© 2006 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FAN5617 Rev. 1.0.1

Circuit Description

The FAN5617 switch capacitor DC/DC converter

automatically configures its internal switches to achieve

high

efficiency,

providing

tightly-regulated

output

currents for the LEDs (see Figure 10 and Figure 11).

An internal voltage detector determines which LED

requires the highest voltage to sustain the pre-set

current levels and adjusts the charge pump regulator

accordingly. Each LED has its own linear current

regulator. In addition, a voltage regulator controls the

output voltage when the battery voltage is within a range

where linear regulation can provide maximum efficiency.

If the battery voltage is too low to sustain the LED

current in linear mode, a fractional 3:2 charge pump is

enabled. When the battery voltage drops and the mode

can no longer sustain proper operation, the pump is

automatically reconfigured to operate in 2:1 mode. As

the battery discharges and the voltage decays, the

FAN5617 switches between modes to maintain a

constant current through the LEDs throughout the

battery life. These transitions have hysteresis to prevent

toggling.

The internal supply voltage of the device is automatically

selected from the VIN or VOUT pins, whichever has a

higher voltage.

The FAN5617 enters shutdown mode to reduce overall

current consumption when the chip is disabled by the

EN pin and control register.

Start-up

When the FAN5617 is enabled, either by EN going high

or on command from the TinyWire™ interface, the soft-

inrush current (see Figure 12). When power is first

is set to maximum brightness (31). If EN is low at initial

power-up, the IC remains in a low-power state until

either EN goes HIGH or a non-0 brightness command is

received. If EN goes from HIGH to LOW, the IC is reset

to the low-power state until either a new brightness

command is received or EN is driven HIGH.

V

IN

V

OUT

PWRUP

250

∝s

Figure 12. Soft-Start

An internal PWRUP signal turns on all of the IC’s logic

control circuitry and starts the charge pump. PWRUP is

high under any of the following conditions:

1.

EN goes from low to high

2.

A non-zero brightness command is received

PWRUP goes low under any of the following conditions:

1.

EN is low when power is first applied and no

subsequent non- zero brightness commands are

received

2.

EN goes from HIGH to LOW

3.

A zero brightness command is received

TinyWire™ Single-Wire Brightness Control

This IC features a digitally controlled static brightness

adjustment to minimize both EMI and applications

processor overhead. The brightness command consists

(

)

SET

BR

LED

R

32

1

N

156

I

•

+

•

=

(1)

BIT4

BIT3

BIT2

BIT1

BIT0

0

0

0

0

0

0

0

1

0

0

0

0

1

260 × 2/32

2

0

0

0

1

0

260 × 3/32

3

0

0

0

1

1

260 × 4/32

4

0

0

1

0

0

260 × 5/32

5

0

0

1

0

1

260 × 6/32

6

0

0

1

1

0

260 × 7/32

7

0

0

1

1

1

260 × 8/32

8

0

1

0

0

0

260 × 9/32

9

0

1

0

0

1

260 × 10/32

10

0

1

0

1

0

260 × 11/32

11

0

1

0

1

1

260 × 12/32

12

0

1

1

0

0

260 × 13/32

13

0

1

1

0

1

260 × 14/32

14

0

1

1

1

0

260 × 15/32

15

0

1

1

1

1

260 × 16/32

16

1

0

0

0

0

260 × 17/32

17

1

0

0

0

1

260 × 18/32

18

1

0

0

1

0

260 × 19/32

19

1

0

0

1

1

260 × 20/32

20

1

0

1

0

0

260 × 21/32

21

1

0

1

0

1

260 × 22/32

22

1

0

1

1

0

260 × 23/32

23

1

0

1

1

1

260 × 24/32

24

1

1

0

0

0

260 × 25/32

25

1

1

0

0

1

260 × 26/32

26

1

1

0

1

0

260 × 27/32

27

1

1

0

1

1

260 × 28/32

28

1

1

1

0

0

260 × 29/32

29

1

1

1

0

1

260 × 30/32

30

1

1

1

1

0

260 × 31/32

31

1

1

1

1

1

260 × 32/32