SMD fuses on a single lithium battery applications
Today, mobile phones, digital cameras (camera), PDA, MP3 / 4 ... more and 74HC14N datasheet and more products using lithium batteries as the power supply system circuit. Focus on the power lithium battery size requirements are smaller, higher energy density and 74HC14N price and no memory effect, but also the advantages of recycling used multiple times. However, lithium battery explosion also occurred recently. P>
2009.1.30 East Road, Yuexiu District, Guangzhou, computer store occurred in association with the cell phone lithium battery explosion inside the neck artery break a young man died on the spot. P>
So for the safety of lithium batteries is also attracting increasing attention. Lithium battery protection board will select the appropriate chip fuse is very important. P>
One. The composition of a single lithium battery P>
Mainly by lithium batteries and 74HC14N suppliers and battery protection board composition (Figure 2) P>
Lithium battery protection board main functions: (1) over-charge protection, (2) over-discharge protection, (3) over current / short circuit protection P>
Lithium battery protection board main components: 1, protection of IC2, MOSFET3, SMDFUSE P>
II. A single lithium battery protection board fuse selection P>
1, Package: According to customers board decided to try size, usually with 1206/0603 size. P>
2, rated voltage: 24V or more P>
3, Rated Current: General by 5A (taking into account the protection of the fuse in the lithium battery protection board is 2, so P>
To take into account the protection delay time protection IC to determine the fuse time) P>
4, cold resistance: 15mΩ the following P>
5, Safety requirements: UL certification P>
6, meet the requirements and Halogen-Free RoHS requirements P>
Give two examples below to illustrate the fuse option. P>
Example 1: A single lithium battery protection circuit board as shown in Figure 3, the protection IC with SII (Seiko) S8261ACJ, the basic parameters as shown in Figure 4. Uses MOS tube BF9028DNJ/BF9028DNJ-A, some parameters as shown in Figure 5. P>
A: Protection circuit working properly.
Protect the IC over-current protection principle: too much current when the discharge current or short circuit occurs, the protection of IC will be activated off (short circuit) current protection, over current detection time is PowerMOS the Rds (on) as inductive impedance to monitor the voltage drop the case, if the ratio set by the overcurrent detection voltage is higher then stop discharging.
According to the formula V-(over-current detection voltage) = I (discharge current) * Rds (on) * 2 can calculate the number of discharge current protection IC to start protection.
1: Short circuit protection cases:
When overcurrent detection voltage 0.9V, MOS tube resistance maximum value, they can detect over-current will be minimum. Calculate the value of time over current 15A, then protect the IC protection delay time 320us;When the over current detection voltage
1.5V, MOS tube resistance take the minimum, they can detect over-current will be maximum.Over-current value is calculated at this time
46.875A, then protect the IC protection delay time 380us.
Conclusion 1: The demand for the time fuse in the fuse when 46.875A greater than 380us, short circuit protection to ensure the case before the fuse will not protect the IC fuse.
B: protection circuit anomalies.
P>At this time of short circuit protection IC
can not play a protective effect, when the load short-circuit when the fuse need the fuse quickly.
Considerations are as follows: P>
Batteries Voltage: 3.8 ~ 4.2V
Batteries internal resistance: Protection board resistance: MOS tube fuse resistance + resistance (15mΩ) + PCB board resistance (10mΩ)
Short-circuit load resistance: 0 ~ 100mΩ
Fast blow fuse to be considered, so consider the minimum short-circuit current, short circuit current can be calculated minimum 11A.
Conclusion 2: This requirement 11A fuse in the fuse current to quickly.
General A, B both cases, this protection board select SARTS0603-F-5.0A meet the requirements.
Example 2: A board used to protect lithium battery protection IC for the MM3177, MOSFET as AO8810
A: We can also protect the IC with an oscilloscope to test their short-circuit protection delay time.
Short: The short-circuit test found several protection IC (MM3177) can play a good short-circuit protection, short circuit delay time 11.4ms. Short circuit short circuit current in Figure 7 (short-circuit tests have found that every small change in delay time, whichever is the larger one), then test to short-circuit current of 16.4A.
According to the test conditions used in this section protect the battery protection board IC (MM3177) when doing output short circuit protection delay time of a protection, short circuit current from the test run time in the 15A ~ 20A, MM3177 short-circuit protection delay time 10ms ~ 13ms.
(1) test the S0603-B-5.0A 20A fuse in the fuse as follows in Table 1
Specification S0603-B-5.0A test date 2007-08-16 fuse time test (BXC-35A fuse tester, Tektronix DPO4032 Oscilloscope) test current time / current characteristics (20A) 55.2 ms 51.1 ms 57.1 ms 56.2 ms 61.4 ms 56.4 ms 52.9 ms 60.8 ms 51.9 ms 56.7 ms P>
Table 1 P>
(2) from the test data, S0603-B-5.0A longer than the 20A fuse protection ICMM3177 first with current circumstances to protect the delay time (11ms ~ 13ms).
(3) The battery protection board (using the MM3177) on the use of S0603-B-5.0A fuse, can better play a protective role.
Can be seen from the examples 1,2, select a single lithium battery protection IC fuse to take into account the short-circuit protection time.
III. Sartre fuse technology for lithium battery applications, reference
Technology Development Co., Ltd. Nanjing Sartre chip fuse focus on the development and production, attention to fuse lithium battery market requirements, have launched the S0603-F-5.0A, S0603-BA-5.0A, S0603-B- 5.0A, and other applications on a single lithium battery and fuse, occupied a place in the market. Sartres customers BYD Li-ion battery, battery Desai, Scud batteries. P>