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Analog Integrated Circuit Device Data
Freescale Semiconductor
23
34701
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
Figure 18. Standard Power-up / Down Sequence
in +5.0V Supply System
STANDARD POWER SEQUENCING
When the power supply IC operates in the Standard Power
Sequencing Mode, the switcher output provides the core
voltage for the microprocessor. This situation and operating
conditions are illustrated in
Figures 17
and
18
.
Table 5
,
page
17
, shows the Power Sequencing Mode selection.
INVERTED POWER SEQUENCING
When the power supply IC is operating in the Inverted
Power Sequencing Mode, the linear regulator (LDO) output
provides the core voltage for the microprocessor, as
illustrated in
Figure 19
.
Table 5
shows the Power
Sequencing Mode selection.
Figure 19. Inverted Power-up Down Sequence in +5.0V
Supply System
ASSUMED REQUIREMENTS
1. I/O supply voltage not to exceed core voltage by more
than 2.0V.
2. Core supply voltage not to exceed I/O voltage by more
than 0.4V.
Methods of Control
The 34701 has several methods of monitoring and
controlling the regulator output voltages, as described in the
paragraphs below. Power sequencing control is also
achieved through the intrinsic operation of the regulators.
The EN1 and EN2 pins can be used to select the proper
Power Sequencing Mode required by the powered system or
to disable the power sequencing (refer to
Table 5
).
Intrinsic Operation
For both the LDO and switcher, whenever the output
voltage is below the regulation point, the LDO external Pass
MOSFET is on, or the buck high side MOSFET is on at a duty
cycle controlled by the switcher. Because these devices are
MOSFETs, current can flow in either direction, balancing the
voltages via the common supply pin. The ability to maintain
the MOSFETs on is dependent on the available gate voltage,
and thus the size of the boost regulator storage capacitor.
V = 2.1 V
Max. Lead
V = 0.4 V
Max. Lag
V = 0.4 V
Max. Lag
1.8V Start-Up
3.3 V I/O Voltage (VLDO)
1.5 V Core Voltage
(VOUT)
5.0 V Input Supply
V = 2.1 V
Max. Lead
RT
VBD
VBST
VDDH (I/Os)
VDDL (Core)
MCU
34701
5.0 V Input
VIN2
CLKSEL
FREQ
GND
SDA
SCL
ADDR
VIN1
LDRV
CS
LDO
LFB
RST
SW
PGND
INV
BOOT
VOUT
CLKSYN
Optional
EN1
EN2
VBST
VDDI
3.3 V
1.5 V
5.0 V
V = 2.1 V
Max. Lead
V = 0.4 V
Max. Lag
V = 0.4 V
Max. Lag
1.8V Start-Up
3.3 V I/O Voltage (VOUT)
1.5 V Core Voltage(VLDO)
5.0 V Input Supply
V = 2.1 V
Max. Lead
RT
VBD
VBST
VDDH (I/Os)
VDDL (Core)
MCU
34701
5.0 V Input
VIN2
CLKSEL
FREQ
GND
SDA
SCL
ADDR
VIN1
LDRV
CS
LDO
LFB
RST
SW
PGND
INV
BOOT
VOUT
CLKSYN
Optional
EN1
EN2
VBST
VDDI
3.3 V
1.5 V
5.0 V