TPS2061DBVRG4 datasheet(22/55 Pages) TI2

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9.1.3 Power Dissipation and Junction Temperature

The low on-resistance on the N-channel MOSFET allows the small surface-mount packages to pass large

currents. The thermal resistances of these packages are high compared to those of power packages; it is good

design practice to check power dissipation and junction temperature. Begin by determining the rDS(on) of the

N-channel MOSFET relative to the input voltage and operating temperature. As an initial estimate, use the

highest operating ambient temperature of interest and read rDS(on) from Figure 6-25. Using this value, the power

dissipation per switch can be calculated by:

• PD = rDS(on)× I2

Multiply this number by the number of switches being used. This step renders the total power dissipation from

the N-channel MOSFETs.

The thermal resistance, RθJA = 1 / (DERATING FACTOR), where DERATING FACTOR is obtained from the

Dissipation Ratings Table. Thermal resistance is a strong function of the printed circuit board construction , and

the copper trace area connecting the integrated circuit.

Finally, calculate the junction temperature:

• TJ = PD x RθJA + TA

Where:

• TA= Ambient temperature °C

• RθJA = Thermal resistance

• PD = Total power dissipation based on number of switches being used.

Compare the calculated junction temperature with the initial estimate. If they do not agree within a few degrees,

repeat the calculation, using the calculated value as the new estimate. Two or three iterations are generally

sufficient to get a reasonable answer.

9.1.4 Thermal Protection

Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for

extended periods of time. The TPS206x implements a thermal sensing to monitor the operating junction

temperature of the power distribution switch. In an overcurrent or short-circuit condition, the junction temperature

rises due to excessive power dissipation. Once the die temperature rises above a minimum of 135°C due

to overcurrent conditions, the internal thermal sense circuitry turns the power switch off, thus preventing the

power switch from damage. Hysteresis is built into the thermal sense circuit, and after the device has cooled

approximately 10°C, the switch turns back on. The switch continues to cycle in this manner until the load fault or

input power is removed. The OCx open-drain output is asserted (active low) when an overtemperature shutdown

or overcurrent occurs.

9.1.5 Undervoltage Lockout (UVLO)

An undervoltage lockout ensures that the power switch is in the off state at power up. Whenever the input

voltage falls below approximately 2 V, the power switch is quickly turned off. The UVLO facilitates the design of

hot-insertion systems where it is not possible to turn off the power switch before input power is removed. The

UVLO also keeps the switch from being turned on until the power supply has reached at least 2 V, even if the

switch is enabled. On reinsertion, the power switch is turned on, with a controlled rise time to reduce EMI and

voltage overshoots.

9.1.6 Universal Serial Bus (USB) Applications

The universal serial bus (USB) interface is a 12-Mb/s, or 1.5-Mb/s, multiplexed serial bus designed for low-to-

medium bandwidth PC peripherals (for example, keyboards, printers, scanners, and mice). The four-wire USB

interface is conceived for dynamic attach-detach (hot plug-unplug) of peripherals. Two lines are provided for

differential data, and two lines are provided for 5-V power distribution.

TPS2061, TPS2062, TPS2063

TPS2065, TPS2066, TPS2067

SLVS490K – DECEMBER 2003 – REVISED JUNE 2024

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