Explanation

LM2940-N/LM2940C voltage drop is usually 0.5V@iou003d1A with the ability to provide 1A output current exceeding 1A, and the voltage drop is usually 0.5V. The maximum is the entire temperature range. Inside, adjust the output voltage 1V before assembly. In addition, it also includes reverse protection of static current to reduce circuits. When the image insertion is inserted, the protection voltage exceeds about 3V. The P current and input-output+product enhancement test of the static output current 1A, therefore, the difference between 5V is only 30 mAh. The higher static current exists only in the regulator in the exit mode (VIN VOUT ≤ 3V). LM2940 also designed -N/LM2940C and all regulatory circuits for car applications are protected from reverse battery installation or two battery jumps. During the transient period of the line, for example, when the input voltage may instantly exceed the maximum working voltage of the specified value, the regulator will automatically turn off to protect the internal circuits and loads. LM2940/LM2940C cannot be damaged by temporary mirrors. Familiar regulator characteristics, such as short circuit and hot overload protection.

The internal short -circuit current limit between the input voltage and the output

Positive voltage regulator

Battery

1. If the regulator is far from the power filter, it needs.

2. It must be at least 22 μF to maintain stability. It may increase without having to temporarily temporarily. Close to the regulator as much as possible. The rated values u200bu200bof the capacitor must perform temperature range as a regulator and ESR under the same operating conditions; see the curve.

(1) Absolute maximum rated value refers to the limit value that may be damaged by the device. The operating condition means that the equipment function is normal, but the specifications may not be guaranteed. For ensuring specifications and test conditions, please refer to electrical characteristics.

(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 of the knot temperature TJ. TJ is the function resistance θja and the ambient temperature TA for the ambient temperature. More than the maximum allowable power consumption will cause excessive mold temperature, and the regulator will enter the heat shutdown state. For the to-220 package, the DDPAK/To-263 package is 80 ° C/W, and the SOT-223 package is 174 ° C/W. The effective value of θJa can be used by using the heat sink (for specific information about the heat sink, please refer to the application prompts). The θja value of the WSON package depends on the tracking area, tracking materials, layers and heating holes of the PCB. Increase heat resistance and the power consumption of WSON packaging, please refer to the application description of AN-1187 (SNOA401). It is recommended to place 6 pass holes under the center pad to improve thermal performance.

(4) Surface Patching Equipment (SMD) Packing back welding shape and conditions see JEDEC J-Std-020C. Unless otherwise explained, temperature and time are only applicable to tin lead (STD).

(5) The ESD rated value is based on human model and discharge 100 PF through 1.5 kΩ.

Electrical features

Unless there are other regulations, VIN u003d VO+5V, IO u003d 1A, CO u003d 22 μF. The temperature range of the device is displayed. Instruction of the temperature range of the device. All other specifications are suitable for TA u003d TJ u003d 25 ° C.

(1) All limits are only specified in the entire operating temperature range of the entire working temperature range of TA u003d TJ u003d 25 ° C (standard font) or indicator device. All limits at TA u003d TJ u003d 25 ° C have 100%production testing. All limits at extreme temperatures use statistical quality control methods through relevant regulations.

(2) All limits are only specified in the entire operating temperature range of TA u003d TJ u003d 25 ° C (standard font) or indicator device. All limits have passed 100%production testing and used to calculate the quality level of factory.

(3) The output current will decrease with the temperature, but it will not be lower than 1A at the highest prescribed temperature.

External capacitors

The output capacitor is important for maintaining the stability of the regulator, and must meet the requirements of the two (equivalent series resistance) and minimum power capacity.

Minimum capacity: The minimum output capacitor required to maintain stability is 22 μF (the value may not increase the limit). The greater the output capacitor value, the better the transient response.

