UCS81003 datasheet(34/108 Pages) MICROCHIP

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UCS81003

DS20005334A-page 34

 2014 Microchip Technology Inc.

7.2

Thermal Management and Voltage

Protection

7.2.1

THERMAL MANAGEMENT

The UCS81003 utilizes two-stage internal thermal

management. The first is named Dynamic Thermal

Management and the second is a Fixed Thermal

Shutdown.

7.2.1.1

Dynamic Thermal Management

For the first stage (active in both current limiting

modes), referred to as Dynamic Thermal Management,

the UCS81003 automatically adjusts port power switch

limits and modes to lower power dissipation when the

thermal regulation temperature value is approached,

as described below.

If the internal temperature exceeds the TREG value, the

port power switch is opened, the current limit (ILIM) will

be lowered by one step and a timer is started

(tDC_TEMP). When this timer expires, the port power

switch is closed and the internal temperature will be

checked again. If it remains above the TREG threshold,

the UCS81003 will repeat this cycle (open port power

switch and reduce the ILIM setting by one step) until ILIM

reaches its minimum value.

If the UCS81003 is operating using Constant Current

Limiting (variable slope) and the ILIM setting has been

reduced to its minimum set point and the temperature

is still above TREG, the UCS81003 will switch to

operating using Trip Current Limiting. This will be done

by reducing the IBUS_R2MIN setting to 120 mA and

restoring the ILIM setting to the value immediately

below the programmed setting (e.g., if the programmed

ILIM is 2.05A, the value will be set to 1.68A). If the

temperature continues to remain above TREG, the

UCS81003 will continue this cycle (open the port power

switch and reduce the ILIM setting by one step).

If the UCS81003 internal temperature drops below

TREG –TREG_HYST, the UCS81003 will take action

based on the following:

If the Current Limit mode changed from CC

mode to Trip mode, then a timer is started. When

this timer expires, the UCS81003 will reset the

port power switch operation to its original

configuration, allowing it to operate using

Constant Current Limiting (variable slope).

If the Current Limit mode did not change from CC

mode to Trip mode, or was already operating in

Trip mode, the UCS81003 will reset the port power

switch operation to its original configuration.

If the UCS81003 is operating using Trip Current

Limiting and the ILIM setting has been reduced to its

minimum set point and the temperature is above TREG,

the port power switch will be closed and the current

limit will be held at its minimum setting until the

temperature drops below TREG –TREG_HYST.

7.2.1.2

Thermal Shutdown

The second-stage thermal management consists of a

hardware

implemented

thermal

shutdown

corresponding to the maximum allowable internal die

temperature

(TTSD). If the internal temperature

exceeds this value, the port power switch will

immediately be turned off until the temperature is below

TTSD –TTSD_HYST.

7.3

VBUS Discharge

The UCS81003 will discharge VBUS through an internal

100

 resistor when at least one of the following

conditions occurs:

• The PWR_EN control is disabled (triggered on the

inactive edge of the PWR_EN control).

• A portable device Removal Detection event is

flagged.

•The VS voltage drops below a specified

threshold (VS_UVLO) that causes the port power

switch to be disabled.

• When commanded into the Sleep power state via

the EM_EN, M1 and M2 controls.

• Before each charger emulation profile is applied.

• Upon recovery from the Error state.

• When commanded via the SMBus (see

Section 10.4 “Configuration Registers”) in the

Active state.

• Any time that the port power switch is activated

after the VBUS bypass switch has been on (i.e.,

whenever VBUS voltage transitions from being

driven from VDD to being driven from VS, such as

going from Detect to Active power state).

• Any time that the VBUS bypass switch is activated

after the port power switch has been on (i.e.,

going from Active to Detect power state).

Note 1: If the temperature exceeds the TREG

threshold while operating in the DCE

Cycle mode after a charger emulation pro-

file has been accepted, the profile will be

removed. The UCS81003 will not restart

the DCE Cycle until one of the control

inputs changes states to restart emulation.

2: The

UCS81003

will

not

actively

discharge VBUS as a result of the

temperature exceeding TREG; however,

any load current provided by a portable

device or other load will cause VBUS to be

discharged when the port power switch is

opened, possibly resulting in an attached

portable device resetting.

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