WT6621 데이터 시트보기 (PDF) - Weltrend Semiconductor

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WT6621

Dual USB Power Control Switch

Weltrend Semiconductor 

WT6621

Dual USB Power Control Switch

FUNCTIONAL DESCRIPTION

The WT6621 is a dual power switches with active low (or active high) enable inputs. Fault

conditions; such as Overcurrent, UVLO, and Thermal Shutdown; turns off or inhibit turn on the

output power switch, and activate the open drain transistor to sink current and asserts an error

flag.

Power Switch

The Power Switch is a CMOS power switch with a maximum on-state resistance of

140mΩ(Vi(IN)=5V , IN (input) is the power supply connection to the drain of the switch and OUT

(output) is the source of the switch to be connected to the load.

Charge Pump

The charge pump supplies power to the gate control circuit and provides the necessary voltage

to the gate of the CMOS power switch.

Thermal Shutdown

Thermal Shutdown circuit shuts off the output of the power switch and the fault flag(/FG) is

asserted when the die temperature rise to approximately 135°C. Approximate 30°C of

Hysteresis prevents the switch from turning on until the die temperature drops to approximately

115°C.

Current Limit Induced Thermal Shutdown

Internal circuitry increases the output of the CMOS Power Switch on-resis-tance until the series

combination of the CMOS Power Switch on-resis-tance and the load impedance limit current to

typically 750mA. The increase in power dissipation, in most cases, will cause the WT6621 to

go into thermal shutdown, disabling affected channels. When this is undesirable, thermal

shutdown can be avoided by externally responding to the fault and disabling the current limited

channel before the shutdown temperature is reached. The delay between the flag indication of

a current limit fault and thermal shutdown will vary with ambient tem-perature, board layout,

and load impedance, but is typically several hundred milliseconds. The USB controller must

there-fore recognize a fault and disable the appropriate channel within this time.

Undervoltage Lockout

UVLO(Undervoltage lockout) circuit prevents the output of power switch from turning on until

input voltage (IN) exceeds 2.5V typical. After the switch turns on, UVLO shuts off the output of

power switch and the fault flag(/FG) is asserted if the input voltage drops below 2.3V.

Current Sensing and Limiting

As an overload or short circuit is encountered, the current sense circuit sends a signal to the

gate control. Then gate control circuit in turn reduces the gate voltage and drives the power

switch into a constant current mode.

Switch Enabled into Short Circuit: If a switch is powered on or enabled into a heavy load or

short-circuit, the switch immediately goes into a constant-current mode, reducing the output

voltage. The fault flag goes low until the load is reduced.

Short Circuit Applied to Output: When a heavy load is applied, a large transient current may

flow until the current limit circuitry will respond. Once this occurs, the device limits current to

less than the short-circuit current limit specification.

Current-Limit Response: TheWT6621 current-limit profile exhibits a small foldback effect of

approximately 500mA. Once this current-limit thresh-old is exceeded the device enters

constant-current mode. This constant current is specified as the short circuit current limit in the

Electrical Characteristics table. It is important to note that the WT6621will deliver load current

up to the current-limit threshold which is typically 0.75A.

Version1.0

27 March, 2000

Weltrend Semiconductor, Inc. All Rights Reserved



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