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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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MAX8725ETI Datenblatt(PDF) 21 Page - Maxim Integrated Products |
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MAX8725ETI Datenblatt(HTML) 21 Page - Maxim Integrated Products |
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21 / 30 page  Multichemistry Battery Chargers with Automatic System Power Selector ______________________________________________________________________________________ 21 • IMIN: Compares the control point (LVC) against 0.15V (typ). If IMIN output is low, then a new cycle cannot begin. This comparator determines whether the regulator operates in discontinuous mode. • IMAX: Compares the charge current (CSI) to the internally fixed cycle-by-cycle current limit. The current-sense voltage limit is 97mV. With RS2 = 0.015Ω, this corresponds to 6A. The high-side MOSFET on-time is terminated if the IMAX output is high and a new cycle cannot begin until IMAX goes low. IMAX protects against sudden overcurrent faults. • ZCMP: Compares the charge current (CSI) to 333mA (RS2 = 0.015Ω). The current-sense voltage threshold is 5mV. If ZCMP output is high, then both MOSFETs are turned off. The ZCMP comparator terminates the switch on-time in discontinuous mode. CCV, CCI, CCS, and LVC Control Blocks The MAX1909/MAX8725 control charge voltage (CCV control loop), charge current (CCI control loop), or input current (CCS control loop), depending on the operating conditions. The three control loops, CCV, CCI, and CCS, are brought together internally at the LVC amplifier. The output of the LVC amplifier is the feedback control signal for the DC-DC controller. The minimum voltage at CCV, CCI, or CCS appears at the output of the LVC amplifier and clamps the other two control loops to within 0.3V above the control point. Clamping the other two control loops close to the lowest control loop ensures fast transition with minimal overshoot when switching between different control loops (see the Compensation section). Continuous Conduction Mode With sufficient battery current loading, the MAX1909/ MAX8725s’ inductor current never reaches zero, which is defined as continuous conduction mode. If the BATT voltage is within the following range: 3.1V ✕ (number of cells) < VBATT < (0.88 ✕ VDCIN) the regulator is not in dropout and switches at fNOM = 400kHz. The controller starts a new cycle by turning on the high-side p-channel MOSFET and turning off the low-side n-channel MOSFET. When the charge current is greater than the control point (LVC), CCMP goes high and the off-time is started. The off-time turns off the high-side p-channel MOSFET and turns on the low-side n-channel MOSFET. The operating frequency is gov- erned by the off-time and is dependent upon VDCIN and VBATT. The off-time is set by the following equation: where fNOM = 400kHz: These equations describe the controller’s pseudo-fixed- frequency performance over the most common operat- ing conditions. At the end of the fixed off-time, the controller can initiate a new cycle if the control point (LVC) is greater than 0.15V (IMIN = high) and the peak charge current is less than the cycle-by-cycle limit (IMAX = low). If the charge current exceeds IMAX, the on-time is terminated by the IMAX comparator. If during the off-time the inductor current goes to zero, ZCMP = high, both the high- and low-side MOSFETs are turned off until another cycle is ready to begin. This condition is discontinuous conduction. See the Discontinuous Conduction section. There is a minimum 0.3µs off-time when the (VDCIN - VBATT) differential becomes too small. If VBATT ≥ 0.88 x VDCIN, then the threshold for minimum off-time is reached and the tOFF is fixed at 0.3µs. The switching frequency in this mode varies according to the equation: Discontinuous Conduction The MAX1909/MAX8725 enter discontinuous-conduc- tion mode when the output of the LVC control point falls below 0.15V. For RS2 = 0.015Ω, this corresponds to 0.5A: where RS2 = 0.015Ω. I V RS A MIN = × = 015 20 2 05 . . f t V VV OFF BATT CSSN BATT = − + 1 1 f tt ON OFF = + 1 where I Vt L RIPPLE BATT OFF = × t LI VV ON RIPPLE CSSN BATT = × − t f VV V OFF NOM CSSN BATT CSSN = − 1 |
Ähnliche Teilenummer - MAX8725ETI |
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Ähnliche Beschreibung - MAX8725ETI |
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