Datasheet
4.5V to 40V Input Automotive
Flyback/Boost/SEPIC Power-Supply Controllers
(t
DISCHARGE
). See Figures 3a and 3b for a coarse selec-
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
OSC
is the oscillator frequency, RT is a resistor
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.
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.
ff
OUT OSC
=
ff
OUT OSC
=
1
2
t
D
f
RT
t
CT
t
CHARGE
MAX
OSC
CHARGE
DISCHARGE
=
=
×
=
07.
2225
1 33 10 3 375
3
.()
(. ( ) ) . ( )
VRTCT
ART V
f
OS
××
××
−
−
CC
CHARGE DISCHARGE
tt
Us
=
+
1
................... ee This Equation If f kHz
tt
OSC
CHARGE DISCHA
≤
+
500
1
RRGE
OSC
ns
Use This Equation If f k
+
>
160
500....... HHz
⎧
⎨
⎪
⎪
⎩
⎪
⎪
Figure 2. Timing Diagram for Internal Oscillator vs. External SYNC and D
MAX
Behavior
RTCT
CLKINT
SYNC
OUT
RTCT
CLKINT
SYNC
OUT
D = 50%
D = 50%
D = 81.25% D = 80%
WITH SYNC
INPUT
MAX15004A/B (D
MAX
= 50%)
MAX15005A/B (D
MAX
= 81%)
WITHOUT
SYNC INPUT
WITH SYNC
INPUT
WITHOUT
SYNC INPUT
MAX15004A/B/MAX15005A/B
13
Maxim Integrated