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ISL12082IB8Z-T bảng dữ liệu(PDF) 9 Page - Intersil Corporation |
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ISL12082IB8Z-T bảng dữ liệu(HTML) 9 Page - Intersil Corporation |
9 / 26 page 9 FN6731.3 November 24, 2008 decoupling capacitor is recommended on the VDD pin to ground. Functional Description Power Control Operation The power control circuit accepts a VDD and a VBAT input. Many types of batteries can be used with Intersil RTC products. For example, 3.0V or 3.6V Lithium batteries are appropriate, and battery sizes are available that can power the ISL12082 for up to 10 years. Another option is to use a Supercapacitor for applications where VDD is interrupted for up to a month. See the “Application Section” on page 22 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 ISL12082 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 ISL12082 are active during battery backup mode unless disabled via the control register. Power Failure Detection The ISL12082 provides a Real Time Clock Failure Bit (RTCF, address 0Bh) 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 ISL12082 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™ and ReSeal™ Battery Saver The ISL12082 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 ISL12082 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. 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 ISL12082 |
Số phần tương tự - ISL12082IB8Z-T |
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Mô tả tương tự - ISL12082IB8Z-T |
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