Datasheet

TPS72710 , TPS72711 , TPS72715 , TPS727185 , TPS72718 , TPS72719 , TPS72725
TPS72727 , TPS727285 , TPS72728 , TPS72730 , TPS72733 , TPS72748 , TPS72750
www.ti.com SBVS128D –JUNE 2009–REVISED FEBRUARY 2014
Feature Description (continued)
The TPS727xx automatically adjusts the soft-start current to supply both the load current and the C
OUT
charge
current. For example, if I
LOAD
= 0 mA upon enabling the LDO, I
SOFT START
= 1 μF × 0.07 V/μs + 0 mA = 70 mA,
the current that charges the output capacitor.
If I
LOAD
= 200 mA, I
SOFT START
= 1 μF × 0.07 V/μs + 200 mA = 270 mA, the current required for charging output
capacitor and supplying the load current.
If the output capacitor and load are increased such that the soft-start current exceeds the output current limit, it is
clamped at the typical current limit of 400mA. For example, if C
OUT
= 10 μF and I
OUT
= 200 mA, 10 μF × 0.07
V/μs + 200 mA = 900 mA is not supplied. Instead, it is clamped at 400 mA.
7.3.3 Shutdown
The enable terminal (EN) is active high and is compatible with standard and low voltage, TTL-CMOS levels.
When shutdown capability is not required, EN can be connected to the IN terminal.
7.3.4 Dropout Voltage
The TPS727xx uses a PMOS pass transistor to achieve low dropout. When (V
IN
– V
OUT
) is less than the dropout
voltage (V
DO
), the PMOS pass device is in the linear region of operation and the input-to-output resistance is the
R
DS(ON)
of the PMOS pass element. V
DO
approximately scales with output current because the PMOS device
behaves like a resistor in dropout.
As with any linear regulator, PSRR and transient response are degraded as (V
IN
– V
OUT
) approaches dropout.
This effect is shown in Figure 15 in the Typical Characteristics section.
7.3.5 Undervoltage Lock-out (UVLO)
The TPS727xx uses an undervoltage lock-out circuit that keeps the output shut off until the input voltage reaches
the UVLO threshold voltage.
7.3.6 Thermal Protection
Thermal protection disables the output when the junction temperature rises to approximately +160°C, allowing
the device to cool. When the junction temperature cools to approximately +140°C the output circuitry is again
enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection
circuit may cycle on and off. This cycling limits the dissipation of the regulator, protecting it from damage as a
result of overheating.
Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate
heatsink. For reliable operation, junction temperature should be limited to +125°C maximum. To estimate the
margin of safety in a complete design (including heatsink), increase the ambient 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 particular application. This
configuration produces a worst-case junction temperature of +125°C at the highest expected ambient
temperature and worst-case load.
The internal protection circuitry of the TPS727xx has been designed to protect against overload conditions. It is
not intended to replace proper heatsinking. Continuously running the TPS727xx into thermal shutdown degrades
device reliability.
7.4 Device Functional Modes
7.4.1 Operation with EN Control
Driving EN over 0.9 V turns on the regulator. Driving EN below 0.4 V puts the regulator into shutdown mode,
thus reducing the operating current to 120 nA, nominal.
Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Links: TPS72710 TPS72711 TPS72715 TPS727185 TPS72718 TPS72719 TPS72725 TPS72727
TPS727285 TPS72728 TPS72730 TPS72733 TPS72748 TPS72750