1 Features

The output voltage can be adjusted from -3 V to -24 V,

is usually -2 V to -25 v

output current exceeds 1 a a

Under 1 A load, the voltage drop is usually 0.6 v

Low -static current

Internal short -circuit current limit

Internal heat shutdown with lagging lag [ 123]

TTL, CMOS compatible switch

LM2941 The functional supplement

Application

Rear switch regulator [123 ]

Local, card, regulations

Battery power supply equipment

Industry

Instrument

Instructions

LM2991 is a low low The output voltage range of the negative film dropout is -3 V to -24 V. LM2991 provides a load current of up to 1 A and has remote opening/turn -off. LM2991 uses new circuit design technology to provide a precision benchmark for low voltage drops, low static currents and low temperature coefficients. The voltage drop when the load current is 1-a is usually 0.6 V, which ensures that the maximum value is 1 V within the entire operating temperature range. This static current is usually 1 mA, and the load is 1 -in -the -current and the input output voltage difference is greater than a unique internal bias circuit. Design power supply to limit the static current to 9 mia (typical). When the regulator is in the exit mode (VOUT (VOUT -Vin ≤ 3 volts). LM2991 is the long -term use of reliability of short -circuit and heat closure to enhance the reliability of an overloaded device. There are 5 types of lm2991 C. The MIL aviation version is also available.

VOUT VREF (1+R2/R1) If the regulator exceeds 6 inches from the power filter capacitor, it needs. 1-μF solid is recommended to use 钽 or 10 μF aluminum electrolytic capacitors. Stable required. It must be at least 10 μF aluminum electrolytic or 1 μF solids to maintain stability.

may increase without having to maintain adjustment during the transient period. Closer the capacitor closer to

regulatory agency. The equivalent series resistance (ESR) is the key. Under the same operating conditions, it should be less than 10Ω as the temperature range of the regulator.

Absolutely maximum rated value

exceeding the free air temperature range (unless otherwise explained) (1) (2)

123]

(1) The stress that exceeds the absolute maximum rated value may cause permanent damage to the device. These are the limited stress level, which does not mean that the function operation of the device under these or any other conditions is beyond the recommended conditions of the suggestion. Long -term exposure to absolute maximum rated conditions may affect the reliability of the device.

(2) If you need military/aviation special equipment, please contact the Texas Instrument Sales Office/dealer to obtain availability and specifications.

(3) The maximum power consumption is the functions of TJ (MAX), RθJA, and TA. The maximum allowable power consumption temperature in any environment is pd (TJ (MAX) – TA)/RθJA. If this loss exceeds this loss, the mold temperature will rise to more than 125 ° C, and LM2991 will eventually enter the heat shutdown state under the TJ of about 160 ° C. For more details, see the heat shutdown.

Electrical features

Unless there are other regulations, vehicle identification number -10 V, output voltage -3 V, output voltage 1 a, output power 47μF, R1 2.7 kΩ , TJ 25 ° C

(1) The typical value is TJ 25 ° C, which represents the most likely parameter model.

Detail A 5-pin, low loss, 1-A negative adjustable voltage regulator and negative power supply, which is very suitable for the dual power system when using the LM2941 series. This device can also be used as a adjustable current remittance load.

Feature description

Open/off sales

LM2991 regulator can apply TTL or CMOS level by the open/off -footing foot. High signal to close. The impedance of the voltage source of this driver's open/off -footing foot must be low enough to provide an current at the open/off -turn foot input to meet the level of the closing threshold voltage level. The maximum value of the 2.4 V is 100 μA. If you do not need to open/off, connect the pin to the GND. Switching sales should not keep floating because this is not a guarantee operating condition. See Figure 15.

The mandatory output is positive

Due to the internal clamp circuit, LM2991 can withstand the positive voltage of its output. If the output of the voltage source is a DC, the current must be limited to 1.5 A. The current feedback of more than 1.5 A to LM2991 may damage the device. LM2991 output can also withstand up to 26 V, without power current limit. However, if the transient duration exceeds 1 ms output, it should be fixed on the ground with the Schottky diode.

