MAX608 Maxim, MAX608 Datasheet - Page 9

• Manufacturer Part Number: MAX608
• Description: 5V or Adjustable / Low-Voltage / Step-Up DC-DC Controller
• Manufacturer: Maxim

current will ramp up to a high level before the current-lim-
it comparator can turn off the switch. The minimum on-time
for the switch (t
inductor that allows the current to ramp up to I
The standard operating circuits use a 22µH inductor.
If a different inductance value is desired, select L such
that:
Larger inductance values tend to increase the start-up
time slightly, while smaller inductance values allow the
coil current to ramp up to higher levels before the
switch turns off, increasing the ripple at light loads.
Figure 4a. Maximum Output Current vs. Input Voltage
(V
Figure 4c. Maximum Output Current vs. Input Voltage
(V
OUT
OUT
= 3.3V)
= 12V)
2.0
1.5
1.0
0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
2.0
2
ON
V
L = 22 H
L = 22 H
R
V
OUT
SENSE
OUT
L ≥ —————----—--
(min)) is approximately 2µs; select an
R
_______________________________________________________________________________________
= 3.3V
SENSE
= 12V
R
= 35m
SENSE
4
V
2.5
= 25m
IN
R
SENSE
INPUT VOLTAGE (V)
= 20m
INPUT VOLTAGE (V)
(max) x 2µs
6
I
LIM
= 100m
3.0
8
R
R
SENSE
SENSE
R
R
R
SENSE
SENSE
SENSE
= 100m
= 25m
10
= 50m
= 50m
= 35m
3.5
5V or Adjustable, Low-Voltage,
12
LIM
.
Step-Up DC-DC Controller
Inductors with a ferrite core or equivalent are recom-
mended; powder iron cores are not recommended for
use with high switching frequencies. Make sure the
inductor’s saturation current rating (the current at which
the core begins to saturate and the inductance starts to
fall) exceeds the peak current rating set by R
However, it is generally acceptable to bias the inductor
into saturation by approximately 20% (the point where
the inductance is 20% below the nominal value). For
highest efficiency, use a coil with low DC resistance,
preferably under 20mΩ. To minimize radiated noise,
use a toroid, a pot core, or a shielded coil.
Table 1 lists inductor suppliers and specific recom-
mended inductors.
Figure 4b. Maximum Output Current vs. Input Voltage
(V
Figure 4d. Maximum Output Current vs. Input Voltage
(V
OUT
OUT
= 5V)
= 15V)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
2
2
R
V
L = 22 H
R
V
L = 22 H
SENSE
OUT
SENSE
OUT
R
R
SENSE
4
SENSE
= 15V
= 5V
R
= 25m
= 35m
SENSE
= 25m
= 20m
6
= 20m
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
3
8
10
R
R
SENSE
SENSE
R
SENSE
R
4
SENSE
R
12
SENSE
= 100m
= 35m
= 50m
= 100m
= 50m
14
16
5
SENSE
9
.