MC34845DEPR2 Freescale Semiconductor, MC34845DEPR2 Datasheet - Page 15

• Manufacturer Part Number: MC34845DEPR2
• Description: IC LED DVR BACKLIGHT 6CH 24QFN
• Manufacturer: Freescale Semiconductor

Specifications of MC34845DEPR2

• Internal Driver: Yes
• Type - Primary: Backlight
• Mounting Type: Surface Mount
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Frequency: 270kHz ~ 330kHz
• Voltage - Supply: 5 V ~ 21 V
• Voltage - Output: 60V
• Package / Case: 24-UFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Operating Supply Voltage: 5 V to 21 V
• Maximum Supply Current: 5 mA
• Maximum Power Dissipation: 3.4 W
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

all external components related with the boost converter and
network compensation.
the MOSFET and Diode should be taken into consideration:
current when the internal switch is off.
Inductor
internal switch and winding resistance of the inductor:
maximum input current:
Input Capacitor
RMS current.
Output Capacitor
should be taken in consideration.
the Output capacitor. For a low output voltage ripple, it is
recommended to use ceramic capacitors that have a very low
ESR. Since ceramic capacitor are costly, electrolytic or
tantalum capacitors can be mixed with ceramic capacitors for
a less expensive solution.
RMS current.
Network Compensation
compensation is needed.
Analog Integrated Circuit Device Data
Freescale Semiconductor
The following formulas are intended for the calculation of
In order to calculate the Duty Cycle, the internal losses of
The average input current depends directly on the output
For calculating the Inductor, consider the losses of the
It is important to look for an inductor rated at least for the
The input capacitor should handle at least the following
For the output capacitor selection the transconductance
The output voltage ripple (ΔV
The output capacitor should at least handle the following
Since this Boost converter is current controlled, a Type II
L
I RMS C
I IN MAX
=
(
----------------------------------------------------------------------------------------------------------------- -
ESR C
V
–
C OUT
–
IN
IN
–
OUT
V
D
=
=
=
SW
=
=
⎛
⎜
⎝
R COMP
-------------------------------------------------------------------------------
I
I IN AVG
IN AVG
V IN
-------------------------------------------------------- -
2 L
–
---------------------------------------------- -
V
I
V OUT
-------------------------------------------------------------------------- -
V
×
IN AVG
(
–
(
OUT
–
OUT
I
1 D
IN AVG
–
×
–
×
(
–
V OUT
V OUT V IN
F SW
+
×
+
×
)
5
V
=
ΔV OUT
×
V
+
OUT
×
×
D
V OUT
D
V IN
-------------------------------------------------------- -
------------ -
1 D
I
2
×
G M
r
OUT
–
×
–
×
–
×
–
V OUT
) depends on the ESR of
×
V
R
V
L
(
F
1 D
×
×
SW
INDUCTOR
IN
×
SW
×
–
(
I OUT
×
V OUT V IN
F SW
F SW
)
0.35
⎞
⎟
⎠
)
×
0.3
×
COMPONENTS CALCULATION
×
×
–
V OUT
L
L
)
) D
×
)
boost converter components need to be known.
out the Right Half Plane Zero to higher frequencies where it
will not significantly affect the overall loop.
location of the Right half plane zero:
should be fixed for all configurations, i.e. R
acceptable performance of the system in different operating
conditions are Ccomp1=33nF and Ccomp2=220pF.
resistor network can be implemented from the PWM pin to
ground with a connection to the compensation network. This
configuration should inject a 1V signal to the COMP pin and
the equivalent Thevenin resistance of the divider should be
close to R
R
implementation guidelines.
(e.g. 1.3V) should be injected to the COMP pin; so the
resistor divider should be modified accordingly but keeping
the equivalent Thevenin resistance of the divider close to
R
SHUNT
COMP
Note that before calculating the network compensation, all
For this type of compensation it is recommended to push
The crossover frequency must be set much lower than the
Since our system has a fixed slope compensation, R
C
The recommended values of these capacitors for an
In order to improve the transient response of the boost a
If a faster transient response is needed, a higher voltage
COMP1
.
= 10k. See
and C
COMP
C COMP2
C COMP1
I
, (i.e. for 2k COMP resistor, R
RMS C
COMP2
f RHPZ
Figure
–
should be calculated as follows:
f
OUT
CROSS
=
=
=
-----------------------------
6.28
V OUT
-------------------------------------------- -
------------------------------------------------------------ -
π
=
I OUT
10,
×
2
I
f CROSS
G M
×
OUT
=
Figure 11
F SW
COMPONENTS CALCULATION
×
f
-------------- -
×
RHPZ
(
×
2π
1 D
5
2
–
TYPICAL APPLICATIONS
×
×
------------ -
1 D
L
R
D
–
)
2
COMP
and
COMP
COMP
Figure 12
= 2 Kohm
= 3.3k and
COMP
for
34845
15