34713 datasheet(10/21 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34713

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

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 MΩ.

POWER GOOD OUTPUT SIGNAL (PG)

This is an active low open drain output that is used to

report the status of the device to a host. This output activates

after a successful power up sequence and stays active as

long as the device is in normal operation and is not

experiencing any faults. This output activates after a 10 ms

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

supply voltage (e.g., VIN).

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

Figure 4. 34713 Block Diagram

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 converter

switching frequency. The switching frequency has a default

value of 1.0 MHz and can be programmed by connecting a

resistor divider to the FREQ pin, between VDDI and GND

pins (See Figure 1).

PROTECTION FUNCTIONS

This block contains the following circuits:

• Over Current Limit and Short Circuit Detection: This

block monitors the output of the buck converter for over

current conditions and short circuit events and alerts the

system control for further command.

• Thermal Limit Detection: This block monitors the

temperature of the device for overheating events. If the

temperature rises above the thermal shutdown

Internal Bias

System Control

Oscillator

Circuits

& Logic

Control &

Protection

Tracking &

Supervisory

Functions

Sequencing

Buck Converter

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