I wonder if you could comment on my design for a 10 amp charger for a 12 volt SLA battery. It will be AC powered with a DC input of 16 volts when the AC is 115 VAC.
Other design parameters are fast charge at 14.7 volts, float at 13.5 volts, and final discharge of 10.5 volts.
I am also interested in any comments on my selection of the FQP47P06 as a pass element.
Also do I really need D1 since the battery is over 100AH, the discharge thru the circuitry is trivial?
I am also not sure about the values for Rt and Rp. I calculated the value for Rp from the evaluation module notes.
I calculated Rt based on: It = Vin - Vt - Vdrop/Rt, where It = .025 amps.
I guess I don't understand how this forum works.
I thought someone from TI occasionally perused the forum and responded to questions.
Did I post in the wrong area or something?
It is best to contact the local Field Rep.
Apparently TI is not interested in helping.
Anyone else have any comments?
The nature of the subject makes it somewhat difficult to verify a design without possible damage to an expensive battery, so any and all comments will be appreciated.
Pertinent parameters of the FQP47P06 are:
60V P-Channel MOSFET
Absolute Maximum Ratings TC = 25°C unless otherwise notedDrain-Source Voltage -60 VDrain Current - Continuous (TC = 25°C) -47 A - Continuous (TC = 100°C) -33.2 ADrain Current - Pulsed -188 AGate-Source Voltage ± 25 VSingle Pulsed Avalanche Energy 820 mJAvalanche Current (Note 1) -47 ARepetitive Avalanche Energy (Note 1) 16 mJPeak Diode Recovery dv/dt (Note 3) -7.0 V/nsPD Power Dissipation (TC = 25°C) 160 W - Derate above 25°C 1.06 W/°C
Off CharacteristicsDrain-Source Breakdown Voltage VGS = 0 V, ID = -250 μA -60 -- -- VZero Gate Voltage Drain Current VDS = -60 V, VGS = 0 V -- -- -1 μA VDS = -48 V, TC = 150°C -- -- -10 μA
On CharacteristicsGate Threshold Voltage VDS = VGS, ID = -250 μA -2.0 -- -4.0 VStatic Drain-Source On-Resistance VGS = -10 V, ID = -23.5 A -- 0.021 0.026 ΩForward Transconductance VDS = -30 V, ID = -23.5 A -- 21 -- S
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Did you ever get your issue resolved? I am trying to design a charger using a PFET and there is not very good information out there. In looking at your design I have the following questions:
How did you calculate a value for Rp?
Do you not need a Dext because of the diode in the PFET?
Does the PFET shut off properly or did you need to add a resistor between the Gate and Source?
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