MAX8513 MAXIM [Maxim Integrated Products], MAX8513 Datasheet - Page 19

• Manufacturer Part Number: MAX8513
• Description: Wide-Input, High-Frequency, Triple-Output Supplies with Voltage Monitor and Power-On Reset
• Manufacturer: MAXIM [Maxim Integrated Products]

diode on the secondary side (Q2 and D2 in the Typical
Applications Circuits). n
turns of the secondary winding and the primary wind-
ing, respectively.
It is important to have the secondary winding tightly
coupled with the primary winding to minimize leakage
inductance for higher efficiency. The positive voltage
generated by the secondary winding can also be
stacked with the main DC-DC step-down converter out-
put to further improve efficiency and reduce winding
cost. In this case, the secondary-side voltage is:
The input-filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the AC-RMS current
through the ESR of the input capacitor (C2 in the Typical
Applications Circuits). The input capacitor must meet
the ripple-current requirement (I
switching currents defined by the following equation:
I
equals twice the output voltage (V
I
ommended due to their low ESR and ESL at high fre-
quency, with relatively low cost. Choose a capacitor that
exhibits less than 10°C temperature rise at the maximum
operating RMS current for optimum long-term reliability.
For applications that require input power-fail warning,
such as dying gasp, add a large-value electrolytic
capacitor (C
device to provide the power to the converter in case of
input power-fail. The capacitor value must be high
enough to meet the desired power-fail warning time,
t
PFO output to when the main output (OUT1) starts
IN_RMS
IN_RMS(MAX)
WARN
Wide-Input, High-Frequency, Triple-Output Supplies
V
I
IN RMS
SEC
, where t
_
has a maximum value when the input voltage
=
(
S
V
=
= I
) to the input as a local energy storage
OUT
WARN
I
OUT
OUT1
1
______________________________________________________________________________________
1
+
with Voltage Monitor and Power-On Reset
is the time from when PFI trips the
×
/ 2. Ceramic capacitors are rec-
V
Q
2
2
V
OUT
and n
)
×



1
IN_RMS
V
n
n
IN
×
2
1
1
IN



Input Capacitor
(
are the number of
V
+
IN
= 2 × V
) imposed by the
V
OUT
-
V
OUT
1
OUT1
- V
1
)
D2
), so
dropping out of regulation. The value of the storage
capacitor, C
where P
converter efficiency, V
the input power-fail (PFI) trip threshold, and V
the input voltage value where V
out of regulation.
V
where R10 and R11 are the resistive-dividers from IN to
PFI to GND in the Typical Applications Circuits.
where D
To ensure for worst-case component tolerances such
as capacitance of C
V
range, it is recommended to select C
the calculated value above.
The key selection parameters for the output capacitor
are the actual capacitance value, the equivalent series
resistance (ESR), the equivalent series inductance
(ESL), and the voltage-rating requirements. All of these
affect the overall stability, output ripple voltage, and
transient response.
The output ripple is composed of three components: vari-
ations in the charge stored in the output capacitor, the
voltage drop across the capacitor’s equivalent series
resistance (ESR), and equivalent series inductance (ESL)
caused by the current into and out of the capacitor.
PFI
DROOP
and V
C
S
MAX
OUT1
’s threshold over the operating temperature
=
DROOP
×



S
0 5
is the maximum duty cycle.
, can be calculated as:
(
V
V
.
V
is the total output power, η is the total
PFI
DROOP
PFI
×
can be calculated as:
t
WARN
- V
=
P
OUT
S
1 22
DROOP
η
, converter efficiency, V
PFI
.
=
1

 ×

V
is the input voltage value at
V
D
OUT
MAX
×
)






1
V
1
PFI
1
Output Capacitor
OUT1
+
R
R
S
-
10
11
at least 1.5 times
starts dropping
V



DROOP
1
DROOP
PFI



, and
19
is