MIC2860_P Datasheet, PDF (9/12 Pages) Micrel Semiconductor – High Efficiency 2 Channel WLED Driver with PWM Control

Micrel Inc.
Application Information
PWM Dimming Interface
The MIC2860-2P can receive PWM signals from the EN
pin for WLED dimming. Dimming is generated by pulsing
the WLEDs on and off in synchronization with the PWM
signal. The MIC2860-2P incorporates an internal
shutdown delay to ensure that the internal control
circuitry remains active during PWM dimming for
optimum performance.
The lower PWM frequency range is recommended at
250Hz due to the minimum standby to shutdown time of
4ms. As the period of 250Hz is 4ms, a 1% duty cycle
would have an on time of 40us and an off time of
3.96ms. To support operation down to 1% duty cycle,
the maximum off time must not exceed 4ms or the
drivers may go into the low Iq shutdown state.
With PWM frequencies higher than 500Hz the T_RISE
(0.7μs) and T_Fall (0.2μs) times will have a greater effect
on the accuracy of the outputs. An upper frequency of
500Hz is recommended to maintain output accuracy with
duty cycles down to 1%. For systems that do not require
a duty cycle below 1%, the frequency of the PWM signal
may be increased. For example, with a minimum duty
cycle of 10% (3.02mA with R_SET = 9.53kΩ) the PWM
frequency can be increased to 10kHz and still maintain
accuracy.
MIC2860-2P
Input Capacitor
The MIC2860-2P is a high performance, high bandwidth
device. Stability can be maintained using a ceramic input
capacitor of 1µF. Low-ESR ceramic capacitors provide
optimal performance with a minimum amount of space.
Additional high frequency capacitors, such as small
valued NPO dielectric type capacitors, help filter out
high-frequency noise and are good practice in any noise-
sensitive circuit. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V dielectrics
lose most of their capacitance over temperature and are
therefore, not recommended.
September 2010
9
M9999-092710-A