 |
 |
|
| TPS72012YZUT |
|
|||||||||||||||||
 TI
|
| |||||||||||||||||
|
12 page 
SHUTDOWN MINIMUM LOAD DROPOUT VOLTAGE OUTPUT REGULATION WITH IN PIN TRANSIENT RESPONSE UNDERVOLTAGE LOCK-OUT (UVLO) Microcontroller TPS720xx TPS62xxx VIN EN SW FB IN OUT BIAS EN GND 2.2mF 10mF 10mH 2.5Vto5.5V Controltoturnon/offthedc/dc Outputofdc/dcisfloatingwhen theTPS62xxxENpinislow GND TPS720xx SBVS100D – JUNE 2008 – REVISED AUGUST 2009........................................................................................................................................................ www.ti.com The enable pin (EN) is active high and is compatible The TPS720xx is stable with no output load. with standard and low voltage, TTL-CMOS levels. Traditional LDOs suffer from low loop gain at very When shutdown capability is not required, EN can be light output loads. The TPS720xx employs an connected to the IN pin. innovative, low-current mode circuit under very light or no-load conditions, resulting in improved output voltage regulation performance down to zero output current. The TPS720xx uses a NMOS pass transistor to achieve low dropout. When (VIN – VOUT) is less than the dropout voltage (VDO), the NMOS pass device is FLOATING in the linear region of operation and the input-to-output resistance is the RDS(ON) of the NMOS The TPS720xx supports a novel feature in which the pass element. VDO approximately scales with output output of the LDO regulates under light loads when current because the NMOS device behaves as a the IN pin is left floating. Under normal conditions, resistor in dropout. when the IN pin is connected to a power source, the BIAS pin draws only tens of milliamperes. However, As with any linear regulator, PSRR and transient when the IN pin is floating, an innovative circuit is response are degraded as (VIN – VOUT) approaches used that allows a mximum current of 500 µA to be dropout. This effect is shown in Figure 19 in the drawn by the load through the BIAS pin, while Typical Characteristics section. maintaining the output in regulation. This feature is particularly useful in power-saving applications where a dc/dc converter connected to the IN pin is disabled, but the LDO is required to regulate the output voltage As with any regulator, increasing the size of the to a light load. output capacitor reduces over/undershoot magnitude but increases duration of the transient response. Figure 27 shows an application example where a microcontroller is not turned off (to maintain the state of the internal memory), but where the regulated supply (shown as the TPS62xxx) is turned off to The TPS720xx uses an undervoltage lock-out circuit reduce power. In this case, the TPS720xx BIAS pin on the BIAS pin to keep the output shut off until the provides sufficient load current to maintain a internal circuitry is operating properly. The UVLO regulated voltage to the microcontroller. circuit has a deglitch feature so that it typically ignores undershoot transients on the input if they are less than 50 µs duration. Figure 27. Example of Floating IN Pin Regulation 12 Copyright © 2008–2009, Texas Instruments Incorporated |