Hot stack

The internal setting of LM2991 Thermal stopping point is usually 160 ° C, which is about delay. The thermal stack temperature point exceeds the specified recommended operating temperature condition range, which is higher than the absolute maximum rated value. The safety function used as an instantaneous failure is limited to the conditions. Avoid continuous operation when the temperature is close to the temperature of the heat, because it may have a negative life of the device.

Equipment function mode

In VOUT (target) –5 v ≥Vin gt; –26 v, if the input voltage is in VOUT (target value) –5 V to –26 v range,, The equipment work. The input voltage exceeds the vehicle identification code requirements, the device cannot work properly, and the output voltage may not reach the target value.

Application and implementation

Note

The information in the application part of the following application is not a part of the TI component, and the technical information does not guarantee its accuracy or integrity. TI's customers are responsible for determining the applicability of parts. Customers should verify and test their design implementation to confirm the system function.

Application information

LM2991 is a 1-A negative voltage regulator, the range of working vehicle recognition numbers is -6 V to -26 V, and a adjustable voltage with 5%accuracy, the maximum, the maximum The rated output current is 1A. The input voltage from the output voltage is from the output voltage, because LM2991 is a linear voltage regulator. In order to achieve the efficient leakage voltage (VIN -VOUT), it is necessary to be as small as possible, so very low LDO is required. The successful implementation of LDO in the application depends on the application needs. If the request is simple input voltage and output voltage, which meets the specifications (such as internal power supplies must be verified to ensure reliable design. If time, start, noise, PSRR, or any other need for transient specifications, the design becomes more challenging. .

Detailed design program

At 400 mAh, the maximum pressure drop of LM2991 exceeds 1 volt of temperature, so the -5 volt air is enough to enter the input Run with the output voltage accuracy. The efficiency of the LM2991 This configuration is VOUT/VIN 50%. In order to obtain the smallest shape factors, select the to-263 (KTT) package. Select the input and output capacitors consistent with the external capacitors. The input is 470 μF to 470 μF. , 50-μF aluminum capacitors choose output capacitors. The efficiency is 50%, and the maximum load is 400 mAh power consumption of 2000MW, corresponding to the 82.5 ° C knot temperature of the TO-263 packaging. The knot temperature is 107.5 ° C.

External capacitors

LM2991 regulator requires an output capacitor to maintain stability. The capacitor must be at least 10 μF aluminum electrolytic or 1-μF solid. Equivalent series resistance (ESR) must be less than 10Ω,Or zero to add to the regulator frequency response through ESR can reduce the phase margin and cause fluctuations. The input capacitor is made of at least 1-μF solid 钽 or 10-μF aluminum electrolyte. If the regulator is more than 6 inches from the input power filter, it also needs.

Input a capacitor

TI is recommended to use solid bodies or ceramic capacitors, the value is at least 1 μF, but the aluminum electrolyte container can be used (≥10 μF). However, the aluminum electrolytic type does not be used to the ambient temperature to be below 0 ° C, because their internal impedance increases the temperature significantly when it is cold.

Output capacitor

The output capacitor must meet the ESR limit shown in Figure 16, which means that it must have about 25 mΩ and 10Ω.

Solid 钽 (value ≥1μF) is the best choice for output capacitors. Aluminum electrolyte (≥10μF) can be used if ESR is within a stable range. It is worth noting that the ESR of typical aluminum electrolytic grooves will increase by 50 times to -40 ° C temperature from 25 ° C to -40 ° C, while the ESR of the 钽 increases by about 2 times the same range. Because of this and other reasons, aluminum electrolytes are not used in low working temperature. The stable ESR limit of 25 MΩ means that ceramic capacitors cannot be used directly in the most developed countries. If the external resistance is connected with the output terminal (1Ω), the ceramics can be used (≥2.2 μF) at the output end. If the temperature range of the application is different, the X7R or X5R electrical medium must be used to be ± 25 ° or more to ensure that the electricity capacity is sufficient.

Ceramic side electric container

Many designers put their value input pins on the integrated circuit in the circuit board with a distributed ceramic capacitor from 1000 PF to 0.1 μF. This may lead to a reduction in phase margin of LDO or an oscillating regulatory agency. The emergence of a multi -layer plate with a dedicated power supply and ground plane is eliminated (previously) to provide the necessary decoupling " to protect the output of the LDO from being influenced by the bypass. Try to avoid using these capacitors as much as possible; if you use ceramic roadside containers