Application Notes

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PT5800 & PT5810 Series

With the sense leads connected, the difference between

measured from Sense(+) to Sense(–), is the amount of IR

drop being compensated by the regulator. This should

be limited to 0.6V. (0.3V maximum between pins 17 &

18, and also between pins 8 & 9).

Note: The remote sense feature is not designed to compensate

for the forward drop of non-linear or frequency dependent

components that may be placed in series with the converter

output. Examples include OR-ing diodes, filter inductors,

ferrite beads, and fuses. When these components are enclosed

by the remote sense connections they are effectively placed

inside the regulation control loop, which can adversely affect

the stability of the regulator.

Over-Current Protection

To protect against load faults, the regulators incorporate

output over-current protection. Applying a load that

exceeds the regulator’s over-current threshold (see data

sheet specifications) will cause the regulated output to

shut down. Following shutdown the ISR will periodically

attempt to recover by initiating a soft-start power-up.

This is often described as a “hiccup” mode of operation,

whereby the module continues in the cycle of successive

shutdown and power up until the load fault is removed.

During this period, the average current flowing into the

fault is significantly reduced. Once the fault is removed,

the converter automatically recovers and returns to nor-

mal operation.

Over-Temperature Protection

An on-board temperature sensor protects the module’s

internal circuitry against excessively high temperatures.

A rise in the internal temperature may be the result of a

drop in airflow, or a high ambient temperature. If the

internal temperature exceeds the OTP threshold (see

data sheet specifications), the regulator’s Inhibit* control

is automatically pulled low. This disables the regulator,

allowing the output voltage to drop to zero as the exter-

nal output capacitors are discharged by the load circuit.

The recovery is automatic, and begins with a soft-start

power up. It occurs when the the sensed temperature

decreases by about 10°C below the trip point.

Note: The over-temperature protection is a last resort mecha-

nism to prevent thermal stress to the regulator. Operation at

or close to the thermal shutdown temperature is not recom-

mended and will reduce the long-term reliability of the module.

Always operate the regulator within the specified Safe Operating

Area (SOA) limits for the worst-case conditions of ambient

temperature and airflow.

Differential Remote Sense

Connecting the Sense(+) and Sense(-) pins to the load

circuit allows the regulator to compensate for limited

amounts of ‘IR’ voltage drop. This voltage drop is caused

by current flowing through the connection resistance

between the regulator and the ‘point of regulation’ some

distance away. Leaving the sense pins disconnected will

not damage the regulator or load circuitry. An internal

15

Ω resistor, connected between each sense pin and its

corresponding output node, keeps the output voltage in

regulation. However, it is important to connect Sense(–)

to GND locally, as this provides a return path for the

regulator’s internal bias currents.

Operating Features and System Considerations

for the PT5800 & PT5810 Regulator Series

The PT5800 (5-V input) and the PT5810 (3.3-V input)

series of integrated switching regulators (ISRs) provide

step-down voltage conversion for output loads of up to

18A.

Power up & Soft-Start Timing

Following either the application of a valid input source

voltage, or the removal of a ground signal to the Inhihit*

control pin (with input power applied), the regulator will

initiate a soft-start power up. The soft start slows the

rate at which the output voltage rises, and also introduces a

power-up characteristic of a PT5801 (3.3V) with a 10-A

load.

Vo (2V/Div)

Vin (2V/Div)

HORIZ SCALE: 5ms/Div

t

d

Figure 1-1