PCE84C882 Datasheet, PDF (14/60 Pages) NXP Semiconductors – Microcontroller for monitor OSD and auto-sync applications

Philips Semiconductors
Microcontroller for monitor OSD
and auto-sync applications
Preliminary specification
PCE84C882
handbook, full pagewidth
t _sub0
t _sub16
t _sub32
t _sub48
tr
t _sub64
t _sub80
t _sub96
t _sub112
t _sub127
111 1110
111 1011
111 1010
PWM8L
MLC755
Fig.10 Fine adjustment output (OUT2).
7.3 A typical PWM output application
A typical PWM application is shown in Fig.11. The buffer is
used to reduce jitter on the OSD. R1 and C1 form the
integration network the time constant of which should be at
least 5 times greater than the repetition period of the PWM
output pattern. In order to smooth a changing PWM output
a high value of C1 should be chosen. The value of C1 will
normally be in the range 1 to 10 µF. The potential divider
chain formed by R2 and R3 is used only when the output
voltage is to be offset. The output voltages for this
application are calculated using Equations (1) and (2).
V_max = ^{R-----3---R--×}---3--s---₊^{u---p--R-R--p------11--l--y------}_×+----v------oRR------l--t-2-2--a----g----e--
(1)
V_min = -R-R--------11----------^+×---------R-RR--------33--2-----^×-₊----s-R-R----u----11--p--------p_+×------l--y--RR--------v3--3----o---l-t--a---g----e--
(2)
The loop from the PWM pin through R1 and C1 to V_SS will
radiate high frequency energy pulses. In order to limit the
effect of this unwanted radiation source, the loop should
be kept short and a high value of R1 selected. The value
of R1 will normally be in the range 3.3 to 100 kΩ. It is good
practice to avoid sharing V_SS (pin 30) with the return leads
of other sensitive signals.
handbook, halfpage
PWMn
PCE84C882
VSS
supply
voltage
R2
R1
analog
output
C1 R3
MGC711
Fig.11 Typical PWM output circuit.
1996 Jan 08
14