MAX15005 Maxim Integrated Products, MAX15005 Datasheet - Page 13

• Manufacturer Part Number: MAX15005
• Description: (MAX15004 / MAX15005) 4.5V to 40V Input Automotive Flyback/Boost/SEPIC Power-Supply Controllers
• Manufacturer: Maxim Integrated Products

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(t
tion of capacitor values for a given switching frequency
and maximum duty cycle and then use the following
equations to calculate the resistor value to fine-tune the
switching frequency and verify the worst-case maximum
duty cycle.
where f
connected from RTCT to REG5, and CT is a capacitor
connected from RTCT to SGND. Verify that the oscilla-
tor frequency value meets the target. Above calcula-
tions could be repeated to fine-tune the switching
frequency.
Figure 2. Timing Diagram for Internal Oscillator vs. External SYNC and D MAX Behavior
f
OS
DISCHARGE
Flyback/Boost/SEPIC Power-Supply Controllers
C C
=
⎧
⎪
⎪
⎨
⎪
⎪
⎩
t
t
CLKINT
CHARGE
CHARGE
CLKINT
OSC
SYNC
SYNC
RTCT
RTCT
OUT
OUT
). See Figures 3a and 3b for a coarse selec-
t
is the oscillator frequency, RT is a resistor
DISCHARGE
+
+
1
t
t
DISCHARGE
DISCHA
1
______________________________________________________________________________________
R R GE
=
t
CHARGE
( .
RT
1 33 10
...................
+
160
=
×
ns
t
0 7 .
CHARGE
2 2 25
.
=
.......
D = 50%
D = 81.25%
−
×
3
D
( )
f
CT
( )
OSC
V
MAX
A
Use This Equation If f
Us
×
×
RT CT
e e This Equation If f
RT
×
)
−
3 375
.
( )
V
4.5V to 40V Input Automotive
OSC
OSC
>
≤
500
500
MAX15005A/B (D
MAX15004A/B (D
k
kHz
H H z
The MAX15004A/B is a 50% maximum duty-cycle part,
while the MAX15005A/B is 100% maximum duty-cycle
part.
for the MAX15004A/B and
for the MAX15005A/B.
The MAX15004A/B/MAX15005A/B can be synchronized
using an external clock at the SYNC input. For proper
frequency synchronization, SYNC’s input frequency must
be at least 102% of the programmed internal oscillator
frequency. Connect SYNC to SGND when not using an
external clock. A rising clock edge on SYNC is interpret-
ed as a synchronization input. If the SYNC signal is lost,
the internal oscillator takes control of the switching rate,
returning the switching frequency to that set by RC net-
work connected to RTCT. This maintains output regula-
tion even with intermittent SYNC signals.
MAX
MAX
= 81%)
= 50%)
WITH SYNC
WITH SYNC
f
INPUT
INPUT
OUT
f
OUT
D = 80%
D = 50%
=
=
1
2
f
SYNC INPUT
SYNC INPUT
OSC
f
WITHOUT
WITHOUT
OSC
13
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