Data Sheet

ADPL42010A

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Rev. 0

20 of 28

Free Resistance with PC Traces

The resistance values shown in Table 5 can easily be made by putting an actual resistor in series with the capacitor,

or by using a small section of PC trace in series with the output capacitor. The wide range of non-critical ESR makes

it easy to use PC trace. The trace width should be sized to handle the RMS ripple current associated with the load.

The output capacitor only sources or sinks current for a few microseconds during fast output current transitions.

There is no DC current in the output capacitor. Worst case ripple current occurs if the output load is a high frequency

(>100kHz) square wave with a high peak value and fast edges (<1µs). Measured RMS value for this case is 0.5 times

the peak-to-peak current change. Slower edges or lower frequency significantly reduces the RMS ripple current in

the capacitor.

Table 5. PC Trace Resistors

10mΩ

20mΩ

30mΩ

0.5oz CU

Width: 0.011in (0.28mm)

Length: 0.102in (2.6mm)

Width: 0.011in (0.28mm)

Length: 0.204in (5.2mm)

Width: 0.011in (0.28mm)

Length: 0.307in (7.8mm)

1.0oz CU

Width: 0.006in (0.15mm)

Length: 0.110in (2.8mm)

Width: 0.006in (0.15mm)

Length: 0.220in (5.6mm)

Width: 0.006in (0.15mm)

Length: 0.330in (8.4mm)

2.0oz CU

Width: 0.006in (0.15mm)

Length: 0.224in (5.7mm)

Width: 0.006in (0.15mm)

Length: 0.450in (11.4mm)

Width: 0.006in (0.15mm)

Length: 0.670in (17mm)

This resistor should be made using one of the inner layers of the PC board which are well defined. The resistivity is

determined primarily by the sheet resistance of the copper laminate with no additional plating steps. Table 5 gives

some sizes for 0.75A RMS current for various copper thicknesses. For more details on resistors made from PC traces,

refer to the Appendix A of the Application Note 69: LT1575 UltraFast Linear Controller Makes Fast Transient Response

Power Supplies.

Overload Recovery

Similar to many IC power regulators, the ADPL42010A-X has a safe operating area (SOA) protection. The SOA

protection decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a

safe operating region for all values of input-to-output voltage. The protection is designed to provide some output

current at all values of input-to-output voltage up to the device breakdown. When power is first turned on, as the

input voltage rises, the output follows the input, which allows the regulator to start up into very heavy loads. During

the start-up, as the input voltage is rising, the input-to-output voltage differential is small, which allows the regulator

to supply large output currents. With a high input voltage, a problem can occur wherein removal of an output short

does not allow the output voltage to recover. Other regulators, such as the LT1085, also exhibit this phenomenon, so

it is not unique to the ADPL42010A-X.

The problem occurs with a heavy output load when the input voltage is high and the output voltage is low. Common

situations are immediately after the removal of a short-circuit or when the SHDN pin is pulled high after the input

voltage has already been turned on. The load line for such a load may intersect the output current curve at two

points. If this happens, there are two stable output operating points for the regulator. With this double intersection,

the input power supply may need to be cycled down to zero and brought up again to make the output recover.

Output Voltage Noise

The ADPL42010A regulators have been designed to provide low output voltage noise over the 10Hz to 100kHz

bandwidth while operating at full load. Output voltage noise is typically 70nV/√Hz over this frequency bandwidth for

the ADPL42010A (adjustable version). For higher output voltages (generated by using a resistor divider), the output