Texas Instruments AN-1502 LP5526 User Manual

1 General Description

The LP5526 is a Lighting Management Unit for portable applications. It can be used to drive display
backlight, keypad LEDs, color LEDs and Flash LEDs. The device can drive 2 separately connected strings
of LEDs with high voltage boost converter. The RGB driver allows driving either individual color LEDs or
RGB LED from separate supply voltage, or it can be used to drive FLASH LEDs.

The MAIN and SUB outputs are high-resolution current mode drivers. RGB outputs can be used in switch
mode and current mode. PWM control can be used for any selected outputs.

The device is controlled through 2-wire low voltage I2C compatible interface that reduces the number of
required connections.

LP5526 is offered in a tiny DSBGA-25 package (2.54 mm × 2.54 mm).

2 Evaluation Kit Overview

LP5526 Evaluation Kit is based on a modular system, where the actual evaluation board is plugged on top
of the PC interface board, see Figure 1. The interface operates through the USB port.

The kit supports complete functional evaluation of the circuit. The evaluation kit consists of:

• LP5526 evaluation board

• USB interface board

• USB interface cable

• CD including:
– Evaluation software for PC
– LP5526 datasheet
– LP5526 application note
– MicroSMD package application note AN1112
– PCB design application note AN1149
– Evaluation kit document (this document)

User's Guide

SNVA177B–January 2007–Revised April 2013

AN-1502 LP5526 Evaluation Kit

3 Evaluation Software

LP5526 evaluation software and some support files are supplied on the delivery CD together with all
available documentation regarding the circuit. You can copy the software and the files to your PC’s hard
disk. The program and the support files must be in the same folder. The software is started by double­clicking its icon. The software does not require any installation.

The evaluation software is organized in tabs according to the main functions of the chip. On the left side of
the tabs is shown the whole register map of LP5526. Below the tabs are shown the registers, which are
affected by the selected tab. Both register displays reflect immediately the changes you make by clicking
the selection boxes or sliders in the tabs. The contents of the tabs should be mostly self-explanatory.
Some example register settings are included in the delivery CD and they can be loaded from the
File/Open menu. You can similarly save your own settings.

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Figure 1. LP5526 Evaluation Board with USB Interface Board

Figure 2. LP5526 Evaluation Software User Interface

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3.1 Common Tab

Only one bit of the Enables register is controlled in the Common tab. The NSTBY bit controls the chip
on/off state.

The Common Tab contains also evaluation board control functions. Automatic writing (Update registers
immediately) is enabled by default. It means that a write operation is done after every mouse click. If you
want to change several settings in one or more tabs and write the register(s) after making all the changes,
you can disable automatic writing. Then after the changes you have to initiate the register write by clicking
the right mouse key with the cursor in the Register Map area. From the pop-up menu you can choose to
write all registers or just a selected register. The same pop-up lets you write default values to one or all
registers and read one or all registers.

After clicking the “Hardware reset” button, all register values will be reset to default value, and a pop-up
window appears where user can accept reading all the registers (this is recommended). Another way to
reset the chip is to disconnect the USB cable (or external power if it is used) for a few seconds, plug it in
again and read all registers to see that they have the default values after the power-on-reset. USB setup
button will restore default setting for USB interface board.

USB board can measure voltages from the evaluation board. On the LP5526 board the circuit V
the converter output voltage V
the Common tab is set. Measurement results are shown on top of the window.

The software can demonstrate external PWM brightness control using the GPIO[0]/PWM input. PWM
signal is generated by the software. External PWM can only reduce the brightness set by internal controls.
All the LEDs have enable bits (en_ext_X_pwm, en_main_pwm, en_sub_pwm) for allowing external PWM
control. These bits are controlled in corresponding LED control Tabs (Color LEDs and Backlight). External
PWM control has no effect to the outputs that do not have enable bit set. You must also set ‘en_pwm_pin’
bit in GPIO tab to set GPIO[0]/PWM pin act as an external PWM input pin.

Note that when Flash button (in Color LEDs Tab) is used and released, it resets the PWM pulse ratio. In
the Common Tab, the External PWM slider controls the duty cycle of the GPIO[0]/PWM input pin.
Measurement polling disturbs the External PWM control and it should be turned off when External PWM is
used.

