Functional description

LM2937 is a positive voltage regulator, which can fully specify that it provides a load current of up to 500 mAh under 40 ° C. Use+125 ° CPNP power transistor to provide a low -voltage difference voltage output current exceeding 500 mA. When the load current is 500 mAh, at the minimum input-output voltage difference of all requirements, the working conditions of the output is 5%tolerant output. Within the temperature, a typical 0.5V voltage drops). The load current adopts a special circuit to make the ESR of the minimum static current. The ESR of this capacitor is still a key design mirror image inserting the protection parameter, but the LM2937 includes the compensation circuit requirements of special relaxation ESR. LM2937 is stable than 3Ω for all ESRs. This allows a low ESR chip capacitor.

LM2937 is an ideal choice for automobile applications

and protect it from any influence of any reverse load

battery connection, two battery jumps, up to

]+60V/-50V load uninstall. Familiar regulators

Short -circuit and heat shutdown characteristics

Protection is also built -in.

Wide output capacitor ESR range, as high as 3Ω, usually only 10 mA, load current is 500 mA

When the output voltage difference is large, the internal short circuit and heat overload

The protection voltage is greater than 3V.

Reverse battery protection LM2937 requires an output bypass electrical container

60V input transient protection stability. Like most low -voltage differences

(1) Absolute maximum rated value indicates the limit of damage to the device. Electrical specifications are not suitable for 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 at any ambient temperature is PMAX u003d (125 TA)/θja, of which 125 is the maximum knotting temperature, TA is the environmental temperature, θja is the environmental thermal resistance of the environmental heat resistance Knot. If this dissipation exceeds, the mold temperature will rise to more than 125 ° C, and the electrical specifications will not be applicable. If the mold temperature is higher than 150 ° C, LM2937 will enter the hot shutdown state. For LM2937, the environmental thermal resistance θJa is 65 ° C/W. For TO-220 package, DDPAK/TO-263 package is 73 ° C/W, and SOT-223 packages are 174 ° C/W. When used with the radiator,θJa is the sum of LM2937-thermal resistance θJC at the shell is 3 ° C/W and the sum of the heat resistance of the radiator. If you use DDPAK/TO-263 or SOT-223 packaging, you can reduce the heat resistance heat connection by increasing the P.C. board copper area (more information about heat dissipation, please refer to the application prompts).

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

(1) Absolute maximum rated value indicates the limit of damage to the device. Electrical specifications are not suitable for operating equipment outside the rated working conditions.

(2) The maximum allowable power consumption at any ambient temperature is PMAX u003d (125 TA)/θJa, of which 125 is the maximum working temperature, TA is the ambient temperature, θja is the environmental thermal resistance of the environmental heat resistance Knot. If this dissipation exceeds, the mold temperature will rise to more than 125 ° C, and the electrical specifications will not be applicable. If the mold temperature is higher than 150 ° C, LM2937 will enter the hot shutdown state. For LM2937, the environmental thermal resistance θJa is 65 ° C/W. For TO-220 package, DDPAK/TO-263 package is 73 ° C/W, and SOT-223 packages are 174 ° C/W. When using it with the radiator, θJa is the sum of the LM2937 knot-the thermal resistance of the shell is 3 ° C/W. If you use DDPAK/TO-263 or SOT-223 packaging, you can reduce the heat resistance heat connection by increasing the P.C. board copper area (more information about heat dissipation, please refer to the application prompts).

Electrical features

For TO-220 and DDPAK/To-263 packaging, vin u003d vnom+5V (1) IOUTMAX u003d 500 ma, for SOT-223 packaging, IOUTMAX u003d 400mA, COUT, COUT u003d 10 μF, unless there is another instructions. The thickness restrictions are applicable to the device shown, and all other specifications are suitable for TA u003d TJ u003d 25 ° C.

(1) The typical value is TJ u003d 25 ° C, which represents the most likely parameter specifications.

Electrical features

For TO-220 and DDPAK/To-263 packaging, vin u003d vnom+5V (1) IOUTMAX u003d 500 ma, for SOT-223 packaging, IOUTMAX u003d 400mA, COUT, COUT u003d 10 μF, unless there is another instructions. The thick body restrictions are suitable for the indicator device, and all other specifications are applicable to TA u003d TJ u003d 25 ° C

[1) The typical value is TJ u003d 25 ° C, which represents the most most Possible parameter specifications.

