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2022-09-16 16:00:09
LTC1504 500mA low -voltage synchronous antihypertensive switch regulator
Features
The 500mA output current at 3.3V output
The peak efficiency of up to 92%
Internal reference adjustment to 1%
Output can be available. Generate or absorb current
Only four external components
Input voltage range: 4V to 10V
adjustable current limit
Small SO-8 packaging
200kHz switch frequency can be synchronized to 500kHz
Small portable digital system
Active terminal
Auxiliary output voltage power supply
minimum parts Number/size conversion switch
Description
LTC #174; 1504 is an independent and efficient synchronous antihypertensive switch regulator. It includes a pair on a pair of 1.5 power switch, so that it can provide up to 500 mAh load current. The maximum efficiency is 92%, minimizing the heat and waste of electricity. Synchronous antihypertensive structure allows output to source or exchange current to maintain the adjustment of the output voltage. LTC1504 There is a variable and fixed 3.3V output version. The adjustable streaming circuit provides overload protection. Internal 1%reference voltage and complex voltage feedback loop provide the best output voltage accuracy and fast load transient response. LTC1504 is specified between 4V and 10V by the designated operation input voltage. Contact the LTC factory to provide the guarantee specifications of 2.7V power. LTC1504 uses plastic SO-8 packaging
Absolute maximum rated value
(Note 1)
Power voltage (VCC to GND) 10 10 3
Peak output current (SW) ± 1 Ann
Input voltage (all other pins) -0.3V to VCC+0.3V
The working temperature range 0 ° C 0 ° C To 70 ° C
Storage temperature range -65 ° C to 150 ° C
Lead temperature (welding, 10 seconds) 300 degrees Celsius
Electric characteristics vcc 5V, TA, TA, TA, TA, TA, TA, TA, TA, TA, TA 25 ° C, unless there are other regulations. (Note 2)
Electrical characteristics
indicate the specification for the entire operation
The temperature range.
Note 1: Absolutely maximum rated value means that the value of exceeding life may damage the device.
Note 2: The current of all entering device pins is positive; the current output from the device is positive. Unless there are other regulations, all voltages are clearly stipulated in reference.
Note 3: This parameter is guaranteed by correlation and is not directly tested.
Note 4: LTC1504 static current is mainly determined by the gate -drive current by the vehicle power switch. Pulling FB or Sense to the VCC output level will stop the switch, and the static and static current can be observed. When FB or Sense is connected normally, the output level can be measured by switching and total dynamic power currents.
Note 5: The GMV and AV values of fixed output components are 2.6 times due to the internal pressure device resistance, which is lower than the specified value.
Note 6: ILIM amplifier can absorb current, but cannot receive the source current. In normal circumstances (unlimited current) operation, the ILIM output current will be zero.
Note 7: The guarantee specifications of the 2.7V power supply,
Typical performance features
VCC (pin 2): power input. The power supply voltage is connected between 4V and 10V. VCC requires a low impedance side electric container to place to the ground to connect to the LTC1504 as much as possible. Relevant electric container selection and resettlement.
SW (pin 3): power switch output. This is the node of the switch BUCK circuit. Connect SW to the external sensor. The other end of the inductors should be connected to the COUT and becomes regulating the output voltage. Avoid SW to GND or VCC.
GND (pin 4): ground. Connect low impedance ground. The input and output bypass power container and its feedback resistor division (only adjustable parts) should be grounded as close to this pins as possible. Pink 4 is used as a radiator in the LTC1504 S0-8 package, and it should be connected to the large copper area as possible to increase the heat dissipation. See more information on the Hot Care section.
FB (LTC1504CS8) (pin 5): feedback. Connect FB to a resistor division from VOUT to GND to set the adjustment output voltage. The LTCS84C feedback circuit put the FB pin of 1.265V. Induction (LTC1504CS8-3.3) (pin 5): output voltage induction. Directly connect to the output voltage node. This LTC1504CS8-3.3 feedback circuit will find the servo sensing 3.3V. The induction connection to an internal resistor separator will load any external partition. For the output voltage than 3.3V, use LTC1504CS8.
