LP2957/LP2957A ...

  • 2022-09-15 14:32:14

LP2957/LP2957A is suitable for 5V low -voltage differential regulator for μP applications

Functional description

LP2957 is a 5V micro -power voltage regulator 2 5V output, the temperature exceeds 1.4%(A level) with electronic shutdown, the error logo, very low

Static current (a typical 150 μA under the 1 ma load), and easy to program, to achieve fast start/rapid disconnection very low voltage drop (250 mAh out of 470 millivoltage output load current).

Ensure that the output current output of 250 mA can be connected to the rapid startup/off operation

The extremely low static current eliminates the transition voltage status when μP work

Low possible It is unpredictable. The required input and output voltage

adjusts the output prying pole (50 mAh typical drop -down current) when the regulator

Turn off or starts the function start.

极为严格的线路和负荷调节

温度系数非常低,零件具有紧密的线和负载调节(0.04%典型值)和低输出温度系数(20 电流和Heat restrictions on PPM/° C typical values).

The error sign signal when the output exceeds

The accuracy of the 5V output is adjusted in the room to ensure that the temperature exceeds the entire working temperature range.

LP2957 can be used for Wutu to-220 and DDPAK/To-263 packaging.

Application

High -efficiency linear regulator

battery power supply regulator

(1) Absolute maximum rated value representation representation The limit value of the component may cause damage. The electrical specifications are not applicable when operating equipment outside the rated working conditions.

(2) If you need military/aerospace special equipment, please contact the Texas Instrument Sales Office/dealer to obtain standardization.

(3) The maximum allowable power consumption is the function (MAX) of the maximum knot temperature T j, which is resistant at the junction of the ambient temperature and the ambient temperature TA. Calculate the maximum allowable power consumption of any ambient temperature:

Excessive allowable power consumption will cause the mold temperature to be too high, and the regulator will enter the heat shutdown state. The thermal resistance of the to-220 (not with a radiator) is 60 ° C/W and 73 ° C/WDDPAK/To-263. If you use DDPAK/TO-263 packaging, you can reduce the area of u200bu200bthe thermal resistance and packaging thermal connection by increasing P.C. plate copper: use a copper area of u200bu200b0.5 square inch, θJa is 50 ° C/W, 1 square inch copper area, θJa It is 37 ° C/W; for 1.6 or more square -inch copper area, θJa is 32 ° C/W. The thermal resistance of the pair shell is 3 ° C/W. ifThe use of external heat sinks, the thermal resistance of the effective pairing environment is the total (3 ° C/W) of the pairing shell resistance, the specified thermal resistance of the selected heat sink, and the radiator and LP2957 (see the application prompt).

Electrical characteristics

The limit of the standard font is suitable for TJ u003d 25 ° C, and the limit of black body characters is suitable for the entire working temperature range. Unless there are other regulations: vin u003d 6V, IL u003d 1MA, CL u003d 2.2μF, vsd u003d 3V.

(1) When used in a dual power supply system, the regulator load returns negative power supply, and the output voltage must be clamped by the diode.

(2) The temperature coefficient of the output voltage is defined as the worst case in the worst case, except for the total temperature range.

(3) Merit and adjust under constant node temperature through a low -occupying pulse test. The load test load range of the parts is regulated by 0.1 mA -1 ma and 1 ma -250 mA. The output voltage changes caused by the heating effect are included in thermal regulation specification.

(4) The drop voltage is defined as the difference between the input and output voltage, and the output voltage is lower than the 100 millival input output output difference measurement.

Electrical characteristics (continued)

The limit of the standard font is suitable for TJ u003d 25 ° C, and the limit of black body characters is suitable for the entire working temperature range. Unless there are other regulations: vin u003d 6V, IL u003d 1MA, CL u003d 2.2μF, vsd u003d 3V.

(5) The ground pins current is the static current of the regulator. The total current from the power supply is the load current plus the ground pin current.

(6) Thermal regulation is defined as changes in the output voltage at the time of T -time T -time output after the power consumption, excluding the effect of load or line regulation. The technical specifications are suitable for VIN u003d 20V (3W pulse) under 200 mA load pulses, T u003d 10ms.

(7) The voltage reference nominal regulating output voltage.

