MP3021 – 1X, 1.5X, 2X AUTO-ADJUST CHARGE PUMP WLED BACKLIGHT DRIVER

MP3021 Rev. 1.0

www.MonolithicPower.com

7

11/21/2007

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© 2007 MPS. All Rights Reserved.

OPERATION

The MP3021 uses a charge pump architecture

optimized to support white LED backlight driver

needs. To maximize power efficiency, it

automatically switches between 1X, 1.5X, and

2X modes. The device provides regulated

current for up to four backlight LEDs.

The charge pump automatically responds to

changing conditions such as supply voltage,

forward diode voltage and mode selection in

order to maintain LED current and maximize

efficiency.

The single pin interface provides on/off control,

individual WLED selection, and brightness

control for the backlight. A 5-bit backlight

brightness register provides 32 levels of current

(brightness)

control.

ISET

controls

the

maximum

brightness

of

the

backlights.

Furthermore, the MP3021 is equipped with a

low brightness backlight mode where the

backlight current can be accurately set down to

100µA.

Soft-start and mode changes limit the inrush

current in the MP3021. The MP3021 uses

charge pump derating over a period of 200µs to

limit inrush current. Before startup the part

checks for a shorted charge pump and

pre-charges its capacitors. This further prevents

inrush and over-current situations.

Single Pin Serial Port Operation

The DATA pin acts as a single wire port for

sending brightness data, LED selection and

protocol is very flexible and easy to use and is

based entirely on short and long pulses (see

Table1). Short pulses having a width within the

specified range are accepted as data. Polarity

of the data matches the pulse polarity. Long

pulses having a pulse width greater than the

minimum specified serve two purposes in the

communication. First, they are used to separate

two similar data values. For example, back-to-

back “1” data must be separated by a long low

pulse otherwise a “0” would be seen between.

Similarly, back-to-back “0”s must be separated

by a long high. Second, long pulses are used to

indicate end of communication by sending two

back-to-back long pulses. Any number of bits

up to a maximum of 11 can be entered during

one communication, always starting with bit 0.

The register value will not change until new

input is received or the register is reset.

Table 1—MPC™ Pulse Detail

Parameter

Minimum

Maximum

Note

Tshort

1.5µs

3.5µs

Accepted

Pulse

Tlong

8µs

NA

Ignored

Pulse

1

Begin on first

acceptable pulse

DATA LINE

Tshort

Send Pattern <11010010101>

End on back-to-back

long pulse

10

0

0

0

0

11

1

1

Tlong

Tlong

Tlong

Tlong

Tshort

Tshort

Tshort

Tshort

Tshort

Tshort

Tshort

Tshort

Tshort

Tshort

Figure 2—Protocol Waveforms