MC34704 FREESCALE [Freescale Semiconductor, Inc], MC34704 Datasheet - Page 41

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

string. It does not need external compensation network, thus
the only components that need to be calculated are:
• L : A boost power stage can be designed to operate in
stage is when the input voltage is equal to one half of the
output voltage, which results in the Maximum ÄI
• C
• R1 and RB (for Voltage feedback control): These two
• RS (For current feedback control with LED string):
•
Analog Integrated Circuit Device Data
Freescale Semiconductor
L
L
C
ESR
RB
CCM for 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:
• Define I
However the worst case condition for the boost power
contribute to its impedance and output voltage ripple are
the ESR, the ESL and the capacitance C. The minimum
capacitor value is approximately:
• Where
• Now calculate
resistors help to set the output voltage to the desire value
using a V
then calculate RB as follows:
This resistor is attached at the end of the LED string and it
controls the amount of current flowing through it. To
calculate this resistor, set the maximum current you want
to flow though the string and use the following formula:
RS
min
min
OUT
OUT
15% of full load:
reach the desired.
=
=
: The three elements of output capacitor that
Vo D 1 D
----------------------------------------- -
-------------------- -
----------- - 1
Vref
Vo T
--------------- -
------------------------------------------ -
⎛
⎝
V
--------- -
16I
Vo
Io
--------------------------- -
--------------------- -
1 D
Io
ref
Fsw Vo
Io
R1
REF
–
max
OB
OB
max
VO
–
2I
max
=0.6V, select R1 between 10k and 100K and
D
as the minimum current to maintain CCM as
Vo
OB
max
r
–
is the desired output voltage ripple.
r
+
r
I
VO
OB
2
T
⎞
⎠
r
the maximum allowed ESR to
[H]
L
[H]
, then:
[F]
[ ]
[ ]
[ ]
voltage in current mode control that is reflected on the FB8
pin.
Regulator 7 (Inverter controller - external compensation
needed)
voltage-mode control DC-DC regulator that drive an external
P-MOSFET to supply a typical voltage of -7V at a maximum
current of 60 mA.
• P-MOSFET: The peak current of the MOSFET is assumed
• Diode D7: The peak value of the diode current is I
• L: The minimum value of inductor to maintain CCM can be
• C
• R1 and RB: These two resistors help to set the output
C
ESR
L
OUT
I
V
Where Vref=230mV is the maximum internal reference
REG7 is a non-synchronous buck/boost inverting PWM
to be I
I
And the voltage rating is given by:
which should also be higher than I
current rating should be higher than the output current low
and the repetition reverse voltage V
determined by using the following procedure:
contribute to its impedance and output voltage ripple are
the ESR, the ESL and the capacitance C. The minimum
capacitor value is approximately:
• Where
• Now calculate the maximum allowed ESR to reach the
voltage to the desire value using a VFB7=0.6V, select R1
between 10k and 150K and then calculate RB as follows:
V
OB
Q
min
RRM
OUT
Q
desired.
from 5 to 15% of maximum current rating.
I
=
----------------------------------------------- -
⎛
⎝
Lpeak
: The three elements of output capacitor that
Io
--------------------------- -
--------------------- -
1 D
D
F
---------------- -
2Io
Vin Vo
–
Io
, which is obtained by the following formula, define
–
SW
max
Vin Vo
VoT
max
max
max
–
=
D
VO
Vo
–
Vo
max
⎛
⎝
–
----------------------------
------------------------------ -
Vo Vin
+
r
r
r
Io
is the desired output voltage ripple.
1 D
------------ -
1 D
Vin
I
–
–
OB
+
–
I
min
OB
⎞
⎠
min
FUNCTIONAL DEVICE OPERATION
⎞
⎠
2
COMPONENT CALCULATION
Lpeak
RRM
. The average
is given by:
[H]
[F]
[ ]
FSM
34704
41