Typical performance characteristics (continued)

Unless otherwise regulations: vin u003d 6V, IL u003d 1MA, cl u003d 2.2μF, v sd u003d 3V, ta u003d 25 ° C

[

123]

(1) The maximum allowable power consumption is the function (MAX) of the maximum temperature T j, and the environmental temperature At the junction of the resistance θja and ambient temperature TA. Calculate the maximum allowable power consumption at any ambient temperature:

Excessive allowable power consumption will cause the mold temperature to be too high, and the regulator will enter the heat shutdown state. The thermal resistance of the to-220 (not with a radiator) is 60 ° C/W and 73 ° C/WDDPAK/To-263. If you use DDPAK/TO-263 packaging, you can reduce the area of u200bu200bthe thermal resistance and packaging thermal connection by increasing P.C. plate copper: use a copper area of u200bu200b0.5 square inch, θJa is 50 ° C/W, 1 square inch copper area, θJa It is 37 ° C/W; for 1.6 or more square -inch copper area, θJa is 32 ° C/W. The thermal resistance of the pair shell is 3 ° C/W. If the external heat sink is used, the thermal resistance of the effective pairing environment is the total (3 ° C/W) of the pairing shell resistance, the specified thermal resistance of the selected heat sink, and the radiator and LP2957 (see the application prompt).

External capacitors

The output pins and grounding need 2.2 μF (or larger) capacitors to ensure stability (see Figure 30) Essence Without this capacitor, parts may oscillate. Most types of tadpoles or aluminum electrolytes work here. The film can be used, but it is more expensive. Many aluminum electrolytic grooves are frozen under 30 ° C. This requires an ESR with an ESR with a solid cavator below 25 ° C about 5Ω or smaller, and the resonance frequency is higher than 500 kHz (ESR can be available for ESR. When a temperature is increased from 25 ° C to 30 ° C, the coefficient is 20 or 30). The value of this capacitor may increase infinitely. At a lower output current value, less output capacitance is required to ensure stability. When this current is lower than 10 mA, the capacitor can be reduced to 0.68 micro -volt; when the current is lower than 1 mA, the capacitor can be reduced to 0.22 micro volt. If the wire between the input pin is more than 10 inches, the 1 μF capacitor should be placed in the ground input and AC filter capacitor, or if the battery is used. If the regulator wiring is used to quickly start/disconnect output, and the power impedance is high (see the card in/disconnect).

The input of the shutdown

When the ""low"" (u0026 lt; 1.2V) is applied to the input of the stop, the logical level signal will turn off the regulator output. In order to prevent possible misunderstanding, the shutdown input must be proactively terminated. If the input from the road set logic, you must connect to the pull -up resistor (20 kΩ to 100 kΩ) from the shutdown place to enter to the regulator input. If the shutdown input is driven by a high -power flat and low level (such as the operation amplifier), the pull -up resistor is not necessary, but it can be used. If you do not use the shutdown function, you can directly enter the regulator input by bundling and closing the cost of pulling the resistor. Important tips: Due to the absolutely maximum rated state, the input of the shutdown cannot exceed 0.3V below the ground. If the input of the shutdown is directly connected to the regulator input. If you need to add a protective resistor between the battery and input, a protection must be used to enter.

Minimum load

It should be noted that in some electricityIn the gas test, the minimum load current must be used to obtain the correlation of these test limits. The part of the part is 100 μA, but it can still work normally under the air load.

Falling voltage

The voltage drop of the regulator is defined as the output voltage kept within 100 millivolttack of the output voltage, and measured with 1V differential measurement. The drop voltage is listed under the electrical characteristics for different load current values. If the regulator is powered by a transformer connected to the AC line, the minimum AC line voltage and the maximum load current must be used to measure the minimum voltage of the input terminal of the regulator. This minimum input voltage includes the minimum voltage level of the ripple of the filter capacitor. It is also recommended to verify the operation at the minimum working environment, because the ESR of the filter capacitor increases due to increased ripple amplitude, which is the worst test.

The heat sink requirements

LP2957 may need to be heat sink, depending on the environmental temperature of maximum power consumption and maximum power consumption application. Under all possible operating conditions, the knot temperature must be within the scope specified at the absolute maximum rated value. To determine whether the radiator is required, the maximum power P (MAX) consumed by the regulator must be calculated. It is important to remember that if the regulator is a transformer connected to the AC power supply wire supply line, the maximum AC input voltage must be used (because this will generate the voltage of the maximum DC input regulator) and the maximum load current must also be used. Essence Figure 30 shows the current in the voltage and circuit. In the article, the power consumption calculation formula of the regulator is also given in Figure 30

ptotal u003d (vin 5) i l+(vin) ig

*See external capacitors

The next parameter that must be calculated is the maximum allowed to allow the temperature rise TR (MAX). This is the use of the following formula calculations: TR (maximum value) u003d TJ (maximum value) t a (maximum value)

