Application information

This formula will not generate a maximum load current of more than 1A, unless the input and output voltage exceeds 5: 1. The only reason is that the larger diode is the worst case of high input voltage and overload (unprecedented) output. Under short -circuit conditions, the folding current limit will reduce the diode current by less than 1A, but if the output overload is not less than 1/3 of the rated output voltage, the folding will not work. In the case of overload, the output current will be increased to the typical value of 1.8A, and the peak switch current limit of 2A is determined VIN 15V, VOUT 4V (5V overload), iOut 1.8A:

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This is safe in a short period of time, but if it is allowed to continue running under these conditions, please contact the diode manufacturer carefully.

Breathing #9251; pin #9251; Note

For most applications, the boost component is 0.33 μF capacitors and 1N914 or 1N4148 diode. The anode is connected to the adjustment output voltage, and the voltage generated by the generator on the voltage capacitor is almost the same adjustment output. In some applications, the anode can be connected to an input voltage that is not adjusted. If the adjustment output voltage is very low ( lt; 3V), or if the input voltage is less than 6V, the efficiency is not affected by the capacitor value, the ESR of the capacitor should be less than 1Ω to ensure that it is completely charged in the worst case of the minimum input voltage. Almost any type of movie or ceramic capacitors work normally. warn! The peak voltage on the feet of the booster tube is an unsettled input voltage plus a lift capacitor. This usually means that the peak enhanced pins voltage is equal to the input voltage plus the output voltage, but when the diode is connected to the regulator, the peak voltage pins voltage is equal to the input twice voltage. Make sure that the voltage of the booster pins does not exceed the maximum rated value

For almost all applications, 0.33μF boost capacitors can work well, but out of curiosity, we provide more details here. The size of the voltage capacitor is driven by the switch to drive current requirements. During the connection time, the drain current on the capacitor is about iOUT/50. The peak load current is 1.25A, and the total leakage current is 25mA. Capacitors ripple voltage is equal to the multiplication leakage current of the connection time to remove the capacitor value; ΔV (ton) (25 mAh/degree Celsius). Keep the capacitor ripple voltage less than 0.5V (a slightly arbitrary number). In the worst case, in Ton 4.7μs, the capacitor requires 0.24μF. The ripple voltage of the voltage capacitor is not a critical value parameter, but if the minimum voltage on the capacitor drops below 3V, the power switch may not be completely saturated and the efficiency will decrease. The formula of the absolute minimum electricity value of the approximate value is:

f switch frequency

vout adjust the output voltage

vin The minimum input voltage

This formula can be obtained by the capacitance value is less than 0.24 μF, but you should use it carefully because the secondary factor, such as the capacitor series resistance, the capacitor changes with the temperature, and the output overload. Turn off function and low -voltage lock

FIG. 4 shows how to add underwriting lock (UVLO) to

LT1576 . Generally, UVLO is used to input power currents limited or has a high source resistance. The power of the switching regulator inhale the power of the power supply, so the power supply current decreases with the power supply voltage. This looks like the negative resistance is loaded to the source, and it may cause the source current limit or lock the low voltage at low power voltage conditions. Ultraviolet radiation prevent the regulator where the problem may occur under the power supply.

The locking threshold voltage is about 2.44V. 3.5 μA bias current flows out of the tube foot at the threshold. This is the internal generated current to force the default high state to close the sales (if the sales are kept open). When the low -level interruption current is not a problem, the error caused by this current can minimize the RLO less than 10 kilometers. If the shutdown current is a problem, the RLO can be increased to 100K, but the error should be considered due to the initial bias current and temperature changes.

VIN minimum input voltage

Keep the connection pins from the resistor to the shutdown, and ensure that the board or surface capacitance of the opening node is minimized Essence If you use a high resistance value, you should bypass the closing foot with 1000PF capacitors to prevent coupling from exchange nodes. If you need to lock the point at the underwriting, you can add a resistor RFB output node. The calculation formula of the resistance value is as follows:

Suggestion 25kvin switch as the input voltage when the input stop is reduced to the sliding level ΔV input voltage level. Example: Output output The voltage is 5V, and the switch stops drops below 12 when the input is input, unless the input rises to 13.5V. 5V therefore is a 1.5V vehicle identification number 12V, and RLO 25K.

Application information

Switch node precautions

In order short. To prevent radiation and high -radiation frequency resonance, it is essential to correctly arrange components connected to the opening node. The B field (magnetic) radiation is minimized by keeping the diode, and the leader of the switching tube and the input bypass container is shorter than possible. The length, area and assistance of all records connected to the switch pins through the minimum connection to the switch pin. The ground plane should always be used to prevent collision between the board under the switch circuit. The recommendation layout of key components is shown in Figure 5. Pay attention to the feedback resistance and retain the compensation component from the exchange node as much as possible.It is also necessary to pay attention to keeping the ground pipes and input capacitors with high current and input capacitors very short, which is separated from the simulation ground line. The diameter of the high -speed switching current is shown in Figure 6. The minimum lead in this path is to ensure that the switch is cleaned and low -electromagnetic interference. Path

Application information

Including switching, capture diode and input capacitors, the only nano -second rising and decreased time. If you walk along this road on your computer layout, you will find that it is not short. If you move the diode or input a capacitor to leave the LT1576, sort out the resume. This other path contains only three waves of DC and 200kHz, so it is not so critical. Parasitic resonance can sometimes at the opening node (see Figure 7). Very high -frequency bell below switch rising time is caused by switch/diode/input caused by the inductance and diode capacitors. The Schot TKY diode has a very high Q " knot capacitance that can cycle many times under high -frequency incentives. If the length of the input capacitor