FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
The 34704 is an multi-channel power management IC
(PMIC) meant to address power management needs for
various multimedia applications microprocessors in various
configurations with a target overall efficiency of > 80% at
typical loads.
The 34704 accepts an input voltage from various sources:
•1 cell Li-Ion/Polymer (2.7 to 4.2 V)
•5.0 V USB supply or AC wall adapter
The different channels are:
REGULATOR
REG1(25)
REG2
REGULATOR TYPE
Synchronous Boost
Synchronous Buck-Boost
Synchronous Buck
VOUT TYP (V)
5.0
IOUT TYP (MA) IOUT MAX (MA)
TARGET APPLICATION
+5.0 V REF
µP I/O
100
200
150
100
150
20
500
500
550
300
500
60
2.8 / 3.3
1.2 / 1.5 / 1.8
1.8 / 2.5
3.3
REG3
µP Core
REG4
Synchronous Buck-Boost
Synchronous Buck-Boost
Synchronous Boost
Inverter Boost
DDR
REG5
µP I/O
REG6(25)
REG7(25)
REG8
15.0
REF+
-7.0
20
60
REF -
Synchronous Boost
15.0
15
30
Backlight Display
Notes
24. Synchronous Buck-Boost: These regulators can work as pure BUCK regulator when the output voltage is lower than the input voltage;
and work as pure BOOST regulator when the input voltage is lower than the output voltage. Compensation should be done for the worst
case scenario, which is in most of the cases when the device is working as a boost converter, after compensating for this scenario it is
recommended to verify the buck operation to assure stability in the whole operating range.
25. Available only on the 34704A
REG1, REG3, REG6, and REG8 use internal
compensation, while REG2, REG4, REG5, and REG7 use
external compensation.
regulators except REG6, 7, and 8, to spread out the current
draw by the individual converters from the input supply over
time, to reduce the peak input current demand. This allows
for better EMI performance and reduction in the input filter
requirements.
The switching frequency of all regulators except REG6, 7,
& 8 can be selected through the FREQ pin between 750 kHz
and 2.0 MHz in 250 kHz steps. The high frequency operation
is meant to minimize the size of external components while
lower operating frequencies will allow for higher efficiency.
REG7 is limited to operate at a lower frequency to minimize
switching noise induced by driving the external switching
MOSFET, but also can operate at the 1.0 MHz value with
proper board layout. REG 6, 7, and 8 switching frequency can
be selected between 250 kHz and 1.0 MHz in 250 kHz steps
through I2C.
Each regulator except REG1 uses an external feedback
resistor divider to set the output voltage. All output voltages
can be adjusted dynamically (Dynamic Voltage Scaling) on
the fly through an I²C serial interface. All converters, except
REG1, utilize automatic soft-start by ramping the reference
voltage to the error amplifier to prevent sudden change in
duty cycle and output current/voltage at power up. REG1
(VG) will limit the inrush current by implementing a peak
current detect and a constant off time.
For all regulators and at lower loads, a pulse skipping
mode is implemented to maintain high efficiency.
The 34704 is equipped with a dual function Power On/Off
pin (ONOFF). This pin can be controlled by a mechanical
switch to turn the device on or off. Pressing and releasing the
mechanical switch turns the 34704 on while pressing and
holding the switch for a time period (programmable through
I2C) turns the 34704 off. Enable/disable control is also
granted through I2C for groups of regulators and the whole
IC.
Note that pulse skipping occurs when the regulator enters
into discontinuous conduction mode (DCM) at very light
loads, however transitions between DCM and CCM may
result in noisy switching nodes, therefore it is recommended
to design the regulators to work in CCM all the time. Pulse
skipping function is not guaranteed by circuit implementation.
The 34704 uses 4 different phases of switching for all
34704
Analog Integrated Circuit Device Data
Freescale Semiconductor
16
FREESCALE [ Freescale ]