(max) is the maximum allowed temperature

TA (max] ) It is the highest environmental temperature (1) calculating values u200bu200busing TR (MAX) and P (MAX), that is, the required resistance of the environmental thermal resistance θ (JA) can now get: θ (ja) u003d TR (maximum)/ P (maximum) (2)

If the calculation value is 60 ° C/W or higher, the regulator can run without an external radiator. If the calculation value is less than 60 ° C/W, an external radiator is required. The required heat -resistant heat sink θ (ha) can be calculated using the following formula: θ (ha) u003d θ (ja) θ (jc) θ (ch)

θ ( JC) is a knot-shell heat resistance, and the specified value of LP2957 is 3 ° C/W


θ (CH) is a radiatorThe condition of thermal resistance depends on the interface material (see Table 1 and Table 2)

θ (ha) Thermal resistance of the environment. This is the validity of the radiator of this specification (the data table listed in the radiator manufacturer). The selected radiator must have the resistance of the θ (ha) value calculated based on the above formula.

Error comparator

When the output exceeds the adjustment range of more than 5%, the comparator will produce ""low"" logic. This picture shows the result of the built -in offset of the comparator 60 MV except the 1.23V reference voltage. Violation of regulations, current limit, current, and current limit conditions may cause the input voltage to be too low. Figure 31 gives a timing diagram that shows the output voltage, error output, and input voltage rising and decreased to the regulator with the increase and decline of the input voltage, and the output is turned off without stuck/quickly. The error signal becomes lower at about 1.3V input. It becomes higher when it is input at about 5V, and the output is equal to 4.75V. Because the voltage drop is related to the load, the input voltage trip point will change with the load current. This output voltage trigger point is unchanged. The comparator has the output of the collector, which requires an external pull -up resistor. This resistor may be connected to the regulator output or other power supply voltage. Using a regulator output can prevent invalidation when the regulator is input, when the comparator output is pulled to the external voltage, the ""high"" voltage will be reduced to below 1.3V. When choosing a value for the pull -up resistor, please note that although the output can be reduced by 400 μA, this current increases the battery consumption. The recommended value range is 100k to 1MΩ. The resistance is not necessary if the output is not used.

1. In the shutdown mode, if the error is pulled to the external power supply, the error will become higher. To avoid invalid response, pull up to the regulator output.

2. The accurate value depends on the voltage drop. It changes with the change of the load current

If a pull -up resistor is connected to About 1.3V input voltage is tilted up and down from 0V to 1.3V. In some cases, the 1.3V signal may be wrongly explained by the μP of 1.3V that is still ""activity"". It is applied to it. To prevent this, users can choose to use two error outputs with equal resistance values u200bu200b(one ground, another output of the regulator). If these two resistors are used, the error output during the power period will only be pulled to about 0.6V (not 1.3V) or power off, so it cannot be explained as a high signal. When the regulator output is adjusted (4.8V to 5V), the error output voltage will be 2.4V to 2.5V, which is obviously a high signal.

Output isolation

regulator output can be adjusted by adjustmentThe input of the device is connected to the active voltage source (such as the battery) and close it, as long as the regulator is grounded. If the ground pin is kept floating, if the output is pulled up by the external voltage source, it may damage the regulator

card input/buckle operation

LP2957 output can be performed through three external resistors through three external resistors. Card in/disconnected operation:

*minimum value (increased according to the requirements of smooth opening features).

When the connection shown in the figure, turn off the input to keep the regulator turn off until the input voltage rises to the opening threshold (V on), and the output is ""quickly open"". When the input power is turned off (the input voltage starts attenuation), when the input voltage reaches the turning threshold, VOFF.

It should be noted that the voltage VOFF must always be lower than VON (the difference between these voltage levels is called magnetic stagnation). The need to lag when the fast opening/fast level output is required, and the minimum lagging amount required depends on any source impedance to provide VIN.

Note: If Von and Voffar are too close (not lagging). When the output suddenly connects, the regulator must suck a sufficient current to charge the output capacitor to the load (in most cases, the regulator will briefly consume the maximum current that allows the maximum current to the internal limiter).

