基于TPS709具有使能端的 150-mA 超低 Iq LDO - 系统集成论坛

　　TPS709 系列线性稳压器是针对功耗敏感型应用而设计的超低静态电流器件。一个精密带隙和误差放大器在温度范围内的精度为 2%。这些器件的静态电流仅为 1µA，因此对于由电池供电、要求闲置状态功耗非常小的常开系统而言，这是非常理想的解决方案。为了增加安全性，这些器件还具有热关断、电流限制和反向电流保护功能。

　　The TPS709 series of devices are ultralow quiescent current, low-dropout (LDO) linear regulators. The TPS709 offers reverse current protection to block any discharge current from the output into the input. The TPS709 also features current limit and thermal shutdown for reliable operation.

　　The TPS709 internal current limit helps protect the regulator during fault conditions. During current limit, the output sources a fixed amount of current that is largely independent of output voltage. In such a case, the output voltage is not regulated, and can be measured as (VOUT = ILIMIT × RLOAD). The PMOS pass transistor dissipates [(VIN – VOUT) × ILIMIT] until a thermal shutdown is triggered and the device turns off. When cool, the device is turned on by the internal thermal shutdown circuit. If the fault condition continues, the device cycles between current limit and thermal shutdown; see the Thermal Protection section for more details.

　　The TPS709 is characterized over the recommended operating output current range up to 150 mA. The internal current limit begins to limit the output current at a minimum of 200 mA of output current. The TPS709 continues to operate for output currents between 150 mA and 200 mA but some data sheet parameters may not be met.

　　The TPS709 use a PMOS pass transistor to achieve low dropout voltage. When (VIN – VOUT) is less than the dropout voltage (VDO), the PMOS pass device is in the linear region of operation and the input-to-output resistance is the RDS(ON) of the PMOS pass element. VDO approximately scales with the output current because the PMOS device functions like a resistor in dropout.

　　The ground pin current of many linear voltage regulators increases substantially when the device is operated in dropout. This increase in ground pin current while operating in dropout can be several orders of magnitude larger than when the device is not in dropout. The TPS709 employs a special control loop that limits the increase in ground pin current while operating in dropout. This functionality allows for the most efficient operation while in dropout conditions that can greatly increase battery run times.

　　The TPS709 uses an undervoltage lockout (UVLO) circuit to keep the output shut off until the internal circuitry operates properly.

　　The TPS709 has integrated reverse-current protection. Reverse-current protection prevents the flow of current from the OUT pin to the IN pin when output voltage is higher than input voltage. The reverse-current protection circuitry places the power path in high impedance when the output voltage is higher than the input voltage. This setting reduces leakage current from the output to the input to 10 nA, typical. The reverse current protection is always active regardless of the enable pin logic state or if the OUT pin voltage is greater than 1.8 V. Reverse current can flow if the output voltage is less than 1.8 V and if input voltage is less than the output voltage.

　　If voltage is applied to the input pin, then the maximum voltage that can be applied to the OUT pin is the lower of three times the nominal output voltage or 6.5 V. For example, if the 1.2-V output voltage version is used, then the maximum reverse bias voltage that can be applied to the OUT pin is 3.6 V. If the 5.0-V output voltage version is used, then the maximum reverse bias voltage that can be applied to the OUT pin is 6.5 V.

　　Enabled: When the enable pin (EN) goes above 0.9 V, the device is enabled. EN is pulled high by a 300-nA current source; therefore, EN can be left floating to enable the device. Do not connect EN to VIN. The EN pin is clamped by a 6.5-V Zener diode. Do not exceed the 7-V absolute maximum rating on the enable pin or excessive current flowing into the Zener clamp will destroy the device.

　　Disabled: When EN goes below 0.4 V, the device is disabled. During this time, OUT is high impedance and the current into IN (I(SHUTDOWN)) is typically 150 nA.

　　Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

　　The TPS709 is a series of devices that belong to a new family of next-generation voltage regulators. These devices consume low quiescent current and deliver excellent line and load transient performance. This performance, combined with low noise and very good PSRR with little (VIN – VOUT) headroom, makes these devices ideal for RF portable applications, current limit, and thermal protection. The TPS709 is specified from –40°C to +125°C.

　　The TPS709 devices are stable with output capacitors with an effective capacitance of 2.0 μF or greater for output voltages below 1.5 V. For output voltages equal or greater than 1.5 V, the minimum effective capacitance for stability is 1.5 µF. The maximum capacitance for stability is 47 µF. The equivalent series resistance (ESR) of the output capacitor must be between 0 Ω and 0.2 Ω for stability.

　　As with any regulator, increasing the output capacitor size reduces over- and undershoot magnitude, but increases transient response duration.