MAX1771 Maxim, MAX1771 Datasheet - Page 10

• Manufacturer Part Number: MAX1771
• Description: 12V or Adjustable / High-Efficiency / Low IQ / Step-Up DC-DC Controller
• Manufacturer: Maxim

DataSheet4U.com
www.DataSheet4U.com
DataSheet
4
U
.com
approximately 2µs; select an inductor that allows the cur-
rent 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.
12V or Adjustable, High-Efficiency,
Low I
Figure 4a. Maximum Output Current vs. Input Voltage
(V
Figure 4c. Maximum Output Current vs. Input Voltage
(V
10
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
Q
R
V
L = 22 H
R
V
L = 22 H
SENSE
OUT
SENSE
OUT
R
, Step-Up DC-DC Controller
R
SENSE
4
L ≥ —————----—--
SENSE
= 15V
= 5V
R
= 25m
= 35m
SENSE
LIM
= 25m
= 20m
6
V
= 20m
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
3
.
IN
(max) x 2µs
8
I
LIM
10
R
R
SENSE
SENSE
R
SENSE
R
4
SENSE
R
12
SENSE
= 100m
= 35m
= 50m
= 100m
= 50m
14
16
5
DataSheet4U.com
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
= 12V)
= 24V)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.8
0.6
0.4
0.2
0
0
2
2
L = 22 H
V
L =150 H
V
R
R
OUT
SENSE
OUT
SENSE
R
SENSE
= 24V
= 12V
R
= 35m
SENSE
4
= 50m
= 25m
6
= 20m
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
6
10
8
R
R
R
SENSE
SENSE
SENSE
R
SENSE
= 100m
= 100m
= 200m
10
= 50m
14
12
SENSE
.