MAX5014CSA+T Maxim Integrated Products, MAX5014CSA+T Datasheet - Page 11

• Manufacturer Part Number: MAX5014CSA+T
• Description: IC CNTRLR PWM CRNT MD 8-SOIC
• Manufacturer: Maxim Integrated Products

Specifications of MAX5014CSA+T

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• Duty Cycle: 85%
• Voltage - Supply: 18 V ~ 110 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 8-SOIC (3.9mm Width)
• Frequency-max: 275kHz
• Duty Cycle (max): 85 %
• Output Current: 1000 mA
• Mounting Style: SMD/SMT
• Switching Frequency: 275 KHz
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Synchronous Pin: No
• Topology: Flyback, Forward
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3) The turns ratio of the transformer is calculated based
Current-Mode PWM Controllers with Integrated
where V
regulator, and R
Figures 2 and 3.
on the minimum input voltage and the lower limit of
the maximum duty cycle for the MAX5015 (44%). To
enable the use of MOSFETs with drain-source
breakdown voltages of less than 200V use the
MAX5015 with the 50% maximum duty cycle.
Calculate the turns ratio according to the following
equation:
Choose N
tance. Use the turns ratio to calculate N
up to the nearest integer. In this example N
and N
For a forward converter choose a transformer with a
magnetizing inductance in the neighborhood of
200µH. Energy stored in the magnetizing inductance
of a forward converter is not delivered to the load
and must be returned back to the input; this is
accomplished with the reset winding.
The transformer primary to secondary leakage
inductance should be less than 1µH. Note that all
leakage energy will be dissipated across the MOS-
FET. Snubber circuits may be used to direct some or
D
cycle (44%).
V
In this example:
where:
N
turns and N
V
V
power Schottky diodes).
IN_MIN
OUT
MAX
D1
S
/N
= Voltage drop across D1 (typically 0.5V for
P
S
= Output voltage (5V).
= Minimum value of maximum operating duty
= Turns ratio (N
= 5.
= Minimum Input voltage (36V).
Startup Circuit for Isolated Power Supplies
REF
P
N
N
N
N
P
S
P
based on core losses and DC resis-
is the reference voltage of the shunt
S
P
is the number of primary turns).
≥
______________________________________________________________________________________
≥
1
V
5V + 0.5V 0.44
V
V
OUT
and R
OUT
REF
D
MAX
0 44 36
(
.
+
S
=
(
2
is the number of secondary
V
×
×
R
D1
are the resistors shown in
1
V
×
R
IN_MIN
+
×
2
V
R
D
2
MAX
)
=
)
0 330
.
S
, rounding
P
= 14
=
4) The reset winding turns ratio (N
5) Choose the tertiary winding turns ratio (N
all of the leakage energy to be dissipated across a
resistor.
To calculate the minimum duty cycle (D
following equation:
where V
low enough to guarantee that the entire energy in
the transformer is returned to V+ within the off cycle
at the maximum duty cycle. Use the following equa-
tion to determine the reset winding turns ratio:
where:
N
D
Round N
The turns ratio of the reset winding (N
determine the peak voltage across the N-channel
MOSFET.
Use the following equation to determine the maxi-
mum drain-source voltage across the N-channel
MOSFET:
V
V
Choose MOSFETs with appropriate avalanche
power ratings to absorb any leakage energy.
that the minimum input voltage provides the mini-
mum operating voltage at V
DSMAX
IN_MAX
R
MAX
/N
P
’ = Maximum value of Maximum Duty Cycle.
= Reset winding turns ratio.
IN_MAX
D
V
= Maximum MOSFET drain-source voltage.
R
= Maximum input voltage.
V
DSMAX
MIN
DSMAX
to the nearest smallest integer.
=
N
N
R
V
is the maximum input voltage (72V).
R
IN_MAX
≥
≤
≤
≥
7
N
1
V
2
4
P
IN_MAX
V
×
V
×
×
OUT
×
1- 0.5
1-D



0.5
D
N
N
1 +
MAX
P
S
MAX
DD
×
- V
=



′
14
14
D1
1 +
14
′
(13V). Use the follow-

 =

R
= 19 8 .
/N
N
N
144
P
R
P
) needs to be



V
MIN
R
) use the
/N
T
/N
P
P
) will
) so
11