Highway 09 Ic Datasheet -

The Highway 09 is a linear regulator. This means:

[ P_D = (V_IN - V_LED) \times I_OUT ]

Example Calculation:

Without a heatsink, a TO-252 package has a junction-to-ambient thermal resistance (θ_JA) of ~60°C/W. At 5.4W, the junction temperature would be: ( T_J = 25°C + (5.4W \times 60°C/W) = 349°C ) → Instant destruction.

Solution:

Understanding the pinout is critical for correct PCB layout. The Highway 09 uses a 3-pin configuration.

| Pin No. | Name | Function | Description | | :--- | :--- | :--- | :--- | | 1 | VIN | Supply Voltage | Input power pin. Bypass with a 100µF electrolytic + 0.1µF ceramic capacitor close to the IC. | | 2 | GND | Ground | Common ground for input, output, and control circuitry. The tab (heatsink) is internally connected to GND. | | 3 | OUT | Current Output | Connected to the cathode of the LED string. An external sense resistor (R_sense) is placed between OUT and GND to set the current. |

A common stumbling block for beginners is interpreting the thermal limits section of the datasheet.

Internally, the Highway 09 integrates the following blocks: highway 09 ic datasheet

A simplified internal diagram would show the input feeding the pass transistor, controlled by the error amplifier comparing a fraction of the output to the 1.25V reference. The current limit and thermal sensors directly pull the error amplifier output low during fault conditions.

Exceeding any of the following ratings will likely destroy the IC. This table is based on typical Highway 09 specifications.

| Parameter | Symbol | Min | Max | Unit | |-----------|--------|-----|-----|------| | Input Voltage | VIN | -0.3 | 45 | V | | Output Voltage | VOUT | -0.3 | VIN + 0.3 | V | | Enable/Adjust Voltage | V_ADJ | -0.3 | 40 | V | | Maximum Output Current | I_OUT | Internally limited | 2.5 | A | | Junction Temperature | T_J | -40 | 150 | °C | | Storage Temperature | T_STG | -65 | 150 | °C | | Lead Temperature (soldering, 10s) | | | 260 | °C |

Caution: Operating near maximum ratings reduces lifetime. Provide adequate heatsinking if I_OUT > 500mA. The Highway 09 is a linear regulator

Note: Absolute Maximum Ratings should never be exceeded, even momentarily.

| Parameter | Symbol | Min | Typ | Max | Unit | | :--- | :--- | :--- | :--- | :--- | :--- | | Input Voltage | V_IN | - | - | 30 | V | | Load Dump Protection | V_IN_surge | - | - | 40 | V | | Output Current | I_OUT | 0 | 1.2 | 1.5 | A | | Current Sense Voltage | V_SENSE | 0.095 | 0.100 | 0.105 | V | | Quiescent Current (no load) | I_Q | 1 | 2 | 5 | mA | | Shutdown Current (VIN<UVLO) | I_SHDN | - | 10 | 50 | µA | | Thermal Shutdown Temp | T_SD | 140 | 150 | 160 | °C | | Thermal Hysteresis | T_HYS | - | 15 | - | °C |

Critical Design Formula: The output current is set by the sense resistor (R_sense) using the internal voltage reference:

[ I_OUT = \fracV_SENSER_SENSE = \frac0.1VR_SENSE ] Without a heatsink, a TO-252 package has a

Example: To achieve 700mA LED current: ( R_SENSE = 0.1V / 0.7A = 0.142\Omega ) → Use a standard 0.15Ω, 1W resistor.