Voltage regulators with fast charge

Thread Starter

dweeb4

Joined Apr 18, 2011
21
I noticed in using a TPS7A4700 voltage regulator to charge a battery & it keeps outputting max current until just before the set voltage is reached - when the current drops off fairly quickly. This is exactly the characteristics I want in a voltage regulator as I'm using it to quickly bring a battery to a set voltage as quickly as possible & more importantly to retain it neat to that set voltage as power is being drawn from the battery. But most voltage regs significantly reduce current output as the load approaches the set voltage.

I see in the block diagram of the TPS7A4700 a block called "fast charge" but no mention of it in the datasheet text. I guess it is a type of internal constant current control - there's no external setting for this current OR maybe the device is running at it's current limit until near the set voltage? I'm wondering if there are other Vregs that operate in this manner?

I know that a CC/CV method is recommended for charging a battery which is fine for initial charging but as I said, I want to try to maintain the battery as near to the set voltage as possible even when current is being drawn from it by a load - I guess this is dependent on where the regulator moves out of CC & into CV mode? - I want this to be as close as possible to the set voltage so even when the battery drops 0.5V, I want it to be recharged back asap.

Any thoughts? Anybody know how this is implemented inside the TPS7A470x regulators or know of other regulators (I need 1A or greater output) that have this characteristic?
 

mvas

Joined Jun 19, 2017
537
There are many CC/CV charging circuits on the AAC website and others.
Do you have the URL link showing the schematic for the TPS7A4700 being used as CC/CV Battery Charger?

I do not think the TPS7A4700 provides CC mode internally, except for amps overload protection:
"...
7.3.1 Internal Current Limit (ICL)
The internal current limit circuit is used to protect the LDO against high-load current faults or shorting events. The
LDO is not designed to operate at a steady-state current limit. During a current-limit event, the LDO sources
constant current. Therefore, the output voltage falls while load impedance decreases. Note also that when a
current limit occurs while the resulting output voltage is low, excessive power is dissipated across the LDO,
which results in a thermal shutdown of the output.
..."

Additional circuitry can be wrapped around the TPS7A4700 to make it a CC/CV charger.
What TYPE of Battery are you charging?
Using a CC/CV Charger with the battery under load can be tricky.

I do not think the term "Fast Charge" in the block diagram has anything to do with Battery Charging
since the target applications for this device are not as a Battery Charger.
 
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Thread Starter

dweeb4

Joined Apr 18, 2011
21
There are many CC/CV charging circuits on the AAC website and others.
Do you have the URL link showing the schematic for the TPS7A4700 being used as CC/CV Battery Charger?

I do not think the TPS7A4700 provides CC mode internally, except for amps overload protection:
"...
7.3.1 Internal Current Limit (ICL)
The internal current limit circuit is used to protect the LDO against high-load current faults or shorting events. The
LDO is not designed to operate at a steady-state current limit. During a current-limit event, the LDO sources
constant current. Therefore, the output voltage falls while load impedance decreases. Note also that when a
current limit occurs while the resulting output voltage is low, excessive power is dissipated across the LDO,
which results in a thermal shutdown of the output.
..."
Ok, that's what I suspected was happening - it's running at current limit - I'm not using it in CC/CV circuit. I have it heatsinked so don't get thermal shutdown of the chip but still not good for the chip.
Additional circuitry can be wrapped around the TPS7A4700 to make it a CC/CV charger.
What TYPE of Battery are you charging?
Using a CC/CV Charger with the battery under load can be tricky.
Lithium nano Phosphate battery

I do not think the term "Fast Charge" in the block diagram has anything to do with Battery Charging
since the target applications for this device are not as a Battery Charger.
Sure, I knew that but I see this "fast charge" function block in the block diagram but nothing about it in the text
 

Thread Starter

dweeb4

Joined Apr 18, 2011
21
What I notice with the TPS7A4700 is that when I draw current from the battery, the TPS reg begins to recharge almost immediately within a small voltage drop away from the set voltage. But more importantly, it does so at a high 1 Amp current charge, not the usual scaled back current that other Vregs seem to follow when the load is near the set voltage.

I'm wondering what it is in the TPS reg that is giving me this characteristic - that's why I thought it involved the "fast charge" block?
 
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