lt3466efe-trpbf Linear Technology Corporation, lt3466efe-trpbf Datasheet - Page 13

• Manufacturer Part Number: lt3466efe-trpbf
• Description: White Led Driver And Boost Converter In 3mm X 3mm Dfn Package
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Figure 9 shows the feedback voltage variation versus the
control voltage. As seen in Figure 9, the linearity of the
graph allows the feedback voltage to be set accurately via
the control voltage.
The boost converter output voltage (V
Thus a linear change in the feedback (FB2) voltage results
in a linear change in the boost output voltage (V
Connect the CTRL2 pin to ground to disable converter 2.
Do not leave the pin floating. Unlike the CTRL1 pin, which
has an internal 100k pull-down resistor, the CTRL2 pin
input impedance is very high (>100MΩ). A small amount
of board leakage current is sufficient to turn on the
converter 2.
OUTPUT DISCONNECT
The LT3466-1 can be used for powering white LEDs
(Channel 1) and an OLED display or, LCD bias (Channel 2).
Some OLED displays require load isolation in order to
reduce the current drained from the battery in shutdown.
The LT3466-1 output can be configured to provide output
disconnect by the use of only one resistor, R
PNP transistor, Q1, as shown in Figure 10.
As a design example, we target a Li-Ion powered driver for
6 white LEDs and an OLED display (16V at 30mA). We can
choose a general purpose PNP switching transistor like
Philips BC807 (Q1) to provide isolation.
V
OUT
2
=
900
800
700
600
500
400
300
200
100
0
V
0
FB
V
V
IN
OUT2
2
= 3.6V
⎛
⎜
⎝
Figure 9. V
1
= 16V
0.4
U
+
R
R
2
1
0.8
⎞
⎟
⎠
V
U
CTRL2
FB2
(V)
1.2
vs V
CTRL2
W
1.6
OUT2
34661 F09
) is given by:
2
BASE
U
OUT2
, and a
).
The R
I
all conditions. The h
Philips BC807 data sheet as:
This yields worst case I
R
C
C
C
L1, L2: TOKO D52LC
Q1: PHILIPS BC807
Thus R
BASE
IN
OUT1
OUT2
BASE
: TAIYO YUDEN JMK107BJ105
I
h
V
I
I
LOAD
BASE
BASE
Figure 10. Li-Ion Powered Driver for 6 White LEDs and a
Secondary OLED Display with Output Disconnect
IN MAX
FE(MIN)
: TAIYO YUDEN GMK316BJ105
, C
R
10Ω
(
must be chosen such that Q1 is in saturation under
FB1
BASE
;
OUT3
is given by:
BASE
= 30mA
: TAIYO YUDEN TMK316BJ474
=
=
C
OUT1
)
1µF
resistor can be calculated as:
≅ 100
0 4 .
0 4 100
+
OFF
30
. (
I
BASE
=
I
h
LOAD
mA
ON
33µH
FE MIN
V
OUT
L1
(
V
FB1
CTRL1
SW1
OUT1
•
)
R
≅
FE(MIN)
2
LT3466-1
)
3V TO 5V
BASE
–
BASE
0 75
V
R
.
V
IN
T
IN MAX
63.4k
1%
1µF
C
CTRL2
+
(
mA
as:
V
SW2
IN
OUT2
can be obtained from the
FB2
V
BE Q
L2
33µH
I
B
OFF
)
( )
A A SE
+
I
1
BASE
ON
V
CE Q
=
+
V
C
0.47µF
CE(SAT)
OUT2
( )
V
LT3466-1
OUT
475k
1
R
–
BASE
Q1
R1
–
2
V
+
R2
24.9k
BE Q
34661 F10
13
V
( )
CE Q
1
C
0.47µF
16V
30mA
34661f
( )
OUT3
1