SHDN (pin 6): Close, low activation. When SHDN is highly logically, LTC1504 will work normally. when? SHDN is low, LTC1504 stops all internal operating power supply currents below 1 μA. When shutting down, the switch sales were pulled down. This can ensure that the output is closed when the event is assertive, but it prevents others from being not activated when the LTC1504 is not activated. Check the application information part to learn more about more details.
SS (pin 7): Soft start. Connect the external capacitor (usually 0.1 μF) from SS to GND to limit the period of power to power output. CSS also compensates the current limit loop, allowing LTC1504 to enter and exit the current restrictions clean and neat. For more information, see some details of the application information.
Compensation (pin 8): external compensation. The external RC network should be connected to the COMP to compensate the feedback circuit. Comp is connected to the internal error placed.
Application information
LTC1504 is a complete synchronous switch regulator control Instrument (see the square diagram). It includes two pieces of 1.5 power MOSFET, without requiring external power equipment and minimized external components. The internal switch is set to the BUCK converter from the P -channel device (Q1) to open the node and the input power device (Q2) of the N channel as a synchronous rectification device to open the joint node. External inductors, input and output bypass power containers and compensation networks complete the control circuit. The adjustable output LTC1504 parts need a pair of additional resistors to set the output voltage. The LTC1504-3.3 parts include a 3.3V output voltage in the plate resistance compressor. Function 3.3V output regulator can be used by LTC1504-3.3 and at least four external components. The LTC1504 feedback circuit includes a accuracy benchmark adjustment to 1%(VREF), a wide -band -wide cross -guide feedback amplifier (FB) and vehicle PWM generator (sound surface wave and pulse width modulation). Two additional feedback comparators (minimum values and maximum values) monitor feedback voltage and the main feedback amplifier when the adjustment output decreases at the window of ± 3%to improve the transient response. The internal jagged oscillator is usually run at 200kHz. Q1 and Q2 can carry the peak current of 500 mAh, and the continuous output power level is limited to heat dissipation packaged through SO8. LTC1504 has 5V input and 3.3V output, which can provide 500mA continuous output current layout. The external resistor on the board can be used to help restrict power differences. For more information, see some information of Hot Care .
Operation theory
LTC1504 main feedback circuit includes error placing large device FB, PWM generator, output drive logic and power switch. Use external inductance and output bypass capacitors. This feedback amplifier is directly used to fixed output versions or the resistance division of the resistor in the external adjustable publishing book. This will compare the feedback voltage with the internal voltage of 1.265V to compare the FB to provide reference voltage and compensate for sale. Comp is a high -impedance node brought to an external pin to optimize loop compensation. Compared with 200kHz sawtooth waves. This original pulse width modulation signal is a logical combination with the output of the transient component before reaching the output stage. The output stage is the P -channel and N -channel power MOSFET, which drives the SW pin wave shape with PWM low impedance images. The typical opening output impedance at the switch is between 1 and 3 depends on the power supply voltage. This high -power pulse string provides a stable DC node at the output end by external inductors and capacitors. The node returns FB or Sense to close the loop. The minimum and maximum comparator in the feedback circuit provides high -speed failure correction FB amplifiers may not respond quickly enough. MIN COM reduces the voltage of the feedback signal to less than 40 millivolves (3%) internal reference. At this time, MIN covers the FB amplifier and forced the loop to reach a fully duty occupation ratio. Similarly, the MAX monitoring output voltage is higher than 3%of the internal voltage. These two comparators prevent the rapid output of extreme output transient disturbances, while at the same time allow the main counterfeit loop stability that allows the best compensation.
