UCS3205 datasheet(15/30 Pages) MICROCHIP

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DS20006433A-page 15

UCS3205

4.2

Overcurrent Detection

An OC (Overcurrent) signal is sent to the digital logic

when the voltage on the ISEN pin exceeds

VSEN = 0.512V. The value of the resistor that must be

connected to the ISEN pin to set the current limit

threshold can be calculated with the following equation:

EQUATION 4-1:

OVERCURRENT

THRESHOLD

For ILIM_MAX = 5.5A (to allow 5A continuous current),

the result is RILIM_MAX =470.

For ILIM_MIN = 0.55A (to allow 0.5A continuous current),

the result is RILIM_MIN =4.7 k.

4.3

Short-Circuit Detection

A SC (Short Circuit) signal is sent to the digital logic

when the voltage on the ISEN pin exceeds

VSEN = 0.820V. This corresponds to a current level that

is 160% of ILIM_MAX.

The short-circuit current limit threshold can be calculated

with the following equation:

EQUATION 4-2:

SHORT-CIRCUIT

THRESHOLD

Thus, for ILIM_MAX = 5.5A (RILIM_MAX = 470), the SC

signal will be sent if the current exceeds 8.8A. For

ILIM_MIN = 0.55A (RILIM_MIN = 4.7 k), the SC signal will

be sent if the current exceeds 0.88A.

4.4

VIN Overvoltage Detection

An OV (Overvoltage) signal is sent to the digital logic

when the voltage on the VOV pin is higher than

VREF = 1.25V. The overvoltage threshold can be con-

figured by selecting the resistor values of the voltage

divider connected to VIN.

4.5

LATCH and DSC Functionality

The LATCH pin controls the retry function. If the LATCH

pin is high at the time when a Fault is detected, the

digital logic remains in a Fault state until the EN pin is

toggled low-to-high and the Fault recovery procedure

begins. If the LATCH pin is low, the device enters into

Auto-Retry mode by running the Fault recovery proce-

dure every tRETRY, until no Fault condition is detected

or until the EN pin is pulled low.

If the DSC pin is high and the switch is off, the

UCS3205 discharges the output for the duration of

tDISCHARGE unless the DSC pin is pulled low (the DSC

pin overrides the discharge timer).

4.6

Fault and Enable Functionality for

Combined Mode

Combined mode is implemented on HUBs that have a

limited amount of pins in multiple port applications. To

alleviate this, both the FAULT and EN pins of the

UCS3205 are connected to PRTCTL of the HUB, which

is internally pulled up.

The HUB must have enough time to Acknowledge a

Fault. The UCS3205 will keep Fault asserted low for

the duration of tFAULT_ACK while EN is low (switched

off).

4.7

Back-Voltage Detection

Back-voltage detection is only valid when the power

switch is on (EN = 1). When the power switch is on

(EN = 1) and the DIR pin is a logic ‘0’, a BV (Back-

Voltage) signal is sent to the digital logic when the output

voltage (on the VOUT pin) is higher than the input

voltage (on the VIN pin) by more than VBV_FAULT_ON.

When the DIR pin is a logic ‘1’, back-voltage detection

is disabled, so the current through the switch is allowed

to flow in either direction; from VIN to VOUT (forward

direction) or from VOUT to VIN (reverse direction). The

FRS pin of the UCS3205 must be grounded for appli-

cations where this functionality is needed. Please note,

the UCS3205 does not monitor or limit the current in

the reverse direction.

4.8

Thermal Shutdown

The thermal shutdown circuitry sends the Thermal

Shutdown (TSD) signal to the digital logic when the die

temperature exceeds TTSD. It has a hysteresis of

TTSD_HYST.

RILIM

VSEN

ILIM

5000

------------

0.512 5000



ILIM

-------------------------------

ISC

VSEN 5000



RILIM

-------------------------------

0.820 5000



RILIM

-------------------------------

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