データシートサーチシステム |
|
LM3420 データシート(PDF) 16 Page - National Semiconductor (TI) |
|
|
LM3420 データシート(HTML) 16 Page - National Semiconductor (TI) |
16 / 17 page Application Circuits (Continued) A rapid charge Lithium-Ion battery charging circuit is shown in Figure 10. This configuration uses a switching regulator to deliver the charging current in a series of constant current pulses. At the beginning of the charge cycle (constant-current mode), this circuit performs identically to the previous LM2575 charger by charging the battery at a constant current of 1A. As the battery voltage reaches 8.4V, this charger changes from a constant continuous current of 1A to a 5 second pulsed 1A. This allows the total battery charge time to be reduced considerably. This is different from the other charging circuits that switch from a constant current charge to a constant voltage charge once the battery voltage reaches 8.4V. After charging the battery with 1A for 5 seconds, the charge stops, and the battery voltage begins to drop. When it drops below 8.4V, the LM555 timer again starts the timing cycle and charges the battery with 1A for an- other 5 seconds. This cycling continues with a constant 5 second charge time, and a variable off time. In this manner, the battery will be charged with 1A for 5 seconds, followed by an off period (determined by the battery’s state of charge), setting up a periodic 1A charge current. The off time is deter- mined by how long it takes the battery voltage to decrease back down to 8.4V. When the battery first reaches 8.4V, the off time will be very short (1 ms or less), but when the battery approaches full charge, the off time will begin increasing to tens of seconds, then minutes, and eventually hours. The constant-current loop for this charger and the method used for programming the 1A constant current is identical to the previous LM2575-ADJ. charger. In this circuit, a second LM3420-8.4 has its V REG increased by approximately 400 mV (via R2), and is used to limit the output voltage of the charger to 8.8V in the event of a bad battery connection, or the battery is removed or possibly damaged. The LM555 timer is connected as a one-shot, and is used to provide the 5 second charging pulses. As long as the battery voltage is less than the 8.4V, the output of IC3 will be held low, and the LM555 one-shot will never fire (the output of the LM555 will be held high) and the one-shot will have no effect on the charger. Once the battery voltage exceeds the 8.4V regulation voltage of IC3, the trigger pin of the LM555 is pulled high, enabling the one shot to begin timing. The charge current will now be pulsed into the battery at a 5 sec- ond rate, with the off time determined by the battery’s state of charge. The LM555 output will go high for 5 seconds (pull- ing down the collector of Q1) which allows the 1A constant-current loop to control the circuit. Figure 11 shows a low dropout constant voltage charger us- ing a MOSFET as the pass element, but this circuit does not include current limiting. This circuit uses Q3 and a Schottky diode to isolate the battery from the charging circuitry when the input voltage is removed, to prevent the battery from dis- charging. Q2 should be a high current (0.2 Ω) FET, while Q3 can be a low current (2 Ω) device. Note: Although the application circuits shown here have been built and tested, they should be thoroughly evalu- ated with the same type of battery the charger will even- tually be used with. Different battery manufacturers may use a slightly dif- ferent battery chemistry which may require different charging characteristics. Always consult the battery manufacturer for information on charging specifications and battery details, and always observe the manufactur- ers precautions when using their batteries. Avoid over- charging or shorting Lithium-Ion batteries. DS012359-16 FIGURE 11. MOSFET Low Dropout Charger www.national.com 16 |
同様の部品番号 - LM3420 |
|
同様の説明 - LM3420 |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |