R2

V

OUT1

R1

TPS82150

V

OUT2

R4

R3

SS/TR

FB

9

TPS82150

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SLVSDN4 – JUNE 2017

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Feature Description (continued)

7.3.3 Switch Current Limit

The switch current limit prevents the device from high inductor current and from drawing excessive current from

the battery or input voltage rail. Excessive current might occur with a heavy load/shorted output circuit condition.

If the inductor peak current reaches the switch current limit after a propagation delay of typically 30ns, the high-

side FET is turned off and the low-side FET is turned on to ramp down the inductor current.

7.3.4 Undervoltage Lockout

To avoid mis-operation of the device at low input voltages, an under voltage lockout is implemented, which shuts

7.3.5 Thermal Shutdown

the device temperature falls below the threshold by 20°C, the device returns to normal operation automatically.

7.4 Device Functional Modes

7.4.1 Enable and Disable (EN)

The device is enabled by setting the EN pin to a logic High. Accordingly, the shutdown mode is forced if the EN

pin is pulled Low with a shutdown current of typically 1.5 μA.

An internal pull-down resistor of 400kΩ is connected to the EN pin when the EN pin is Low. The pull-down

resistor is disconnected when the EN pin is High.

7.4.2 Soft Startup (SS/TR)

The internal voltage clamp controls the output voltage slope during startup. This avoids excessive inrush current

and ensures a controlled output voltage rise time. When the EN pin is pulled high, the device starts switching

after a delay of typically 55μs and the output voltage rises with a slope controlled by an external capacitor

connected to the SS/TR pin. Using a very small capacitor or leaving the SS/TR pin floating provides fastest

startup time.

The TPS82150 is able to start into a pre-biased output capacitor. During the pre-biased startup, both the power

MOSFETs are not allowed to turn on until the internal voltage clamp sets an output voltage above the pre-bias

voltage.

When the device is in shutdown, undervoltage lockout or thermal shutdown, the capacitor connected to SS/TR

pin is discharged by an internal resistor. Returning from those states causes a new startup sequence.

7.4.3 Voltage Tracking (SS/TR)

The SS/TR pin is externally driven by another voltage source to achieve output voltage tracking. The application

circuit is shown in Figure 4.

Figure 4. Output Voltage Tracking