V

O(DO) +

V

ref

TPS61045

www.ti.com

SLVS440C – JANUARY 2003 – REVISED DECEMBER 2014

Feature Description (continued)

7.3.2 Softstart

If no special precautions are taken, all inductive step-up converters exhibit high inrush current during start up.

This can cause voltage drops at the input rail during start-up, which may result in an unwanted or premature

system shutdown.

When the device is enabled, the internal input switch (Q1) is slowly turned on to reduce the inrush current

charging the capacitor (C2) connected to pin L. Furthermore, the TPS61045 device limits this inrush current

the next 256 switch cycles.

7.3.3 Enable (CTRL Pin)

The CTRL pin serves two functions. One function is the enable and disable of the device. The other function is

the output voltage programming of the device. If the digital interface is not required, the CTRL pin is used as a

standard enable pin for the device.

Pulling the CTRL pin high enables the device beginning with the softstart cycle.

Pulling the CTRL pin to ground for a period of

≥560 μs shuts down the device, reducing the shutdown current to

0.1

μA (typical). During shutdown, the internal input switch (Q1) remains open and disconnects the load from the

input supply of the device.

The user must terminate this pin. For more details on how to use the interface function, see Digital Interface

(CTRL).

7.3.4 DAC Output (DO)

The TPS61045 device allows digital adjustment of the output voltage using the digital CTRL interface, as

described in Digital Interface (CTRL). The DAC output pin (DO) drives an external resistor (R3) connected to the

output voltage is set to 0 V, the external resistor (R3) is more or less in parallel with the lower feedback resistor

Internally, a 6-bit DAC is used with 64 steps and 0 as the first step. This gives a typical voltage step of 19.6 mV,

which is calculated as:

(3)

See Setting the Output Voltage for further information.

After start-up, when the CTRL pin is pulled high, the DO output voltage is set to its center voltage, which is the

7.3.5 Digital Interface (CTRL)

When the CTRL pin is pulled high, the device starts up with softstart and the DAC output voltage (DO) sets to its

center voltage with a typical output voltage of 607 mV.

The output voltage can be programmed by pulling the CTRL pin low for a certain period of time. Depending on

this time period, the internal DAC voltage increases or decreases one digital step, as outlined in Table 2 and

output voltage. If the DAC is programmed to its maximum output voltage equal to the internal reference voltage,

Table 2. Timing Table

DAC OUTPUT DO

TIME

LOGIC LEVEL

Increase one step

Low

Decrease one step

Low

Shutdown

Low

Delay between steps

High

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