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DETAILED DESCRIPTION

OPERATION

PEAK CURRENT CONTROL

I

peak(typ) +

I

LIM )

V

IN

L

100 ns

I

peak(typ) +

400 mA )

V

IN

L

100 ns for the TPS61040

I

peak(typ) +

250 mA )

V

IN

L

100 ns for the TPS61041

(1)

TPS61040

TPS61041

SLVS413C – OCTOBER 2002 – REVISED AUGUST 2007

Table 1. Terminal Functions

TERMINAL

I/O

DESCRIPTION

NAME

DBV NO.

DRV NO.

This is the enable pin of the device. Pulling this pin to ground forces the device into shutdown

EN

4

3

I

mode reducing the supply current to less than 1

μA. This pin should not be left floating and needs

to be terminated.

This is the feedback pin of the device. Connect this pin to the external voltage divider to program

FB

3

4

I

the desired output voltage.

GND

2

1

–

Ground

NC

–

5

–

No connection

Connect the inductor and the Schottky diode to this pin. This is the switch pin and is connected to

SW

1

6

I

the drain of the internal power MOSFET.

5

2

I

Supply voltage pin

The TPS61040/41 operates with an input voltage range of 1.8 V to 6 V and can generate output voltages up to

28 V. The device operates in a pulse-frequency-modulation (PFM) scheme with constant peak current control.

This control scheme maintains high efficiency over the entire load current range, and with a switching frequency

up to 1 MHz, the device enables the use of very small external components.

The converter monitors the output voltage, and as soon as the feedback voltage falls below the reference voltage

of typically 1.233 V, the internal switch turns on and the current ramps up. The switch turns off as soon as the

inductor current reaches the internally set peak current of typically 400 mA (TPS61040) or 250 mA (TPS61041).

See the Peak Current Control section for more information. The second criteria that turns off the switch is the

maximum on-time of 6

μs (typical). This is just to limit the maximum on-time of the converter to cover for extreme

conditions. As the switch is turned off the external Schottky diode is forward biased delivering the current to the

output. The switch remains off for a minimum of 400 ns (typical), or until the feedback voltage drops below the

reference voltage again. Using this PFM peak current control scheme the converter operates in discontinuous

conduction mode (DCM) where the switching frequency depends on the output current, which results in very high

efficiency over the entire load current range. This regulation scheme is inherently stable, allowing a wider

selection range for the inductor and output capacitor.

(TPS61040) or 250 mA (TPS61042). Due to the internal propagation delay of typical 100 ns, theactualcurrent

exceeds the dc current limit threshold by a small amount. The typical peak current limit can be calculated:

The higher the input voltage and the lower the inductor value, the greater the peak.

By selecting the TPS61040 or TPS61041, it is possible to tailor the design to the specific application current limit

requirements. A lower current limit supports applications requiring lower output power and allows the use of an

inductor with a lower current rating and a smaller form factor. A lower current limit usually has a lower output

voltage ripple as well.

Copyright © 2002–2007, Texas Instruments Incorporated

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3

Product Folder Link(s): TPS61040 TPS61041