このリファレンス・デザインでは、TPS92682-Q1 と TPS92520-Q1 を使用して、ヘッドライト・アプリケーション向けに 3 チャネル LED ドライバの包括的な機能を自己完結型で実現する方法を紹介します。このデザインは、車載のボディ・コントロール・モジュールと互換性のある、低コストのハロゲン・ヘッドライト・モジュールの代替品で使用することを意図しています。3 つの LED チャネルは、ハイビームとロービーム、方向指示器 (ウィンカー)、昼間点灯ライト (DRL)、ポジション・ランプ (車幅灯) の駆動に使用できます。このデザインは、1 つの TPS92682-Q1 デュアル・チャネル・コントローラを、定電圧昇圧と定電流 SEPIC に使用しています。また、この昇圧回路を電源とする 1 つの TPS92520-Q1 も使用し、2 つの定電流同期整流降圧コンバータを駆動します。この基板は、グランド・ストリップを採用する設計であり、CISPR 25 Class 5 伝導型の試験結果を含め、EMI 関連規格に準拠した電力段を密閉することができます。

• 2 段の定電圧昇圧コンバータは、2 つの同期整流降圧コンバータに電力を供給し、ハイビームやロービーム、および方向指示器 (ウィンカー) の駆動に対応

• 昼間点灯ライト (DRL) と車幅灯向けの SEPIC コンバータ

• ボディ・コントロール・モジュールから供給される電力との互換性を確保

• ハイビームとロービームや、方向指示器向けに、単一 LED の短絡や、出力の短絡と開路の検出を実施し、故障の報告と該当回路の無効化で対処

• 逆極性バッテリ保護

• 最大 30W のハイビーム / ロービーム

• ターン・インジケータは、1.5Hz で最大 15W、50% デューティ・サイクルに対応

• 方向指示器入力から出力までの遅延時間は 10ms 未満

• 昼間点灯ライト / 車幅灯：最大 15W

• ボディ・エレクトロニクスおよびライティング

This reference design demonstrates a three channel LED driver for front headlight applications. The design uses a single channel of the TPS92682-Q1 for a constant voltage boost converter driving a two channel constant current synchronous buck converter, the TPS92520-Q1. Channel one of the TPS92520-Q1 provides up to 30 watts for Highbeam/Lowbeam applications. The Highbeam input is used to open or shunt the Highbeam section of the LED string, this determines Highbeam or Lowbeam operation. The second channel of the TPS92520-Q1 provides up to 15 watts for Turn Indicator applications. A switched input power of 1.5 Hz drives the Turn Indicator LED string with less than a 10 ms delay from the rising Turn Indicator input. The second channel of the TPS92682-Q1 is set up as a constant current SEPIC to provide up to 15 watts for Day Time Running Light/Position Marker Light. The mode of operation is determined by the Highbeam/Lowbeam and Turn Indicator inputs. The design contains a MSP432 processor to program the TPS92682-Q1 and TPS92520-Q1 via SPI bus, control the headlight functions, read LED string voltages and report faults to the Body Control Module. Each function has its own reverse battery protected input.

This design has single LED short-fault reporting for Highbeam/Lowbeam and Turn Indicator. A Highbeam/Lowbeam fault reduces Lowbeam input current to zero to notify the automotive Body Control Module there is a fault. There is also an open collector fault line available. The Turn Indictor fault is an open collector fault line. Turn Indicator fault goes low when there is an open string, shorted string or shorted LED and the Turn Indicator is disabled. The Printed Circuit Board is setup to use an edge card connector, EC1. The board also has a ground strip to allow enclosing the power stages to meet CISPR 25 Class 5 conducted EMI levels.

Terminology

This reference design is a self-contained LED headlight driver. Three power inputs, Lowbeam, Turn Indicator and Daytime Running Light/Position Marker Light are reverse battery protected. A fourth reverse battery protected signal input, Highbeam, determines whether to shunt or open via a MOSFET the Highbeam portion of the Highbeam/Lowbeam LED string. Daytime Running Light/Position Market light, as setup for testing, is always powered. Daytime Running Light/Position Marker Light function is determined by the other two power inputs Lowbeam and Turn Indicator. The test board is one of many possible configurations. A table shows light function based on inputs as configured for functional testing:

The printed circuit board is 56 mm X 102 mm including the edge card connector. Low profile components are on the top side to allow for a thermal interace to an enclosure for heatsinking. A ground strip is provided to enclose the power stages for EMI compliance. All tall components are on the bottom side including a connector for programming the MSP432 via JTAG, connector J3.

PCB top side with low profile parts, PCB bottom side with tall components

Thermal pad can be used to conduct heat to an enclosure to remove heat from this side of the printed circuit board.

The TPS92682-Q1 is a dual-channel, peak current mode controller with SPI communication interface. The device is programmable to operate in constant-voltage (CV) or constant-current (CC) modes. In CV mode, TPS92682-Q1 can be programmed to operate as two independent or dual-phase Boost voltage regulators. The output voltage can be programmed using an external resistor voltage divider, and a SPI-programmable 8-bit DAC.

In CC mode, the device is designed to support dual channel step-up or step-down LED driver topologies. LED current can be independently modulated using analog or PWM dimming techniques. Analog dimming with over 28:1 range is obtained using a programmable 8-bit DAC. PWM dimming of LED current is achieved either by directly modulating the PWM input pins with the desired duty cycle, or using a SPI-programmable 10-bit PWM counter. The optional PDRV gate driver output can be used to drive an external P-Channel series MOSFET.

The TPS92682-Q1 incorporates an advanced SPI programmable diagnostic and fault protection mechanism including: cycle-by-cycle current limit, output overvoltage and undervoltage protection, ILED overcurrent protection, and thermal warning. The device also includes an open-drain fault indicator output per channel. The TPS92682-Q1 includes an LH pin, when pulled high, initiates the limp home (LH) condition. In LH mode, the device uses a separate set of SPI programmed registers.