LTC1504 also includes another feedback circuit control current operation. ILIM amplifier monitors the voltage of the SW pin when Q1 is turned on. It compares this voltage with the voltage on the IMAX pin. As the peak current of Q1 rises, the voltage of Q1 decreases due to its proportion of Ron. When the SW drops below IMAX, it means that the current of Q1 has increased more than the expected value, and ILIM starts to pull the A A controllable current output SS, and the outside soften starts. When SS decreases, it will lower the Comp to limit the control ratio and reduce the output voltage current. The speed response of the current limit circuit is set by the external soft startup capacitor.
external component selection
The external components required for the LTC1504 include three categories: input bypass, output filtering and compensation. It is usually included to set up soft startup and current limit. The minimum LTC1504 circuit can consists of four circuits for external components; all LTC1504S functions usually include eight or nine external components. Two additional feedback resistors are required for adjustable components. For examples of external component connection, please refer to the typical application part.
Enter the bypass
Entering the bypass container is the key operation of the correct LTC1504. LTC1504 includes a precision benchmark and a pair of high -power switching power supply VCC pins. If VCC does not have enough bypass, the switching pulse will be sufficient in VCCThe ripples that cause damage reference voltage and LTC1504 will not be able to adjust accurately. Symptoms of insufficient bypass include poor load adjustment at the SW and/or unstable waveforms. If the oscilloscope cannot be triggered in the SW pin clearly when watching, there is no enough input bypass.
Ideally, LTC1504 needs low impedance bypass is in a slightly farther place in chip and a larger capacitor. This requirement is usually LTC1504 and an electrolytic capacitor next to the ceramic capacitor (usually 10 μF to 100 μF, depending on the expected load current), somewhere nearby. In some cases, the output by the volume capacitor input terminal can meet the required supply. When an application or input power supply voltage running under a very high load current is greater than 6V, the local ceramic capacitor may require 1 μF or higher. In some ways, including low impedance and single capacitors of body capacitors can meet the requirements, the installation is very close to the LTC1504. Low ESR organic semiconductor (OS-Con) electrolytic capacitors or surface stickers tested by the waves can have sufficient low voltage to keep the LTC1504 maintain good impedance in certain circuits. Generally, the average root current capacity of the bypass power container is more important to select the capacitor than the value. Input difficulty capacitors like LTC1504, because the current is full of current and close to zero during each clock cycle. In the worst case (50%duty or VOUT 0.5vin) RMS input current current is half current in the capacitor and half of the ripple current in the inductor Essence This current flows over the ESR bypass power container at the input terminal, heating and shortening the life, sometimes dramatic. Many ordinary electrolytic milk pacows are okay at first glance, but they have not been rated as a current check RMS rated current before specifying the device! If the RMS rated current specifies, it should not be used as an input bypass container. Again, low ESR electrolytic and wave rushing tests 钽 Usually applied in the LTC1504 application and high -balanced square root current rated values. Local ceramic side capacitors usually have negative ESRs, allowing it to withstand large -scale square -root current without failure. Table 1 shows the input bypass container in the acceptable typical surface installation capacitor LTC1504.
Note: Use multiple parallel devices or limit output currents to prevent the capacitor from overload. 
LTC1504 requires an external electromoter to connect from the swing node to the output node load connection. The requirements for electrical sensors are quite simple; its rated value must be able to process continuous DC current with the maximum load current
Application information
should choose half of the ripple current and its value based on its value based on The expected ripple current and/or output current requirements. Large value sensor reduces ripple current and decreasesThe required output capacitance, but the speed of the LTC1504 changes the output current, and the output transient response is limited. Small value sensors will generate higher ripple current and increase the requirements for output capacitors, but allow faster output current conversion rates and the same DC current rated value, smaller and cheaper. The typical inductors used in the ALTC1504 application may have a maximum rated current between 500mA and 1A and between 33 μH and 220 μH. Different core materials and shapes will change the current and price/current of the size/induction. The shielding tank core in the ring or Poomo alloy material is small and does not radiate too much energy. However, the cost is generally higher than that of the powder iron heart sensor. What type of inductor price and demand to choose often depends on the price radiation field/EMI requirement than the LTC1504. Table 2 shows an inductor for some typical surface installations for LTC1504 applications.
