LND3526 查看數據表（PDF） - Linear Dimensions Semiconductor

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LND3526

DUAL USB POWER CONTROL SWITCH

Linear Dimensions Semiconductor 

FUNCTIONAL DESCRIPTION

Input and Output

IN is power supply connection to the logic

circuitry and the drain of the output MOSFET. In

a typical circuit, current flows from IN to OUT

toward the load. If Vout is greater that VIN ,

current will flow form out to in, since the switch is

bi-directional when enabled. The output

MOSFET and driver circuitry are also designed

to allow the MOSFET source to be externally

forced to a higher voltage than the drain (Vout

>Vin) when the switch is disabled. In this

situation, the LND3526 prevents undesirable

current flow from OUT to IN.

Thermal Shutdown

Thermal shutdown is employed to protect the

device from damage should the die temperature

exceed safe margins due mainly to short circuit

faults. Each channel employs its own thermal

sensor. Thermal shutdown shuts off the output

MOSFET and asserts the FLG output if the die

temperature reaches 135°C. The other channel

is not effected.

The LND3526 will automatically reset its output

when the die temperature cools down to 125°C.

The LND3526 output and FLG signal will

continue to cycle on and off until the device is

disabled or the fault is removed.

Depending on PCB layout, package, ambient

temperature etc., it may take several hundred

milliseconds from the incidence of the fault to

the output MOSFET being shut off.

Current-limit response

The current-limit threshold is present internally.

The preset level prevents damage to the output

MOSFET and external load but allows a

minimum current of 0.5A through the output

MOSFET of each channel. The current-limit

circuit senses a portion of the output FET switch

current. The reaction to an overcurrent

condition varies with three scenarios:

LND 3526

(i) Switch Enabled into Short Circuit

If a switch is powered on or enabled into a heavy

load of short circuit, the switch immediately goes

into constant-current mode, reducing the output

voltage. The fault flag goes low until the load is

reduced.

(ii) 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.

(iii) Current-Limit Response

The LND3526 current-limit profile exhibits a small

foldback effect of approximately 500mA. Once

this current-limit threshold 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 mote that the device will deliver load

current up to the current-limit threshold, which is

typically 1.6A

Fault Flag

FLG is an N-channel, open-drain MOSFET output.

The fault-flag is active (low) for one or more of the

following conditions: undervoltage (while

2V<Vin<2.7), current limit, or thermal shutdown.

Undervoltage Lockout

UVLO (undervoltage lockout) prevents the output

MOSFET from turning on until VIN exceeds

approximately 2.5V. In the undervoltage state,

the FLAG will be low. After the switch turns on, if

the voltage drops below approximately 2.3V,

UVLO shuts off the output MOSFET and signals

fault flag. Undervoltage detection functions only

when at least one switch is enabled.

• Linear Dimensions, Inc. • 445 East Ohio Street, Chicago IL 60611 USA • tel 312.321.1810 • fax 312.321.1830 • www.lineardimensions.com •

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