34717 datasheet(18/25 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34717

TYPICAL APPLICATIONS

OPERATIONAL MODES

CONFIGURING THE OUTPUT VOLTAGE:

Both channels for the 34717 are general purpose DC-DC

converters. The resistor divider to the INV node is

responsible for setting the output voltage. The equation is:

For channel 1: VREF=VBG=0.7V.

For channel 2: The second channel of the 34717 has an

internal reference selector, thus VREF can be either the

voltage at VREFIN terminal or the internal reference voltage

VBG. The reference value is given by the following condition:

VREF=VREFIN if VREFIN is less than VBG=0.7V. Otherwise,

VREF=VBG. Usually the output regulation voltage is

calculated using the internal reference VBG, and the condition

VREF=VREFIN is used for tracking purposes.

SWITCHING FREQUENCY CONFIGURATION

The switching frequency will have a value of 1.0 MHz by

connecting the FREQ terminal to the GND. If the smallest

frequency value of 200 KHz is desired, then connect the

FREQ terminal to VDDI. To program the switching frequency

to another value, an external resistor divider must be

connected to the FREQ terminal to achieve the voltages

given by Table 5.

Table 5. Frequency Selection Table

SOFT START ADJUSTMENT

Table 6 shows the voltage that should be applied to the

ILIM1and ILIM2 pins to get the desired soft start timing.

Table 6. Soft Start Configurations

Figure 8. Resistor divider for Frequency and Soft Start

Adjustment

FREQUENCY

VOLTAGE APPLIED TO PIN FREQ

200

2.341 – 2.500

253

2.185 - 2.340

307

2.029 - 2.184

360

1.873 - 2.028

413

1.717 – 1.872

466

1.561 – 1.716

520

1.405 - 1.560

573

1.249 - 1.404

627

1.093 - 1.248

⎟

⎠

⎞

⎜

⎝

⎛

REF

OUT

680

0.936 - 1.092

733

0.781 - 0.936

787

0.625 - 0.780

840

0.469 - 0.624

893

0.313 - 0.468

947

0.157 - 0.312

1000

0.000 - 0.156

SOFT START [MS]

VOLTAGE APPLIED TO ILIM

3.2

1.19 - 1.49V

1.6

1.50 - 1.81V

0.8

1.82 - 2.13V

0.4

2.14 - 2.50V

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