LT3466EDD-1 Ver la hoja de datos (PDF) - Linear Technology

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LT3466EDD-1

White LED Driver and Boost Converter in 3mm × 3mm DFN Package

Linear Technology 

LT3466-1

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:

VOUT2 = VFB2 ⎛⎝⎜1+ RR21⎞⎠⎟

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 (>100MΩ). A small amount

of board leakage current is sufficient to turn on the

converter 2.

900 VIN = 3.6V

800 VOUT2 = 16V

700

600

500

400

300

200

100

0

0

0.4 0.8 1.2 1.6

2

VCTRL2 (V)

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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.

3V TO 5V

COUT1

1µF

L1

33µH

CIN

1µF

IBASE RBASE

L2

33µH

Q1

+–

VCE(SAT)

SW1 VIN SW2

VOUT1

VOUT2

LT3466-1

R1

475k

COUT2

0.47µF

16V

30mA

COUT3

0.47µF

FB1

FB2

RFB1

CTRL1 RT CTRL2

10Ω

OFF ON

63.4k

1%

CIN: TAIYO YUDEN JMK107BJ105

COUT1: TAIYO YUDEN GMK316BJ105

COUT2, COUT3: TAIYO YUDEN TMK316BJ474

L1, L2: TOKO D52LC

Q1: PHILIPS BC807

OFF ON

R2

24.9k

34661 F10

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

Secondary OLED Display with Output Disconnect

The RBASE resistor can be calculated as:

ILOAD = 30mA

IBASE

=

ILOAD

0.4hFE(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:

30mA

IBASE = 0.4(100) ≅ 0.75mA

RBASE is given by:

VIN(MAX) + IBASE • RBASE + VBE(Q1) = VOUT2 + VCE(Q1)

Thus; RBASE

=

VOUT2

–

VIN(MAX) + VCE(Q1)

IBASE

–

VBE(Q1)

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