ADUM5240BRZ AD [Analog Devices], ADUM5240BRZ Datasheet - Page 9

• Manufacturer Part Number: ADUM5240BRZ
• Description: Dual-Channel Isolators with Integrated DC/DC Converter, 50 mW
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
APPLICATION INFORMATION
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.
The ADuM524x’s internal DC/DC converter state is controlled
by the input V
operating mode, V
internal DC/DC converter is enabled. When/if it is desired to
disable the DC/DC converter, V
2.7 V and 4.0 V. In this mode, the V
user and the ADuM524x’s signal channels continue to operate
normally.
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 V
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.
The start-up issue is affected by several circuit and
environmental conditions: slew rate applied to V
temperature, and V
the PC board layout section address the V
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 V
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.
ISO
start-up issue is strongly temperature dependant. The
DD
voltage as defined in Table 6. In normal
ISO
DD
ISO
output to the 5.25V target voltage at
is set between 4.5 V and 5.5 V and the
capacitive load. The recommendations in
DD
is lowered to a value between
ISO
supply is supplied by the
DD1
slew rate
DD1
, ambient
Rev. PrN | Page 9 of 10
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.
Table 14. Special Usage Conditions for Pre-production
Devices
1
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 (C
ensure proper power-up. For all models bypass capacitance is
recommended with C
C
associated with larger capacitors such as C
that both C
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.
Figure 8. Recommended Application Circuit. C
omitted for ADuM5242, and L
where EMI is a concern.
Value of load capacitor C3 in Figure 8
ADuM5240
ADuM5241
ADuM5242
3
=10 nF on the isolated side. Due to high inductance
Max Temperature by Load Capacitance
1
and C
ADuM5240/ADuM5241/ADuM5242
2
be used on the ADuM5240 and
105
105
10nF
80
1
2
=0.1 μF on the non-isolated side and
) of 44 μF is required at the V
°
°
°
C
C
C
1
and L
Not Recommended
2
should be included
1
100nF
65
80
, it is recommended
°
°
C
C
1
1
may be
DD
input to