The A6271 is a DC-DC converter controller, providing a
programmable constant-current output for driving high-power
LEDs in series. 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, and
buck (ground-referenced switch).
The A6271 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 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 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 undervoltage (buck
or buck-boost), input supply (VIN) undervoltage, 5 V Regulator
(VREG) output undervoltage, high-side supply (PWM PMOS)
undervoltage, and thermal protection.
