MC34717(2007) 查看數據表（PDF） - Freescale Semiconductor

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MC34717
(Rev.:2007)

5.0 A 1.0 MHz Fully Integrated Dual Switch-Mode Power Supply

Freescale Semiconductor 

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

SD = 0

VIN < 3.0V

VOUT2 < = VUVF2

Shutdown

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VVOOUUTT22==DDiisscchhaarrggee

PG = 1

PG = 1

Power Off

VOUT1 = OFF

VOUT2 = OFF

PG = 1

VOUT1 < = VUVF1

VOUT2 > = VOVR2

VOUT2

Undervoltage

VOUT1 = ON

VOUT2 = ON

PG = 1

TJ > = 170˚C

VOUT2

Overvoltage

VOUT1 = ON

VOUT2 = ON

PG = 1

Channel 2

VOUT2 > = VUVR2

VOUT2 < = VOVF2

TJ < = 145˚C

tTIMEOUT Expired

Thermal Shutdown

VOUT1 = ON

VOUT2 = OFF

PG = 1

tTIMEOUT

Expired

Channel 2

IOUT2 > = ILIM2

For > = 10ms

Overcurrent

VOUT1 = ON

VOUT2 = OFF

PG = 1

tTIMEOUT = 1

SD = 1

3.0V < = VIN < = 6.0V

Normal

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VVOOUUTT11 = ON

VVOOUUT22 = ON

PPGG == 00

tTIMEOUT

Expired

VOUT2

Short Circuit

VOUT1 = ON

VOUT2 = OFF

PG = 1

tTIMEOUT = 1

tTIMEOUT

Expired

VOUT1

Short Circuit

VOUT1 = OFF

VOUT2 = ON

PG = 1

tTIMEOUT = 1

VOUT1

Undervoltage

VOUT1 = ON

VOUT2 = ON

PG = 1

VOUT1 > = VOVR1

VOUT1 > = VUVR1

VOUT1 < = VOVF1

VOUT1

Overvoltage

VOUT1 = ON

VOUT2 = ON

PG = 1

TJ < = 145˚C

tTIMEOUT Expired

Channel 1

TJ > = 170˚C

Thermal Shutdown

tTIMEOUT

Expired

VOUT1 = OFF

VOUT2 = ON

PG = 1

Channel 1

Overcurrent

VOUT1 = OFF

VOUT2 = ON

PG = 1

tTIMEOUT = 1

IOUT1 > = ILIM1

For > = 10ms

IOUT2 > = ISHORT2

IOUT1 > = ISHORT1

Figure 5. Operation Modes Diagram

MODES OF OPERATION

The 34717 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 34717 consumes the least

amount of power since almost all of the internal blocks are

disabled.

START-UP SEQUENCE

When power is first applied, the 34717 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 set to high, the VDDI internal supply voltage and

the bias currents will be established, so the internal VDDI POR

signal can be released. The rest of the internal blocks will be

enabled and the buck converter switching frequency and soft

start timing values are determined by reading the FREQ,

ILIM1, and ILIM2 pins. A soft start cycle is then initiated to

ramp up the output of the buck converter. The first channel

uses an internal 0.7 V reference for its error amplifier while

the second channel’s 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 allows the second output to

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

34717

14

Analog Integrated Circuit Device Data

Freescale Semiconductor

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