DFE252012C datasheet(21/63 Pages) TI1

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9.4.4 Current Limit Operation

The TPS6128xD/E device features a valley inductor current limit scheme.

In dc/dc boost mode, the TPS6128xD/E device employs a current limit detection scheme in which the voltage

drop across the synchronous rectifier is sensed during the off-time. In the TPS61280D the current limit threshold

can be set via an I2C register. TPS6128xD/E devices have a fixed current limit threshold. See Section 6 for

detailed information.

The output voltage is reduced as the power stage of the device operates in a constant current mode. The

maximum continuous output current (IOUT(MAX)), before entering current limit (CL) operation, can be defined by

Equation 6.

O U T

I N

)

O U T ( M A X _ D C

L I M I T

(6)

where

• η is the efficiency

• The inductor peak-to-peak current ripple (ΔIL) is calculated by Equation 7

(7)

The output current, IOUT(DC), is the average of the rectifier ripple current waveform. When the load current is

increased such that the trough is above the current limit threshold, the off-time is increased to allow the current

to decrease to this threshold before the next on-time begins (so called frequency fold-back mechanism). When

the current limit is reached the output voltage decreases during further load increase.

Figure 9-5 illustrates the inductor and rectifier current waveforms during current limit operation.

ΔI

IVALLEY

IPEAK

Rectifier

Current

IOUT(DC)

Inductor

Current

Increased

Load Current

IIN(DC)

Current Limit

Threshold

IOUT

DIL

Figure 9-5. Inductor/Rectifier Currents in Current Limit Operation (DC/DC Boost Mode)

During pass-through mode, the TPS6128xD/E device is short-circuit protected by a very fast current limit

detection scheme. If the current in the bypass FET exceeds approximately 7.5Amps a fault is declared and the

device cycles through a start-up procedure.

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TPS61280D, TPS61281D, TPS61282D,, TPS61280E

SLVSEA0B – JANUARY 2018 – REVISED JUNE 2023

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DFE252012C Datasheet(PDF) 21 Page - Texas Instruments

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