Datasheet

through the Manual view and basic operations of the LP5523. The other views are Program, Code memory and History; these
views are presented in 2. LP5523 Programming.
Tip: The context-sensitive buttons in the lower part of the window can be used for direct Write/Read operations of the registers.
The target register is indicated by red cross, and the target can be changed by clicking on the desired register on the indicator
panel.
DIRECT CONTROL
Enabling the Device and Starting the Charge Pump
The first step to start with the LP5523 is to enable the chip; tag the Chip enabled check box. At first it is best to use the following
settings: Clock internal and Charge pump gain 1.5x (see Figure 4). At this point it is good to ensure the charge pump output voltage
with the LP5523 built-in LED error detection. To do this, select VOUT from the LED test drop down menu and tag Start conversion.
Use the adjacent RD button to read the result: it should be around 4.5 volts. Also click on the RD button on the Status/Interrupt
section to verify that the internal clock is used (Ext clk indicator light should be OFF) and that the LED test is done (LED test done
indicator should be ON).
Setting the Led Current and PWM
The next step is to set the desired LED currents. This is done by Current slider. Set 5 mA current for LED1 and set PWM to 50%
= 7Fhex. You should have a green LED switched on now. Note: When the Update immediately tag is set, the evaluation software
will write the new settings immediately to the LP5523 registers. Otherwise you need to click on the Update button.
The basic idea behind LP5523 operation is to first set the LED currents to the required level and after that the current settings are
not touched any more – all the fade-in and fade-out sections (ramps) and the temperature compensation is done by PWM . Each
LED has its own constant current output and all the outputs can be controlled independently. Therefore LED pre-selection (matched
LEDs) is not required and this kind of architecture supports also color control. The PWM, current and temperature compensation
controls are organised under tabs labelled by LED1 to LED 9. Now, let’s set 5 mA current and 50% PWM for LED2 and 3.5 mA
current and 50% PWM for LED7. As a result, D1 on evaluation board should emit white light.
Master Fader
The PWM of LED driver outputs can be controlled individually as as described above, or alternatively the drivers can be grouped
by function to provide a quick control. The LP5523 has three master fader registers, so it is possible to form three master fader
groups. To assign an LED to a group, use the Master Fader drop down menu. Select Group 1 for LEDs 1, 2, and 7. Now you can
control all the three outputs with a single master fader register. There is a Master fader slider provided on the right side of the control
panel and dragging the slider under tab labelled by 1 controls now LEDs 1, 2, and 7. Note that the initial PWM and current for LEDs
in a group needs to be set before using the master fader control, since master fader is simply a multiplier, which acts on the PWM
registers.
Logarithmic vs Linear PWM Response
Logarithmic response is used to give the impression of a linear light intensity increase/decrease as the PWM duty cycle is raised/
reduced. Logarithmic response is visually more pleasing especially when the overall brightness is low. To activate the logarithmic
response, tag logarithmic adjustment. Activate logarithmic adjustment for LEDs 1, 2 and 7. Set also 5 mA current for LEDs 3 and
4, set 3.5mA for LED8. Set 50% PWM for LEDs 3, 4 and 8. Assign LEDs 3, 4 and 8 to the master fader group 1 so that you can
control all the six LEDs with one slider. Now you should have logarithmic control over the LEDs 1, 2, 7 and linear control over the
LEDs 3, 4, 8. To see the difference between the lin and log response, move the slider backwards and forwards to alter the intensity
of all the six LEDs at once.
Temperature Compensation
The LP5523 has a temperature compensation function to correct for variations in light intensity and color caused by changes in
ambient temperature.
Reset the LP5523 and start the charge pump as shown in Figure 4. Set 5 mA current, 50% PWM for LEDs 1 and 2; Set 3.5 mA
current, 50% PWM for LED 7.
In order to activate the compensation function tag the check box next to Correction factor slider. The slope for the temperature
compensation line can be set by the slider. A simple approximation for the RGB LED temperature compensation would be +1.3%/
°C for red LED and +0,2%/°C for green and blue so that the intensity of all the colors remain approximately the same over the
temperature from 25°C to 60°C .
To observe the effect of the compensation on color, try the following: Under Temperature label, tag Start conversion (this enables
the LP5523 internal temperature sensor) and continuous measurement (continuous temperature measurement). Enter 25°C to the
External sensor box and click on WR button to write the reading to the LP5523 memory. Now toggle between internal sensor and
external sensor as you warm up the LEDs and LP5523 with a hair dryer. When the “external sensor” is active, the temperature
information is read from register TEMPERATURE WRITE (addr. 40H). When the temperature is 25°C all the compensation settings
have no effect, so when you have the external sensor activated, you will see the “uncompensated” situation. When you activate
the internal sensor, you will see the effect of the compensation as the ambient temperature is raised. Without compensation emitted
light will be drifted somewhat towards a more bluish white, because the red LED element of the RGB LED shows the strongest
temperature dependence.
AN-2227 - LP5523 Evaluation Kit
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