Advanced Monolithic Systems, Inc.

6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140

AMS2501/AMS2502

APPLICATION HINTS

Protection Diodes

Unlike older regulators, the AMS2501/AMS2502 family does not

need any protection diodes between the adjustment pin and the

output and from the output to the input to prevent die over-stress.

Internal resistors are limiting the internal current paths on the

AMS2501/AMS2502 adjustment 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 driven on a transient basis

±7V with respect to the

output without any device degradation.

needed. Microsecond surge currents of 10A to 25A can be

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. If high value output capacitors are used, such as

1000

µF to 5000µF and the V

to ground, damage can occur. A diode from output to input is

recommended, when a crowbar circuit at the input of the

AMS2501/AMS2502 is used (Figure 6). Normal power supply

cycling or even plugging and unplugging in the system will not

generate current large enough to do any damage.

CONTROL

POWER

OUTPUT

AMS2501

SENSE

ADJ

R1

R2

V

OUT

V

POWER

+

+

+

D2*

D1*

V

CONTROL

Figure 6. Optional Clamp Diodes Protect Against

Input Crowbar Circuits

If the AMS2501/AMS2502 is connected as a single supply device

with the control and power input pins shorted together the

internal diode between the output and the power input pin will

protect the control input pin. As with any IC regulator, none the

protection circuitry will be functional and the internal transistors

will break down if the maximum input to output voltage

differential is exceeded.

Thermal Considerations

The AMS2501/AMS2502 series have 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.

Control section can run up to 125

°C, and the Power section can

run up to 150

°C. 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 0.5W the temperature gradient will be less

than 25

°C 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 0.5W the temperature

gradient will be greater than 25

°C 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 0.5W.

The power in the device is made up of two components: the

power in the output transistor and the power in the drive circuit.

The power in the control circuit is negligible.

The power in the drive circuit is equal to:

The power in the output transistor is equal to:

The total power is equal to:

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 from this area of the package to the

PCB proper mounting is required.