Datasheet

LT3464
8
3464f
V
OUT
(V)
I
OUT
(mA)
3464 F02
10
25
20
15
10
5
0
25
15 20 30 35
L = 22µH
L = 47µH
L = 4.7µH
L = 10µH
V
OUT
(V)
I
OUT
(mA)
3464 F03
25
20
15
10
5
0
25
15 20 30 35
L = 22µH
L = 47µH
L = 4.7µH
L = 10µH
V
OUT
(V)
I
OUT
(mA)
3464 F01
10
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0
25
15 20 30 35
L = 22µH
L = 10µH
L = 47µH
L = 4.7µH
APPLICATIO S I FOR ATIO
WUU
U
Choosing an Inductor
The low current limit and fast switching of the LT3464
allow the use of very small surface mount inductors. The
minimum inductor size that may be used in a given
application depends on required efficiency and output
current. Some inductors that work with the LT3464 are
listed in Table 1, although there are many other manufac-
turers and devices that can be used. Consult each manu-
facturer for more detailed information and for their entire
selection of related parts. Many different sizes and shapes
are available.
Table 1. Recommended Inductors
PART NUMBER µH DCR CURRENT MANUFACTURER
(
Ω) (mA)
LQH32CN680K53 68 2.2 130 Murata
LQH32CN470K53 47 1.3 170 814-237-1431
LQH32CN220K53 22 0.71 250 www.murata.com
ELJPC220KF 22 4.0 160 Panasonic
ELJPA470KF 47 2.25 135 714-373-7334
www.panasonic.com
CMD4D11-47 47 2.2 180 Sumida
847-956-0666
www.Sumida.com
LB2016-220 22 1.0 105 Taiyo Yuden
LEM2520-220 22 5.5 125 408-573-4150
LEM2520-330 33 7.1 110 www.t-yuden.com
LEMC2520-220 22 2.7 160
LEMC2520-330 33 4.8 120
LEMF2520-220 22 1.2 105
LEMC3225-680 68 3.3 120
LEMC3225-101 100 4.3 100
in discontinuous mode. If the left hand side of inequality 1
evaluates to less than t
OFF
, then use Equation 3 to calculate
maximum output current. Otherwise, use Equation 2.
This inequality is true when the LT3464 is operating in
discontinuous mode.
LI
VVV
t
LIM
OUT IN F
OFF
(– )+
<
(INEQUALITY 1)
Use this equation to calculate the maximum output current
when the LT3464 is operating in continuous mode.
I
LI t V V V V V
LV V V
OUT CM
LIM OFF IN OUT F IN CESAT
OUT CESAT F
()
( ( – – ))( – )
(– )
=
+
+
2
2
(2)
Use this equation to calculate the maximum output current
when the LT3464 is operating in discontinuous mode.
I
LI V V
LI V t t V V V V
OUT DCM
LIM IN CESAT
LIM IN OFF OFF CESAT IN OUT F
()
(– )
( – )(– )
=
+++
2
2
(3)
Where V
F
is the Schottky forward voltage, I
LIM
is the switch
current limit, t
OFF
is the switch off time, and V
CESAT
is the
switch saturation voltage. See the Electrical Specifications.
Figures 1 through 3 show the worst-case maximum output
current as given by Equations 2 and 3 using 20% inductor
derating and worst-case LT3464 specifications. Also note
that for some applications the maximum output current is
limited to 25mA by the output disconnect circuitry.
The following set of formulas can be used to calculate
maximum output current given V
IN
, V
OUT
and L values.
Inequality 1 is used to determine if the LT3464 is operating
Figure 3. Maximum Output Current
V
IN
= 8.4V
Figure 2. Maximum Output Current
V
IN
= 5V
Figure 1. Maximum Output Current
V
IN
= 3.6V