Technical Note

7/10

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2011.06 - Rev.B

© 2011 ROHM Co., Ltd. All rights reserved.

BD1604MUV, BD1604MVV

GND

ISET

LED1

LED2

LED3

LED4

EN

SEL0

SEL1

SEL2

Battery

VBAT

VOUT

×1, ×1.5, ×2

Charge pump

Over Voltage

Protect

OSC

TSD

Control

Vout Control

Charge Pum p

Mode C ontrol

ISET

Resistor Driver

Current Driver

C1

C2

Cin

Rset

Cout

PWM signal input (ON

for the signal set to High)

●

Cautions on layout pattern

When designing a layout pattern, lay out wires to a power line in a way that the layout pattern impedance can be minimized

and connect a bypass capacitor if necessary.

The GND pin and

Cin must be

placed nearby.

Wiring from the VBAT pin

to Cin must meet a low

impedance.

LED

LED

LED

LED

VBAT

GND

1μF

1μF

1μF

1μF

RSET

VOUT

GND

Fig.15 Example of BD1604MUV Layout Pattern

Fig.16 Example of BD1604MUV Layout Pattern

(Front, Top View)

(Rear, Top View)

●

LED Current Control

There are two methods for LED current control. One method uses an external PWM signal and another changes the

resistance value of RREF (RSET) connected to the IREF (ISET) pin. For details, refer to the respective circuit examples.

Don’t make the setting of 30mA or more per channel for BD1604MUV/MVV.

1) Controlling the current by using the PWM method

The PWN signal must be input to the EN pin.

PWM signal “H” level: 1.4V or more

PWM signal “L” level: 0.4V or less

When PWM Duty is used in an area of 10% or less, the PWM cycle must be a range from 100Hz to 200Hz. When extremely

high-speed PWM control takes place, the linearity of LED current value to PWM duty is lost if the PWM duty is small (for

example, 10% or less) or it is large (for example, 90% or more).

2) Controlling the current by changing the SET resistance value

Rset-Rset1=Rset2// … //Restn.

This means that the current can be adjusted more finely by adding the types of resistance values.

ILED=480/Rset [A]

The approximate LED current can be obtained from the above expression. Because the current of 30mA or more per LED is not

permitted, make the setting in a way that the Rset resistance value can be maintained to be greater than or equal to16kΩ.

GND

ISET

LED1

LED2

LED3

LED4

EN

SEL0

SEL1

SEL2

Battery

VBAT

VOUT

×1, ×1.5, ×2

Charge pump

Over Voltage

Protect

OSC

TSD

Control

Vout Control

Charge Pum p

Mode C ontrol

ISET

Resistor Driver

Current Driver

C1

C2

Cin

Rset1

Cout

Rset2

Rsetn

Fig.17 Controlling the Current

by Using the PWM Method

Fig.18 Controlling the Current

by Changing the Resistance Value