TPS62040
TPS62042, TPS62043
TPS62044, TPS62046
SLVS463B − JUNE 2003 − REVISED OCTOBER 2005
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SOFTSTART
The TPS6204x series has an internal softstart circuit that limits the inrush current during start up. This prevents
possible voltage drops of the input voltage in case a battery or a high impedance power source is connected to the
input of the TPS6204x.
The softstart is implemented with a digital circuit increasing the switch current in steps of typically I /8, I /4, I /2
LIM
LIM
LIM
and then the typical switch current limit 1.85 A as specified in the electrical parameter table. The start-up time mainly
depends on the output capacitor and load current, see Figure 13.
SHORT-CIRCUIT PROTECTION
As soon as the output voltage falls below 50% of the nominal output voltage, the converter switching frequency as
well as the current limit is reduced to 50% of the nominal value. Since the short-circuit protection is enabled during
start-up, the device does not deliver more than half of its nominal current limit until the output voltage exceeds 50%
of the nominal output voltage. This needs to be considered in case a load acting as a current sink is connected to
the output of the converter.
THERMAL SHUTDOWN
As soon as the junction temperature of typically 150_C is exceeded the device goes into thermal shutdown. In this
mode, the P-Channel switch and N-Channel rectifier are turned off. The device continues its operation when the
junction temperature falls below typically 150°C again.
ENABLE
Pulling the EN low forces the part into shutdown mode, with a shutdown current of typically 0.1 µA. In this mode, the
P-Channel switch and N-Channel rectifier are turned off and the whole device is in shut down. If an output voltage
is present during shut down, which could be an external voltage source or super cap, the reverse leakage current
is specified under electrical parameter table. For proper operation the enable (EN) pin must be terminated and should
not be left floating.
Pulling EN high starts up the TPS6204x with the softstart as described under the section Softstart.
UNDERVOLTAGE LOCKOUT
The undervoltage lockout circuit prevents device misoperation at low input voltages. It prevents the converter from
turning on the switch or rectifier MOSFET with undefined conditions.
12
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