Datasheet

(Fixed Voltage Version)
dVńdt +
V
OUT
C
OUT
80kW ø R
LOAD
(Adjustable Voltage Version)
dVńdt +
V
OUT
C
OUT
80kW ø
(
R
1
) R
2
)
ø R
LOAD
TPS736xx
SBVS038T –SEPTEMBER 2003–REVISED AUGUST 2010 www.ti.com
TRANSIENT RESPONSE After the EN pin is driven low, no bias voltage is
needed on any pin for reverse current blocking. Note
The low open-loop output impedance provided by the
that reverse current is specified as the current flowing
NMOS pass element in a voltage follower
out of the IN pin due to voltage applied on the OUT
configuration allows operation without an output
pin. There will be additional current flowing into the
capacitor for many applications. As with any
OUT pin due to the 80kΩ internal resistor divider to
regulator, the addition of a capacitor (nominal value
ground (see Figure 1 and Figure 2).
1mF) from the OUT pin to ground will reduce
undershoot magnitude but increase its duration. In For the TPS73601, reverse current may flow when
the adjustable version, the addition of a capacitor, V
FB
is more than 1.0V above V
IN
.
C
FB
, from the OUT pin to the FB pin will also improve
the transient response.
THERMAL PROTECTION
The TPS736xx does not have active pull-down when
Thermal protection disables the output when the
the output is over-voltage. This allows applications
junction temperature rises to approximately +160°C,
that connect higher voltage sources, such as
allowing the device to cool. When the junction
alternate power supplies, to the output. This also
temperature cools to approximately +140°C, the
results in an output overshoot of several percent if
output circuitry is again enabled. Depending on power
load current quickly drops to zero when a capacitor is
dissipation, thermal resistance, and ambient
connected to the output. The duration of overshoot
temperature, the thermal protection circuit may cycle
can be reduced by adding a load resistor. The
on and off. This limits the dissipation of the regulator,
overshoot decays at a rate determined by output
protecting it from damage due to overheating.
capacitor C
OUT
and the internal/external load
Any tendency to activate the thermal protection circuit
resistance. The rate of decay is given by:
indicates excessive power dissipation or an
inadequate heat sink. For reliable operation, junction
temperature should be limited to +125°C maximum.
To estimate the margin of safety in a complete design
(including heat sink), increase the ambient
(4)
temperature until the thermal protection is triggered;
use worst-case loads and signal conditions. For good
reliability, thermal protection should trigger at least
+35°C above the maximum expected ambient
condition of your application. This produces a
worst-case junction temperature of +125°C at the
(5)
highest expected ambient temperature and
worst-case load.
REVERSE CURRENT
The internal protection circuitry of the TPS736xx has
The NMOS pass element of the TPS736xx provides
been designed to protect against overload conditions.
inherent protection against current flow from the
It was not intended to replace proper heat sinking.
output of the regulator to the input when the gate of
Continuously running the TPS736xx into thermal
the pass device is pulled low. To ensure that all
shutdown degrades device reliability.
charge is removed from the gate of the pass element,
the EN pin must be driven low before the input
voltage is removed. If this is not done, the pass
element may be left on due to stored charge on the
gate.
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