Evaluation Software

are measured. Measurements are enabled, when the Polling interval in

BOOST

DDIO

and

3.2 Boost Tab

In this tab, Figure 3, the LP5526 boost converter can be enabled, and the output voltage can be set from
the pull-down menu. The internal active load can be enabled to eliminate pulse skipping of the boost
converter. Active load will consume some power when the boost output current is small. It will decrease
efficiency at very light load conditions. See datasheet for boost converter typical performance graphs.

Figure 3. Boost Tab

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3.3 Color LEDs Tab

In this tab, Figure 4, are all RGB LED controls. RGB outputs are enabled with 'RGB' selection box, every
color output has also individual enable. 'RGB PWM' enables the internal PWM generation and color
selection. RGB outputs' mode can be selected either 'Current sink', or 'Switch mode'. Default is 'Switch
mode'. In 'Switch mode' the outputs are low ohmic switches. 'Switch mode' should be used only when
external ballast resistors are used in series with the LEDs.

With 'RGB color and bright' section it is possible to control the RGB LED color with PWM. In overlapping
mode color cannot be selected. In the diagram the LED on/off times are presented.

'RGB maximum' current can be selected for each output from 25% to 100%. Evaluation board resistor R23
and R27 limits the maximum RGB current; default value 2.4 kΩ or 2.4 + 3.3 = 5.7 kΩ when jumper J26 is
disconnected. Current limiting function is active only if 'Current Sinks' is selected.

Remember that with Flash LED, only the Current Sink mode should be used, NOT Switch mode since
there is no current limiting resistor in series with Flash LEDs. Switch mode should be used only when
RGB led is used and current limiting resistors are not bypassed (jumpers J6-J8 off).

External PWM control can be enabled to each output. These must be enabled, when the Flash function is
used. Flash button forces GPIO[0]/PWM pin to high. It is active only when it is kept pressed down, and will
be low only after release the Flash button. Remember to set USB PortA GPIO[0] as output and set 'en
pwm pin' from GPIO tab.

'Check bit' button can be used any time to read back the 'safety_set' bit value. The bit is set when safety
function has switched LED's off due to 1s timeout. 'safety_set' bit is read automatically always when user
pushes Flash button down and also when it is released.

The 'R
It is for calculation purposes only and does not control the current in any way.

calculator' selection can be used to estimate required R

RGB

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resistor value for the specific current.

RGB

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Figure 4. Color LEDs Tab

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3.4 GPIO Tab

In this tab, Figure 5, it is possible to control GPIO bits and configure USB board for reading/writing. Port A,
B and L refer to USB interface boards ports. Direction of the LP5526 GPIO pins can be set with 'oenx'
controls. With the 'datax' controls it is possible to set the state of the GPIO pins, when they are set as
output (oenx = 1 / pressed down). When the GPIO pins are set as input, these 'datax' buttons work as an
indicator, and you can read the state of the pins with the read-button.

With the USB interface I/O section it is possible to set/read the GPIO pins state.
It is possible to configure port A of USB board as output or input. If you want to use LP5526’s GPIO0…2

as output, you have to configure port A as input.
It is important that ‘en_pwm_pin’ bit is set and GPIO0 (in USB interface I/O) is set as output, if you want to

use GPIO0 as PWM input for any purpose (RGB, WLED or FLASH triggering).

Evaluation Software

3.5 Backlight Tab

In this tab, Figure 6, the backlight LEDs can be controlled. Main and Sub outputs can be enabled
individually. If you select Large display mode, all LEDs are controlled by the main WLEDs controls (also
fading).

Current setting for the outputs are done with the sliders. You can move the slides with arrow keys for more
precise control, or write values directly. Pressing ‘Write’ button writes adjusted values to registers.

You can enable fade function by setting ‘Automatic fade enabled’. When new current value is set, the
WLED currents will automatically fade smoothly to new value. You can select which LEDs fade effects.
When ‘Large’ display mode is on, set ‘Fade control switch’ to Main WLEDs to enable fading of all WLEDs.

‘Fade execution time’ refers to the time to execute full range current change in WLEDs.
External PWM control can be enabled to both Main and Sub individually. External PWM input pin is

GPIO[0].

Figure 5. GPIO Tab

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