(

)

1

He(s)

Se

s

1

(1 D) 0.5

2

S

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1

2

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0.32 V R

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16 (1 D) 6 pF

6 pF

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IN

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TPS55330

www.ti.com

SLVSBX8A – MAY 2013 – REVISED DECEMBER 2014

Feature Description (continued)

(3)

7.3.5 Soft-Start

The TPS55330 has a built-in soft-start circuit which significantly reduces the start-up current spike and output

voltage overshoot. When the IC is enabled, an internal bias current source (6 µA typical) charges a capacitor

the peak current and duty cycle of PWM controller. Limiting the peak switch current during start-up with a slow

ramp on the SS pin will reduce in-rush current and output voltage overshoot. Once the capacitor reaches 1.8V,

the soft-start cycle is completed and the soft-start voltage no longer clamps the error amplifier output. When the

EN is pulled low for at least 1ms, the IC enters the shutdown mode and the SS capacitor is discharged through a

5k

Ω resistor to prepare for the next soft-start sequence.

7.3.6 Slope Compensation

The TPS55330 has internal slope compensation to prevent subharmonic oscillations. The sensed current slope

of boost converter can be expressed as Equation 4:

(4)

The slope compensation dv/dt can be calculated using Equation 5.

(5)

In a converter with current mode control, in addition to the output voltage feedback loop, the inner current loop

including the inductor current sampling effect as well as the slope compensation on the small signal response

should be taken into account, which can be modeled as seen in Equation 6:

where

•

•

•

D is the duty cycle

(6)

NOTE

control, and Equation 6 is no longer valid.

7.3.7 Enable and Thermal Shutdown

The TPS55330 enters shutdown when the EN voltage is less than 0.68 V (min) for more than 1 ms. In shutdown,

the input supply current for the device is less than 10 µA (max). The EN pin has an internal 950k

Ω pull down

resistor to disable the device if the pin is floating.

An internal thermal shutdown turns off the device when the junction temperature exceeds 165°C (typical). The

device restarts when the junction temperature drops by 15°C.

Copyright © 2013–2014, Texas Instruments Incorporated

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