Function

Wide input range: up to 30 volts

High -voltage input application

Rating output current 100 mAh

]低压差：100 mA时为380 mV（典型值）

低静态电流：75μA（典型值）

LP2950和LP2951设备是双极的，低-

[ 123] Tight -line adjustment: 0.03%(typical value) voltage voltage regulator, which can adapt to A

Tight load adjustment: 0.04%(typical value) wide input power supply voltage range, as high as 30 V

[ 123] High V is easy to use, 3 -pin LP2950 can be used for fixed output O precision

Voltage is 5 V, 3.3 V and 3 V. However, 1.4%LP2951 can output fixed or adjustable -2%ultra -temperature output from the same device at the 8 -needle -25 ° C. By bundled output can be used as a regulator or reference and sensing tube foot, feedback and VTAP pin together, LP2951 outputs a fixed 5V, stable low ESR ( gt; 12 m ) capacitors 3.3 volts or 3 volts or 3 volts or 3 volts or 3 volts or 3 volts Fu (depending on the model).

The current limit and thermal restriction function, by leaving the Sense and VTAP pins

Only LP2950 (3 tap packaging) open and connect the feedback to the external -5V, 3.3V and 3V resistance divisions The fixed output voltage of the pressure dealer can be set to any value between 1.235 to 30 volts. Limited to LP2951 (8 cuts)-fixed or adjustable output voltage

Electric characteristics

vin u003d vout (nominal) +1 V, IL u003d 100 μA, CL u003d 1 μF (5-5- V version) or CL u003d 2.2 μF (3-v and 3.3-V versions),

8-needle version: feedback connected to VTAP, output connected to Sense, vSHUTDOWN ≤ 0.7 v

123]

(1) The output or reference voltage temperature coefficient is defined as the worst case and the voltage change is divided by the total temperature range.

(2) The adjustment is measured by using a low -occupied pulse test under constant knot temperature. Because the thermal regulation specification covers the thermal effect.

(3) The definition of the voltage drop is defined as the input and output difference. Under the difference, the output voltage drops 100 millivolves, the measurement value below 1 volt

There is a difference. The minimum input power supply voltage 2 V (exceeding temperature 2.3 V).

(4) Thermal regulation refers to the output voltage (T TThe change of) does not include the load or line regulation effect. The technical specifications are suitable for VIN u003d 30 V, VOUT u003d 5 V (1.25-W pulse) and 50 mA load pulse when T u003d 10 ms.

Electric characteristics (continued)

vin u003d vout (nominal) +1 v, IL u003d 100 μA, CL u003d 1 μF (5-v version) or CL u003d 2.2 μF (3-v v And 3.3-v version),

8-needle version: feedback connection to VTAP, output connection to Sense, vshutdown ≤ 0.7 v

(5) Comparison comparison The device threshold is equal to the nominal reference voltage (in VIN -Vout u003d 1 V) minus the feedback end voltage. Use the output voltage change to indicate these thresholds, multiplied by an error amplifier gain u003d VOUT/VREF u003d (R1+R2)/R2. For example, when the programming output voltage is 5 V, the error output is specified when the output decreases 95 mv × 5 v/1.235 V u003d 384 MV. The percentage of the threshold as VOUT remains unchanged (like VOUT), and the low output warning occurs at 6%and 7.7%(maximum value) below the nominal value (typical value).

Detail The LP2951 device is bipolar, low voltage differential voltage voltage, which can adapt to a wide range of input power voltage range of up to 30 volts. Easy to use, 3 stitch LP2950 can be used for a fixed output voltage of 5 volts, 3.3 V and 3 V. However, the 8 -needle LP2951 device can from the same device. By connecting the output and sensing pins, and the feedback and the VTAP pin, the LP2951 device outputs fixed 5V, 3.3V or 3V (depending on the version). Another choice is to leave the rational and VTAD pins and connect to the external resistor division. The output can be set to an arbitrary value between 1.235 V and 30 V. In addition, LP2958 also provides additional features, especially suitable for LP2951 applications. For example, the logical compatible closing function allows the regulator to be in the standby mode for power saving. In addition, there is a built -in manager reset function, which is low in error output due to vehicle recognition number (VIN), current restrictions or heat shutdown. The design purpose of the LP2950 and LP2951 devices is to minimize all errors to the output voltage. Use a strict output tolerance (0.5%at 25 ° C), extremely low output voltage temperature coefficient (typical value is 20 PPM), very good lines and load adjustments (0.3%and 0.4%typical values), and remote sensing sensing Ability, parts can be used as low power voltageThe benchmark or 100 mAh regulator.

