34713 datasheet(12/21 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34713

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Figure 5. Operation Modes Diagram

MODES OF OPERATION

The 34713 has two primary modes of operation:

Normal Mode

In normal mode, all functions and outputs are fully

operational. To be in this mode, the VIN needs to be within its

operating range, Shutdown input is high, and no faults are

present. This mode consumes the most amount of power.

Shutdown Mode

In this mode, activated by pulling the SD pin low, the chip

is in a shutdown state and the output is disabled and

discharged. In this mode, the 34713 consumes the least

amount of power since almost all of the internal blocks are

disabled.

START-UP SEQUENCE

When power is first applied, the 34713 checks the status

of the SD pin. If the device is in a shutdown mode, no block

will power up and the output will not attempt to ramp. Once

the SD pin is released to enable the device, the VDDI internal

supply voltage and the bias currents are established and the

internal VDDI POR signal is also released. The rest of the

internal blocks will be enabled and the buck converter

switching frequency and soft start values are determined by

reading the FREQ and ILIM pins respectively. A soft start

cycle is then initiated to ramp up the output of the buck

converter. The buck converter error amplifier uses the

voltage on the VREFIN pin as its reference voltage until

VREFIN is equal to 0.7 V, then the error amplifier defaults to

the internal 0.7 V reference voltage. This method helps

achieve multiple tracking configurations as will be explained

later in this document.

Soft start is used to prevent the output voltage from

overshooting during startup. At initial startup, the output

capacitor is at zero volts; VOUT = 0 V. Therefore, the voltage

across the inductor will be PVIN during the capacitor charge

phase which will create a very sharp di/dt ramp. Allowing the

inductor current to rise too high can result in a large

difference between the charging current and the actual load

current that can result in an undesired voltage spike once the

capacitor is fully charged. The soft start is active each time

the IC goes out of standby or shutdown mode, power is

recycled, or after a fault retry.

After a successful start-up cycle where the device is

enabled, no faults have occurred, and the output voltage has

reached its regulation point, the 34713 pulls the power good

output signal low after a 10 ms reset delay, to indicate to the

host that the device is in normal operation.

Shutdown

OUT = Discharge

REF = Discharge

3.0V < = V

IN < = 6.0V

Power Off

OUT = OFF

REF = OFF

IN < 3.0V

Normal

OUT= ON

REF = ON

Thermal

Shutdown

OUT = OFF

REF = OFF

Undervoltage

OUT= ON

REF = ON

Overvoltage

OUT = ON

REF = ON

Over Current

OUT = OFF

REF = ON

J > = 170°C

OUT < VUV

OUT > VOV

Short Circuit

OUT = OFF

REF = OFF

OUT > = ILIM

For > = 10ms

OUT > = ISHORT

OUT > VUV

OUT < VOV

J < = 145°C &

TIMEOUT Expired

SD = 0

PG = 1

SD = 1

PG = 1

PG = 0

PG = 1

Shutdown

OUT = Discharge

REF = Discharge

3.0V < = V

IN < = 6.0V

Power Off

OUT = OFF

REF = OFF

IN < 3.0V

Normal

OUT= ON

REF = ON

Thermal

Shutdown

OUT = OFF

REF = OFF

Undervoltage

OUT= ON

REF = ON

Overvoltage

OUT = ON

REF = ON

Over Current

OUT = OFF

REF = ON

J > = 170°C

OUT < VUV

OUT > VOV

Short Circuit

OUT = OFF

REF = OFF

OUT > = ILIM

For > = 10ms

OUT > = ISHORT

OUT > VUV

OUT < VOV

J < = 145°C &

TIMEOUT Expired

SD = 0

PG = 1

SD = 1

PG = 1

PG = 0

PG = 1

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