General features

0.8V start voltage

High 5.5V working input voltage

Internal synchronization rectifier

1.8V adjustable output voltage

3.3V and 5V fixed output voltage

Battery low voltage detection

Reverse battery protection

750mA input current limit

switch The frequency is as high as 1MHz

1.23V reference voltage

from 1 to 3 alkali,

nickel -metalized, nickel -cadmium battery or 1 lithium ion Battery

PDA and handheld instrument

Digital camera

Mobile

GPS

distributed power supply

Instructions [ 123]

L6920DB is a high -efficiency single -chip switching converter integrated circuit battery power supply application. The package is MSOP8 for minimizing PCB space. It only needs three external components to change the battery voltage to the selected output voltage. The minimum output voltage is 1.8V: suitable for providing the most advanced ASIC and μP. The high -opening frequency allows low posture, small electromotors and output capacitors have been used. Reference voltage, low -battery detection and shutdown are provided with overcurrent.

Table 4. Electrical characteristics

(vin u003d 2V, FB u003d GND, TJ u003d 25 ° C, unless there are other regulations)

[ 123] Detailed description

L6920DB is a high -efficiency, low -voltage increased DC/DC converter for 1 to 3 batteries (lithium ion/polymer, NIMH) battery conversion. These properties are achieved by greatly reducing static current (only 10 μA) and using synchronous correction, which also means that costs are reduced in the application (no external diode). The operation is based on the maximum opening time-minimum closing time control, and the current restrictions are set to 800mA. The simplified frame diagram is shown below.

Working principle

In L6920DB, controlled a comparator -based comparator, which continuously checked the output voltage. If the output voltage is lower than the expected value, the control function is L6920DB to transmit the energy stored in the inductor to the load. This completes the alternation between the two basic steps:

ton phase: By short -circuit LX, the energy is transferred from the battery to the inductor nodePass the ground. If the current in the current inductor reaches 750mA or is set to 5 μs at the maximum connection time.

TOFF phase: The energy stored in the inductor is at least 1 μs by the minimum turnover time of the synchronous switch. After that, the synchronous switch will flow to zero once the output voltage is lower than the regulated voltage or current flows in the sensor.

Therefore, in the case of light load, the device works in the PFM mode, as shown in Figure 8:

Considering the current in the inductor in the inductor in the inductor, the current in the inductor in the inductor in the inductor in the inductor in the inductor in the inductor device The limit is 800mA, and the maximum load current is the following relationship. The following relationship is defined:

In the formula, ILIM u003d 750ma. Figure 8)

Start

L6920DB's main features is to start when the power supply voltage drops to 0.8V (see the chart in Figure 4 To. During the start, the switch is turned off, and the energy is through the diode of the body. Because the internal charge pump is used for bias power MOS grid. Due to this modified behavior, the number of TON/TOFF is extended. The current limit and zero test are still available.

Close

In the turnover mode (SHDN lowered), all internal circuits were closed, thereby minimizing the current provided by the battery (in a typical case, ISHDN LT; 100 NA)) Essence Both switches are turned off, and the output of the low battery comparator is forced to be in high level impedance.

Synchronous switching diodes are also inevitable output in power and downtime.

Low power detection

L6920DB includes a low -battery detector comparator. The threshold is VREF voltage, and a lag is added to avoid slowly entering the threshold when the input crosses occurs. LBO is an output of the drain, so a pull -up resistor is needed correctly.

Low battery input

You can use an external resistor division to fix the LBO threshold to adapt to pass the following equal formula and perform LBO detection at the correct input source:

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[ 123]

Reverse polarity

In order to avoid damage to L6920DB and batteries, it was designed to be damaged when the battery insertion was inserted. In addition, the design of this circuit has the opposite polarity to zero the current of the battery. If the battery can be inserted reverse, the non -polarized capacitor should be installed in the C2 position.

Output voltage selection

The output voltage that acts on FB pin must be selected. There are three options: fixed 3.3V, 5V or throughOutput settings with adjustable external resistors.