0.6 to 5.5V working input voltage

1V starts input voltage

Internal synchronization rectifier

Zero -off current

3.3V and 5V fixed fixation Or adjustable

Output voltage (2V to 5.2V)

120m Internal source switch

Battery low voltage detection

reverse battery Protection

Application

One to three battery devices

PDA and handheld instrument

mobile phone-numeric rope phone

Tel

[ 123] The paging machine

GPS

Digital camera

Instructions

L6920

is an efficient boost controller, only needed Three external components can achieve the output voltage from the battery voltage to the selected output voltage. Make sure that the starting voltage is 1V, and the operating voltage of the device drops to 0.6V. The internal synchronization rectifier uses 120m P channel MOSFET. In order to improve the efficiency, the variable frequency speed adjustment is achieved. Electric characteristics (VIN 2V, FB GND, TAMB -40 ° C to 85 ° C, TJ LT; 125 ° C, unless there are regulations)

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Detailed description

L6920 is a high -efficiency, low -voltage boost DC/DC converter, which is especially suitable for 1 to 3 batteries (lithium -ion batteries /Polymer, nickel -metal hydride) The battery is converted. These properties are achieved by significantly reduced static currents (only 10 μA) and using synchronous rectification, which also means reducing application costs (no external diode). The operation is based on the maximum opening time-minimum closing time control, and the current limit is set to 1A.A simplified box diagram as shown below.

Working principle

In L6920, controlled a comparator -based, the comparator continuously check the state of the output voltage. If the output voltage is lower than the expected value, the control function of the L6920 will guide the stored energy to the load in the inductor. This is done by two basic steps: -t phase: short-circuit LX nodes on the ground through the N-channel power switch, and transferring energy from the battery to the inductor. If the current in the inductors reaches 1A or sets the maximum connection time to 5 μs, the switch is turned off. -TOFF phase: The energy stored in the inductors is passed to the shortest shutdown time of the load through the synchronous switch of AT. After that, the synchronous switch immediately turns off the voltage lower than the specified voltage or the current of the induction of the inductive sensor drops to zero. So it is lightIn the case of load, the device works in PFM mode, as shown in Figure 5.

When ILOAD is heavier, the pulse sequence is overlap. Figure 5.2-5.4 show some possible behaviors. Considering that the current in the inductor is limited to 1A, the maximum load current defines the following relationship:

The middle η is efficient, Ilim 1A. Of course, if ILOAD is greater than ILOAD IU Lim, it is lost (Figure 6)

Starting

L6920 is that the power supply voltage drops to 1V 1V 1V Start at time (see the chart in the chart 3. in the case of heavy load). The device retains the running mode of the running. Once the voltage exceeds 1.4V when the startup, the switch is turned off simultaneously, and the energy is transmitted to the load through its inherent body diode. The N channel switch has a very low RDSON. Because of this change of behavior, the ton/flight time is extended. The current limit and zero test are still available.

Turn off

In the shutdown mode (SHDN lower), all internal circuits are closed to minimize the current of the battery (in typical cases, ISHDN LT; 100 NA). Both switches were turned off, and the battery electricity output was forced to output in high impedance. The synchronous switching diodes will generate a parallel path between the power supply and the output that can be avoided when the parallel path that cannot work properly.

Low -power detection

L6920 includes a low -battery power detector comparator. The threshold is VREF voltage and increases the lagging of 1.3%to avoid slowly entering the threshold when the input cross occurs. LBO is output for the leakage of the road, so a pull -up resistor is required to use it correctly.

Anti -polarity

In order to avoid L6920 and batteries, both battery insertion errors are destroyed. In addition, the design of the circuit makes the battery's current current zero, and vice versa.

Application information

Output voltage selection must choose the output voltage that acts on the FB pin. There are three options: fixed 3.3V, 5V, or output that can be adjusted by an external resistor.

R4, R5, the range of 100K -10m The consumption and errors generate through FB pins (small NA).

Output capacitor selection

The output capacitor affects both efficiency and output ripples, so the choice must be specially considered carefully. The capacitance value should be within a range of about 10 μF-100 μF. Another smaller low ESThe R capacitor can be used in parallel to high -frequency filtering. Typical values can be about 1 μF. If you need very high performance in terms of efficiency and output voltage ripples, you must choose a very low ESR capacitor. Ceramic capacitors are the lowest ESR, but they are very expensive. Other possibilities are low ESR 容 capacitors, which can be from Kemet, AVX and other sources. POSCAP's Sanyo capacitors and Panasonic polyphors are also good. The upper limit value and the rated voltage are only the possibility of suggestion

Sensor selection

Generally, the inductor with a range between 5 μH and 40 μH meets most of the majority application. The small value sensor has a smaller physical size to ensure that the load transient response is faster, but the stable output voltage produces a large ripple. In fact, the output ripple voltage is given ESR by Ipeak. In addition, as shown in formula (1), the size of the electrical sensor will also affect the maximum current of the load. Finally, if a very high efficiency value is required, it is recommended to use a low -string connected resistor. In any case, the saturation current of the clutch ring should be higher than the peak current limit of the device (1A). COILCRAFTS, Coiltronics, Murata, and other Souc Es provide good surface installation sensors. The following table lists some recommended components.

Layout Guide

In order to reduce noise, high -frequency resonance problems and electromagnetic interference, the circuit board layout is very important. The important thing is to maintain a small high switching circulation path as possible to reduce the problem of radiation and resonance. Therefore, the capacitance of the output and input terminals should be very close to the device. The external resistor division (such as use) should be as close to the pins (FB and LBIs) as possible, as well as as far as possible away from the large current circulation path to avoid picking noise. Large trajectory large current paths and extended ground planes help reduce noise and increase efficiency. For examples of the recommendation layout, please refer to the following evaluation board