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ACT2823 Fiches technique(PDF) 17 Page - Active-Semi, Inc |
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ACT2823 Fiches technique(HTML) 17 Page - Active-Semi, Inc |
17 / 25 page ACT2823 REV 1, 01-DEC-2016 Innovative PowerTM ActiveSwitcherTM is a trademark of Active-Semi. 17 The following equations calculate the proper external resistor network to set the upper and lower charging temperature thresholds. ) 8 ( hot Rc I V CHG TCL ) 9 ( cold R I V CHG TCH ) 10 ( R Ra R Ra Rb hot NTCh NTCh Rc ) 11 ( R Ra R Ra Rb cold NTCc NTCc R From (7) (8) (9) and (10) calculate Ra and Rb in charge mode, as the same method, the resistors in discharge mode can be calculated. For example, using an NXRT15XH103 NTC resistor and a temperature charging range of 0 to 45 ,we know RNTCC=27.219k and 4.917k at 0 and 45 respectively. We can calculate Ra=33kΩ and Rb=2.87kΩ based on the above formulas. Follow this procedure for any other NTC and charging temperature range. If temperature sensing is not used, connect TH to ground through a 10kΩ resistor. I2C Serial Interface The ACT2823 provides the user with the ability to change operating parameters via I2C commands. The Customer Register Map section of the datasheet shows the parameters that can be modified. All changes to I2C registers are volatile. All registers reset to their default settings when power is recycled. The ACT2823 operates as a slave device, and is ad- dressed using a 7-bit slave address of 0x5Ah, followed by an eighth bit, which indicates whether the transaction is a read-operation or a write-operation, 1011010x. “x” is a 0 for write operation and 1 for a read operation. Use address 0xB4h for write operations and 0xB5h for read operations. There is no timeout function in the I2C packet pro- cessing state machine, however, any time the I2C state machine receives a start bit command, it immediately resets the packet processing, even if it is in the middle of a valid packet. APPLICATION INFORMATION Inductor Selection The ACT2823 uses current-mode control and a proprietary internal compensation scheme to simplify external component selection. It is optimized for operation with 4.7μH inductors. Choose an inductor with a low DC-resistance, and avoid inductor saturation by choosing inductors with DC ratings that exceed the maximum output current by at least 30%. Design for an inductor ripple current that is approximately 30% of the maximum output current. The following equation calculates the inductor ripple current is ∆ 1 ∗ ∗ 12 Where VOUT is the 5V output voltage, VBAT is the battery voltage, FSW is the switching frequency, and L is the inductor value. Output Capacitor Selection VOUT requires high quality, low-ESR, ceramic capacitors. Three 22uF capacitors are typically suitable. An additional smaller 0.1uF capacitor assists with high frequency filtering. Smaller capacitors can be used with smaller loads but the capacitance should not go below 44uF for stability reasons. Choose the capacitance to keep the output ripple voltage less than approximately 50mV. The following equation calculates the output voltage ripple. VRIPPLE ∆ 8∗ ∗ 13 Be sure to consider the capacitor’s DC bias effects and maximum ripple current rating when using capacitors smaller than 0805. A capacitor’s actual capacitance is strongly affected by its DC bias characteristics. The output capacitor is typically an X5R, X7R, or similar dielectric. Use of Y5U, Z5U, or similar dielectrics are not recommended due to their wide variation in capacitance over temperature and voltage ranges. Input Capacitor Selection The input capacitor on VIN requires a high quality, low- ESR, ceramic input capacitor. A 22uF capacitor is typically suitable, but this value can be increased without limit. Smaller capacitor values can be used with lighter output loads. Choose the input capacitor value to keep the input voltage ripple less than 50mV. Battery Capacitor Selection The BAT pin requires high quality, low-ESR, ceramic capacitors. Two 22uF capacitors are typically suitable. An additional smaller 0.1uF capacitor assists with high frequency filtering. Smaller capacitors can be used with smaller loads but the capacitance should not go below 22uF. These capacitors are the output capacitors to the charging boost converter and the input capacitors to a discharging buck converter, so they must be placed as close as possible to the BAT pin and be directly to the PGND plane. Choose the capacitance to keep the ripple voltage less than 50mV. Use the following equation to calculate the minimum input capacitance. |
Numéro de pièce similaire - ACT2823 |
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Description similaire - ACT2823 |
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