Therefore, it is best to assume that the LP2957 may drive a peak current of about 600 mAh from the power supply (that is, the maximum short -circuit load current list of 530 mAh plus the ground pins current 70 mAh). This peak current causes the amount of VIN to decrease equal to the source impedance multiplication of the current. If V in drops below the VOFF, the regulator will be closed and stopped from the power supply. This will allow Vin to return to Feng's upper above, and the cycle will start again. The regulator will never be included in the scope of the oscillating mode.

The stagnation of the power supply of the transformer

Application: If the unsettled DC input voltage of the regulator comes from the transformer, it is easy to generate the required hysteresis with the resistance loading power supply to measure.

If the regulator is powered by the battery, the power impedance may be compared to another low consideration factors (see design example#2). In order to obtain the best results, the load resistance for testing the transformer should be selected as the maximum load current test of 600 mA, because this is the maximum peak current that LP2957 can expect from the source. The input voltage difference measured during the air load and the full load defines the required stagnation of the magnetic stagnation correctly/fast shutdown operation (programming lag must be greater than the voltage difference).

Calculating resistance value:

R1, R2 and R3 values u200bu200bcan be calculated, assuming the designer knows the stagnation. In the application of most transformer power supply, it can be assumed that VOFF (input voltage at the time of disconnection) should be set to about 5.5V, because this allows about 500 millibolia to pass LP2957 to keep the output adjustment until it is closed. VON (input voltage when turning on) is obtained by adding a lagging voltage to the VOFF. R1, R2, and R3 are pins obtained by the current node equation that enters the closest to stopped nodes (write the threshold for opening and shut down).停机引脚偏置电流(10毫安典型值)不包括在计算中:

由于这两个方程包含三Unknown (R1, R2, and R3), so it is necessary to assume that one resistance value must be assumed, and the remaining two values u200bu200bcan be obtained by solving the equation. The node equation will be simplified by solving the two equations of R2, and then the two are represented by R1 and R3.

If the designer assumes that the value of R1 or R3 is one of the resistors.

The easiest way is to assume the value of R3. The best result is usually about 20kΩ and 100kΩ (so that low -current consumption can be maintained, but it can also generate another actual value resistor). The minimum value of R3 is not limited, but the current should minimize, because the energy it generates will exhaust the power without loading.

Summary: Solve R1, R2 and R3:

1. The assumption value is R1 or R3.

2. Solve another variable with the equation of R1 or R3.

3. Take the values u200bu200bof R1 and R3, then insert them back to the equation of R2, and then solve this value. Design example#1: 5V adjustment output is powered by the secondary transformer that is rectifier and filter. The voltage is measured at zero -current and maximum current (600 mAh) to determine the minimum allowable stagnation. Use the oscilloscope to measure the vehicle identification number (for the sake of clear, the two records are displayed on the same grid):

The full -load voltage waveform of the transformer power supply will have as shown in the figure. The ripple voltage shown. The correct value of the correct measuring point is the lowest value of the waveform. The 1.2V difference between the air load and the full load means that the lag of at least 1.2V is required for the correct fast start/off operation (in this example, we will use 1.5V). As a starting point, we assume: VOFF u003d 5.5V Von u003d V level+HYST u003d 5.5+1.5 u003d 7V R3 u003d 49.9K

Design Example#2:

A 5V adjustable output will be consisted of one Power consisting of six nickel -cadmium batteries. The cell data is:

battery voltage (full charging): 1.4V

battery voltage (90%discharge): 1.0V

Typical electricityThe internal resistance of the pool is low enough. When the regulator is turned on, the source load will not be reduced. It is usually a problem. In the application of battery power supply, the voltage VOFF should be selected to turn off the regulator when the battery power reaches 90%(excessive discharge will damage the battery). In this case, the battery voltage of 90%of the discharge point is 6.0V (because there are 6 batteries, and the voltage of each battery is 1.0V). This means that for this application, VOFF will be set to 6.0V. In order to understand the best voltage choice, the best performance of the battery needs to be understood. If the nickel cadmium battery discharge (battery voltage 1.0V) and the load is removed, the battery voltage will rise. The voltage regulator must be set enough to prevent the regulator from restarting during this period of time, or the switch may have pulse mode. If the regulator is restarted when the voltage of the discharge battery is rising, the load on the battery will cause the battery voltage to drop below the confine level, causing the regulator to close. The battery voltage will continue to rise and the switching cycle will continue. For nickel -cadmium batteries, the good battery voltage of VON is about 1.2V per battery. In this application, the VON value generated is 7.2V. We can now find R1, R2, and R3. Assuming: voltage u003d 6.0V open u003d 7.2V R3 u003d 49.9K