BD6155FVM

Communication ICs

4/7

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Circuit operation

1) Charge pump driver

Charge pump is consisted capacitor pin (pin7), external schotky diodes and capacitors.

Output voltage at no loading is 2VBAT-2VF. (VF is as same as schotky’s VF )

Output voltage at loading is referred Fig2. As standard example, however it depends on external components.

VBAT

Shotky diodes

RB521-S30

Charge pump output

LED

1

µF

C (Pin7)

1

µF

20

40

0

60

80

100

15

3

0

6

9

12

OUTPUT LOAD :

(mA)

Fig.2 Charge pump loading characteristics

(Typical operating characteristics)

VBAT=2.9V

VBAT=3.6V

VBAT=5.5V

2) Fixed current driver

LED driver fixed current is determined by resistor value between LEDS pin (pin4) and GND.

At current control set up voltage1 (Current1, 2=High) resistor value between LEDS-GND is set as 2.7

Ω.

205mV

÷ 2.7Ω = 75.9mA

(2 expressions)

The above current is loaded to LED as fixied current.

LED

LED (5Pin)

+

−

LEDS (4Pin)

RSENSE

CURRENT1

CURRENT2

• LED drive current fix example

LEDS pin voltage

(mV)

LED drive current (mA)

RSENSE=2.7

Ω RSENSE=5.1Ω

105.0

38.9

20.6

Current control setup voltage 1 (Current 1=High Current 2=High)

Current control setup voltage 2 (Current 1=Low Current 2=High)

Current control setup voltage 3 (Current 1=High Current 2=Low)

Current control setup voltage 4 (Current 1=Low Current 2=Low)

205.0

40.2

75.9

57.4

155.0

30.4

55.0

10.8

20.4

The less RSENSE, the bigger fixed current for LED drive.

Resistors value should be determined with confirmation of charge pump loading characteristics (Fig.2) and LED's I-V characteristics.