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LT3466-1

34661f

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 (VOUT2) is given by:

OUT

22 1

⎛

⎝⎜

⎞

⎠⎟

Thus a linear change in the feedback (FB2) voltage results

in a linear change in the boost output voltage (VOUT2).

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 (>100M

Ω). A small amount

of board leakage current is sufficient to turn on the

converter 2.

The RBASE resistor can be calculated as:

ILOAD = 30mA

BASE

LOAD

FE MIN

()

IBASE must be chosen such that Q1 is in saturation under

all conditions. The hFE(MIN) can be obtained from the

Philips BC807 data sheet as:

hFE(MIN) ≅ 100

This yields worst case IBASE as:

BASE =

≅

0 4 100

075

)

RBASE is given by:

IN MAX

BASE

BE Q

OUT

CE Q

(

)

()

+•

Thus R

BASE

OUT

IN MAX

CE Q

BE Q

;

––

(

)

()

ASE

Figure 10. Li-Ion Powered Driver for 6 White LEDs and a

Secondary OLED Display with Output Disconnect

CTRL1

CTRL2

SW1

SW2

VIN

3V TO 5V

16V

30mA

µH

CIN

µF

RBASE

IBASE

VCE(SAT)

COUT1

µF

COUT2

0.47

µF

63.4k

µH

LT3466-1

CIN: TAIYO YUDEN JMK107BJ105

COUT1: TAIYO YUDEN GMK316BJ105

COUT2, COUT3: TAIYO YUDEN TMK316BJ474

L1, L2: TOKO D52LC

Q1: PHILIPS BC807

VOUT1

FB1

RFB1

Ω

24.9k

475k

34661 F10

VOUT2

FB2

OFF

COUT3

0.47

µF

+–

Figure 9. VFB2 vs VCTRL2

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, RBASE, and a

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.

VCTRL2 (V)

400

600

34661 F09

200

300

500

100

0.4

0.8

1.6

1.2

900

800

700

VIN = 3.6V

VOUT2 = 16V

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