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LTC4089 Datasheet(PDF) 12 Page - Linear Technology |
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LTC4089 Datasheet(HTML) 12 Page - Linear Technology |
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12 / 24 page  LTC4089/LTC4089-5 12 40895fb IIN ILOAD(mA) 0 300 400 500 400 500 300 4089 G01 200 100 100 200 0 ILOAD IBAT (CHARGING) IBAT (IDEAL DIODE) IIN ILOAD(mA) 0 60 80 100 80 100 60 4089 G02 40 20 20 40 0 ILOAD IBAT (CHARGING) IBAT (IDEAL DIODE) ILOAD (mA) 0 300 400 500 400 500 300 4089 G03 200 100 100 200 0 IIN ILOAD IBAT = ICHG IBAT = ICL = IOUT IBAT (CHARGING) IBAT (IDEAL DIODE) input current as well as control battery charge current as a function of IOUT. The input current limit, ICL, can be programmed using the following formula: I R V V R CL CLPROG CLPROG CLPROG = ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ = 1000 1000 • where VCLPROG is the CLPROG pin voltage (typically 1V) and RCLPROG is the total resistance from the CLPROG pin to ground. For best stability over temperature and time, 1% metal film resistors are recommended. The programmed battery charge current, ICHG, is defined as: I R V V R CHG PROG PROG PROG = ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ = 50 000 50 000 , • , Input current, IIN, is equal to the sum of the BAT pin output current and the OUT pin output current. VCLPROG will typically servo to 1V, however, if IOUT + IBAT < ICL then VCLPROG will track the input current according to the following equation: II I V R IN OUT BAT CLPROG CLPROG =+ = • 1000 The current limiting circuitry in the LTC4089/LTC4089-5 can and should be configured to limit current to 500mA for USB applications (selectable using the HPWR pin and programmed using the CLPROG pin). OPERATIO Figure 2. Input and Battery Currents as a Function of Load Current The LTC4089/LTC4089-5 reduces battery charge current such that the sum of the battery charge current and the load current does not exceed the programmed input current limit (one-fifth of the programmed input current limit when HPWR is low, see Figure 2). The battery charge current goes to zero when load current exceeds the programmed input current limit (one-fifth of the limit when HPWR is low). Even if the battery charge current is set to exceed the allowable USB current, the USB specification will not be violated. The battery charger will reduce its current as needed to ensure that the USB specification is not exceeded. If the load current is greater than the current limit, the output voltage will drop to just under the battery voltage where the ideal diode circuit will take over and the excess load current will be drawn from the battery. In USB applications, the minimum value for RCLPROG should be 2.1k. This will prevent the input current from exceeding 500mA due to LTC4089/LTC4089-5 tolerances and quiescent currents. A 2.1k CLPROG resistor will give a typical current limit of 476mA in high power mode (HPWR = 1) or 95mA in low power mode (HPWR = 0). When SUSP is driven to a logic high, the input power path is disabled and the ideal diode from BAT to OUT will supply power to the application. (a) High Power Mode/Full Charge RPROG = 100k and RCLPROG = 2k (b) Low Power Mode/Full Charge RPROG = 100k and RCLPROG = 2k (c) High Power Mode with ICL = 500mA and ICHG = 250mA RPROG = 200k and RCLPROG = 2k |
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