Application Notes

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PT6460 & PT6470 Series

Output Remote Sense

The (+)Sense pin allows the regulator to compensate for

limited amounts of ‘IR’ voltage drop in the positive output

connection resistance. This is the voltage drop incurred

in the PCB trace between Vout (pins 9 & 10) of the regu-

lator and the load some distance away. Connecting (+)Sense

to the positive load terminal improves the voltage regu-

lation at the load, particularly when the load current

fluctuates. Although not recommended, leaving (+)Sense

disconnected will not damage the regulator or the load

circuitry. An internal 10

Ω resistor, connected between

the sense pin and the output, keeps the output voltage in

regulation.

With the sense pin connected, the difference between

regulator, and that measured from (+)Sense to GND, is

the amount of IR drop being compensated by the regula-

tor. This should be limited to 0.3 V maximum.

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.

Pre-Bias Startup

In complex digital systems an external voltage can some-

times be present at the output of the regulator during

power up. For example, this voltage may be backfed

through a dual-supply logic component such as an FPGA

or ASIC. Another path might be via a clamp diode (to a

lower supply voltage) as part of a power-up sequencing

implementation.

Although the PT6460 (5-V input) and PT6470 (3.3-V

input) series of regulators will sink current under steady-

state conditions, they will not do so during startup. This

feature allows these regulators to start up while an external

voltage is simultaneously applied to the output. To facilitate

this feature the input voltage must always be greater than

or equal to the output voltage throughout the power-up

and power-down sequence. Startup includes both the

application of a valid input source voltage, or the removal

of a ground signal from the Inhibit* control (pin 1) with

a valid input source applied. The output of the regulator

is also effectively off (tri-state), during the period that

the Inhibit* control is held low.

Note: If the pre-bias is greater than the nominal regulation

voltage, the module will begin sinking current at the end of its

soft-start power-up sequence. This could overstress the regulator if

the current exceeds its rated output.

Over-Current Protection

To protect against load faults, these ISRs incorporate

output over-current protection. Applying a load that

exceeds the over-current threshold (see data sheet speci-

fications) 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 a 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 normal

operation.

Operating Features and System Considerations

for the PT6460 & PT6470 Regulator Series

The PT6460 (5-V input) and the PT6470 (3.3-V input)

series of integrated switching regulators (ISRs) provide

step-down voltage conversion for output loads of up to

14 A.

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. A soft start slows the rate at

which the output voltage rises and introduces a short time

Figure 1-1 shows the power-up characteristic of a PT6464

(5-V input, 1.8-V output) with a 8.5-A load.

Vo (1V/Div)

Iin (2A/Div)

Vin (2V/Div)

HORIZ SCALE: 5ms/Div

t

d

Figure 1-1