Output capacitor 
LTC1504 has two ways: it provides a transient load step jumping The defense has a great impact on the compensation required for maintaining the stability of the LTC1504 feedback circuit. The transient load response circuit of the LTC1504 is almost completely controlled by the output capacitor and the inductors. When the stable load is running, the current in the average electrical sensor will match the load current. The load current suddenly changes, and the inductor is seriously loaded with an error current. The time switch that requires at least several self -correction has a cycle of typical LTC1504 inductor value. Even if the LTC1504 has spiritual media capabilities, it can immediately assume that the correct duty cycle ratio is still related to its value and will not change the moment. Before the inductor current is adjusted to matching the load current, the output capacitor must compensate the difference. Applications that require special transient response (instantaneous full load jump to 2%or higher) will require a relatively large value and low ESR output capacitor. Applications with a more medium -to -medium transient load can usually get rid of the traditional standard ESR electrolytic capacitor at the output end to use a larger value sensor with the smallest output capacitance value. Note that the average root current in the output capacitor is slightly higher than the half of the current-input of the input bypass. The life of the output capacitor is usually not a factor in the typical LTC1504 application. Output bypass provides excellent ESR characteristics for large -capacity ceramic capacitors, but it makes it difficult to compensate circuits. See the loop compensation section.
Circle compensation
Circular compensation is very large -capacitively affected by the output. From the perspective of the stability of the ring circuit, the output inductance and capacitance form a series of RLC resonance circuits. L is set by the inductor value, and the ESR of the output capacitor and R is controlled by the output control capacitor. The amplitude response and phase shifts are stable because these components are closed by RS and CS on the CONP PIN (Hope) feedback circuit.Certainly. In terms of qualitatively, L and output level C forms a 180 ° second -order rolling shift; the RMB formed by R caused by the ESR to form a single zero -point frequency can be reduced, and the phase shift reduction to 90 to 90 can be reduced to 90 to 90 °. If the ESR of the output capacitor is relatively high, it appears to 180 ° before the beginning of the initial phase shift. The loop only requires a small capacitor to keep it stable from COMP to GND (Figure 4A). If, on the other hand, when the output capacitor is a low ESR type maximum transient response, the ESR zero point can increase the frequency from a stage of ten years or more than ten years before turning, the shift may be very close to 180 ° to 90 to 90 Spend. Large-value ceramics, OS-CON electrolytic and low impedance capacitor declines belong to this category. These cycles require additional zero insertion to compensation and campaigns; C -grounded C -grounded C -ground with ... connected in -line can usually ensure stability. Figure 4B shows a typical compensation network to optimize the transient response of most output capacitors. The adjustable output part can add a feed capacitor to further improve the phase of the phase through the feedback resistor. The typical application in this data table
Show compensation value to work with multiple external components, starting with them. For complex situations or stubborn oscillations, please contact the LTC application department. 
The external Schutki diode can include internal N channel switches (Q2) that can be increased. The diode is turned on in the LTC1504 to turn on Q1 and Q2 to prevent the current of the current diode connecting the current diode in the current current. This diode will improve the efficiency of one or two percentage points higher than the output current close to 500 mAh, which will help minimize the unstable behavior parasitic current flowing at the very peak value level caused by over -current current. Motorola MBRS0530L is usually sufficient, and cathode is connected to SW and anode ground. Note that this diode is not required to run normally, and the impact can be ignored when the output current is not low ( lt; 250mA) output current.
