E7804BHF Semtech, E7804BHF Datasheet - Page 25

• Manufacturer Part Number: E7804BHF
• Manufacturer: Semtech

Specifications of E7804BHF

• Operating Temperature (max): 100C
• Package Type: MQFP
• Mounting: Surface Mount
• Lead Free Status / Rohs Status: Not Compliant

Application Information (continued)
The value of the thermal resistance of the Edge7804
package junction to air with 400 linear feet per minute
(LFPM) of airflow is specified at 22˚C/W. At operating
points greater than or equal to this value, no additional
heatsinking is needed to keep the die temperatures below
the maximum 100˚C as long as the ambient temperature
of the 400 LFPM air does not exceed 35˚C.
More information on heatsink system selections can be
read on heatsink vendors’ web sites and in the Semtech
Application Note #ATE-A2 Cooling High Power, High
Density Pin Electronics.
Protection Considerations
The Edge7804 has ESD protection on its input and
outputs.
The Edge7804 has internal, high voltage, disconnect
switches for VIO and POUT pins. When open, these provide
protection against voltages input into VIO and POUT which
might have damaged drivers, comparators, and other
internal circuits.
Power Supply Sequencing/Latch-Up Protection
In order to avoid the possibility of latch-up when powering
this part up (or down), be careful that the conditions listed
in the Absolute Maximum Ratings are never violated. That
is, the power supplies should never be reverse-polarity
with respect to ground, and the input signals should never
go beyond the power supply rails.
Furthermore, the lower-voltage analog supplies should
never be greater than the higher-voltage supplies
(VAA < VCC < VXX). This can easily be implemented by
utilizing the diode circuit depicted in Figure 14 for each
PCB that has Edge7804 devices on it. The following
conditions must be met at all times during power-up and
power-down.
TEST AND MEASUREMENT PRODUCTS
2005 Semtech Corp. / Rev. 5, 12/6/05
1. VEE
2. GND
3. VEE
4. GND
GND
Analog Inputs
VDD
Digital Inputs
VAA
VCC
VCC
VCC or VXX
VDD
VXX
The following sequencing can be used as a guideline when
powering up:
The recommended power-down sequence is the reverse
order of the power-up sequence.
One approach to ensure that the power supply polarities
do not become reversed is to use Schottky diodes, as
shown in Figure 8. One set of these diodes should be
used per board. The optimum type of Schottky will depend
on how much current the power supplies can source.
25
1. VEE
2. VXX
3. VCC
4. VAA
Figure 8. Board Level Supply Diodes
VXX
VCC
VAA
VEE
5. VDD
6. Digital Inputs
7. Analog Inputs
Schottky's such as 1N5820
Low forward voltage drop
VDD
Edge7804
PRELIMINARY
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