HCPL-261A_13 Datasheet, PDF (14/17 Pages) AVAGO TECHNOLOGIES LIMITED – HCMOS Compatible, High CMR, 10 MBd Optocouplers High speed: 10 MBd typical

SINGLE CHANNEL PRODUCTS
Application Information
V_CC BUS (FRONT)
N.C.
N.C.
N.C.
N.C.
GND BUS (BACK)
0.1µF
0.1µF
ENABLE
(IF USED)
OUTPUT 1
ENABLE
(IF USED)
OUTPUT 2
V_CC BUS (FRONT)
10 mm MAX. (SEE NOTE 16)
DUAL CHANNEL PRODUCTS
GND BUS (BACK)
0.1µF
OUTPUT 1
OUTPUT 2
10 mm MAX. (SEE NOTE 16)
Figure 19. Recommended printed circuit board layout.
VCC
*
HCPL-261A/261N
1
8
357 Ω
(MAX.)
2
7
357 Ω
(MAX.)
3
6
74LS04
OR ANY TOTEM-POLE
OUTPUT LOGIC GATE
GND1
4
5
SHIELD
*
0.01 µF
VCC+
350 Ω
VO
GND
GND2
Common-Mode Rejection for HCPL-
261A/HCPL-261N Families:
Figure 20 shows the recomm­ ended
drive circuit for the HCPL-261N/-
261A for optimal common-mode
rejection performance. Two main
points to note are:
1. The enable pin is tied to V_CC rather
than floating (this applies to
single-channel parts only).
2. Two LED-current setting resistors
are used instead of one. This is
to balance I_LED variation during
common-mode transients.
If the enable pin is left floating, it is
possible for common-mode tran-
sients to couple to the enable pin,
resulting in common-mode failure.
This failure mechanism only occurs
when the LED is on and the output
is in the Low State. It is identified as
occurring when the transient output
voltage rises above 0.8 V. Therefore,
the enable pin should be connected
to either V_CC or logic-level high for
best common-mode performance
with the output low (CMR_L). This
failure mechanism is only present
in single-channel parts (HCPL-261N,
-261A, ‑061N, -061A) which have the
enable function.
Also, common-mode transients can
capacitively couple from the LED an-
ode (or cathode) to the output-side
ground causing current to be shunt-
ed away from the LED (which can be
bad if the LED is on) or conversely
cause current to be injected into the
LED (bad if the LED is meant to be
off ). Figure 21 shows the parasitic
capacitances which exists between
LED anode/cathode and output
ground (C_LA and C_LC). Also shown in
Figure 21 on the input side is an AC-
equivalent circuit.
* HIGHER CMR MAY BE OBTAINABLE BY CONNECTING PINS 1, 4 TO INPUT GROUND (GND1).
*Higher CMR may be obtainable by connecting pins 1, 4 to input ground (Gnd1).
Figure 20. Recommended drive circuit for HCPL-261A/-261N families for high-CMR
(similar for HCPL-263A/-263N).
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