Function description

LM2623 is a high-efficiency and universal, with good efficiency-efficient battery voltage DC-DC switching voltage voltage power supply in a very wide load range And low input voltage system. It receives a small volume, VSSOP-8 package (input voltage accounted for half of 0.8 to 14 volts, and the conversion standard 8-needle SOIC packaging), the output voltage is between 1.24 and 14. 1.09 mm packaging height can achieve an efficiency of up to 90%LM2623.

The frequency of switching is as high as 2 MHz

In order to adapt to multiple applications, the working voltage is LM2622, LM2731, LM2733 and LM2621.

8V to 14V

LM2623 allows designers to change the output

1.1V startup voltage, operating frequency (300kHz to 2MHz)

1.24V-14V can be available. The output voltage and the duty ratio (17%to 90%) are optimized to optimize the performance of the component. The selected value can be fixed, or the 2A load current can be reached at a low output voltage with a battery voltage or input output voltage change

0.17Ω internal MOSFET ratio. LM2623 uses a very simple switch

up to 90%of the regulator efficiency adjustment mode to generate good efficiency and stable operation within the wide range of working. The typical working current of 80 μA (entering the VDD pin usually skip the switching cycle during power supply) to achieve the adjustment limit (pulse frequency lt; 2.5μA's shutdown and modulation power supply current specified in 2.5μA).

4mm x 4mm thermal enhanced WSON Note: Please read non -linear effects and packaging options, select the design program part in the correct C3 capacitors, so use this component to design any challenges Before the design/layout circuit board, the camera, paging machine and mobile phone should be considered.

PDA, palm computer, GPS device

White -light LED drive, TFT or scan LCD

flash memory programming

Handheld instrument

1 , 2, 3 or 4 battery alkaline system

1, 2 or 3 battery lithium ion system

Electric characteristics

The limit of standard fonts is suitable for TJ u003d 25 ° C. The limit of black bodies is suitable for 40 ° C to+85 ° C. Unless there are other regulations: VDD u003d VOUT u003d 3.3V.

(1) VDD is on the trunk and EN pin. The frequency pin is connected to the VDD through the 121K resistance. Vdd_ST u003d VDD when activated. Vehicle identification number is VDD+D1 voltage (usually 10-50 MV when starting)

(2) This is a current that enters the VDD pin.

(3) This is the total current of input pins VDD, BOOT, SW and FREQ.

(4) The maximum power consumption must be reduced at high temperature, and it is determined by TJMAX (maximum temperature), θja (condensed to environmental thermal resistance) and TA (environmental temperature). In any case, the maximum allowable power consumption temperature is PDMAX u003d (TJMAX-TA)/θJa or the given value given in the absolute maximum rated value, which is lower.

(5) The thermal resistance (θja) of the environment is taken from the thermal simulation results, and under the set conditions and guidelines, the JEDEC standard JESD51-17 is performed. The test board is a 4-layer FR-4 board, with a size of 102mm x 76mm x 1.6mm, and the size is 3 x 2 heating hole array. The horizon on the board is 50mm x 50mm. The thickness of the copper layer is 36mm/18mm/18mm/36mm (1.5 ounces/10 ounces/1 ounce/1.5 cow). The ambient temperature in the simulation is 22 ° C, static air. The power consumption is 1W (DAP is welded) or more information about WSON theme, and WSON installation and welding specifications, please refer to (SNOA401) Application 1187: Lead -free lead frame packaging (LLP).

(6) The exposed 1 ounces of 1 square inch area of u200bu200bthe exposed 1 ounce of 1 ounce was exposed. Using more copper can reduce thermal heat dissipation.

(7) When EN pin is lower than Venu Lu, the regulator is closed; when EN PIN is higher than Venu Hi, the regulator work

Working principle

LM2623 is designed to provide a boost DC-DC voltage adjustment system under battery power supply and low input voltage. It combines the voltage switching voltage voltage, N -channel power MOSFET, built -in current limit, and the limit of the hot single 8 -pin VSSOP package and reference voltage diagram 9. The switch-type DC-DC regulator increases the input voltage between .8V and 14V, adjusting the output voltage between 1.24V and 14V. LM2623 starts from 1.1V input and keeps below 0.8V. After optimization, the device can be used for mobile phones and other applications that require small size and low outlines, such as and low static current to maximize the life of the battery during the standby and shutdown. High -efficiency door control oscillator topology can provide up to 2A outputs under low output voltage. The additional functions include the limitation of the internal peak switching current and the thermal protection circuit.

Door -control oscillator

lm2623 The switching mode of 3 and its ultra -low static current leads to good efficiency within a wide load range. The frequency of internal oscillator can use external resistor programming to keep it constant or change with the battery voltage. Add a capacitor to programming frequency to allow designers to adjust the duty cycle and optimize according to the application. In addition to the capacitor, adding a resistor can make the dynamic compensation input/output voltage ratio of the duty cycle. We call it an adaptive ratio door control oscillator circuit. For examples of application circuits, see application notes. Use the correct RC to adjust the component of the oscillator to allow components to allow components to run loads and input/output voltage in a wide range in a wide range in a wide range.

