TPS61301 datasheet(39/77 Pages) TI

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IIN (DC)

Inductor

Current

Rectifier

Current

DIL

ΔI

DIL

CurrentLimit

Threshold

IVALLEY = ILIM

IIN (DC)

Increased

LoadCurrent

IOUT (CL)

DIL

IPEAK

(=I

)

OUT(DC)

LED

OUT

OUT(CL)

VALLEY

OUT

= (1

I ) with I =

and D

TPS61300

TPS61301

TPS61305, TPS61305A

www.ti.com

SLVS957D – JUNE 2009 – REVISED OCTOBER 2012

CURRENT LIMIT OPERATION

The current limit circuit employs a valley current sensing scheme. Current limit detection occurs during the off

time through sensing of the voltage drop across the synchronous rectifier. The detection threshold is user

selectable via the ILIM bit. The ILIM bit can only be set before the device enters operation (i.e., initial shutdown

state).

Figure 66 illustrates the inductor and rectifier current waveforms during current limit operation. The output

current, IOUT, is the average of the rectifier ripple current waveform. When the load current is increased such

that the lower peak is above the current limit threshold, the off time is lengthened to allow the current to decrease

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

Both the output voltage and the switching frequency are reduced as the power stage of the device operates in a

constant current mode. The maximum continuous output current (IOUT(CL)), before entering current limit operation,

can be defined as:

(1)

The TPS6130x device also provides a negative current limit (c.a. 300mA) to prevent an excessive reverse

inductor current when the power stage sinks current from the output (i.e., storage capacitor) in the forced

continuous conduction mode.

Figure 66. Inductor/Rectifier Currents in Current Limit Operation

To minimize the requirements on the energy storage capacitor present at the output of the driver (HC_SEL = 1),

the TPS6130x device can contribute to a larger extent in supporting directly the high-current LED flash strobe. In

fact, the device can dynamically adjust it’s current limit setting according to the Tx-MASK input.

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TPS61301 Datasheet(PDF) 39 Page - Texas Instruments

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