MAX5027 MAXIM [Maxim Integrated Products], MAX5027 Datasheet - Page 9

• Manufacturer Part Number: MAX5027
• Description: 500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters
• Manufacturer: MAXIM [Maxim Integrated Products]

where V
If the boost converter remains in the discontinuous
mode of operation, then the approximate peak inductor
current, I
where T
is the input voltage, I
the efficiency of the boost converter.
Table 1. Inductor Vendors
Figure 1. Functional Diagram
Coilcraft
Sumida
Toko
3
2
5
FB
REF
GND
V
CC
REF
S
VENDOR
LPEAK
I
is the period, V
Determining Peak Inductor Current
LPEAK
is 1.25V
-A
+A
+C
-C
, is represented by the formula below:
ULVO
R
MAIN PWM
COMPARATOR
500kHz, 36V Output, SOT23, PWM Step-Up
=
1
_______________________________________________________________________________________
=
CURRENT-
LIMIT
COMPARATOR
OUT
2
R
2
T



S
OUT
is the output current, and η is
V
V
(
OUT
REF
V
OSCILLATOR
OUT
is the output voltage, V
CONTROL
LOGIC
847-639-6400
847-545-6700
847-297-0070
-
η
1



L
−
PHONE
V
MAX5025
MAX5026
IN OUT
)
SHUTDOWN
I
THERMAL
N
SHDN
PGND
LX
4
6
1
IN
847-639-1469
847-545-6720
847-699-7864
47µH is the recommended inductor value when the out-
put voltage is 30V and the input voltage is 5V. In gener-
al, the inductor should have a current rating greater
than the current-limit value. For example, the inductor’s
current rating should be greater than 150mA to support
a 4mA output current. Equivalent series resistance
(ESR) should be below 1Ω for reasonable efficiency.
Due to the MAX5025–MAX5028’s high switching fre-
quency, inductors with a ferrite core or equivalent are
recommended. Powdered iron cores are not recom-
mended due to their high losses at frequencies over
500kHz. Table 1 shows a list of vendors and 47µH
inductor parts.
For 4mA output current and output voltages other than
30V, the inductor can be simply scaled in value
according to the following formula:
Use the following formula to calculate the upper bound
of the inductor value at different output voltages and
output currents. This is the maximum inductance value
for discontinuous mode operation.
Calculate the lower bound, L
inductance value using the following formula, which will
allow the maximum output current to be delivered with-
out reaching the peak current limit:
Notice that the switch current limit, (V
function of the input voltage, V
the inductor should be greater than the switch current
limit.
FAX
L
LOWER
L
UPPER
DC-DC Converters
Determining the Inductor Value
L
DT1608C-473
CDRH4D28-470
A915BY-470M
=
=
=
PART NUMBER OF 47µH INDUCTOR
(
V
47
2
IN
2
T
µ
η
(
S
2
H V
V



OUT
I
)
OUT
(
(
V
V
(
25
5
IN
OUT
LOWER
OUT
V
−
V
(
IN
)
V
OUT
260
2
IN
−
. The current rating of
−
)
V
V
mA
T
, for the acceptable
IN OUT
IN
S
IN
)
η
)
)
I



/5)(260mA), is a
2
9