PCA9955B, PCA9956B : 16 & 24-channel constant current LED driver

PCA9955B and PCA9956B are I²C-bus controlled 16-channel constant current LED driver optimized for dimming and blinking.

Hello World

Import programPCA9955A_Hello

Hello world code for PCA9955A class library. The PCA9955A is a 16-channel Fm+ I2C-bus 57mA/20V constant current LED driver. This program shows its basic operation of PWM and current settings.

Last commit 21 Jun 2022 by InetrfaceProducts NXP

Library

Import libraryPCA995xA

PCA9955A and PCA9956A class library. The PCA9955A is a 16-channel and the PCA9956A is a 24-channel Fm+ I2C-bus 57mA/20V constant current LED driver. The PCA9955A has a extended feature which called "Gradation control".

Last commit 16 Jun 2022 by InetrfaceProducts NXP

Pinout

Notes

Chip compatibility : PCA995xB , PCA995xA and PCA9955(non-A or B)

B-version and A-version

The latest version of the PCA995x has "B" at end of the type number.
This "B version" pin and software compatible to "A version". So The "B" can be used for drop-in-replace for "A".

PCA9955B == PCA9955A != PCA9955

PCA9955(non-A version) is not software/hardware compatible to PCA9955B or PCA9955A.
There are several differences between A and non-A versions.
Differences are on register mapping/functions and pin assignments. Please make sure you are using PCA9955B or "A".

High-level API is available

A high-level API that can be used as the "PwmOut" of bed-SDK is available.
This API enables to make instances of each LED output pins and control PWM duty cycle by assignment.
Output current also controllable by API function.
For detail information, refer API document of LedPwmOutCC Class class which is included in PCA995xA class library.

#include "mbed.h"
#include "PCA9956A.h"

PCA9956A    led_cntlr( p28, p27, 0xC4 );  //  SDA, SCL, Slave_address(option)
LedPwmOutCC led( led_cntlr, L0 );

int main()
{
    while( 1 ) {
        for( float p = 0.0f; p < 1.0f; p += 0.1f ) {
            led     = p;
            wait( 0.1 );
        }
    }
}

About the chips

PCA9956B

The PCA9956B is an I2C-bus controlled 24-channel constant current LED driver optimized for dimming and blinking 57 mA LEDs. Each LED output has its own 8-bit resolution (256 steps) fixed frequency individual PWM controller that operates at 31.25 kHz with a duty cycle that is adjustable from 0 % to 99.6 % to allow the LED to be set to a specific brightness value.

Datasheet: http://www.nxp.com/documents/data_sheet/PCA9956B.pdf

PCA9955B

The PCA9955B is an I2C-bus controlled 16-channel constant current LED driver optimized for dimming and blinking 57 mA LEDs in amusement products. Each LED output has its own 8-bit resolution (256 steps) fixed frequency individual PWM controller that operates at 31.25 kHz with a duty cycle that is adjustable from 0 % to 100 % to allow the LED to be set to a specific brightness value.

On addition to this, the PCA9955B has "Gradation control".
The gradation control is a new feature of PCA995xA series. After the register setting and start the control, the PCA9955A performs dimming cycles automatically without MCU intervention.

Datasheet: http://www.nxp.com/documents/data_sheet/PCA9955B.pdf

PCA9952 and PCA9955 (non-A/B version)

The PCA9955 and PCA9955 (no-A at end of the type number) is not supported by this component class.

How the API works?

When the instance is made, all set up for PWM operation are done automatically.
For the operation, user can control the LED brightness in two ways.

  • PWM
  • Current

PCA9955A and PCA9956A have internal 31.25kHz oscillator to generate internal PWM waveform. This signal switchs the output current ON and OFF. The class' function pwm() controls duty-cycle of this output.

Another control is current. Since the PCA9955A and PCA9956A are constant current type LED driver, those have internal current sources. The current source on each channels has independent control of output current. The class' function current() provides interface to current change.

API_and_output

Tips for the chips

PCA995xA family

This PCA995xA components library can be used for both PCA9955A(16-channel) and PCA9956A(24-channel).
If you are using both chips on the I2C bus, those can be operated like..

#include "mbed.h"
 
#include "PCA9955A.h"
#include "PCA9956A.h"

PCA9955A    led0( p28, p27, 0xC0 );    //  SDA, SCL, Slave_address=0xC0 (16-channel chip)
PCA9956A    led1( p28, p27, 0xC2 );    //  SDA, SCL, Slave_address=0xC2 (24-channel chip)
 
int main()
{
    led0.current( ALLPORTS, 1.0 ); //  Set all ports output current 100%
    led1.current( ALLPORTS, 1.0 ); //  Set all ports output current 100%

    led0.pwm( ....    //  PWM control for PCA9955A(16-channel chip)
    led1.pwm( ....    //  PWM control for PCA9956A(24-channel chip)
    ...

Other sample code

For PCA9955B and PCA9955A : http://developer.mbed.org/users/nxp_ip/code/PCA9955A_Hello/
For PCA9956B and PCA9956A : http://developer.mbed.org/users/nxp_ip/code/PCA9956A_Hello/
For Gradation control of PCA9955B and PCA9955A http://developer.mbed.org/users/nxp_ip/code/PCA9955A_Gradation_control/

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