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ISL6292EVAL2 Datasheet(PDF) 11 Page - Intersil Corporation |
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ISL6292EVAL2 Datasheet(HTML) 11 Page - Intersil Corporation |
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11 / 19 page  11 FN9105.6 July 25, 2005 The following events initiate a new charge cycle: •POR, • a new battery being inserted (detected by TEMP pin), • the battery voltage drops below a recharge threshold after completing a charge cycle, • recovery from an battery over-temperature fault, • or, the EN pin is toggled from GND to floating. Further description of these events are given later in this data sheet. Recharge After a charge cycle completes, charging is prohibited until the battery voltage drops to a recharge threshold, VRECHRG (see Electrical Specifications). Then a new charge cycle starts at point t6 and ends at point t8, as shown in Figure 19. The safety timer is reset at t6. Internal Oscillator The internal oscillator establishes a timing reference. The oscillation period is programmable with an external timing capacitor, CTIME, as shown in Typical Applications. The oscillator charges the timing capacitor to 1.5V and then discharges it to 0.5V in one period, both with 10 µA current. The period TOSC is: (EQ. 3) A 1nF capacitor results in a 0.2ms oscillation period. The accuracy of the period is mainly dependent on the accuracy of the capacitance and the internal current source. Total Charge Time The total charge time for the CC mode and CV mode is limited to a length of TIMEOUT. A 22-stage binary counter increments each oscillation period of the internal oscillator to set the TIMEOUT. The TIMEOUT can be calculated as: (EQ. 4) A 1nF capacitor leads to 14 minutes of TIMEOUT. For example, a 15nF capacitor sets the TIMEOUT to be 3.5 hours. The charger has to reach the end-of-charge condition before the TIMEOUT, otherwise, a TIMEOUT fault is issued. The TIMEOUT fault latches up the charger. There are two ways to release such a latch-up: either to recycle the input power, or toggle the EN pin to disable the charger and then enable it again. The trickle mode charge has a time limit of 1/8 TIMEOUT. If the battery voltage does not reach VMIN within this limit, a TIMEOUT fault is issued and the charger latches up. The charger stays in trickle mode for at least 15 cycles of the internal oscillator and, at most, 1/8 of TIMEOUT, as shown in Figure 19. Disabling TIMEOUT Limit The TIMEOUT limit for the fast charge modes can be disabled by pulling the TOEN pin to LOW or shorting it to GND. When this happens, the charger becomes a current- limited LDO (low-dropout) supply with its voltage regulated at the final charge voltage VCH and the current limit determined by the IREF pin. If the LDO load current drops below the end-of-charge current (refer to End-of-Charge section), the STATUS pin will indicate. The trickle charge time limit, however, is not disabled even when the TOEN pin is pulled to LOW. The charger operates in the trickle mode at the beginning of a charge cycle even if the TIMEOUT is disabled. Leaving the TOEN pin floating is recommended to enable the TIMEOUT. Driving the TOEN pin above 3.0V is not recommended. Charge Current Programming The charge current is programmed by the IREF pin. There are three ways to program the charge current: 1. driving the IREF pin above 1.3V 2. driving the IREF pin below 0.4V, 3. or using the RIREF as shown in the Typical Applications. The voltage of IREF is regulated to a 0.8V reference voltage when not driven by any external source. The charging current during the constant current mode is 100,000 times that of the current in the RIREF resistor. Hence, depending on how IREF pin is used, the charge current is, (EQ. 5) The 500mA current is a guaranteed maximum value for high-power USB port, with the typical value of 450mA. The 100mA current is also a guaranteed maximum value for the low-power USB port. This design accommodates the USB power specification. The internal reference voltage at the IREF pin is capable of sourcing less than 100 µA current. When pulling down the IREF pin with a logic circuit, the logic circuit needs to be able to sink at least 100 µA current. When the adapter is current limited, it is recommended that the reference current be programmed to at least 30% higher than the adapter current limit (which equals the charge current). In addition, the charge current should be at least 350mA so that the voltage difference between the VIN and the VBAT pins is higher than 100mV. The 100mV is the offset voltage of the input-output voltage comparator shown in the block diagram. TOSC 0.2 10 6 CTIME ⋅ ⋅ = onds sec () TIMEOUT 2 22 TOSC 14 CTIME 1nF ------------------ ⋅ = ⋅ = minutes () IREF 500mA 0.8V RIREF ----------------- 10 5 × A () 100mA = VIREF 1.3V > RIREF VIREF 0.4V < ISL6292 |
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