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BQ24705 Datasheet(PDF) 19 Page - Texas Instruments |
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BQ24705 Datasheet(HTML) 19 Page - Texas Instruments |
19 / 32 page ISYNSET SYN SENSE 250 V R = I x R W (5) ISYNSET SRP SRN 3.3V 1 V R SENSE 5kW 20x SYNCH R ISYNSET UCP I=1V/R ISYNSET I SYN HIGH ACCURACY IADAPT USING CURRENT SENSE AMPLIFIER (CSA) INPUT OVERVOLTAGE PROTECTION (ACOV) INPUT UNDERVOLTAGE LOCK OUT (UVLO) bq24705 www.ti.com............................................................................................................................................... SLUS779B – DECEMBER 2007 – REVISED MARCH 2009 IRIPPLE_MAX happens when the duty-cycle, D is mostly near to 0.5 at given Vin, fs,and L. The ISYNSET comparator, or charge undercurrent comparator, compares the voltage between SRP-SRN, and the threshold set by an external resistor RISYNSET, which can be calculated by: Figure 29. ISYNSET Comparator Block An industry standard, high accuracy current sense amplifier (CSA) is used to monitor the input current by the host or some discrete logic through the analog voltage output of the IADAPT pin. The CSA amplifies the input sensed voltage of ACP – ACN by 20x through the IADAPT pin. The IADAPT output is a voltage source 20 times the input differential voltage. Once PVCC is above 5 V and ACDET is above 0.6V, IADAPT no longer stays at ground, but becomes active. If the user wants to lower the voltage, they could use a resistor divider from IOUT to AGND, and still achieve accuracy over temperature as the resistors can be matched their thermal coefficients. A 100-pF capacitor connected on the output is recommended for decoupling high-frequency noise. An additional RC filter is optional, after the 100-pF capacitor, if additional filtering is desired. Note that adding filtering also adds additional response delay. ACOV provides protection to prevent system damage due to high input voltage. The controller enters ACOV when ACDET > 3.1 V and charge is disabled. ACOV is not latched—normal operation resumes when the ACDET voltage returns below 3.1 V. ACOV threshold is 130% of the adapter-detect threshold. The system must have a minimum 4 V PVCC voltage to allow proper operation. This PVCC voltage could come from either input adapter or battery, using a diode-OR input. When the PVCC voltage is below 4 V the bias circuits REGN and VREF stay inactive, even with ACDET above 0.6 V. Copyright © 2007–2009, Texas Instruments Incorporated Submit Documentation Feedback 19 Product Folder Link(s) :bq24705 Not Recommended for New Designs |
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