AL8807 — 30V 1A Step-Down Buck Constant-Current LED Driver

Overview

The AL8807 (AL8807W5-7 / AL8807MP-13) is a step-down (buck) constant-current LED driver IC manufactured by Diodes Incorporated. Packaged in a compact SOT-25 (SOT-23-5) or MSOP-8EP housing, it drives high-brightness LEDs at continuous currents up to 1.0 Amp from input supply voltages ranging from 6.0V to 30.0V DC.

Operating at switching frequencies up to 1.0 MHz, the AL8807 achieves up to 96% efficiency using a high-side current-sense circuit. Its multi-function CTRL pin supports both PWM dimming (up to 1 kHz) and DC voltage analog dimming ( $0.5\text{V} \dots 2.5\text{V}$ ).

Quick reference


Input Supply Voltage (`VIN`)	6.0 V to 30.0 V DC
Output LED Current	Up to $1.0\text{ A}$ continuous (Set by sense resistor $R_S$ )
Current Accuracy	$\pm 5\%$ output current accuracy
Switching Frequency	Up to $1.0\text{ MHz}$
Efficiency	Up to $96\%$ typical
Dimming Modes	PWM Dimming ( $100\text{ Hz} \dots 1\text{ kHz}$ ) or DC Voltage Analog Dimming
Package	SOT-25 (SOT-23-5) / MSOP-8EP

Pinout (SOT-25 / SOT-23-5 Package)

text

             ┌───┴───┐
        SW  1│ 1   5 │ VIN (+6V to +30V)
       GND  2│       │
      CTRL  3│ AL8807│ 4 SET (Sense Input)
             └───────┘

Pin	Name	Type	Description
1	`SW`	Output	Internal MOSFET Switch Drain (Connect to Freewheeling Diode & Inductor)
2	`GND`	Power	Ground Reference (0 V)
3	`CTRL`	Input	Control Pin (Open = 100% LED Current; Low = Shutdown; PWM or DC Analog Voltage Input)
4	`SET`	Input	High-Side Current Sense Input (Connect sense resistor $R_S$ between `VIN` and `SET`)
5	`VIN`	Power	Power Supply Input (+6.0V to +30.0V DC)

High-Side Buck LED Driver Circuit

text

  +6V to +30V DC Supply ───┬─── [Pin 5: VIN]
                           │
                   [Sense Resistor R_S]
                           │
                           ├─── [Pin 4: SET] ───► ( + ) LED String (1 to 8 LEDs in series)
                           │                               │
                      [AL8807]                             └─── [Inductor L1] ───┬─── [Pin 1: SW]
                           │                                                     │
                           └─── [Pin 2: GND] ─── Cathode Schottky Diode ─────────┘

Output Current Formula

The constant LED current ( $I_{LED}$ ) is set by high-side sense resistor $R_S$ connected between VIN and SET:

$I_{LED} = \frac{100\text{ mV}}{R_S} = \frac{0.10\text{V}}{R_S}$

$\text{For } I_{LED} = 700\text{ mA} \implies R_S = \frac{0.10\text{V}}{0.70\text{A}} \approx 0.143\ \Omega.$

Common mistakes

Leaving CTRL (Pin 3) grounded: CTRL turns the IC OFF when pulled below $0.4\text{V}$ . For 100% constant brightness, leave CTRL floating or pull HIGH to 3.3V/5V.
Using non-Schottky freewheeling diodes: High 1MHz switching speed requires an ultra-fast low-forward-voltage Schottky diode (such as B140 or SS14).

Notes

AL8807 vs PT4115: AL8807 comes in a small 5-pin SOT-25 package; PT4115 is packaged in SOT-89-5. Both use high-side current sensing with $100\text{ mV}$ reference.