Datasheet AL5873Q (Diodes) - 10

AL5873Q Function Description
The AL5873Q is a cost-effective three-channel, constant-current linear driver optimized for automotive LED applications. Each channel can drive up to 250mA with a total driving current up to 750mA. The channel can be controlled by digital PWM signal or analog dimming signal. The integrated low-side current sinks allow LED common-anode connections for cost effectiveness or different anode voltages for efficiency

optimization.
N
The AL5873Q detects fault conditions and reports its status on the FAULTB pin. It features LED open detection, LED short detection, Over
IO
Temperature Protection (OTP), and Under Voltage Lockout (UVLO).
T
Integrated thermal foldback function reduces the regulated current level at high junction temperatures to limit power dissipation.
A M LED Current Setting R
The AL5873Q channel current is set by the current setting resistor RREF1 or RREF2. Figure 4 illustrates LED current setting with FULL pin status.
O F
Given that FULL = low, the LED channel current is pulse-width modulated at 200Hz frequency with fixed 25% duty cycle, and the amplitude of the LED channel current is set by RREF1. The average LED channel current is expressed as below:
IN
𝑉 𝐼 𝑅𝐸𝐹1 × 25%
D
𝐿𝐸𝐷𝑋 = 4000 × 𝑅𝑅𝐸𝐹1
E C
Given that FULL = high, the LED channel current is set by RREF2. The LED channel current level is expressed as below:
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𝑉 𝐼 𝑅𝐸𝐹2
A
𝐿𝐸𝐷𝑋 = 4000 × 𝑅 𝑅𝐸𝐹2
V D
Where VREF1 and VREF2 are nominally 1.5V, ILEDX is in mA, and RREF1 and RREF2 are in kΩ. For example, if RREF1 and RREF2 are both 24kΩ, the
A
AL5873Q provides 250mA / 62.5mA output current per channel when FULL = high / low. While the recommended maximum ILED1, ILED2 and ILED3 are at 250mA for the AL5873Q, by setting RREF2 at 24kΩ, the system design can drive an LED string with higher current by connecting the cathodes of the LED string to two or more LED channel outputs (LEDx). The total current through the LED string is the sum of the current through the individual channels. High FULL Max:5ms Low V Low REF 2 4000  R V REF 2 REF1 V 4000  REF 1 4000  RREF1 R REF 1 Max:5ms I 200Hz 200Hz LEDX 25% duty 25% duty 0 0
Figure 4. Current Setting Diagram Under Voltage Lockout
Under-voltage lockout function (UVLO) guarantees that the device is initially off during start-up. The AL5873Q is not turned on until the power supply has reached 5.0V. Whenever the input voltage falls below approximately 4.7V, the device is turned off. The UVLO circuit has a hysteresis of 300mV. FAULTB status will be reported when UVLO happens.
Enable and Start-up LED Drivers
The AL5873Q is enabled when the voltage at the PWM pin is greater than typical voltage of 1.4V, and disabled when the PWM is lower than 0.4V. Upon the PWM pin is asserted and VIN pin is ramped up beyond minimum operation voltage, a start-up process will be performed. When the PWM is pulled to ground longer than 25ms, the LED Driver will enter standby mode with ultra-low standby current.
Standby Mode
When PWM pin is pulled down to voltage lower than 0.4V for 25ms or longer, the AL5873Q will automatically enter the standby mode for power saving purpose. When in the standby mode, most of blocks in the AL5873Q are turned off to reduce the quiescent supply current. When the PWM pin is pulled up to voltage higher than 1.4V, the AL5873Q will automatically exit the standby mode and perform its designated functions properly.

AL5873Q 10 of 16 February 2021 Document number: DS42780 Rev. 2 - 2
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