Pulse frequency modulation

pulse frequency modulation is usually achieved by continuous switches until the voltage limit is reached and then the cycle is maintained to maintain it. This will lead to some lag operation mode. This when the current rises to high electricity, the coils store more energy in each cycle. When the voltage limit is reached due to the energy stored in the coil, the system is usually over -adjusted to the voltage higher than the required voltage (see Figure 10). When the system starts to switch again, it will also be a bit unseen, because it has exhausted the energy in all the storage coils that require more energy to achieve a balance with the load. In this case, larger output capacitors can reduce ripples. However, the frequency of filtering is not the most basic switching frequency. It is a lower frequency parameter determined by load, input/output voltage and circuit. This operation mode is useful in the case of significant load changes. Power management, for example, a computer system may change from zero to full load when the system is turned on, which is usually the preferred adjustment mode of such systems.

PFM

When the load is not changed in a large range (such as zero to full load), the ratio self -adaptation circuit technology can be used to realize the cycle -to -cycle PFM regulation and low -grained rod (or or or low ripple (or or Smaller output capacitors). The key to success is the matching of the input output voltage ratio of the matching ratio of the matching ratio. This then needs to be dynamically adjusted according to the changes in the input voltage (usually caused by battery operation). The selected ratio should be allowed to transmit most of the energy in each switching cycle to the load and only store a small amount. When the adjustment limit is reached, the over -adjustment volume will be small, and the system will stabilize at a balance point. At this balance point, it adjusts the shutdown time in each switching cycle to meet the current load requirements. After each time the specified time is exceeded, the regulator loop is turned off until the voltage drops to the limit below the limit to start the next switching cycle. The current coil will never return to zero or input/output voltage to not match the duty cycle in the lag working mode of the circuit with a large load change. Optimized the duty cycle input/output voltage of the given group can be achieved by using the circuit value in the application annotation.

Low pressure start

lm2623 can be from lowThe voltage of 1.1 volt is started. When starting, the control circuit continuously switches N -channel MOSFET until the output reaches 3 volts. After reaching this output voltage, the normal boost regulator feedback and the door control oscillator control scheme are taken over. Once the device is adjusted, it can operate as low as 0.8V input, because the internal power of IC can use VDD pins.

Close

LM262 has a shutdown mode, which can reduce the static current to the 2.5UA temperature below the specified 2.5UA. In the application of battery power supply, this can extend the service life of the battery. During the shutdown, all the feedback control circuits are closed. The output voltage of the regulator is dropped to the bottom diode below the input voltage. Entering the shutdown mode is controlled by the activated low-logical input pin EN (PINH-2). When the logic input is pulled below 0.15VDD, the device enters the shutdown mode. The logic input of this pin should be higher than 7VDD for device to work in normal boost mode.

Internal current limit and thermal protection

Internal circulation current restrictions are used for protection functions. The settings are high enough (the typical value is 2.85A, and the maximum value is about 4A) to avoid taking effect under normal operation conditions. When the internal heat should be temperature (TJ) exceeding about 160 ° C, the protection circuit disables the MOSFET power switch. When TJ drops to about 135 ° C, the switch is reopened.

Non -linear effect

LM2623 is very similar to LM2621. LM2623 is based on LM2621, except for LM2623 using non -linear effects to make the duty cycle programming. The C3 capacitor is used to release the charge on the FREQ pin to control the duty cycle of the internal oscillator. In order to make the pulse frequency modulation, the components are deceived in some way to work (PFM) to boost the switching regulator.

Select the correct C3 capacitor

C3 capacitor allows the internal oscillator to be programmed. Choosing the correct C3 capacitor to get a duty cycle for specific application circuits is a trial and error. The non -linear effect generated by C3 depends on the input voltage and output voltage value. The correct C3 cannot calculate a capacitor with specific input and output voltage values. It is best to choose the correct C3 capacitor. It is best to check and error, and it must not be too close to the current limitation of the device with one of the peak current envoys of the electrical sensor. As the C3 capacitor value increases, the duty cycle also increases. Conversely, as the C3 capacitor value decreases, the duty cycle is reduced. The wrong selection of the C3 capacitor may cause the premature jump current limit and/or dual pulse of the component, which may cause the output voltage unstable.

Set the output voltage

The output voltage of the boost regulator can be set and RF2 by connecting the feedback resistor division made of RF1. The choice of resistance value is as follows: RF1 u003d RF2*[(VOUT/1.24) 1]

It is recommended that the value of RF2 is 50K to 100K. Then, you can use the above formula to select RF1.

VDD power supply

For LM2623, the VDD power supply must be between 3 and 5 volts. This voltage can reduce the input voltage from just connecting the VDD pin to VOUT. If the VDD power supply voltage is not a low -ripple voltage source (less than 200 millivolta), it is recommended to use RC filters for cleaning. The ripples on the VDD will reduce the efficiency.

Set the switch frequency

The switching frequency of the oscillator is selected and the frequency pin is selected by selecting the external resistor (R3) connected between Vin. Please refer to the typical performance feature part of the title ""Frequency and Vin"" chart to select the R3 value to obtain the data table that obtains the required switching frequency. The high -push frequency allows the use of very small surface paste and capacitors, and produces very small solutions. A is recommended to switch between 300kHz and 2MHz.

Output diode selection

The output diode should be used in the Syntky diode. The positive current of the diode should be higher than the peak input current, and the back voltage rated value must be higher than the output voltage. Do not use ordinary rectifier diode. Due to the slow switching speed and long recovery time, efficiency and load are supervised. Table 1 shows the list of diode manufacturers.

WSON package device

LM2623 is provided in the 14-drawing WSON surface installation package to increase power consumption compared with VSSOP-8. For detailed thermal performance and installation and welding specifications, see (SNOA401) application description AN-1187.