Features

-Ad the use of 1 lithium or 2 alkaline/nickel-metal hydride/nickel-cadmium batteries to power

-The adjustable output voltage

]

- gt; 75%efficiency

-Eight-level digital programmable current limit

-The charging instruction

-The integrated IGBT drive with a trigger [ 123]

-Wexedy diode in the first side

-The thin packaging (0.75 mm nominal height)

Application

-D digital camera flash

[[

123] -F film camera flash

-Cat phone flash

-E emergency flash

a8439 It is a highly integrated integrated circuit, which is charged for the flashing light capacitors for digital cameras and film cameras. Integrate the MOSFET switch to the anti -gratifying top -to -top transformer. It also has an integrated IGBT driver, which is conducive to flash memory discharge function and saving board space.

Start A8439 for charging pins and start charging output capacitors. When the specified output voltage is reached, the A8439 stops charging until the charging pin is switched again. Pulling the charging needle to stop charging. When reaching the specified output voltage, #39; #39; D #39; #39; #39; O #39; N #39; #39; E #39; 39; Tube feet are a leaky indicator. The peak current limit can be adjusted to 270 mAh to 1.4 A. This allows users to flash even under low battery voltage.

A8439 can be used together with two alkaline/nimh/nicad or a single -core lithium battery connected to a transformer. Connect the vehicle identification number to 3.0 to 5.5 V power supply, which can be a system guide or lithium battery (if used).

The configuration of A8439 is very low -key (0.75 points mm) 10 -terminal 3 × 3 mm MLP/TDFN packaging, which is very suitable for applications with limited space. It is lead, 100%matte tin leading framework.

Figure Figure

Performance characteristics

Application in FIG. 8 The test performed by the circuit, if the Iswlim settings are set to 1.4A (the upper edge of the single upper on the charging pins), unless there is another instructions.

Unless otherwise explained, it is set to 1.4A in Iswlim(Single upper edge on the charging pin), use the application circuit shown in Figure 8 for testing.

Test the application circuit shown in FIG. illustrate.

Function description

Overview

A8439 is a flashing light capacitor control with adjustable input current limit and automatic refresh function IC. It also integrates an IGBT driver for the flash operation of the flash tube. Compared with the separated flash operation solution, it greatly saves the circuit board space. Control logic as shown in the functional frame diagram.

The charging operation of A8439 starts from the low to high signal on the charging pins. The primary peak current is set by the input clock signal from the charging pipe foot. When the charging cycle starts, the one -sided side of the transformer one side current I rises linearly linearly linearly by the comprehensive effect of the battery voltage VBATT and the first -side inductance,

LPRIMARY. When the iPrimary reaches the current limit iswlim, the internal MOSFET is immediately closed, so that the energy is pushed into the flash capacitance COUT from the second winding. The secondary side current decreases linearly with the increase in charge. The charging cycle begins again. After the transformer is reset, or after the scheduled time period, the TOFF (MAX) (18μs) is subject to the first occurrence.

When the internal MOSFET switch is turned off, the output voltage VOUT is sensing from the anode D1 connected to the anode D1 connected to the output diode. This resistance string forms a pressure division, feeds back to the FB pin. The size of the resistor must reach the required output voltage level according to the typical value of 1.205 V at the FB pin. Once the VOUT reaches the required value, the charging process will end. When the internal voltage induction circuit detects the output voltage by 10%, the A8439 automatically starts a new charging cycle. Switching the charging pipe foot can also start the refresh operation.

Automatic refresh

A8439 has an automatic refresh function when connecting the feedback resistance network at the output end. When the output voltage drops to the ≈ 90%of the stop voltage of the resistance network, automatically reflects. The operation is shown in Figure 3.

Enter the current limit

By timing the charging pipe foot, you can adjust the peak current limit to eight different levels, from 270 mAh to 1.4. The internal digital circuit decodes the input clock signal to the counter, and the counter setting the charging time. This flexible solution allows users to operate the flash circuit according to different batteries input voltage. By setting lower current limits at low battery voltage, the battery life can be effectively extended.

FIGCase agreement. The total time of ILIM sets Tilim (SU) indicates that the decoder circuit receives Ilim input and sets the time required for Iswlim. The typical duration is 60 μs.

FIG. 5 shows the regular definition of the main stream circuit. At the end of the setting cycle, Tilim (SU), a current starts to rise to the settings. As long as the charging pin is high, the Iswlim settings remain effective. To reset the ILIM counter, pull the charging pin and lower the charging pin before setting the timing.

After the first startup or ILIM counter is reset, each new current limit can be set by sending pulses to the charging pins. The first rising along the ILIM counter, up to 8 rising edges will be counted to set the ISWLIM level. The charging needle will remain at a high position. The user has a maximum of 32 μs clock input pulse. The four panels in Figure 6 show the example of pulse flow and the current level.

