The controller is based on a programmable fixed-frequency, peak current-mode control architecture. The DC-DC converter can be configured in a myriad of different switching configurations including boost, buck-boost, buck (ground-referenced switch), and SEPIC.
The A6271-1 provides a cost-effective solution using an external logic-level MOSFET and minimum additional external components. The maximum LED current is set with a single external sense resistor and can be accurately modulated using a current reference input (analog control). External PWM dimming is possible via the PWMIN input, which also provides a shutdown mode. As an alternative, an internal PWM dimming circuit can be used by programming the PWMIN and DR pins. Either PWM scheme controls the PWMOUT output which drives an external p-channel MOSFET connected in series with the LED string. This MOSFET is also used to isolate the load during certain fault conditions, including output shorts to ground
The A6271-1 has been carefully designed to minimize electromagnetic emissions through distributed decoupling and an externally programmable frequency dither circuit configured for the EMI specification CISPR 25. It is also possible to program the fundamental switching frequency below 150 kHz where most EMI standards begin.
The A6271-1 has a comprehensive set of integrated protection features to protect the IC, the LED driver system, and the LED string against faults. Fixed-output overvoltage protection ensures no maximum voltage rating violations, even under a single point failure of the programmable-output overvoltage protection circuit. Other protection features include: LED overload (boost), output under voltage (buck or buck-boost), input supply (VIN) under voltage, 5 V regulator (VREG) output under voltage, high-side supply (PWM PMOS) under voltage, and thermal protection.
Comparison Summary to A6271:
- A6271 and A6271-1 are not universally interchangeable
- Only if using external PWM signal (or no PWM)
- A6271-1 could be dropped in and improve transient response, but fault pin response is slightly different and compensation components may need modification
- A6271-1 has improved internal PWM performance at low duty cycle, and also can be used in SEPIC topology (A6271 cannot)