(1) The maximum allowable power consumption at any ambient temperature is pmax u003d (125 ta)/θja, of which 125 is the 125 is The maximum work temperature, TA is the ambient temperature, θJa is the knot of environmental thermal resistance. If this dissipation exceeds, the mold temperature will rise to more than 125 ° C, and the electrical specifications will not be applicable. If the mold temperature is higher than 150 ° C, LM2937 will enter the hot shutdown state. For LM2937, the environmental thermal resistance θJa is 65 ° C/W. For TO-220 package, DDPAK/TO-263 package is 73 ° C/W, and SOT-223 packages are 174 ° C/W. When using it with the radiator, θJa is the sum of the LM2937 knot-the thermal resistance of the shell is 3 ° C/W. If you use DDPAK/TO-263 or SOT-223 packaging, you can reduce the heat resistance heat connection by increasing the P.C. board copper area (more information about heat dissipation, please refer to the application prompts).

1. If the regulator is more than 3 inches from the power filter capacitor from the power filter, it needs.

2. Stability requirements. COUT must be at least 10 μF (the entire expected working temperature range) and is located as close to the regulator as possible. The equivalent series resistance ESR of this capacitor can be as high as 3Ω.

External capacitors

The output capacitor is critical to maintain the stability of the regulator, and must meet the requirements of the two (equivalent series resistance) and minimum power capacity.

Minimum capacitance: The minimum output capacitor required to maintain stability is 10 μF (the value can be limited without limit). The greater the output capacitor value, the better the transient response.

ESR limit:

Excessive or too low ESR of output capacitors will lead to unstable circuit. 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.

It is worth noting that for most capacitors, ESR only stipulates at room temperature. However, designers must ensure that ESR is designed within the limit of the entire operating 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 method is to connect aluminum electrolytes with solids. The total capacitor is divided by about 75/25%. Aluminum is a larger value.123]

Heating

According to the maximum power consumption and maximum environmental temperature application. Under all possible operating conditions, the knot temperature must be specified under the absolute maximum rated value within the range. To determine whether the radiator is required, the power PD consumed by the regulator must be calculated. The figure below shows the voltage and current in the circuit, and the power consumed in the calculating regulator:

The next parameter that must To. This is the use of the following formula calculations: TR (maximum value) u003d TJ (maximum value) TA (maximum value)

(MAX) is the maximum allowed temperature, for commercialized parts, 125 °, 125 ° C

TA (MAX) is the calculation value of TR (MAX) and PD encountered in the application (1) the highest ambient temperature encountered in the application (1). ) Now you can get: θ (j a) u003d TR (maximum)/pd (2)

important items: If you find the maximum permission of the θ (j a) of the to-220 packaging Value ≥53 ° C/W, ≥DDPAK/TO-263 package is 80 ° C/W, and SOT-223 package is ≥174 ° C/W, because the packaging can emit sufficient heat to meet these requirements. If the calculation value of θ (j a) is lower than these limits, the radiator is required.

Heating to-220 packaging parts

TO-220 can be connected to a typical radiator, or a copper plate fixed on the PC board. If it is used by copper aircraft, the value of θ (j a) will be the same as the next section of DDPAK/To-263. If you want to choose the manufactured heat sink, the value of the heat sink to the ambient thermal resistance θ (H a) must first calculate: θ (h a) u003d θ (j a) θ (C u0026#8722, h) θ (j c)

θ (j C) is defined as the thermal resistance from the connector to the surface of the housing. The value of 3 ° C/w can be assumed θ (j c) for this calculation

θ (c h) defined as the heat resistance between the shell and the surface of the radiator. Value

θ (C H) changes between about 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) (3) is 2 ° C/W. When the value of the equations shown in the use of the value of θ (h a), you must choose a radiator with the following value. : Smaller than or equal to this number. θ (H A) The radiator manufacturer specifies in the directory in the directory, or the temperature and power consumption of the heat sink in the curve is used to represent the curve. DDPAK/TO-263 and SOT-223 packaging parts DDPAK/TO-263 (""S"") and SOT-223 (""MP"") packaging use copper planes on PCB and PCB as a heat sink. In order to optimize the heat dissipation capacity of plane and PCB, the packaged convex ear welding was welded to the aircraft. Figure 26 shows that for DDPAK/TO-263, a typical PCB of A is used, and the copper content is 1 ounce. There is no weld cover for the copper area used for heat dissipation.

As shown in the figure, the copper area is increased to more than 1 square inch, and there is almost no improvement. It should also be noted that the minimum value of the θ (J a) installed on the PCB package on PCB is 32 ° C/W. As a design assistance, Figure 27 shows the maximum allowable power consumption compared with the ambient temperature for the DDPAK/TO-263 device (assuming θ (J A) is 35 ° C/W, and the maximum knot temperature is 125 ° C) Essence

SOT-22 Welding Suggestions

It is not recommended to use hand-welded or peak welding to connect small SOT-223 packaging to the printing board on the print. Excessive temperature may cause the packaging to break. Qi phase or infrared flow welding technology is the preferred welding connection method package for SOT-223.