IL600 Rhopoint Components, IL600 Datasheet - Page 9

• Manufacturer Part Number: IL600
• Description: Passive-input Digital Isolators ? Cmos Outputs
• Manufacturer: Rhopoint Components

Failsafe Operation
Internal failsafe biasing ensures the output will always switch to the high state if the input coil is open-circuit. This is true for
either 5 V or 3.3 V output supplies. The specifications on pages 5 and 6 show the enhanced failsafe conditions available with the
IL600-Series Isolators that cover the non-open circuit condition. The output will remain in the state specified, or will switch to that
state, if the specified current is flowing in the coil. Note that positive values of current mean current flow into the In− input (pin 3
in Test Circuit 1).
Single-Ended or Differential Input
The IL610, IL611, IL613, and channel 1 of the IL614 can be run with single-ended or differential inputs. In differential mode, coil
current reverses each cycle. In single-ended mode, a “boost capacitor” placed across the current limit resistor provides pulsed
current reversal for correct operation. In the differential mode, current will naturally flow through the coil in both directions
without the boost cap, although the cap can still be used if application factors such as increased external field immunity or
improved PWD performance mandate. Absolute Maximum recommended coil current in single-ended mode is 25 mA while
differential mode allows up to ±75 mA to flow. The difference in specifications is due to the risk of electromigration of coil metals
under constant current flow. In single ended mode, long-term DC current flow above 25 mA can cause erosion of the coil metal
(rather like river flow does to its banks). In differential mode, erosion takes place in both directions as each current cycle reverses
and has a net effect of zero up to the fuse current. A current of more than 100 mA will cause the coil to irreparably fuse open.
There are many applications where the differential option can be very useful. One advantage over optocouplers and other high-
speed couplers is that no reverse bias protection for the input structure is required for a differential signal. This reduces cost and
complexity. One of the more common applications is for an isolated Differential Line Receiver. For example, RS-485 can drive an
IL610 directly for a fraction of the cost of an isolated RS-485 node (see Illustrative Applications section).
Typical Resistor Values
Applications Information section for circuit ideas allowing more generalized resistor selection.
Boost Capacitor
Dynamic Power Consumption
Power consumption is proportional to duty cycle, not data rate. The use of NRZ coding minimizes power dissipation since no
additional power is consumed when the output is in the high state. In differential mode, where the logic high condition may still
require a current to be forced through the coil, power consumption will be higher than a typical NRZ single ended configuration.
Power Supply Decoupling
47 nF ceramic capacitors are recommended to decouple the power supplies. The capacitors should be placed as close as possible to
the appropriate V
V
3.3 V
5 V
Figure 3. C
Rise/Fall Time (ns)
Rise/Fall Time (ns)
COIL
Signal
Signal
boost
1000
1000
500
500
0.125W, 10% Resistor
560 Ω
910 Ω
3
3
DD
Selector
pin for optimal output wave shaping.
16
16
C
C
Boost
Boost
(pF)
(pF)
2500
2500
5000
5000
The table shows typical values for the external resistor in 5 V and 3 V logic systems.
As always, these values as approximate and should be adjusted for temperature or
other application specifics If the expected temperature range is large, 5% or even 1%
tolerance resistors may provide additional design margin. Alternatively, see the
The boost capacitor in parallel with the current-limiting resistor boosts
the instantaneous coil current at the signal transition. The boost pushes
the GMR bridge output through the comparator threshold voltage with
less propagation delay and pulse width distortion.
The instantaneous boost capacitor current is proportional to input edge
speeds (
the input signal to be isolated that provides approximately 20 mA of
additional “boost” current. Figure 3 is a guide to boost capacitor
selection. For standard logic signals (t
recommended. The capacitor value is generally not critical, and can often
vary ±50% with little noticeable difference in device performance.
9
C
dV
dt
). Select a capacitor value based on the rise and fall times of
r
,t
f
< 10 ns), a 16 pF capacitor is
IL600 Series