AMC7580 Datasheet, PDF (9/12 Pages) List of Unclassifed Manufacturers – 7A LOW DROPOUT REGULATOR

AMC DOC. #: AMC7580_E (LF)
Feb 2005
AMC7580
7A LOW DROPOUT REGULATOR
Protection Diodes
In normal operation, AMC7580 family does not need any protection diodes between the adjustment pin and the
output and from the output to the input to prevent die overstress. Internal resistors are limiting the internal current
paths on the ADJ pin. Therefore even with bypass capacitors on the adjust pin no protection diode is needed to
ensure device safety under short-circuit conditions. The Adjust pin can be driver on a transient basis ±7V with
respect to the output without any device degradation.
A protection diode between the Output pin and V_POWER pin is not usually needed. Microsecond surge currents of 50A
to 100A can be handled by the internal diode between the Output pin and V_POWER pin of the device. In normal
operations it is difficult to get those values of surge currents even with the use of large output capacitances. Only
with high value output capacitors, such as 1000µF to 5000µF and the V_POWER pin is instantaneously shorted to
ground, damage an occur. A diode from output to input is recommended (Figure 6). If AMC7851 is connected as
single supply device with the control and power input pins shorted together the internal diode between the output and
power input pin will protect the control input pin.
Thermal Consideration
The AMC7580-ADJ series has internal power and thermal limiting circuitry designed to protect the device under
overload conditions. However maximum junction temperature ratings should not be exceeded under continuous
normal load conditions. Careful consideration must be given to all sources of thermal resistance from junction to
ambient, including junction-to-case, case-to-heat sink interface and heat sink resistance itself.
Junction temperature of the Control section can run up to 125 ^OC. Junction temperature of the Power section can run
up to 150 ^OC. Due to the thermal gradients between the power transistor and the control circuitry there is a significant
difference in thermal resistance between the Control and Power sections.
Virtually all the power dissipated by the device is dissipated in the power transistor. The temperature rise in the
power transistor will be greater than the temperature rise in the Control section making the thermal resistance lower
in the Control section. At power levels below 12W, the temperature gradient will be less than 25 ^OC and the
maximum ambient temperature will be determined by the junction temperature of the Control section. This is due to
the lower maximum junction temperature in the Control section. At power levels above 12W, the temperature
gradient will be greater than 25 ^OC and the maximum ambient temperature will be determined by the Power section.
In both cases the junction temperature is determined by the total power dissipated in the device. For most low
dropout applications the power dissipation will be less than 12W.
The power in the device is made up of two components: the power in the output transistor and the power in the
control circuit.
The power in the control circuit is negligible, which is equal to: P_CONTROL = (V_CONTROL – V_OUT) / I_CONTROL,
where I_CONTROL is equal I_OUT / 100(typ)
The power in the output transistor is equal to: P_OUTPUT = (V_POWER –V_OUT) / I_OUT
The total power is equal to: P_CONTROL + P_OUTPUT
Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly below the die.
This is the lowest resistance path for the heat flow. In order to ensure the best possible thermal flow this area of the
package to the heat sink proper mounting is required. Thermal compound at the case-to-heat sink interface is
recommended. A thermally conductive spacer can be used, if the case of the device must be electrically isolated, but
its added contribution to thermal resistance has to be considered.
Copyright © 2002, ADD Microtech Corp.
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