MC34708 datasheet(57/159 Pages) FREESCALE

57 / 159 page

Analog Integrated Circuit Device Data



Freescale Semiconductor

MC34708

Functional Block Description

Figure 14. SW4 Dual Phase Output Mode Block Diagram

The peak current is sensed internally for over-current protection purposes. If an over-current condition is detected the regulator

will limit the current through cycle by cycle operation and alert the system through the SW4xFAULT SPI bit and issue an SCPI

interrupt via the INT pin.

SW4A/B has a high output range (2.5 V, 3.15 V) and a low output range (1.2 V – 1.85 V). The SW4A/B output range is set by the

PUMS configuration at start-up and cannot be changed dynamically by software. This means that If the PUMS are set to allow

SW4A to come up in the high output voltage range, the output can only be changed between 2.5 V or 3.15 V. It cannot be

programmed in the low output range. If software sets the SW4AHI[1:0] = 00 when the PUMS is set to come up in the high voltage

range, the output voltage will only go as low as the lowest setting in the high range, which is 2.5 V. If the PUMS are set to start-

up in the low output voltage range, the voltage is controlled through the SW4x[4:0] bits by software, it cannot be programmed

into the high voltage range. When changing the voltage in either the high or low voltage range, the regulator should be forced

into PWM mode to change the voltage.

Table 44. SW4A/B Output Voltage Select

SW4xHI[1:0]

Set point selected by

Output Voltage

SW4x[4:0]

See Table 45

SW4xHI[1:0]

2.5 V

SW4xHI[1:0]

3.15 V

Invalid

Driver

Controller

Internal

Compensation

SW4IN

SW4ALX

SW4AFB

ISENSE

COSW4A

CINSW4A

LSW4A

SPI

Interface

GNDSW4A

SW4

SW4AMODE

SW4AFAULT

VREF

DAC

SPI

Driver

Controller

Internal

Compensation

SW4BIN

SW4BLX

SW4BFB

ISENSE

COSW4B

CINSW4B

LSW4B

GNDSW4B

SW4BMODE

SW4BFAULT

VREF

DAC

SPI

SW4CFG

VCORE

DSW4A

DSW4B

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