The TPS92830-Q1 is touted as a controller that requires the use of external MOSFETs, as opposed to the internal MOSFETs integrated into conventional LED drivers. Though it is often advantageous (or at least more convenient) to use ICs that require fewer external components, in this case, TI believes that the use of external MOSFETs ensures that engineers gain greater flexibility in their automotive lighting designs.
Figure 1. Simplified schematic. Image taken from the datasheet (PDF).
Why Use Linear Regulators?
According to the datasheet's description, in an effort to achieve better lighting homogeneity in front and rear automobile lamps, high-current LEDs are used together with LED lighting diffusers. As a side note: Is it just me or are some (many) of the LED brake lights in new cars about as bright as the sun?! I'm not picking on TI here; I’m just making a general comment regarding automotive LEDs. I wonder if there are federal guidelines/requirements for controlling how bright a car's headlights/tail lights/brake lights can or must be?
Anyways, the use of linear constant-current regulators helps car manufacturers to meet strict EMC and reliability requirements. Apparently, however, the challenge with this approach is being able to deliver high-current when using integrated power MOSFETs. Enter TI's TPS92830-Q1.
Protections and Features
This IC seems to have plenty of features:
- Ambient operating temperature range: -40°C to 125°C. Although impressive, this wide ambient operating temperature range is not uncommon for automotive ICs. In fact, this range is normal, and anything less would not be considered automotive grade. Only military-grade ICs (-55°C to 125°C) have a wider ambient operating temperature range.
- LED Short-to-GND and Open-Circuit Detection: Both the short-to-GND and open-circuit detection features are channel-independent. Once an open-circuit or short-to-GND condition is detected, the TPS92830-Q1 disables the faulty channel and enters an automatic retry mode. When, and if, the auto-retry mechanism determines that the faulty condition is resolved, the IC resumes normal operation.
Figure 2. LED short-to-GND and open-circuit scenarios. Image taken from the datasheet (PDF).
- LED dimming options: The IC's PWM functionality allows for three methods of dimming the LEDs:
- Internally generated PWM: The device has an on-board PWM generator that supports synchronization between various ICs. In other words, the IC be connected as a master or as a slave.
- Externally generated PWM: Each of the three LED channels can be individually controlled via the three PWM input pins (PWM1, PWM2, PWM3).
- Power supply dimming: This occurs when the entire LED driver itself is dimmed by applying PWM to the supply voltage.
TI has provided multiple application and implementation guidelines. In one example, TI offers hints for a typical application circuit for automotive external lighting. This includes a schematic (see image below), design requirements, and a detailed design procedure, including fixed parameters and component values.
Figure 4. Schematic for an automotive exterior lighting application, taken from the datasheet (PDF).
TI also provides layout guidelines (see image below) that include the following: use 2 oz copper PCBs in order to effectively dissipate the heat generated from the MOSFETs and LEDs; and place capacitors as close to the associated pins as possible.
Figure 5. Recommended layout. Image taken from the datasheet (PDF).
One thing that they don't offer and which would be really handy—at least as a starting point—is recommendations for possible MOSFETs to use; yes, I mean manufacturer names and part numbers. Perhaps I could request this information via phone or e-mail, but it would be more convenient to find it right there in the datasheet.
Have you had a chance to use this new 3-channel high-current LED controller? If so, leave a comment and tell us about your experiences.
Featured image created from Texas Instruments collateral.