Preliminary Technical Data
ADuM5240/ADuM5241/ADuM5242
APPLICATION INFORMATION
When these guidelines are followed, pre-production samples
may be used for prototype and evaluation. As mentioned above
this issue will be corrected in final silicon and the ADuM524x
will operate at specified load and temperature conditions.
DC/DC CONVERTER
The ADuM524x can be operated with the internal DC/DC
enabled or disabled. With the internal DC/DC converter
enabled, the Pin 8 isolated supply provides output power as well
as power to the part’s isolated-side circuitry. Since the power
consumed by the ADuM524x is a function of the input signals’
data rate, the available isolated output power is determined by
the data rate at which the part’s data channels are operating.
Table 14. Special Usage Conditions for Pre-production
Devices
Max Temperature by Load Capacitance1
10nF
105°C
105°C
80°C
100nF
The ADuM524x’s internal DC/DC converter state is controlled
by the input VDD voltage as defined in Table 6. In normal
operating mode, VDD is set between 4.5 V and 5.5 V and the
internal DC/DC converter is enabled. When/if it is desired to
disable the DC/DC converter, VDD is lowered to a value between
2.7 V and 4.0 V. In this mode, the VISO supply is supplied by the
user and the ADuM524x’s signal channels continue to operate
normally.
ADuM5240
ADuM5241
ADuM5242
Not Recommended
65°C
80°C
1 Value of load capacitor C3 in Figure 8
PC BOARD LAYOUT
The ADuM524x digital isolators require no external interface
circuitry for the logic interfaces. Power supply bypassing is
strongly recommended at the input and output supply pins as
shown in Figure 8. For the ADuM5240 and ADuM5241, a
bypass capacitance (C1) of 44 μF is required at the VDD input to
ensure proper power-up. For all models bypass capacitance is
recommended with C2=0.1 μF on the non-isolated side and
C3=10 nF on the isolated side. Due to high inductance
associated with larger capacitors such as C1, it is recommended
that both C1 and C2 be used on the ADuM5240 and
GUIDELINES FOR PRE-PRODUCTION SAMPLES
Pre production samples meet all data sheet specifications;
however, a limitation in the internal circuitry of the ADuM524x
prevents proper start-up under all load conditions. This
limitation will be corrected in the final product.
At certain temperature and load conditions the ADuM524x will
not regulate its VISO output to the 5.25V target voltage at
converter start-up. The output stabilizes at just under 4V with
no external load or as low as 3V with an external load. If the
converter starts successfully, the output voltage will continue to
regulate properly even as temperature and load conditions
change.
ADuM5241. The bypass capacitors should be placed as close as
possible to the ADuM524x device.
In cases where EMI is a concern, inductance should be added
between the system supply and ground and the ADuM524x
supply and ground as shown in Figure 8. Inductance can be
added in the form of discrete inductors or ferrite beads, and it’s
recommended the value correspond to an impedance between
50Ω and 100Ω at approximately 300MHz.
The start-up issue is affected by several circuit and
environmental conditions: slew rate applied to VDD1, ambient
temperature, and VISO capacitive load. The recommendations in
the PC board layout section address the VDD1 slew rate
dependence in most cases. Good results have been obtained
when the system power supply slews at ~0.5V/μS. Faster slew
rates can be tolerated but should be verified over temperature.
Table 14 contains guidelines for the maximum reliable start-up
temperature for two common values of load capacitance.
The VISO start-up issue is strongly temperature dependant. The
ADuM542x dissipates between 40 and 63mW under normal
operation, causing the internal temperature of the device to be
higher than ambient during normal operation. A “warm start”
after the device has reached its equilibrium temperature is the
worst case condition and will give the highest probability of
incorrect regulation of output voltage. The guidelines in Table
14 are based on “warm start” at full load. Cold start will be
successful at higher ambient temperatures.
Figure 8. Recommended Application Circuit. C1 may be
omitted for ADuM5242, and L1 and L2 should be included
where EMI is a concern.
Rev. PrN | Page 9 of 10
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