MC34704 FREESCALE [Freescale Semiconductor, Inc], MC34704 Datasheet - Page 37

• Manufacturer Part Number: MC34704
• Description: Multiple Channel DC-DC Power Management IC
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

• 1CVG : Use a 47uF capacitor from Ground to VG.
• D1 : Use a fast recovery schottky diode rated to 10V at 1A.
Regulator 2, 4 and 5 (Synchronous Buck-Boost regulator
with external compensation)
voltage mode control DC-DC regulator that can operate at
various output voltage levels. Since each of the regulators may
work as a buck or a boost depending on the operating voltages,
they need to be compensated in different ways for each
situation.
operating input voltage range is set from 2.7 - 4.2 V, then the
following scenarios are possible:
• NOTE: Since these 3 regulators can work as a buck or a
Compensating for Buck operation:
• L: A buck power stage can be designed to operate in CCM for
Analog Integrated Circuit Device Data
Freescale Semiconductor
These three regulators are 4-Switch synchronous buck-boost
Since the 34704 is meant to work using a LiIon battery, the
boost in a single application, a good practice to configure
these regulators is to compensate for a boost scenario and
then verify that the regulator is working in buck mode using
that same compensation.
load currents above a certain level usually 5 to 15% of full
load. The minimum value of inductor to maintain CCM can be
determined by using the following procedure:
ESR
desired
Regulator
------------------------------------------ -
⎛
⎝
--------------------- -
1 D
2
4
5
Io
–
max
VO
max
Vo
r
.
+
r
I
2.8 V
3.3 V
3.3 V
1.8 V
2.5 V
3.3 V
3.3 V
OB
Vo
⎞
⎠
Input voltage
3.0 - 4.2
2.7 - 3.0
3.5 - 4.2
2.7 - 4.2
2.7 - 4.2
2.7 - 3.0
3.5 - 4.2
range
[ ]
Operation
Boost
Boost
Buck
Buck
Buck
Buck
Buck
• C
during the current rising time and is define as:
indistinctly, the first one indicates the output voltage ripple, while
the second one is the maximum output voltage overshoot
(transient response).
• R1 and RB: These two resistors help to set the output voltage
• Compensation network. (C1,C2,C3, R2, R3): For
L
min
1. Define I
1. First calculate the dt_I (inductor current rising time) given
2. Then the output capacitor can be chosen as follow:
3. Finally find the maximum allowed ESR to allow the
C
ESR
dtI
to its impedance and output voltage ripple are the ESR, the
ESL and the capacitance C. A good approach to calculate the
minimum real capacitance needed is to include the transient
response analysis to control the maximum overshoot as
desired.
Where the parameter
• Where
NOTE: Do not use the parameters
to the desire value using a Vref=0.6V, select R1 between 10k
and 100K and then calculate RB as follows:
compensating a buck converter, 3 important frequencies
referring to the plant are:
RB
OUT
Iostep
OUT
15% of full load.
by:
overshoot expressed as a percentage of the output
voltage, typically from 3 to 5% of Vo.
desired transient response:
=
max
-------------------------------------------------------------------------------------------------------- -
Vo
: The three elements of output capacitor that contribute
=
------------------- -
Io
Io
--------------------- -
Iostep
-------------------- -
----------- - 1
Vref
=
max
=
Vo
+
Vo
max
OB
R1
Io
⎛
⎝
------------------------------------- -
VO
Vo 1 D
T
D
------------ -
max
Vo
Fsw
max
dtI
–
as the minimum current to maintain CCM as
max
max
r
⎞ Vin
⎠
Fsw L
R
–
⎛
⎝
DSONLSFET
is the maximum allowed transient
------------------------------ -
FUNCTIONAL DEVICE OPERATION
min
2I
min
Io_step is the maximum current step
OB
L
COMPONENT CALCULATION
–
Vo
+
⎞
⎠
R
L
D
VO
min
r
and
T
[A]
[s]
D
VO
[ ]
[ ]
MAX
[A]
34704
max
37
T
[H]
----------- -
2I
Vo
OB