Datasheet

Analog Integrated Circuit Device Data
57 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 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
00 SW4x[4:0] See Table 45
01 SW4xHI[1:0] 2.5 V
10 SW4xHI[1:0] 3.15 V
11 Invalid Invalid
Driver
Controller
EA
Z1
Z2
Internal
Compensation
SWAIN
SW4ALX
SW4AFB
I
SENSE
C
OSW4A
C
INSW4A
L
SW4A
SPI
Interface
GNDSW4A
SW4
SW4AMODE
SW4AFAULT
V
REF
DAC
SPI
BP
Driver
Controller
EA
Z1
Z2
Internal
Compensation
SW4BIN
SW4BLX
SW4BFB
I
SENSE
C
OSW4B
C
INSW4B
L
SW4B
GNDSW4B
SW4BMODE
SW4BFAULT
V
REF
DAC
SPI
BP
SW4CFG
VCORE
D
SW4A
D
SW4B