OUT

FB

R2

R1

V

1.21 V(1

) I

R2

=

+

+

´

TPS73801

SLVS915C – FEBRUARY 2010 – REVISED JULY 2015

www.ti.com

The output voltage can be set using the following equations:

(1)

(2)

(3)

Output Range = 1.21 to 20 V

(4)

7.3.2 Fixed Operation

The TPS73801 can be used in a fixed voltage configuration. By connecting the FB pin to OUT the TPS73801 will

regulate the output to 1.21 V. During fixed voltage operation, the FB pin can be used for a Kelvin connection if

routed separately to the load. This allows the regulator to compensate for voltage drop across parasitic

resistances (RP) between the output and the load. This becomes more crucial with higher load currents.

Figure 25. Kelvin Sense Connection

7.3.3 Overload Recovery

Like many IC power regulators, the TPS73801 has safe operating area protection. The safe area 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, allowing the regulator to

start up into very heavy loads. During start up, as the input voltage is rising, the input-to-output voltage

differential is small, allowing 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 also

exhibit this phenomenon, so it is not unique to the TPS73801.

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

Common situations occur immediately after the removal of a short circuit or when the shutdown 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.

7.3.4 Output Voltage Noise

The TPS73801 regulators have been designed to provide low output voltage noise over the 10-Hz to 100-kHz

bandwidth while operating at full load. Output voltage noise is typically 40 nV/

√Hz over this frequency bandwidth

for the TPS73801. For higher output voltages (generated by using a resistor divider), the output voltage noise is

gained up accordingly. This results in RMS noise over the 10-Hz to 100-kHz bandwidth of 14

μVRMS for the

TPS73801.

Higher values of output voltage noise may be measured when care is not exercised with regards to circuit layout

and testing. Crosstalk from nearby traces can induce unwanted noise onto the output of the TPS73801.

Powersupply ripple rejection must also be considered; the TPS73801 regulators do not have unlimited power-

supply rejection and pass a small portion of the input noise through to the output.

12

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