TS2026

5-7

2005/11 rev. A

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

flow from OUT to IN, since the switch is bidirectional when enabled. The output MOSFET and driver circuitry are also

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

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

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.

2

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:

Where:

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

Fault Flag

The FLG signal is an N-channel open-drain MOSFET output. FLG is asserted (active-low) when either an over current

or thermal shutdown condition occurs. In the case of and over current condition, FLG will be asserted only after the flag

erroneous error reporting is eliminated. For example, false over current condition can occur during hot plug event when

a highly capacitive load is connected and causes a high transient inrush current that exceeds the current-limit threshold

Undervoltage Lockout

Undervolrage lockout (UVLO) prevents the output MOSFET from turning on until VIN exceeds approximately 2.5V.

Undervoltage detection function only when the switch is enabled.