Features

LM2766 CMOS charge pump voltage converter

Input power supply voltage doubled

as a permanent input voltage

SOT-23 6针封装，1.8 V至5.5 V，两个低成本电容器

20Ω典型输出阻抗和二极管用于提供

20毫安20毫安输出电流时，90%的典型Conversion efficiency.

The typical shutdown current of 0.1-μA LM2766 works under 200 kHz

Reduce the frequency of the output resistance and voltage

2 application ripples. The working current is only 350 μA (operating efficiency is greater than 90%, most mobile phone loads) and the typical shutdown current of 0.1-μA provides ideal LM2766 battery performance-PDA power supply system. The device is packaged in SOT-23 6.

Computing amplifier power supply

Interface power supply equipment information

Handheld instrument

Electrical characteristics

Unless otherwise specified, the typical limit is to be the typical limit is TJ u003d 25 ° C, the minimum and maximum limit is suitable for the entire operating temperature range: v+u003d 5V, C1 u003d c2 u003d 10 μF. (1)

(1) in the place In the test circuit, the capacitor C1 and C2 are 10 μF and the maximum ESR capacitor with a maximum 0.3Ω. A capacitor with higher ESR may increase the output resistance and reduce the output voltage and efficiency.

(2) The specified output resistance includes internal switch resistance and capacitor ESR. For more information, see the application and implementation of the positive voltage multiplescender.

(3) The operating frequency of the output switch is half of the frequency of the oscillator, that is, the #402; osc u003d 2 × #402; SW.

Typical features

(typical performeter application circuit, VIN u003d 5 V, TA u003d 25 ° C, unless there are other regulations)

Detailed description

Overview

LM2766 CMOS charge pump voltage converter is used as a voltage range of 1.8V to 5.5V. This circuit uses two low -cost capacitors and a diode (required at startup).

function description

Test circuit

LM2766 contains four large CMOS switches, these switches switch in order to double the input power supply double Voltage. Energy transmission and storageProvided by external capacitors. Figure 10 shows the voltage conversion scheme. When S2 and S4 are closed, C1 is charged to the power supply voltage V+. During this time, the switch S1 and S3 were disconnected. In the next time interval, S2 and S4 are opened; at the same time, when the S1 and S3 open and close, the input voltage V+and the voltage on the C1 gives a 2 V+output voltage, when there is no loading. The output voltage when adding a load is reduced by the MOSFET switch and the ESR of the capacitor) and the charge transfer loss between the capacitors. Further details of application and implementation.

Equipment function mode

shutdown mode

In normal circumstance In the operation mode of 0.1 μA, the SD pins are connected to V+. Through the application, the device can enter the closing mode until the SD pin A voltage is less than 20%of the voltage of V+pin.

Application information

LM2766 provides a simple and effective method to generate an input voltage. Without a electrical sensor, the size of the application solution can be compared with the magnetic material small DC-DC converter solution.

Typical application

The main application of LM2766 is to double the input voltage.

The output characteristics of this circuit can use an ideal voltage source and a resistance. The voltage source is equal to 2 V+. The output resistance path is the internal MOSFET switch, the frequency of the oscillator, the capacitance and ESR of C1 and C2. Because the switching current charging C1 is about twice the output current, the ESR effects of the pump capacitor C1 are multiplied by 4 in the output resistance. The output capacitor C2 is charging and the discharge current is about the output current, so its ESR only in the output resistance. A good approximate value of ROT is:

RSW is the sum of the internal MOSFET switch in Figure 12.

Peak to peak output voltage ripples from ESR of the frequency of oscillator and capacitor and output capacitors C2:

High capacitors, low ESR capacitors can reduce the output Resistance and voltage ripples.

Schottky diode D1

You only need to protect the device without opening your parasitic diode lock. During the startup process, the D1 will quickly charging the output capacitor until VIN minus the diode voltage drop and reduce the startup time. Therefore, the Schottky diode D1 must have sufficient load capacity to charge the output capacitor when starting, and at the same time provide it with a low positive voltage to prevent the internal parasitic diode from opening. The Schottky diode, such as 1N5817, can be used for most applications. If inputThe smaller slope Schottky diode (such as MBR0520LT1) with smaller slope is less than 10V/ms can be used to reduce the size of the circuit.

Capacitor selection

As discussed in the positive voltage multiplier, the output resistance and ripple voltage depend on the capacitor and ESR value of the external capacitor. The output voltage drop is the load current multiplication of the output resistance, and the power efficiency is

IQ (V+) is the static power loss of the device; and IL2rout is the Academy of Social Sciences. The choice of capacitors is based on the output voltage ripples of the drop voltage (equal to the output current) and the efficiency of the converter. It is recommended to use a low ESR capacitor (Table 2) to maximize the efficiency and high efficiency, reduce the output voltage drop and voltage ripple.

parallel device

Any LM2766 device can be connected in parallel to reduce the output resistance. Because there is no closed loop feedback, as found in the adjustment circuit, stable operation is guaranteed. Each device must have its own pump capacitor C1, and only one output capacitor is required, as shown in Figure 13. The output resistance of the composite material is:

Class joint device

Class LM2766 device is a simple way to gene As shown in Figure 14). Effective output resistance is equal to the weightedness of each separate installation: route u003d 1.5 route 1+route 2 Note, the increase in the number of levels is actually limited, because it significantly reduces high efficiency, increases the output resistance and output voltage pattern Wave.

regulating valve

You can use a low-voltage difference regulator (such as LP2980-5.0) to adjust the output of LM2766. This entire converter is shown in Figure 15. Using LP2980-3.3, LP2980-3.0 or LP2980-ADJ can get different output voltages. The worst case design must meet the following conditions at the same time:

2vin minimum value gt; output minimum value+VDROP maximum value (LP2980)+output maximum value × path maximum value (LM2766)

2 Vehicle vehicle vehicle The maximum value of the identification code lt; maximum value+minimum value (LP2980)+output minimum value × path minimum value (LM2766)

Power recommendation The input voltage range of 1.8 V and 5.5 V is designed as a inverter. The input power supply must be well adjusted and can provide the required input current. If the input power supply is located in the place where the device is far away, except for ceramic bypass, it mayAlso need an additional volume electric capacitor.

Layout

layout guide

The high switching frequency and large switching current of LM2766 make the choice of layout very important. Please refer to the following steps to ensure that the equipment is stable and maintains the appropriate LED current to adjust the operating voltage and current range. Place CIN on the top layer (the same layer as LM2766) and get closer to the device as much as possible. The connection input capacitor reaches the V+and GND pins through a short and wide trajectory, thereby reducing the spikes that appear during the inductive voltage switch to damage the V+line.

Put the COUT on the top layer (the same layer as LM2766) and approach the OUT and GND pins as much as possible.

The return value of CIN and COUT must be concentrated at a point, as close to the GND pin as much as possible.

Connecting the COUT through short, wide traces reduces the series of inductors in the output and ground pins, can damage the VOUT and GND lines, and cause excessive noise in the device and surrounding circuits. Place C1 on the top layer (the same layer as the LM2766 device) and get closer to the device as much as possible. Connect the flying capacitor to the hat+and hat-to sell through a short and wide trace wire.