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UC2909MDWREP датащи(PDF) 11 Page - Texas Instruments |
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UC2909MDWREP датащи(HTML) 11 Page - Texas Instruments |
11 / 21 page RG1 RG2 ¾ = 5 · V RS ¾ VLOGIC CA- - = 5 · V RS ¾ 5 - 2.3 V V = 5 · V RS ¾ 2.7 V = I RS 1.852 · · BULK ITC = ¾ I RG TRCK_CONTROL · 1 RS · 5 V = V OC REF ( ) · ( 1 + 2 + 3 RS RS RS RS4) ¾ ( 3 RS RS4) UC2909-EP www.ti.com SLUSA72 – JULY 2010 Control Loop Current Sense Amplifier This amplifier measures the voltage across the sense resistor RS with a fixed gain of five and an offset voltage of 2.3 V. This voltage is proportional to the battery current. The most positive voltage end of RS is connected to CSensuring the correct polarity going into the PWM comparator. CSO = 2.3 V when there is zero battery current. RS is chosen by dividing 350 mV by the maximum allowable load current. A smaller value for RS can be chosen to reduce power dissipation. Maximum charge current, Ibulk, is set by knowing the maximum voltage error amplifier output, VOH = 5 V, the maximum allowable drop across RS, and setting the resistors RG1 and RG2 such that: (4) The maximum allowable drop across RS is specified to limit the maximum swing at CSO to approximately 2 V to keep the CSO amplifier output from saturating. No charge/load current: VCSO = 2.3 V Max charge/load current: Vmax(CSO) = 2.3 V - 2 V = 0.3 V Voltage Error Amplifier The voltage error amplifier (VEA) senses the battery voltage and compares it to the 2.3-V - 3.9-mV/°C thermistor generated reference. Its output becomes the current command signal and is summed with the current sense amplifier output. A 5-V voltage error amplifier upper clamp limits maximum load current. During the trickle charge state, the voltage amplifier output is opened (high impedance output) by the charge enable comparator. A trickle bias current is summed into the CA- input which sets the maximum trickle charge current. The VEA, VOH = 5 V clamp saturates the voltage loop and consequently limits the charge current as stated in Equation 4. During the trickle bias state the maximum allowable charge current (ITC) is similarly determined: (5) ITRCK_CONTROL is the fixed control current into CA-. ITRCK_CONTROL is 10 µA when RSET = 11.5 KΩ. See RSET pin description for equation. Current Error Amplifier The current error amplifier (CA) compares the output of the current sense amplifier to the output of the voltage error amplifier. The output of the CA forces a PWM duty cycle which results in the correct average battery current. With integral compensation, the CA will have a very high DC current gain, resulting in effectively no average DC current error. For stability purposes, the high frequency gain of the CA must be designed such that the magnitude of the down slope of the CA output signal is less than or equal to the magnitude of the up slope of the PWM ramp. Charge Algorithm Trickle Charge State STAT0 = STAT1 = STATLV = logic 0 When CHGNB is less than VREF (2.3 V - 3.9 mV/°C), STATLV is forced low. This decreases the sense voltage divider ratio, forcing the battery to overcharge (VOC). (6) Copyright © 2010, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): UC2909-EP |
Аналогичный номер детали - UC2909MDWREP |
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Аналогичное описание - UC2909MDWREP |
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