TS2026L Просмотр технического описания (PDF) - TSC Corporation

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TS2026L

Dual-Channel Power Distribution Switch

TSC Corporation 

Function Description

Input and Output

IN is the power supply connection to the logic circuitry and the drain of the output MOSFET. OUT is the source of

the output MOSFET. In a typical circuit, current flows from IN to OUT toward the load. If VOUT is greater than VIN,

current will flow from OUT to IN, since the switch is bidirectional 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 TS2026 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 140 oC and the overheated channel is in

current limit. The over channel will be shut off. Upon determining a thermal shutdown condition. The TS2026 will

automatically reset its output when the die temperature cools down to 120 oC . The TS2026 output and FLG signal

will continue to cycle on and off until the device is disabled or the fault is removed. Figure 1. Depicts typical timing.

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. This time will be shortest in the case of dead short on

the output.

Power Dissipation

The device’s junction temperature depends on several factors such as the load, PCB layout, ambient temperature

and package type. Equations that can be used to calculate power dissipation of each channel and junction

temperature are found below.

PD = RDS(ON) x IOUT2

Total power dissipation of the device will be the summation of PD for both channels. To relate this to junction

temperature, the following equation can be used:

TJ = PD x θJA + TA

Where:

TJ = junction temperature

TA = ambient temperature

θJA = is the thermal resistance of the package

Current Sensing and Limiting

The current-limit threshold is preset internally. The preset level prevents damage to the device and external load but

still allows a minimum current of 500mA to be delivered to the load. The current-limit circuit senses a portion of the

output MOSFET switch current. The current-sense resistor shown in the block diagram is virtual and has no voltage

drop. The reaction to an over current condition varies with three scenarios.

Switch Enable into Short-Circuit

If a switch is enabled into a heavy load or short-circuit, the switch immediately enters into a constant-current mode,

reducing the output voltage. The FLG signal is asserted indicating an over current condition.

Switch Enable Applied to Enabled Output

When a heavy load or short-circuit is applied to an enabled switch, a large transient current may flow until the

current limit circuitry responds. Once this occurs the device limits current to less than the short circuit current limit

specification.

Current-Limit Response-Ramped Load

The TS2026 current-limit profile exhibits a small fold back effect of about 200mA. Once this current-limit threshold is

exceeded the device switches into a constant current mode. It is important to note that the device will supply current

up to the current-limit threshold

TS2026L

5-7

2005/11 rev. A

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