Datasheet
SLVS399A − JANUARY 2002 − REVISED MAY 2006
19
www.ti.com
APPLICATION INFORMATION
programming the adjustable LDO regulator (continued)
Table 1. Output Voltage Programming Guide
OUTPUT VOLTAGE R1 R2 Cf
3.3 619 kΩ 200 kΩ NR
†
3.0 549 kΩ 200 kΩ NR
†
2.5 422 kΩ 200 kΩ 2 pF
1.8 249 kΩ 200 kΩ 6 pF
1.5 174 kΩ 200 kΩ 10.3 pF
1.0 49.9 kΩ 200 kΩ 46 pF
†
NR − Not required
overcurrent
When an overcurrent condition is detected, the device maintains a constant output current. Complete shutdown
occurs only if the fault is present long enough to activate thermal limiting.
Three possible overload conditions can occur. In the first condition, the output is shorted before the device is
enabled. Once enabled the TPS2140/41/50/51 sense the short and immediately switch to a constant-current
output.
In the second condition, the short occurs while the device is enabled. At the instant the short occurs, very high
currents may flow for a very short time before the current-limit circuit can react. After the current-limit circuit has
tripped (reached the overcurrent trip threshold), the device switches into constant-current mode.
In the third condition, the load has been gradually increased beyond the recommended operating current. The
current is permitted to rise until the current-limit threshold is reached or until the thermal limit of the device is
exceeded. The TPS2140/41/50/51 are capable of delivering current up to the current-limit threshold without
damaging the device. Once the threshold has been reached, the device switches into its constant-current mode.
dual current limit
The TPS2140/41/50/51 has a dual-current-limited power switch. When the output voltage of the power switch
is below a defined power-good threshold voltage, the typical current the switch can conduct is approximately
75 mA. Therefore, the inrush current can be limited to about 75 mA even if there is a very large capacitor on
the load. When the switch output voltage reaches the power-good threshold voltage, the internal controller
enables the higher current limit, which is at least 0.8 A and at most 1.8 A. This dual-current-limit feature
completely solves the large inrush current problems that most power management applications experience.
Figure 7 shows the inrush currents with different load capacitance. The current spike at C
L
= 600 µF is due to
voltage difference between input and output once the higher current limit is enabled.
Because the lower current limit is only about 75 mA, the initial resistive load or equivalent load current on the
switch output must be less than 50 mA, excluding the load capacitors.