MAX8631XEVKIT 查看數據表（PDF） - Maxim Integrated

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MAX8631XEVKIT

MAX8631X Evaluation Kit

Maxim Integrated 

MAX8631X Evaluation Kit

0

ENM1 AND ENM2

OR ENF

tSOFT-START

INITIAL tHI

≥ 200μs

32/32

IM_ OR IF_

SHDN

1

2

34

5

27 28 29 30 31 32

tLO

tHI

tSHDN

31/32

30/32

29/32

500ns TO 250μs

28/32 27/32

≥ 500ns

5/32 4/32

3/32

2/32 1/32

32/32 31/32

(2.5ms)

SHDN

Figure 1. ENM_ and ENF Timing Diagram

The 32nd pulse sets the LED current back to 100%.

Figure 1 shows a timing diagram for single-wire pulse

dimming. Because soft-start is longer than the initial tHI,

apply dimming pulses quickly upon startup (after initial

tHI) to avoid LED current transitioning through full

brightness. Note there is a 2.2kΩ pullup resistor from

ENM2 to IN on the EV kit and a 100kΩ pulldown resistor

connected to ENF.

Flash LED

To test the flash feature, press the button labeled

FLASH. This button should only be held for short dura-

tions to prevent overheating of the flash LED module.

Jumper JU4 is provided to allow for lower current test-

ing of the flash LED module, typically called movie

mode in cell phone applications. The shunt on jumper

JU4 can be removed for testing the flash LED module

at 75mA total (18.7mA per F_). To test without the push-

button switch, use ENF to control the flash LED opera-

tion; refer to the MAX8631X/MAX8631Y IC data sheet

for more information. Note that there is a 100kΩ pull-

down resistor connected to ENF.

Adjusting the MAIN 100% Brightness Level

The full-brightness LED current for the main display is

adjustable by changing the resistor R1. Calculate the

value of R1 with the following equation, where IM_ is the

sink current through each M_ current regulator with the

dimming set to 100%:

R1 = 0.6V × 230

IM_

Adjusting the Flash 100% Brightness Level

The full-brightness LED current for the flash is

adjustable by changing resistors R2 and R3. Calculate

the value of RT with the following equation, where

IF_FLASH is the sink current through each F_ current

regulator with the dimming set to 100%:

RT

=

0.6V × 690

IF_FLASH

where RT is the parallel combination of R2 and R3. R3

is the low-current-set resistor, which must be calculated

first using the equation below. IF_MOVIE is the sink cur-

rent through each F_ current regulator in movie mode:

R3 =

0.6V × 690

IF_MOVIE

Once R3 is determined, then R2 can be calculated

using the following equation:

R2 = R3 × RT

R3 − RT

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