STLED325 datasheet(14/62 Pages) STMICROELECTRONICS

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Functional description

STLED325

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Doc ID 17576 Rev 1

3.8

LED drivers

The constant current capability is up to 40 mA per output segment and is set for all the

outputs using a single external resistor. When acting as digit drivers, the outputs source

current to the display anodes. When acting as segment drivers, the LED outputs sink current

from the display common cathodes. The outputs are high impedance when not being used

as digit or segment drivers.

Each port configured as a LED segment driver behaves as a digitally-controlled constant

current sink. The LED drivers are suitable for both discrete LEDs and common anode (CA)

numeric LED digits. When fully configured as a LED driver, the STLED325 controls up to 8

LED segments in a single digit with individual 8-step adjustment of the constant current

through each LED segment. A single resistor sets the maximum segment current for all the

segments, with a maximum of 40 mA per segment. The STLED325 drives any combination

of discrete LEDs and common anode (CA) digits for numeric displays.

The recommended value of RSET is the minimum allowed value, since it sets the display

driver to the maximum allowed segment current. RSET can be a higher value to set the

segment current to a lower maximum value where desired. The user must also ensure that

the maximum current specifications of the LEDs connected to the drivers are not exceeded.

3.9

Over temperature cut-off

The STLED325 contains an internal temperature sensor that turns off all outputs when the

die temperature exceeds 140°C. The outputs are enabled again when the die temperature

drops below 125°C. Register contents are not affected, so when a driver is over-dissipating,

the external symptom will be the load LEDs cycling between on and off as the driver

repeatedly overheats and cools, alternately turning the LEDs off and then back on again.

This feature will protect the device from damage due to excessive power dissipation. It is

important to have good thermal conduction with a proper lay-out to reduce thermal

resistance.

3.10

Standby mode

By utilizing the standby function, the host processor and other ICs can be turned off to

reduce power consumption. The STLED325 is able to wake-up the system when

programmed hotkeys are detected to signal that the full operation of the system is required.

The hotkeys can be entered to the system through the front panel keys or through the

infrared (IR) remote control or the Real Time Clock (RTC) alarm or through the wake-up pin.

STLED325 supports multiple remote control protocols decoding by setting the appropriate

The STLED325 is able to cut-off the power to the main board for standby operation for good

power management. STBY will be set to high when READY signal goes from high to low, I2C

command for standby is seen or when the guard timer has finished counting down to 0,

whichever occurs first.

In the normal mode of operation, the STBY is asserted only when the guard timer has

finished counting down to 0. This is meant to put the system into stand-by even though

standby command was not issued by the host or READY signal did not go low. This occurs

as the guard timer register was not cleared before it finished counting down to 0.

STLED325 数据表(PDF) 14 Page - STMicroelectronics

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