AL1781/1782

Document number: DS41312 Rev. 1 - 2

8 of 18

www.diodes.com

August 2018

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AL1781/1782

Functional Description

The AL1781 and AL1782 are single-channel and dual-channel constant-current regulators optimized for 1-channel Dimmable White and 2-channel

Tunable White Smart Connected Lighting (SCL) applications. It supports E-flicker free High Frequency PWM dimming with Deep Dimming

Capability: Support 40kHz down to 4%, 10kHz down to 1.0%, 4kHz down to 0.4%, or 1kHz down to 0.1% with good dimming linearity. When no

PWM signal is detected by AL1781/1782, it will automatically enter the low-power mode for power saving purpose to be in compliance with Energy

Star standby power requirement for SCL bulbs. It also integrates Adaptive Thermal Management (ATM) scheme to minimize non-productive power

dissipation. The AL1781/1782 has abundant of protection features, including Under-Voltage-Lockout (UVLO), LED string Open/Short protection

and Over-temperature protection (OTP); when detecting these fault conditions, it will report the fault status on FAULTB pin.

1.

Enable and Soft-Start LED Drivers

The AL1781/1782 is enabled when the voltage at any PWMx pin is greater than approximately 2.5V, and disabled when all PWMx are lower than

0.4V. Upon any PWMx pin is asserted and VIN pin is ramped up beyond minimum operation voltage, a soft start will be performed with a slew-

rate-controlled current ramp over 2

00μs at LEDx output pins to minimize current overshoot through LED strings for optimal system reliability.

When all PWMx are inactive for 4ms, The LED Driver will enter Low-Power mode with ultra-low standby power.

2.

LED Current Setting and Capability

(1)

LED Current Setting

level is expressed as below:

For AL1781:

For AL1782:

AL1782 provides same current amount of 500mA.

(2)

LED Current Capability

The maximum current of each channel can drive up to 750mA with a total driving current up to 1500mA (refer to Table 1 below). The minimum

channel current is recommended as in Table 2 in order to meet channel current accuracy and short protection specifications. Each channel can

still be individually controlled by digital PWM dimming. The integrated low-side current sinks allow LED common-anode connections for cost

effectiveness or different anode voltages for efficiency optimization.

Model Name

Channel 1

Channel 2

Total IC Current

AL1781

1500mA

Not Applicable

1500mA

AL1782

750mA

750mA

1500mA

Table 1 Recommended Maximum Channel Current and Total IC Current for AL1781/1782

Model Name

Channel 1

Channel 2

Total IC Current

AL1781

300mA

Not Applicable

300mA

AL1782

150mA

150mA

300mA

Table 2 Recommended Minimum Channel Current and Total IC Current for AL1781/1782

Along with bus-mode fault reporting, multiple devices can be employed together to increase current driving capability or channel count versatility.

Any two or more channels can be tied together to drive one LED string with aggregated current. So when current needed for any channel is

greater than the maximum value the device can provide, two or more channels or devices can be paralleled together to provide the drive current

needed.