Such as: mobile phone, PDA, GPS, etc. Vehicle charger should not only consider the actual demand of lithium battery charging (constant voltage CV, constant current CC, overvoltage protection OVP), but also consider the harsh environment of vehicle battery (transient peak voltage, system switching noise interference, EMI, etc.). ); Therefore, the power management IC selected in the vehicle charging scheme must meet the requirements of high voltage resistance, high efficiency, high reliability and low frequency (conducive to EMI design).
Common car charging schemes are briefly described as follows:
[1] Schematic diagram of low-end car charging scheme realized by single chip microcomputer 34063A
Advantages: low cost;
Disadvantages:
(1) has poor reliability and single function; No safety measures such as over-temperature protection and short-circuit protection;
(2) Although the output is DC voltage, the way to control the output constant current charging current is the maximum switching current peak limit, and the accuracy is not high enough;
(3) Because 34063 is 1.5A switching current PWM+PFM mode (there is no error amplifier inside).
The DC voltage and current ripple output by the on-board charging scheme is relatively large and not pure enough; The output current capability is also very good.
Limit; (common in low-end car charging schemes between 300 ma and 600 ma)
[2] Schematic diagram of vehicle charging scheme with 34063+NPN (NMOS) for current expansion.
Advantages: Based on the [1] scheme, the current is expanded to meet the increasing demand for charging current capacity.
Disadvantages: [1] The scheme has similar disadvantages.
[3] Schematic diagram of using 2576+358+ voltage regulator.
Advantages:
(1) Because 2576 has built-in safety measures such as over-current protection and over-temperature protection, it has realized functions such as constant voltage CV, constant current CC and over-voltage protection OVP by combining with 358 (dual operational amplifier). A reliable, safe and perfect lithium battery charging scheme is realized.
(2) Because 2576 is a fixed 52K PWM converter, the EMI design of vehicle charger is relatively easy.
(3) Because both 2576 and 358 are manufactured by 40V high-voltage bipolar process, they are more "solid".
(4) This scheme is commonly used in 0.8A ~ 1.5A car charger;
Disadvantages:
(1) system is relatively complex and the cost is high.
(2) Constant current CC and overvoltage protection OVP are realized by the output of 358 controlling the EN of 2576, so the charging current ripple is relatively large, and the response speed of CC and OVP is not fast enough (realized by switching whether 2576 works or not).
[4] XLSEMI design schematic diagram of single-vehicle charging IC XL4002
Based on the system requirements in the field of vehicle charging, a series of single-chip ics dedicated to vehicle charging schemes are provided. In addition to the conventional over-current protection, over-temperature protection and output short-circuit protection, CV, CC and OVP special for lithium battery charging are also built in. It is equivalent to integrating all functional modules such as 2576+358+ voltage regulator in scheme [3] into one IC.