function description

Error function (only LP2951)

LP2951 device has a low pressure device. The detector, when the output voltage drops at 6%from the nominal value, when VOUT reaches 95%of the nominal value, the output logic is high. By removing the built-in migrant of the v60 MV at 1.235-V gap, 95%of the nominal value can be obtained, and the programming output voltage is independent of the nominal value. For example, the trigger point threshold (high output high) 5 volt output is usually 4.75 volts, and 12 volt transmission is 11.4 volts. Generally, there is a lag 15 MV between the high and low error output threshold. Figure 31 shows the timing map of the error and VOUT (5V), and VIN is tilted up and down. Error becomes effective (low) when Vin≈ 1.3 V. When Vin≈5 V, Vout u003d 4.75 V, which causes an error to increase. Because the voltage drop depends on the load, the output trigger threshold is reached under different VIN values, which depends on the load current. For example, at a higher load current, a slightly higher VIN value will increase, and the lower load current will be increased, as well as vice versa. Regardless of the load, the output voltage trigger point remains ~ 4.75 V. Note that when Vin ≤ 1.3V, the output of the error comparator is turned off and pulled it to its pull voltage. If you are used as a pull -up voltage, not an external 5V power, the error is usually ~ 1.2V. In this case, the effective pressure division (10 ) of a sterilizer is suitable for low -separation logic. Under any failure, the logic high level is still enabled during normal operation.

Because the error comparator has an open set output, an external pull -up resistor is required to pull the output of the output of up to the VOUT or other power supply voltage (up to 30 V). The output of the comparator drops to 400 μA. The appropriate value range of the pull -up resistor is 100 k to 1 m If you do not use errors, it can keep it open

Programming output voltage (only LP2951)

A unique feature of the LP2951 device is that it can output a fixed voltage or adjustable voltage, depending on the external external exterior Point connection. To output the fixed voltage of internal programming, please tie the induction pin to the output pin, and the feedback pins to the VTAP pin. Alternatively, the user's programmable voltage range from the internal 1.235-V reference voltage to the maximum value of 30-V can be set by using an external resistor division. This resistor division is connected to VOUT, and the voltage after division is directly connected to the feedback in order to reference voltage with the internal 1.235 volt. In order to meet the two input -equal stable conditions, the error placing the large -device drive output is equal to equal formula 1:

VREF u003d 1.235 V is applied to R2 (see Figure 32). If B u003d feedback bias current, it is usually 20 NA that must maintain a minimum regulator output current of 1 μA. Therefore, under the expected conditions (for example, the CMOS circuit is in a standby state), the minimum current of the 1-μA must be performed by the resistance to the maximum value R2 u003d 1.2 m (1.235 v/1.2 m # 8777; 1 μA). If B u003d 20 NA, an error of #8777; 0.02%is introduced in Vout. This can be offset by trimming R1. Alternatively, increase the importance of frequency division to reduce the importance of IFB, thereby reducing its error contribution. For example, using R2 u003d 100 K By increasing the frequency divider current to #8777; 12 μA, the contribution of IFB error to 0.17%is compared with the typical static current of 600μA of LP2951, and the increase in the voltage device current is still increased. Very empty.

Shipping mode

These devices can be placed in the shutdown mode, and the logic of the shutdown pin is high. If the logic level is not used, it is low to the restoration operation or connect to the ground.

Capacitor value

For VOUT ≥ 5 V, at least 1 μF. For lower VOUTs, the loop gain of the regulator is closer to unity. Therefore, it has a lower phase margin. Therefore, larger capacitors are needed to maintain stability. For VOUT u003d 3 V or 3.3 V, the recommended minimum value is 2.2 μF. In the worst case, Vout u003d 1.23 V (using ADJ version), it is recommended to be at least 3.3 μF. It can increase infinitely, and only improve the stability and transient response of the regulator. Regardless of its value, the output capacitor should have a resonant frequency greater than 500 kHz. The minimum capacitor value given above is suitable for a maximum load current of 100 mAh. If the maximum expected load current is less than 100 mAh, the lower value can be used. For example, if IOUT LT; 10 mAh, then COUT only needs 0.33 μF. For iOUT LT; 1 MA, 0.1 μF is enough to meet the stability requirements. Therefore, for the worst case of 100 MA loads and VOUT u003d VREF u003d 1.235 V (representing the highest load current and the recommended minimum load in the load is 3.3 μF). For LP2950/51, no load stability is inherent in the design. This is the ideal characteristic of the CMOS circuit (such as the RAM Keep Alive application). If LP2951 uses an external resistor to set the output voltage, it is recommended to pass the minimum load current of the resistor to 1 μA.

