MAX5033 MAXIM [Maxim Integrated Products], MAX5033 Datasheet - Page 10

• Manufacturer Part Number: MAX5033
• Description: 500mA, 76V, High-Efficiency, MAXPower Step-Down DC-DC Converter
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX5033 features internal compensation for opti-
mum closed-loop bandwidth and phase margin. With
the preset compensation, it is strongly advised to sense
the output immediately after the primary LC.
The choice of an inductor is guided by the voltage dif-
ference between V
current, and the operating frequency of the circuit. Use
an inductor with a minimum value given by:
where: D = V
current required, and f
125kHz. Use an inductor with a maximum saturation
current rating equal to at least the peak switch current
limit (I
higher efficiency.
The MAX5033 requires an external Schottky rectifier as
a freewheeling diode. Connect this rectifier close to the
device using short leads and short PC board traces.
Choose a rectifier with a continuous current rating
greater than the highest expected output current. Use a
rectifier with a voltage rating greater than the maximum
expected input voltage, V
Schottky rectifier for proper operation and high efficien-
cy. Avoid higher than necessary reverse-voltage
Schottky rectifiers that have higher forward-voltage
drops. Use a Schottky rectifier with forward-voltage
drop (V
500mA, 76V, High-Efficiency, MAXPower
Step-Down DC-DC Converter
Table 1. Diode Selection
10
7.5 to 36
7.5 to 56
7.5 to 76
V
IN
(V)
______________________________________________________________________________________
LIM
FB
). Use inductors with low DC resistance for
DIODE PART NUMBER
) less than 0.45V at +25°C and maximum
MBRS240, MBRS1540
MBRD360, MBR3060
50SQ100, 50SQ80
OUT
MBRM5100
15MQ040N
CMSH3-60
L
30BQ060
/V
B240A
B360A
=
B240
IN
IN
. 0 3
, I
(
SW
and V
V
OUTMAX
×
IN
I
OUTMAX
IN
is the operating frequency of
−
. Use a low forward-voltage
V
Selecting a Rectifier
OUT
OUT
Inductor Selection
is the maximum output
, the required output
)
Central Semiconductor
Central Semiconductor
×
×
ON Semiconductor
ON Semiconductor
MANUFACTURER
f
D
SW
Diodes, Inc.
Diodes, Inc.
Diodes, Inc.
IR
IR
IR
load current to avoid forward biasing of the internal
body diode (LX to ground). Internal body-diode con-
duction may cause excessive junction temperature rise
and thermal shutdown. Use Table 1 to choose the
proper rectifier at different input voltages and output
current.
The discontinuous input-current waveform of the buck
converter causes large ripple currents in the input
capacitor. The switching frequency, peak inductor cur-
rent, and the allowable peak-to-peak voltage ripple that
reflects back to the source dictate the capacitance
requirement. The MAX5033 high switching frequency
allows the use of smaller-value input capacitors.
The input ripple is comprised of ∆V
capacitor discharge) and ∆V
the capacitor). Use low-ESR aluminum electrolytic
capacitors with high ripple-current capability at the input.
Assuming that the contribution from the ESR and capaci-
tor discharge is equal to 90% and 10%, respectively, cal-
culate the input capacitance and the ESR required for a
specified ripple using the following equations:
I
f
example, at V
input capacitance are calculated for the input peak-to-
peak ripple of 100mV or less, yielding an ESR and
capacitance value of 130mΩ and 27µF, respectively.
Low-ESR, ceramic, multilayer chip capacitors are recom-
mended for size-optimized application. For ceramic
capacitors, assume the contribution from ESR and capac-
itor discharge is equal to 10% and 90%, respectively.
The input capacitor must handle the RMS ripple current
without significant rise in temperature. The maximum
capacitor RMS current occurs at about 50% duty cycle.
OUT
SW
where
is the oscillator switching frequency (125kHz). For
is the maximum output current of the converter and
IN
ESR
C
= 48V and V
∆
I
IN
L
=
IN
=
(
I
OUT
V
=
IN
D
∆



Input Bypass Capacitor
V
=
I
V
OUT
−
Q
IN
×
V
V
∆
ESR
V
D
×
OUT
OUT
V
×
OUT
IN
(
ESR
f
+
1
SW
f
SW
−
(caused by the ESR of
∆
)
2
D
I
×
= 3.3V, the ESR and
L
×
)
V



L
Q
OUT
(caused by the