ESR limit: Excessive or too low ESR of the output capacitor will cause the circuit to be unstable. The relationship between the acceptable range ESR and the load current is shown in the figure below. The output capacitor must meet these requirements or oscillations may cause

It is worth noting that for most capacitors, ESR only stipulates at room temperature. However, designers must ensure that ESR remains in design throughout the working temperature. For aluminum electrolytic capacitors, the temperature is reduced from 25 ° C to 40 ° C. This capacitor is not suitable for low temperature operation. The solid electric container has a more stable ESR at high temperature, but it is more expensive than aluminum. Sometimes an economic effective way to use is about 75%of the total capacitance with aluminum electrolytic and solids. If the two capacitors are connected in parallel, ESR is the parallel parallel to two individual values. ""Facing""ESR 止 can prevent effective ESR from rising rapidly at low temperature.

Heating

According to the maximum power consumption and the highest environmental temperature application. Under all possible operating conditions, the knot temperature must be at the time of the knotting temperature must be at all possible operating conditions. The scope is specified under the absolute maximum rated value. To determine whether the radiator is needed, the power PD consumed by the regulator must be calculated. The following figure shows the voltage and current in the circuit, and the power consumed in the calculating regulator:

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123]

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) – TA (maximum value value )

TJ (MAX) is the maximum allowed temperature. For commercial -grade parts 125 ° C.

TA (MAX) is the highest ambient temperature encountered in the application.

Use the calculation values u200bu200bof TR (MAX) and PD, and the maximum allowable value resistance θ (JA) connected to the environmental heat can now get: TR (PD) u003d the details on the maximum value of the outer packaging
[[

123] To-220 can be connected to a typical radiator, or a copper plate fixed on the PC board. If it is a copper aircraft in use, the value of θ (ja) will be with the next one of the DDPAK/To-263. The section is the same. If you want to choose the manufactured heat sink, the value of the heat sink to the environmental thermal resistance θ (H a) must be calculated first: θ (h a) u003d θ (ja) θ (c h) θ (j c)

θ (j The value can be hypothetical θ (j c) for this calculation.

θ (c h) is defined as the thermal resistance between the shell and the radiator surface. Value θ (C u0026# 8722; H) changes range of approximately 1.5 ° C/W to about 2.5 ° C/W (depending on the connection method, insulator, etc.). If the exact value is unknown, it should be assumed that θ (C H) should be 2 ° C 2 ° C. /W.#123] When the value of the (H A) is found in the use of the equations in the display of the equations, you must choose a radiator with the following values: less than or equal to this number. Θ (h a) The radiator manufacturer is specified in the form of numbers in the directory, or the temperature and power consumption of the heat sink is represented by the curve. Deta DDPAK/TO-263 (KTT) on the outer packaging Heats. To optimize the heat dissipation capacity of plane and PCB, the encapsulated ears welded into the plane. Figure 37 shows that for DDPAK/TO-263, the use of typical copper plating and copper plating area exceeds 1.

]

As shown in the figure, the copper area is increased to 1 square inch inch.It should also note that the minimum θ (JA) value of DDPAK/To-263 installed on PCB is 32 ° C/W.As a design assistance, Figure 38 shows the maximum allowable power consumption compared with the ambient temperature for DDPAK/TO-263 device.Suppose that the θ (JA) of 1 square inch 1 ounce copper is 35 ° C/W, and the highest temperature (TJ) is 125 ° C.

Details on the outer packaging

SOT-223 (DCY) packaging uses copper planes and PCB itself as a heat sink with PCB.Optimize the heat dissipation capacity of plane and PCB to weld the packaging of the packaging into the plane.Figure 39 and Figure 40 show the information of the SOT-223 package.Figure 40 assume that θ (JA) is 74 ° C/W for 1 square inch 1 ounce copper and 51 ° C/W (for 1 square inch 2 ounce copper), the maximum environmental temperature (TA) is 85 ° C, the highest knot is the highest knotWarm (TJ) is 125 ° C.For the technologies for increasing the heat resistance and power consumption of SOT-223 packaging, please refer to the application description of AN-1028 (SNVA036).