Capacitor type

BigMost 电 or aluminum electrolytes are suitable for use at the input end. Film capacitors can also work, but the cost is higher. When operating at low temperature, you should use aluminum electrolytic groove electrolytes to freeze at -30 ° C. Therefore, the solid electric container should be used below -25 ° C at temperature. You can use ceramic capacitors, but because of its low ESR (as low as 5 m to 10 m ), they may not meet the minimum ESR requirements of previous discussions. If you use ceramic capacitors, you must add 0.1 to 2 to meet the minimum ESR requirements. In addition, ceramic capacitors have a clear disadvantage-poor temperature coefficient, and the capacitance changes greatly with the temperature. For example, a large -capacity ceramic capacitor (≥2.2 μF) will lose more. When the temperature increases from 25 ° C to 85 ° C, the capacitor is more than half of the capacitor. Therefore, 2.2-μF capacitors at 25 ° C decrease well than the minimum value required when the environmental temperature increases. Therefore, select a capacitor with a minimum of 2.2μF required to maintain a stable 2.2μF in the entire working temperature range.

CBYPASS: Improvement of noise and stability

In the LP2951 device, an external feedback foot that directly connects to an error amplifier can not be converted into input allowed to allow mixed capacitors to cause instability, by diversion errors The amplifier is fed back to GND, especially at high frequencies. If the output voltage is set with a high -value external resistor, it will deteriorate, because the resistance allows the messy capacitors to play a more important role, that is, there is a large phase between the output of the larger RC delay error amplifier and the feedback input input. Poor, which leads to a large phase difference and a lower margin. A solution is to add a 100PF bypass power container between the output and feedback; because CBYPASS and R1 are connected in parallel, it actually reduces the impedance during high frequency feedback by providing more feedback at a higher frequency to provide more feedback at a higher frequency to provide more feedback at a higher frequency. Break off the effects of parasitic capacitors. More, under a minimum error, the gain of the feedback amplifier should increase a 3.3μF to improve the phase of the regulator. CBYPASS can also be used to reduce the output noise in the LP2951 device. This bypass capacitor reduces the closed -loop gain of the error amplifier at high frequency, so the noise no longer changes with the output voltage. This improvement is more obvious when the output voltage is higher, and the loop gain is the largest. A Appropriate CBYPASS calculation as the equivalent 2:

on the 3 -needle LP2950 device, you can achieve noise reduction by increasing the output capacitor, which will cause the regulator to adjust the regulator. Bandwidth should be reduced to eliminate high -frequency noise. However, this method is relatively inefficient, because increasing COUT from 1 μF to 220 μF will only reduce the output noise of the regulator 430 μV to 160 μV (more than 100 kHz bandwidth).

ESR range

The regulator control loop relying on the ESR of the output capacitor to provide zero point to increase the amount of stability of the stability of the unconditional regulator; A response in the area of u200bu200b20 decibel/decadence attenuation. This can ensure that the phase is always less than 180 ° when the unit gain is always less than 180 ° (phase margin is greater than 0 °). Therefore, the minimum and maximum range of ESR must be observed. The upper limit of this ESR range is that the high ESR may cause the fact that the fact that zero is determined too fast, resulting in the reduction of the income too slowly. This in turn allows the third pole to appear before unity and introduce sufficient phase shifts to cause instability. This usually limits the maximum ESR to about 5 On the contrary, the lower limit of the ESR range is linked to the fact that the facts of the zero -point offset are too far with the ESR. °. Usually, this limits the minimum ESR to about 20 m to 30 m For specific ESR requirements, see typical features.

Power recommendation

The maximum input voltage should be limited to 30 volts for normal work. Place the input and output capacitors in the nearby position so that the device is as high -frequency noise filtering as much as possible.

layout guide

ensure that the trajectory of the equipment input and output is wide enough to process the required current. For this device, the output trajectory needs to be larger to adapt to larger available currents. The input and output capacitors are close to the device as much as possible to use their high -frequency characteristic noise filtering characteristics.