Assessments - 3, GPA: 4.3
(
)
)
|
Facilidade de uso
The 34676 is a dual 28V input voltage and fully-integrated single cell Li-Ion battery charger, targeting smart handheld applications. One of the inputs is optimized for charging with a USB port, and the second is optimized for an AC/DC adapter power source. The charger has two 28V power devices, to eliminate the need of any external power source selection and input over-voltage protection circuitry. Each of the power devices independently controls the charge current from the input, and performs as an independent charger. Only one of the two chargers operate at a time. The AC charger current and the USB charger current are programmable, up to 1.2A and 400mA, with an external resistor respectively. The voltage across the two external resistors is also used to monitor the actual charge current through each charger respectively. The EOC current of both chargers is the same, and programmable by an external resistor. The 4.85V regulator can be used to power a sub-system directly. The 34676 has a 5% constant current accuracy for the AC Charger over -40 to 85oC, and a 1.0% constant voltage accuracy over -40 to 85oC. A charge current thermal foldback feature, limits the charge current when the IC internal temperature rises to a preset threshold. 3.1Dual-Input Standalone Charger The MC34676B can be used as a dual-input standalone Li-Ion charger. Figure 1 is the typical application circuit. Two LEDs indicate the charge status. MC34676BACCHGISETPPRUSBUSBOUTBATBATDETUSBENGNDIMINIUSBOFFONC2C1RIMINRIUSBRISETC3C4 Figure 1. The dual-input Li-Ion Charger 3.2Embedded Charger When the MC34676B is embedded in the system, the system MCU can control the charger through the USBEN pin and get the charge status through PPR and CHG pins. Figure 2 is the typical application circuit. ACUSBGNDIMINIUSBISETCHGPPRUSBOUTBATVDDIOMCUMC34676BACUSBC1C2RIMINRIUSBRISETC3C4USBENBATDET Figure 2. The Li-Ion Charger Embedded in the Hand Held System The evaluation board is designed to work as a standalone charger, or as an embedded charger in a handheld system. Figure 3 shows its schematic circuit. The normal operation range of the evaluation board is: For AC charger: VAC_MIN = 4.3V, VAC_MAX = 6.8V IAC_MAX = 1200mA For USB charger: VUSB_MIN = 4.3V, VUSB_MAX = 5.85V IUSB_MAX = 400mA J10HDR_1X212J11HDR_1X212R913.3KR813.0KBATBATR11200KC51.0UFR1028.7KJ12HDR_1X212R36.49R213.0KR126.1KTP26IUSBU1MC34676BAC1USB2PPR3CHG4USBEN5IMIN6IUSB7GND8ISET9USBOUT10BAT11BATDET12E- PADTP28IMINC2NCTP1AC1TP10VLogic1TP13USBEN1R5470 OHMR4470 OHMTP3USB1J5HDR_1X3123J4HDR_1X3123R7100KR6100KD2GREEN21D1RED21TP25GNDJ13HDR_1X212TP17USBTP22/CHGTP15ACTP16BATDETTP18VBATTP19USBOUTTP24GNDTP23GNDTP20ISETTP27USBENTP21/PPRTP11/CHG1TP7/PPR1J2HDR_1X212J1HDR_1X212J3HDR_1X212JH12J6HDR_1X212J9HDR_1X212J8HDR_1X212C41.0UFC31.0UFC11.0UFBAT Figure 3. The Schematic Circuit of the Evaluation Board 5.1Input capacitors C1 and C3 The input capacitor is used to minimize the input voltage transient that may cause instability. A ceramic capacitor of 1.0.F or above is required for most applications. X5R and X7R dielectrics have better temperature stability. The evaluation board uses 1.0.F X5R ceramic capacitors. Considering the maximum input voltage rating of the MC34676B is 28V, the input capacitor must have 16V DC rated voltage. 5.2Output capacitors C4 and C5 The charger output capacitor is used for stable operation. An X5R ceramic capacitor minimum of a 1.0.F is required for the charger output. Depending on the load transient current, a larger capacitance may be required. Because the highest output voltage of the MC34676B is 4.2V, a 6.3V DC rated voltage is high enough for the output capacitor. The regulator output capacitor is used for stable operation, too. An X5R ceramic capacitor minimum of a 1.0.F is required for the regulator output. A 6.3V DC rated voltage is high enough for the regulator output capacitor because the highest output voltage of the output regulator is 5V. 5.3AC CC-mode charge current setting resistors R1, R2, and R3 The resistor between the ISET pin and GND sets the AC CC-mode charge current by the following equation: IAC3950RISET--------------= where RISET is in units of ., IAC is in units of amps. A metal film with a 1% tolerance resistor should be used for temperature stability. As a result, the charge current will be accurate over the whole temperature range. On the evaluation board, three resistors with two pin header jumpers are used for the user to conveniently configure different charge current values. Table 1 shows the charge current with the different settings of pin headers J6 and J7. 5.4USB CC-mode charge current setting resistors R8 and R9 The resistor between the IUSB pin and GND sets the USB CC-mode charge current by the following equation: IUSB1975RIUSB--------------= where RUSB is in units of ., IUSB is in units of amps. A metal film with a 1% tolerance resistor should be used for temperature stability. As a result, the charge current will be accurate over the whole tem...