WT6621
Dual USB Power Control Switch
GENERAL DESCRIPTION
The WT6621 is a dual integrated power switch optimized for self-powered and bus-powered
Universal Serial Bus (USB) applications. Few external components are necessary to satisfy
USB requirements. With independent enable and error flag functions, the WT6621 can ease
control the supplied power conditions of USB down stream; each switch channel can supplies
up to 500mA to downstream devices; the switch low on-resistance meets USB voltage drop
requirements; fault current is limited to typically 750mA, and a flag output is available to
indicate fault conditions to the local USB controller. Additional features include thermal
shutdown to prevent switch failure from high-current loads, undervoltage lockout (UVLO) to
ensure there is a valid input voltage present, and 3.3V and 5V logic compatible enable inputs.
FEATURES
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Compliant to USB specifications
Max. Continuous load current: 500mA
140mΩ maximum on-resistance per channel.
110uA typical on-state supply current
1uA typical off-state supply current
Enable input is compatible with both 3V and 5V Logic
Logic Over current output
Undervoltage lockout
Short Circuit Protection
Thermal Shutdown
Active-high or active-low enable versions
12KV output, 6KV input ESD protection.
Packages: 8pin SOIC and 8pin DIP
Applications
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USB host and Self-power hubs
USB bus-powered hub
General purpose power switch applications
Version1.0
Weltrend
Semiconductor, Inc. All Rights Reserved
27 March, 2000
WT6621
Dual USB Power Control Switch
PIN ASSIGNMENT
WT6621
/EN1
1
8
OUT1
/FG1
2
7
IN
/FG2
3
6
GND
/EN2
4
5
OUT2
PIN DESCRIPTIONS
Pin Number
1
Pin Name
/EN1
I/O
I
Function Descriptions
Enable input: Logic Compatible input to turns the
power switch on. (-NX Active Low, -PX active
High)
Fault Flag: Logic output, open drain output. /FG1
is asserted active low to indicate Overcurrent,
UVLO, and Thermal Shutdown.
Fault Flag: Logic output, open drain output. /FG2
is asserted active low to indicate Overcurrent,
UVLO, and Thermal Shutdown.
Enable input: Logic Compatible input to turns the
power switch on. (-NX Active Low, -PX active
High)
Power Switch output
Ground
Supply Input
Power Switch output
2
/FG1
O
3
/FG2
O
4
/EN2
I
5
6
7
8
OUT2
GND
IN
OUT1
O
I
O
Package and Ordering Information
Part Number
WT6621-SL
WT6621-DL
WT6621-SH
WT6621-DH
Enable (/EN)
Active Low
Active Low
Active High
Active High
Package
8-pin SOIC
8-pin DIP
8-pin SOIC
8-pin DIP
Version1.0
Weltrend
Semiconductor, Inc. All Rights Reserved
27 March, 2000
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
Weltrend
Semiconductor, Inc. All Rights Reserved
27 March, 2000
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