Microchip Technology MCP1664, User Manual

Page: 17 / 29

Installation and Operation

2015 Microchip Technology Inc. DS50002363A-page 17
The R
1
and R
2
resistors affect not only the operating frequency but also the amplitude
of the triangular wave. Considering the maximum voltage of the triangular waves
(V
TH
) and the minimum voltage of the triangular waves (V
TL
), the amplitude swing and
the threshold voltages can be calculated by means of the following equation:
EQUATION 2-3: TRIANGULAR WAVE AMPLITUDE SWING
For the MCP1664 LED Driver Evaluation Board, the components were chosen so that
they feature a PWM Dimming frequency of 125 Hz and an amplitude swing from
5% V
DD
to 95% V
DD.
FIGURE 2-5: Obtaining the Dimming Signal - 84% Duty Cycle.
VTH VTL –
R4
R2
------VDD =
Where: R
4
< R
2
REFERENCE
VOLTAGE
DIMMING
SIGNAL
TRIANGULAR
WAVE