34717 datasheet(12/25 Pages) FREESCALE

12 / 25 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34717

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

delay and must be pulled up by an external resistor to a

supply voltage like VIN.

SHUTDOWN INPUT (SD)

If this pin is tied to the GND pin, the device will be in

Shutdown Mode. If left unconnected or tied to the VIN pin, the

device will be in Normal Mode. The pin has an internal pull up

of 1.5 M

Ω.

REFERENCE VOLTAGE INPUT (VREFIN)

The output of channel two will track the voltage applied at

this pin.

FREQUENCY ADJUSTMENT INPUT (FREQ)

The buck converters switching frequency can be adjusted

by connecting this pin to an external resistor divider between

VDDI and GND pins. The default switching frequency (FREQ

pin connected to ground, GND) is set at 1.0 MHz.

SOFT START ADJUSTMENT INPUT (ILIM1, ILIM2)

Soft Start can be adjusted by applying a voltage between

1.25V and VDDI on each ILIM pin.

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

Figure 4. Block Illustration

INTERNAL BIAS CIRCUITS

This block contains all circuits that provide the necessary

supply voltages and bias currents for the internal circuitry. It

consists of:

• Internal Voltage Supply Regulator: This regulator

supplies the VDDI voltage that is used to drive the digital/

analog internal circuits. It is equipped with a Power-On-

Reset (POR) circuit that watches for the right regulation

levels. External filtering is needed on the VDDI pin. This

block will turn off during the shutdown mode.

• Internal Bandgap Reference Voltage: This supplies the

reference voltage to some of the internal circuitry.

• Bias Circuit: This block generates the bias currents

necessary to run all of the blocks in the IC.

SYSTEM CONTROL AND LOGIC

This block is the brain of the IC where the device

processes data and reacts to it. Based on the status of the SD

pin, the system control reacts accordingly and orders the

device into the right status. It also takes inputs from all of the

monitoring/protection circuits and initiates power up or power

down commands. It communicates with the buck converter to

manage the switching operation and protects it against any

faults.

OSCILLATOR

This block generates the clock cycles necessary to run the

IC digital blocks. It also generates the buck converters

switching frequency. The switching frequency can be

programmed by connecting a resistor divider to the FREQ

pin, between VDDI and GND pins (See Figure 1).

Internal Bias

System Control

Oscillator

Circuits

& Logic

Control &

Protection

Tracking &

Supervisory

Functions

Sequencing

2 x Buck Converter

34717 датащи(PDF) 12 Page - Freescale Semiconductor, Inc

34717 датащи(HTML) 12 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

датащи скачать

ссылки URL