WS3215
resistance, the LED output current can be controlled
within 5% variation. A dedicated DIM input accepts a wide
range of a DC voltage or pulsed dimming. Applying a
voltage of 2.5V or higher to the DIM pin will turn on the
power MOSFET completely, however, 0.3V or lower will
turn the output off. Therefore, it is available to receive a
PWM dimming frequency range from 100Hz to 20KHz.
Otherwise, an external resistance can be used to set the
LED output current. Linking with the internal pull-up
resistance (typically 1.2 Mohm) , which is connected to the
inner regulated 5V, a voltage applied to the DIM can be
achieved. By changing the ratio between the outer and
inner resistance, the dimming voltage can be different and
brightness of LED can be adjustable.
Operation Description
Applying WS3215 with inductor (L) and current sensing
resistance （RS）forms a self-oscillating step-down continuous
current mode inductive LED controller. When Vin increases at
the beginning, LED output current are zero initially through
inductor, sensing resistance. Meanwhile, the CS comparator
turns high, the voltage of SW is low and the internal power
MOSFET is conductible. Through the external components
and internal power MOSFET to GND, output current gets
greater with a constant rate determined by the voltage
difference between inductor’s two terminals, then generate a
sensing voltage on the RS. If (Vin-Vcsn)>110mV, CS
comparator turns low and internal power MOSFET turn off, the
state can not change until (Vin-Vcsn)<90mV. As a result, the
Average LED output current can be caculated by the following
During the turn-off phase, the quiescent current is only
60uA although the inner reference module is still at work..
For the consideration of reliability, over-temperature
protection in WS3215 is necessary. It avoids the WS3215
suffering over-temperature damage and guarantees the
maximum LED output current after recovery to normal.
0.09 + 0.11
2× Rs
equation:
0.1
=
Iout =
Rs
High-side current sensing circuit is applied for less
external components. With 1% accuracy of sensing
8/9
Steady, keep you advance
WINSEMI [ SHENZHEN WINSEMI MICROELECTRONICS CO., LTD ]
