13892 datasheet(63/75 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

13892

FUNCTIONAL DEVICE OPERATION

Because of an order from the United States International Trade Commission, BGA-packaged product lines and part numbers indicated here currently are not

available from Freescale for import or sale in the United States prior to September 2010: MC13892VK and MC13892VL in 139, 186 MAPBGA packages.

The dummy conversion inserted between the different

readings is to allow the references in the system to be pre-

biased for the change in touch screen plate polarity and will

read out as ‘0’.

MODES OF OPERATION

In inactive mode, the inputs TSX1, TSX2, TSY1, and TSY2

can be used as general purpose inputs. They are respectively

mapped on ADC channels 4, 5, 6, and 7.

In interrupt mode, a voltage is applied to the X-plate

(TSX2) via a weak current source to VCORE, while the Y-

plate is connected to ground (TSY1). When the two plates

make contact both will be at a low potential. This will generate

a pen interrupt TSI to the processor. This detection does not

make use of the ADC core or the TSREF regulator, so both

can remain disabled.

In touch screen mode, the XY coordinate pairs and the

contact resistance are read. The X-coordinate is determined

by applying TSREF over the TSX1 and TSX2 pins while

performing a high-impedance reading on the Y-plate through

TSY1. The Y-coordinate is determined by applying TSREF

between TSY1 and TSY2 while reading the TSX1 pin. The

contact resistance is measured by applying a known current

into the TSY1 terminal of the touch screen and through the

terminal TSX2, which is grounded. The voltage difference

between the two remaining terminals TSY2 and TSX1 is

measured by the ADC, and equals the voltage across the

contact resistance. Measuring the contact resistance helps in

determining if the touch screen is touched with a finger or

stylus.

LED DRIVERS FOR LIGHTING SYSTEM

BACKLIGHT LED DRIVERS

The lighting system includes backlight drivers for main

display, auxiliary display, and keypad. The backlight LEDs

are configured in series and supplied from an inductive boost

supply See Boost Converters on page 53. Three additional

drivers are provided for RGB or general purpose signaling.

Ramp up and ramp down patterns are implemented in

hardware to reduce the burden of real time software control

via the SPI, to orchestrate dimming and soft start lighting

effects.

These patterns are guaranteed by design.

The current level is programmable in a low range mode

and in a high range mode from 0 to 21 mA and from 0 to

42 mA respectively. This facilitates the current setting, in

case two or more serial LED strings are connected in parallel

to the same driver, or when using super bright LEDs.

The boost switcher SWLED supplying the backlight LEDs

is shared between all three backlight drivers. However, a

maximum of only two backlight drivers can be activated at the

same time, for instance the main display plus keypad. If all

three backlight drivers are enabled meaning none of the duty

cycles equals 0/32, then none of the drivers will be activated.

SIGNALING LED DRIVERS

The signaling LED drivers LEDR, LEDG, and LEDB are

independent current sink channels. Each driver channel

features programmable current levels from 0 to 21 mA as well

as programmable PWM duty cycle settings. 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.

Blue LEDs or bright green LEDs require more headroom

than red and normal green signal LEDs. In the application, a

5.0 V or equivalent supply rail is therefore required. This is

provided by the integrated boost converter SWBST. As with

the backlight driver channels, the signaling LED drivers

include ramp up and ramp down patterns are implemented in

hardware.

In addition, programmable blink rates are provided.

Blinking is obtained by lowering the PWM repetition rate of

each of the drivers, while the on period is determined by the

duty cycle setting. To avoid high frequency spur coupling in

the application, the switching edges of the output drivers are

softened."

CONNECTIVITY (USB INTERFACE)

The 13892 contains the regulators required to supply the

PHY contained in the i.MX51, i.MX37, i.MX35, and i.MX27

processors. The regulators used to power the external PHY

in the i.MX51 and i.MX37 are VUSB, VUSB2, and VUSB for

the i.MX35 and i.MX27 processors. The IC also provides the

5.0 V supply for USB OTG operation. The USB interface may

be used for portable product battery charging. Finally

included are comparators/detectors for VBUS and ID

detection. VBUS is the power rail of the USB cable that must

be connected to the UVBUS pin.

The USB interface is illustrated in Figure 13.

13892 Datasheet(PDF) 63 Page - Freescale Semiconductor, Inc

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