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ISL1208IRT8Z-TK 数据表(PDF) 9 Page - Intersil Corporation |
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ISL1208IRT8Z-TK 数据表(HTML) 9 Page - Intersil Corporation |
9 / 24 page 9 FN8085.8 September 12, 2008 the ISL1208 for up to 10 years. Another option is to use a Super Cap for applications where VDD is interrupted for up to a month. See the “Application Section” on page 18 for more information. Normal Mode (VDD) to Battery Backup Mode (VBAT) To transition from the VDD to VBAT mode, both of the following conditions must be met: Condition 1: VDD < VBAT - VBATHYS where VBATHYS ≈ 50mV Condition 2: VDD < VTRIP where VTRIP ≈ 2.2V Battery Backup Mode (VBAT) to Normal Mode (VDD) The ISL1208 device will switch from the VBAT to VDD mode when one of the following conditions occurs: Condition 1: VDD > VBAT + VBATHYS where VBATHYS ≈ 50mV Condition 2: VDD > VTRIP + VTRIPHYS where VTRIPHYS ≈ 30mV These power control situations are illustrated in Figures 9 and 10. The I2C bus is deactivated in battery backup mode to provide lower power. Aside from this, all RTC functions are operational during battery backup mode. Except for SCL and SDA, all the inputs and outputs of the ISL1208 are active during battery backup mode unless disabled via the control register. The User SRAM is operational in battery backup mode down to 2V. Power Failure Detection The ISL1208 provides a Real Time Clock Failure Bit (RTCF) to detect total power failure. It allows users to determine if the device has powered up after having lost all power to the device (both VDD and VBAT). Low Power Mode The normal power switching of the ISL1208 is designed to switch into battery backup mode only if the VDD power is lost. This will ensure that the device can accept a wide range of backup voltages from many types of sources while reliably switching into backup mode. Another mode, called Low Power Mode, is available to allow direct switching from VDD to VBAT without requiring VDD to drop below VTRIP. Since the additional monitoring of VDD vs VTRIP is no longer needed, that circuitry is shut down and less power is used while operating from VDD. Power savings are typically 600nA at VDD = 5V. Low Power Mode is activated via the LPMODE bit in the control and status registers. Low Power Mode is useful in systems where VDD is normally higher than VBAT at all times. The device will switch from VDD to VBAT when VDD drops below VBAT, with about 50mV of hysteresis to prevent any switchback of VDD after switchover. In a system with a VDD = 5V and backup lithium battery of VBAT = 3V, Low Power Mode can be used. However, it is not recommended to use Low Power Mode in a system with VDD = 3.3V ±10%, VBAT ≥ 3.0V, and when there is a finite I-R voltage drop in the VDD line. InterSeal™ Battery Saver The ISL1208 has the InterSeal™ Battery Saver which prevents initial battery current drain before it is first used. For example, battery-backed RTCs are commonly packaged on a board with a battery connected. In order to preserve battery life, the ISL1208 will not draw any power from the battery source until after the device is first powered up from the VDD source. Thereafter, the device will switchover to battery backup mode whenever VDD power is lost. Real Time Clock Operation The Real Time Clock (RTC) uses an external 32.768kHz quartz crystal to maintain an accurate internal representation of second, minute, hour, day of week, date, month, and year. The RTC also has leap-year correction. The clock also corrects for months having fewer than 31 days and has a bit that controls 24-hour or AM/PM format. When the ISL1208 powers up after the loss of both VDD and VBAT, the clock will not begin incrementing until at least one byte is written to the clock register. VBAT - VBATHYS VBAT VBAT + VBATHYS BATTERY BACKUP MODE VDD VTRIP 2.2V 1.8V FIGURE 9. BATTERY SWITCHOVER WHEN VBAT < VTRIP FIGURE 10. BATTERY SWITCHOVER WHEN VBAT > VTRIP VTRIP VBAT VTRIP + VTRIPHYS BATTERY BACKUP MODE VDD VTRIP 3.0V 2.2V ISL1208 |
类似零件编号 - ISL1208IRT8Z-TK |
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类似说明 - ISL1208IRT8Z-TK |
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