MC34708 datasheet(87/159 Pages) FREESCALE

87 / 159 page

Analog Integrated Circuit Device Data



Freescale Semiconductor

MC34708

Functional Block Description

7.8.3

General Purpose LED Drivers

By default, the general purpose LED drivers are set to auto USB charger detect. If the VBUS pin is connected to detect what kind

of accessory is attached to the USB port, the red LED can illuminate when a charger is attached in the following use case. If the

both the main battery is dead (battery < UVDET) and coincell is dead (LICELL < 1.8 V) and power is applied to VBUS > 4.35 V,

the red LED will automatically turn on.

If the COINCELL (LICELL > 1.8 V) or battery > UVDET and the CHREN bit is set to 0, and power is applied to VBUS > 4.35 V,

the LED's will stay off. To turn on the LED's the following bits must be set, CHRLEDxEN = 1, CHRGLEDOVRD =1, THERM

bit = 1, and programming the duty cycle > 0/32.

The general purpose LED drivers, CHRGLEDR, and CHRLEDG are independent current sink channels. Each driver channel

features programmable current levels via CHRGLEDx[1:0], as well as programmable PWM duty cycle settings with

CHRGLEDxDC[5:0]. By a combination of level and PWM settings, each channel provides flexible LED intensity control. By driving

LEDs of different colors, color mixing can be achieved.

The general purpose LED drivers include ramp up and ramp down patterns implemented in hardware. Ramping is enabled for

each of the drivers using the corresponding CHRGLEDxRAMP bits, only when the repetition rate is 256 Hz.

Table 81. LED Driver Control

THERM

CHRGLEDxEN(65)

CHRGLEDOVRD

CHRGLEDx(65)

0 (default)

Auto USB charger detect

Off

Notes

65.

“x” represents R or G

Table 82. General Purpose LED Drivers Current Programming

CHRGLEDx[1:0]

CHRGLEDx Current Level (mA)

3.4

6.6 (default)

9.8

12.5

“x” represents for R, and G

Table 83. General Purpose LED Drivers Duty Cycle Programming

CHRGLEDxDC[5:0]

Duty Cycle

000000

0/32, Off

000001

1/32

…

010000

16/32

…

011111

31/32

1xxxxx

32/32, Continuously On

“x” represents R, and G

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