MAX1984ETP 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1984ETP

Ultra-High-Efficiency White LED Drivers

Maxim Integrated 

Ultra-High-Efficiency White

LED Drivers

capacitor can be connected from BITB to ground to

increase the total time constant. Use the following

equation to calculate the total time constant:

τ = 0.2MΩ ✕ CEXT + 0.098ms

where CEXT is the external capacitance.

The recommended DPWM duty-factor range is from

20% to 100% for DPWM frequencies between 20kHz

and 2MHz, using the internal 0.1ms filter. For lower

DPWM operating frequencies, use CEXT and ensure the

voltage on CEXT (BITB), including ripple, remains

above DFMIN ✕ 0.75 ✕ VREF, where DFMIN is the mini-

mum reliable DPWM duty factor of 15%.

In DPWM mode, the MAX1984/MAX1985/MAX1986

enter shutdown mode when the DPWM duty cycle is

below 5% (typ) and BITC is a logical low level.

Analog Control

To use the analog control mode, connect MODE, BITA,

and BITC to IN. Connect BITB to a DC voltage that sets

the LED current. The operational range for the analog

control is from 140mV (15%) to 0.75 ✕ VREF (100%).

The LED current is given by the following equation:

ILED

=



K1 + K2

×

VBITB

0.75 × VREF





× ILED(FS)

where K1 = 0.0465, K2 = 0.953, VBITB is the voltage at

the BITB pin, VREF is the 1.25V internal reference voltage,

and ILED(FS) is the full-scale LED current set by SETI.

In analog mode, the MAX1984/MAX1985/MAX1986

enter shutdown mode when both VBITA and VBITB are

logic low.

Parallel Control

The MAX1984/MAX1985/MAX1986 also support 2-bit or

3-bit parallel control. To use the 3-bit parallel control

mode, connect MODE to ground. BITA is the most sig-

nificant bit and BITC is the least significant bit. To use

the 2-bit parallel control, connect MODE to IN and BITC

to ground. BITA is the most significant bit and BITB is

the least significant bit. In parallel mode, the

MAX1984/MAX1985/MAX1986 enter shutdown mode

when BITA, BITB, and BITC are logic low. Tables 3 and

4 are the truth tables.

MODE

BITA

BITB

BITC

SETI

RSETI

SHUTDOWN

THRESHOLD

0.75 x VREF

DECODER

DAC

3-BIT

0.75 x VREF

LEVEL

200kΩ

9.8MΩ

SHIFT

10pF

VIN

1

100

SHUTDOWN

IREF

TO CURRENT

REGULATORS

38Ω

300kΩ

18mA DEFAULT

SETI

SETI

VIN - 0.7V

0.045V

200kΩ

0.5mA TEST

7.2MΩ

Figure 5. Brightness Control Equivalent Functional Diagram

______________________________________________________________________________________ 13

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