Texas Instruments LP8556TM-Evaluation module LP8556TM-EVM/NOPB LP8556TM-EVM/NOPB Ficha De Dados
Códigos do produto
LP8556TM-EVM/NOPB
7.
LP8556 Usage and Programming
The LP8556 white LED driver requires configuration of the boost converter and dimming operation. The
boost converter can operate at three switching frequencies. Options can be set for spread spectrum and
slew rate control. The dimming can be done with a full PWM output, linear current control, or an adaptive
combination of the two for the greatest power savings. Phase-shift modes are available for the PWM output.
Additional safety features also need to be configured.
boost converter can operate at three switching frequencies. Options can be set for spread spectrum and
slew rate control. The dimming can be done with a full PWM output, linear current control, or an adaptive
combination of the two for the greatest power savings. Phase-shift modes are available for the PWM output.
Additional safety features also need to be configured.
7.1. In Circuit Operation
The LP8556 white LED driver can be controlled during operation either with I2C register accesses or by
external resistor selection. For either case, a configuration must be saved in EPROM which is specific for
the chosen control scheme. If I2C register access is used to control the LP8556, then saved configuration
values in the EPROM can be overwritten to change settings during setup for operation. The following
sections highlight the configuration steps needed for both. A complete configuration should be written to the
device and the EPROM burn sequence described below must be completed for operation without I2C register
access. In circuit
external resistor selection. For either case, a configuration must be saved in EPROM which is specific for
the chosen control scheme. If I2C register access is used to control the LP8556, then saved configuration
values in the EPROM can be overwritten to change settings during setup for operation. The following
sections highlight the configuration steps needed for both. A complete configuration should be written to the
device and the EPROM burn sequence described below must be completed for operation without I2C register
access. In circuit
control using external resistors will be referred to as “Resistor Config” in the following text.
A configuration is saved in EPROM and the external resistors complete the configuration. The only change
made to the LP8556 device in circuit is done by the PWM input to set the dimming value. Control using I2C
register access will be referred to as “I2C Control”. The term control is used because the configuration of the
device is still stored in EPROM but the LP8556 may also be updated via I2C during operation. Another
possible usage model is to have a preset configuration saved in EPROM, not use external resistors, and not
update the registers during operation. The register configuration for this model is the same as for “I2C
Control
made to the LP8556 device in circuit is done by the PWM input to set the dimming value. Control using I2C
register access will be referred to as “I2C Control”. The term control is used because the configuration of the
device is still stored in EPROM but the LP8556 may also be updated via I2C during operation. Another
possible usage model is to have a preset configuration saved in EPROM, not use external resistors, and not
update the registers during operation. The register configuration for this model is the same as for “I2C
Control
” except the BL_ON bit must be set in CFG2 to allow the backlight to turn on.
7.2. Enable and Standby
The EN/VDDIO pin controls enabling and shutdown of the LP8556. A zero value on this pin holds the device
in shutdown with minimum current consumption. Register access is not available during shutdown. Once
enabled, a standby mode is available using the PWM input detector. If the PDET_STBY bit is set in CFG1,
the LP8556 will enter a low power standby mode when a zero level is detected on the PWM pin for more than
50 ms. In standby mode the boost and led driver are shut down. The oscillator remains on allowing
detection of activity on the PWM signal to resume operation.
in shutdown with minimum current consumption. Register access is not available during shutdown. Once
enabled, a standby mode is available using the PWM input detector. If the PDET_STBY bit is set in CFG1,
the LP8556 will enter a low power standby mode when a zero level is detected on the PWM pin for more than
50 ms. In standby mode the boost and led driver are shut down. The oscillator remains on allowing
detection of activity on the PWM signal to resume operation.