Soft startup and current limit
Soft start and current are limited in LTC1504. Soft Start's way of working is simple. The current source connected to the SS pin in the internal 12 μA will pull up the external capacitor at a certain speed to the GND from the SS to the GND by the capacitor value. The compressor clipped to a diode and dropped above the SS; as SS rose, the COMP would rise at the same speed. When the compensation reaches about 2 volts, the duty cycle will begin to increase slowly until the output adjustment. With the continuous rise of the SS, the feedback amplifier took over the COMP, that is, clamp release and SS rose to VCC. The minimum feedback comparator in the soft starting loop is banned to prevent cover compensation pins and forced output to a maximum duty cycle. The current is limited by pulling down soft starting pin when it detects overload conditions at the output end. This flow restriction (ILIM) The voltage drop at the internal P channel switch (Q1) to reach the IMAX pin voltage during the opening period. IMAX includes a 12μA drop -down, allowing resistors between a single VCC and IMAX. When the influence of the q1 crossing the voltage drop of the IMAX resistor, the ILIM driving current starts from the external soft startup capacitor to reduce the voltage at the SS. Use a soft startup capacitor if the current restrictions are enabled. SS, in turn, lower the compressor, limit the output occupation ratio and control the output current. When the current is eliminated, the ILIM amplifier releases the SS to make it rising again, as if it is a soft startup loop. The speed of the capacitor control current restrictions at the size of the external softness is detected and the output recovers once the overload is detected and the overload is eliminated. The soft startup capacitor can also compensate the feedback circuit generated by the ILIM amplifier. Because the ILIM loop is a current feedback circuit, the export -out -of -phase displacement should not enter the coil and capacitors to play through a single capacitor to fully compensate. Generally, 0.1 μF ceramic capacitors from SS to GND provide sufficient soft startup behavior and acceptable current restrictions.
This type of current limiting circuit is overloaded in a mild current, and no external current sensitive resistance is required, which is attractive to the LTC1504. These identical features also hinder the output voltage of the current restrictions very close when the current restricted circuit is very close. In this case, the LTC1504 must run the cycle ( lt; 5%) under the narrow load to control the current. When the connection time is lower than the time required for the inductive current is in Q1, the LTC1504 responds to the frequency by reducing the oscillator, increasing the closing time to reduce the duty cycle and allow it to maintain some control current to the output. The frequency of the oscillator may decline in the coefficient of a severe current overload. The connection time of extreme short circuit (such as screwdriver) will be reduced to LTC1504 will lose control of the output current. At this time, the output current will rise until the inductors are saturated, and the current will be limited by the inductor parasitic ESL and the RON of Q2 in the LTC1504. This current is usually non -destructive because the output voltage is very low. The typical LTC1504 circuit can withstand such short -circuit seconds without damage. The test circuit in FIG. 1 will usually be able to withstand the direct output short circuit of more than 30 minutes without damage to the LTC1504. In the end, the continuous short circuit may cause the mold temperature to rise to destructive level.
Please note that the current limit is mainly to protect the LTC1504 from being damaged and not intended to use an accurate constant current output. The RON and current that changes in the internal switch as a mold temperature under the current limit conditions will change the limitation threshold to move. Ron will also from the gap between parts and parts due to manufacturing tolerances. The IMAX resistor should be selected from the outside to leave enough space without considering the current restrictions on the maximum expected load current. A current restriction setting is about twice the expected load. It is usually a good compromise solution to eliminate accident current restrictionsAt the same time, prevent the actual failure of the circuit. If necessary, the current limit can be disabled by floating IMAX tube feet; the internal current source pulls the IMAX to GND, and the ILIM amplifier will be disabled. Closing the LTC1504 includes the logical level control of the micro -power shutdown. SHDN's logic allowed components to work normally. SHDN's logic low stops all internal switches, pulls the compressor, SS and SW to ground, and the static current is usually lower than 1 μA. Note that when the internal N ditch power MOSFET comes from SW asserting SHDN, to GND is opened. This ensures that when the LTC1504 is closed, the output voltage is reduced to zero, but other devices are prevented from the output when the LTC1504 is disabled.
