100-VIN primary side regulation flyback controller with low IQ and low EMI

The LM5185 is a primary-side regulated (PSR) flyback controller with high efficiency

over a wide input voltage range of 4.5 V to 100 V. The isolated output voltage

is sampled from the primary-side flyback voltage, eliminating the need for an optocoupler,

voltage reference, or third winding from the transformer for output voltage regulation.

The high level of integration results

in a simple, reliable, and high-density design with only a transformer crossing the

isolation barrier. Boundary conduction mode (BCM) switching enables a compact magnetic

design and better than ±1.5% load and line regulation performance. BCM supports applications

of up to 100-V input with enhanced headroom

for line transients.

The LM5185 flyback controller simplifies

implementation of isolated DC/DC supplies with optional features to optimize

performance for the target end equipment. The output voltage is set by one resistor,

while an optional resistor improves output voltage accuracy by negating the thermal

coefficient of the flyback diode voltage drop. The LM5185 controller, with the integrated

high-current MOSFET gate driver, extends the power range from less than 1 W to more

than 50 W, making the device a scalable and easy-to-migrate design over a wide power

range. The tunable compensation using the COMP pin and the adjustable peak current

limit with the current-sensing resistor make the design flexible and an excellent

choice towards different application requirements.

Additional features include an internally-fixed or

externally-programmable soft start, optional external VCC for higher efficiency,

precision enable input with hysteresis for adjustable line UVLO, peak current-mode

control with shunt current sensing, hiccup-mode overload protection, a high-current

MOSFET gate driver, and thermal shutdown protection with automatic recovery. A

connection to the high-voltage MOSFET drain is not required, thus increasing safety

and simplifying PCB clearance distance requirements.

The

LM5185 flyback controller is available in a 14-pin, 5-mm × 4.4-mm, thermally-enhanced

HTSSOP package with 0.65-mm pin pitch.