FIG. 7 shows the last charging cycle, when the charging pipe foot is the voltage of the SW node. Before the charging is completed, as long as the voltage is lower than the compulsory low voltage. 1.2 V, turn on the switch again at the next charging cycle. However, when the flash of the flashing capacitor charger starts, the A8439 realizes the adaptive shutdown time TOFF control. When the low output voltage, the switch may be triggered after the switch is disconnected to limit the time, and the sensor circuit tracking the anti -excite maximum switch to 20 μs.

Transformer design

Turn ratio ratio. The minimum transformer ratio ratio n, (Secondary: Primary) should choose the formula according to the following conditions:

In the formula: VOUT (V) is the required output voltage level, the output voltage level, VD_DROP (V) is the positive voltage of the output diode. VBATT (V) is a transformer battery power supply, and

40 (v) is the rated voltage of the internal MOSFET switch, indicating that the maximum allowable reflex voltage is output to the switch pipe tube. foot.

For example, if VBATT is 3.5 V, VD_ pressure drop is 1.7 V (this may be when two high -voltage diodes are connected in series), and the expected VOUT is 320 V, the number of turning ratio should be at least at least for at least it is 8.9.

In the worst case, when VBATT is the highest, VD_ decreases and VOUT will be higher when its maximum tolerance limit. VBATT 5.5V, VD_DROP 2V, VOUT 320V × 102% 326.4V is the worst case, N can be determined to be 9.5.

In practice, be sure to choose a turn ratio higher than the calculation value to give a certain security. In the worst case, the recommended minimum turn ratio is toN 10.

Primary inductance. The minimum closing time of A8439 is TOFF (min) to 300 NS to ensure the correct opening node voltage induction. When selecting the primary inductance LPRIMARY (μH), use the following formula as a loose guidance:

In ideal, the charging time is not affected by the primary inductance of the transformer. However, in practice, it is recommended to choose between 10 μH and 20 μH. When an inductance is less than 10 μH, the parasitic element related to the rejuvenation of the transformer will cause the efficiency to decrease and the charging time is prolonged. When LPRIMARY is greater than 20 μH, the rated power of the transformer must be greatly increased to process the required power density, and the series resistance is usually high. A optimized design to achieve a small -scale solution will have a 12 to 14 μH once, the smallest leakage and secondary capacitance, and minimize the one -and -second series resistance. See the details of the form of the form, please refer to the recommended component.

Leakage and secondary capacitors. The original design of the transformer should minimize the leakage to ensure that the cutting voltage peak at the opening node does not exceed 40V limit. However, for this application, the minimum leakage can be affected by the increase of parasitic capacitors. In addition, transformer secondary capacitors should minimize. Any secondary capacitance will multiply to N2 when reflected to a capacitor, which causes the initial current swing when the switch is turned on and reduces efficiency.

Adjust the output voltage

A8439 induced output voltage during the closure. This causes the compressor network R1 to R3 (see Figure 8) connected to the anode of the high -voltage output diode D1, so as to eliminate power loss caused by the feedback network during the charging. By selecting the appropriate voltage resistance value, the output voltage can be adjusted. Use the following formula to calculate the value of RX (ω):

R1 and R2 need to have a breakdown voltage of at least 300 V. The typical 1206 surface -installed resistor has a breakdown voltage of 150 V. It is recommended that R1 and R2 have similar values to ensure that the voltage stress between them is uniform. The recommended value is: R1 R2 4.99 MΩ (1206) R3 39 KΩ (0603), and the two stop voltage of 303 V together.

The higher resistance rated value of R1, R2 and R3 does not significantly improve the efficiency, because the power loss of the feedback network mainly occurs in the shutdown time, and the shutdown time is only a small part of each charging cycle.

Output diode selection

Select the rectifier diode D1, small parasitic capacitor (short reverse recovery time), and at the same time meet the reverse voltage and forward current requirements.

The peak reverse voltage of the diode VD_PEAK occurred in the recommendation departmentThe MOSFET switch inside the table is closed, and the one -side current starts to rise.可计算为：

整流二极管的峰值电流ID_peak计算如下：

输入电容器选择

[ 123] It is recommended to enter a ceramic capacitor with X5R or X7R medium. Its rated value should be at least 4.7 μF/6.3V to enter VBATT in the one -side battery on the disconnection of the transformer. When using a separate partial pressure, the A8439 vehicle recognition number power supply is connected at least 0.1 μF/6.3 V bypass electric container to the vehicle identification number pin.

Layout Guide

The key to the good layout of the flash of lighting capacitor charger is to minimize the parasitic on the power switch loop (primary side of the transformer) and rectifier loop (secondary side). Use a short and thick line to connect to the transformer once with the switching foot.

The output voltage sensing circuit component must be far away from the open joint node, such as SW PIN. The important thing is that D "