VISTEK V1679 single-mode fibre
data transceiver
HU-V1679
13
3.3.4
CMOS Output
5V CMOS families with sourcing/sinking capabilities of as low as ± 4mA, such as HC or HCT, can be also
used to drive a V1679 GPI Input. In order not to violate the CMOS Buffer's output specification, an additional
current limiting resistor could be necessary. If the Buffer can source -24mA, (AC, ACT Families), no
additional resistor is required since the on-board 100Ohm series resistor provides sufficient current limiting.
1 0 0 R
3 9 0 R
1 K 8
G P IO n -
G P IO n +
+ 5 V
+ 1 2 V
1 N 4 1 4 8
In p u t B i a s V o lta g e S e le c tio n J u m p e r
( o p e n )
S h o r t to G N D J u m p e r
( o p e n )
O n - b o a r d p o w e r s u p p li e s
R e a r C o n n e c t o r S id e
B o a rd S id e
N o t e :
A n e x t r a s e rie s r e s is to r is re q u ire d in o rd e r to lim it th e c u rr e n t t h ro u g h th e C M O S
B u f fe r to c o m p ly w it h its s p e c if ic a t io n . N o t e th a t th e B u f fe r's o u t p u t v o lt a g e in th e
h ig h s ta te ( V
O H
) is o n ly g u a ra n te e d u p t o a c e rta in c u r re n t lim it d ra w n f r o m th e
o u tp u t (I
O H
).
A s it c a n b e s e e n in t h e d ia g ra m , u s in g a C M O S B u ffe r c a n b e im p le m e n te d to
b e 'e a rth -fre e ' ( i. e . n o G N D c o n n e c t io n b e tw e e n t h e c o n tro l u n it a n d th e V 1 6 7 9 's
G N D ), w h ic h m e a n s n o tr o u b le c a u s e d b y g ro u n d lo o p c u r re n ts (w h ic h c a n p ro v e
t o b e r a t h e r d iff ic u lt to c o p e w ith ). H o w e v e r, c a b le - le n g t h a n d s p e e d re s t r ic tio n s
a p p ly . T h e s lo w e r th e s e le c t e d C M O S o u tp u t in te rm s o f it s s le w r a t e , th e b e t te r!
G N D
0
0
0
0
0
5 V C M O S B U F F E R
3 3 0 R
Figure 7 : Example 4