Synchronous outer clock
LTC1504 SHDN pin can also be used as a synchronous clock or faster switching speed. The SHDN pin terminates the internal jagged wave and reset immediately when the oscillator becomes low, but wait 50 μs to turn off other internal circuits before turning off. The clock signal is directly applied to the SHDN pin, which will force the LTC1504 to internal oscillator to lock its frequency as long as the external clock runs fast frequency than the internal oscillator. The maximum internal frequency of attempt to synchronize to the largest frequency of 250kHz may cause the pulse width to be inconsistent, and it is not recommended to improve. Because sawtooth waves rose in the interior at a fixed rate, it will reduce the wavelets of the magnifier PWM comparator to see the outer clock by synchronizing it to FAST in advance, effectively increasing the gain from COMP to SW. The maximum 500kHz recommended synchronization frequency; the higher the frequency, the smaller the semi -wave amplitude, the smaller the LTC1504 may run unstable.
Thermal factors
The resistance of the internal power switch per LTC1504 at room temperature is about 1.5 and if the current limit is set high or unconnected. Since the electrical sensor current has always flowing through other internal switches, a typical application provides a 500 mAh load current will lead to continuous changes in about 375 MW. The SO-8 scheme has a thermal resistance of about 90 ° C/W, which means that the mold will start to rise to the power level of 34 ° C higher than the ambient temperature. The RON of the internal power switch increases with the rise of the mold temperature. The feedback circuit continues to maintain the output current to 500mA. At high environmental temperatures, this cycle may continue to the chip melting because the LTC1504 does not include any form of heat shutdown. The application can safely pull the peak current to the 500 mAh level above, but the average power consumption should be carefully calculated to ensure that the maximum 115 ° C mold does not exceed the temperature. LTC1504 passes through pins, especially GND (pin 4). By connecting GND to a large copper, it can optimize the area on the heat resistance PCB of the environment, and it will be used as a radiator. The application that runs the LTC1504 when it is close to the maximum power level or must bear the short circuit should maximize all sales of the copper area to ensure that there are more airflows on the partsThe remaining calories. For the help of the layout that may cause power consumption, please contact the LTC application department. The current limit circuit can be used to limit the power to the safe level slightly, but if the output is severely overloaded, it may still cause the mold temperature to rise. For current restrictions, see the current restriction section.
Precautions for layout
Like all precision switching regulators, LTC1504 needs to pay special attention to the layout to ensure the best performance. The large peak current and DC current will jointly prevents the output from the layout. If the layout is not planned carefully, it should be adjusted appropriately. A operational amplifier or data converter circuit layout will not be able to give you the performance you want, but it usually shows like an operational amplifier or data converter. A bad LTC1504 circuit does not look like a regulator. Winding or inserting prototypes are not suitable for bread board LTC1504 circuit! Perhaps the most important thing for the correct performance of the LTC1504 is the layout and input position and output capacitor of the ground node. The two inputs and output bypass containers should be close to the LTC1504 ground pins at the same time as possible. The compensation network can be connected to the trajectory according to its own trajectory, and it should return directly to this common ground ground. The input power ground and load circuit should also be connected to this public point. Each ground line should be in the center of the stars. This node should be a region for the radiator when a large copper needs. The second important thing is to enter bypass electric containers close to low ESR (usually ceramic). It should be as close as possible to the LTC1504 VCC and GND pins. Ideally, the capacitor should be located on the bag and span on the SW pin. Application of peak current or VCC is more than 6V. It may require 1 μF or larger ceramic capacitor. A less important node is SW. The additional lead length or the narrow record on this pin will only increase the parasitic inductance and the external inductors, and slightly increase its value. Software tracking only requires enough to support the maximum peak current when the short circuit may be 1A. If a trajectory needs to be compressed to make the layout work, this is one. Please note that considering that the signal will not be washed away, the long trajectory on the SW node may increase EMI. If the Sytki diode is used at the SW node, it should be located near the device pin at the LTC1504 end. The LTC application department has built hundreds of layout parts for LTC1504 and related devices. Many parts of them have played a role, and some parts are now used in the poor layout of the Hall of Fame.