating Curve