- Wed Dec 12, 2012 6:27 pm
#153141
As I read the LTC4412 datasheet, the Vin (Vcc ?) is the battery voltage. It gets switched (or not) to the load by an external FET which is controlled, on or off, by the Gate signal. The Sense signal is connected after the FET (on the load side) and whenever it sees a voltage that's >20 mV above the Vin level, it turns the FET off. The Stat signal is an open drain that can be used to let other circuitry know the state of the Gate signal.
So as I understand it, yes it's for switching between a battery and another source. You still need a low voltage cutoff. You might be able to use this (2 of them) in place of the steering diodes that your design (above) has to connect the 2 LiPos. But it's tricky. You've set yourself for a more complicated situation than your premise of "a circuit that functions similar to what a laptop would do: when it's plugged in, it charges the battery, and when unplugged it runs off of battery". By requiring that you have redundant batteries, you now require each battery to have enough capacity to run everything on it's own (for some period of time). And because you might hot swap a dead or failed battery, you can't just wire the 2 LiPos in parallel because their state of charge (SOC) might be drastically different (even if they're otherwise matched batteries). That then means you have to have 2 separate charging circuits for the 2 separate LiPos. Which then means 2 diodes to combine the LiPo outputs ... or 2 of these ... maybe. I'm not sure how these would work. I'd guess that tying the load to the output side of the 2 FETs would mean that only 1 LiPo is running everything at any one time, until the SOCs equalize. And then some load sharing might happen, or perhaps the LTC4412's will be switching back and forth as the current draw through each LiPos internal resistance changes their respective output voltages. I dunno.
I have a failing memory that some one-IC-to-rule-them-all LiPo switching/charging/cutoff IC was previously discussed in this forum. Alas I can't recall the thread or part number. I wonder if the LTC1479 might be that part ?
The LTC®1479 is the “heart” of a total power management solution for single and dual battery notebook computers
and other portable equipment. The LTC1479 directs power from up to two battery packs and a DC power source to the
input of the main system switching regulator. It works in concert with related LTC power management products
(e.g. LTC1435, LT®1511, etc.) to create a total system solution; starting from the batteries and the DC power
source, and ending at the input of each of the computer’s complex loads. A system-provided power management
mP monitors and actively directs the LTC1479.
The LTC1479 uses low loss N-channel MOSFET switches to direct power from three main sources. An adaptive
current limiting scheme reduces capacitor and battery inrush current by controlling the gates of the MOSFET
switches during transitions. The LTC1479 interfaces directly to the LT1510, LT1511 and LT1620/LTC1435 battery
charging circuits.
Battery Voltage Monitoring
The LTC1479 has the ability to independently monitor both battery packs. (Because of this, one battery pack may be
discharged as the other is being charged.) A low-battery detector signals when the selected battery pack has dropped to the level where a shutdown sequence should be initiated or the other battery pack engaged.
(click on to enlarge)
So as I understand it, yes it's for switching between a battery and another source. You still need a low voltage cutoff. You might be able to use this (2 of them) in place of the steering diodes that your design (above) has to connect the 2 LiPos. But it's tricky. You've set yourself for a more complicated situation than your premise of "a circuit that functions similar to what a laptop would do: when it's plugged in, it charges the battery, and when unplugged it runs off of battery". By requiring that you have redundant batteries, you now require each battery to have enough capacity to run everything on it's own (for some period of time). And because you might hot swap a dead or failed battery, you can't just wire the 2 LiPos in parallel because their state of charge (SOC) might be drastically different (even if they're otherwise matched batteries). That then means you have to have 2 separate charging circuits for the 2 separate LiPos. Which then means 2 diodes to combine the LiPo outputs ... or 2 of these ... maybe. I'm not sure how these would work. I'd guess that tying the load to the output side of the 2 FETs would mean that only 1 LiPo is running everything at any one time, until the SOCs equalize. And then some load sharing might happen, or perhaps the LTC4412's will be switching back and forth as the current draw through each LiPos internal resistance changes their respective output voltages. I dunno.
I have a failing memory that some one-IC-to-rule-them-all LiPo switching/charging/cutoff IC was previously discussed in this forum. Alas I can't recall the thread or part number. I wonder if the LTC1479 might be that part ?
The LTC®1479 is the “heart” of a total power management solution for single and dual battery notebook computers
and other portable equipment. The LTC1479 directs power from up to two battery packs and a DC power source to the
input of the main system switching regulator. It works in concert with related LTC power management products
(e.g. LTC1435, LT®1511, etc.) to create a total system solution; starting from the batteries and the DC power
source, and ending at the input of each of the computer’s complex loads. A system-provided power management
mP monitors and actively directs the LTC1479.
The LTC1479 uses low loss N-channel MOSFET switches to direct power from three main sources. An adaptive
current limiting scheme reduces capacitor and battery inrush current by controlling the gates of the MOSFET
switches during transitions. The LTC1479 interfaces directly to the LT1510, LT1511 and LT1620/LTC1435 battery
charging circuits.
Battery Voltage Monitoring
The LTC1479 has the ability to independently monitor both battery packs. (Because of this, one battery pack may be
discharged as the other is being charged.) A low-battery detector signals when the selected battery pack has dropped to the level where a shutdown sequence should be initiated or the other battery pack engaged.
(click on to enlarge)
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