MAX8901B(2007) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX8901B
(Rev.:2007)

Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package

Maxim Integrated 

Highest Efficiency Supply for 2 to 6

Series WLEDs in a 2mm x 2mm TDFN Package

Pin Description

PIN

NAME

FUNCTION

WLED Overvoltage Protection Input. OVP monitors voltage at the WLEDs. Connect OVP to the

1

OVP

positive terminal of the output capacitor. If an OVP condition is detected, the MAX8901_ latches off.

Cycle VIN or toggle VON to restart the IC.

Enable and Dimming Control Input. Drive ON high to enable the IC. Drive ON low for greater than

1.33ms (typ) to shutdown the WLED current regulator.

For the MAX8901A: After VIN is above VUVLO and ON is driven high, the MAX8901A enters soft-start

and increases the WLED current to full brightness. Apply a minimum 30kHz (500kHz max) PWM

2

ON

signal to ON to adjust the WLED brightness from 100% to off, proportional to the duty cycle of the

PWM signal. See the PWM Dimming Control (MAX8901A) section for more details.

For the MAX8901B: After ON is driven high for 40µs (min), the MAX8901B enters soft-start and

increases the WLED current to full brightness. Subsequent pulses on ON cause the MAX8901B

WLED current to decrease in 32 equal steps. See the Serial-Pulse Dimming Control (MAX8901B)

section for more details.

Power Supply Input. Bypass IN to GND with a 1µF ceramic capacitor placed as close as possible to

the IC. If VIN exceeds the input overvoltage lockout threshold (6.5V max, VIN rising), the IC stops

3

IN

switching and no WLED current flows (if the forward voltage of the WLED string is greater than VIN).

When VIN falls below the overvoltage lockout hysteresis level (6.0V min, VIN falling), soft-start is

initiated and normal operation resumes.

4

LX

Boost Inductor Node. Connect an inductor between IN and LX. LX is high impedance in shutdown.

5

PGND Power Ground. Connect to GND and the exposed paddle (EP) with a short, wide trace.

6

GND

Analog Ground. Connect GND to the exposed paddle with a short, wide trace.

WLED Boost Compensation Node. Connect a 0.022µF ceramic capacitor from COMP to GND.

7

COMP CCOMP stabilizes the converter and sets the soft-start time. COMP discharges to GND when in

shutdown.

WLED Current Sense Input. For the MAX8901A, connect a current-sense resistor from CS to GND.

Voltage sensed at CS regulates the WLED current. For the MAX8901B, do not connect a sense

8

CS

resistor from CS to GND. The MAX8901B provides an internal current source from CS to GND to

program the WLED current. The MAX8901B regulates VCS to 0.5V (typ) for all ILED. The MAX8901A

regulates VCS to 0.5V (typ) for maximum duty cycle only.

—

EP

Exposed Metal Paddle. Connect EP to GND. For good thermal dissipation, the exposed paddle must

be connected to a large ground plane.

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