K
Kris Krieger
Guest
Hi, All,
I am looking at a datasheet for a battery charging IC, and at a sample
circuit which uses it in switch-mode.
Firstly, I'm not a student and this is not a homework question; I'm just
trying to learn some things on my own
The sample circuit is for switchmode, and is described as functioning as an
error comparitor - it uses a sensing resistor to turn on/off the V-ch pin
of the IC. ThE datasheet says that, in comparator mode, during "fast
charge", the IC, to quote" "regulates the voltage across the sense resistor
to about -107mV ( V sub fc + 0.5 X V sub hys-fc)".
The value for the sense resistor is given as
V sub fc + 0.5 X V sub hys-fc
R = ---------------------------------
desired current
Under the conditions are that, in the "Electrical Characteristics:
Charging" chart, are Input Voltage is between 4.5V and 16.5V, Temp between
0 deg C and 45 deg C and "fast charge comparator threshold":
V sub fc has
MIN = -127mV, TYP = -121mV, and MAX = -115mV
V sub hys-fc has
MIN = 31mV, TYP = 28mV, and MAX = 25mV
In the example circuit, the current is described as being 1.07A, and the
sense resistor value is 0.1 Ohm. Input voltage is 9V. Now, this is
probably obvious to most of you (sorry) but, am I correct in assuming that
the above means, for me to find the resistor I'd need for an input of 5V
and 500mA, I'd use the following:
121mV + 0.5 X 28mV 107mV
R = ------------------------ = ----------- = 0.214 Ohm
0.5A 0.5A
??
Or do I have it mixed up?
I have a second question. There is a pin for an LED, with an associated 1k
Ohm resistor, that shows the progress/state fo the charging cycle. If I
just left off the LED and its resistor, would that cause an "imbalance" in
the rest of ti circuit? IOW, do I need to keep it in there, or can it just
be left off without mucking up the rest of the works?
Many thanks in Advance!
- Kris
I am looking at a datasheet for a battery charging IC, and at a sample
circuit which uses it in switch-mode.
Firstly, I'm not a student and this is not a homework question; I'm just
trying to learn some things on my own
The sample circuit is for switchmode, and is described as functioning as an
error comparitor - it uses a sensing resistor to turn on/off the V-ch pin
of the IC. ThE datasheet says that, in comparator mode, during "fast
charge", the IC, to quote" "regulates the voltage across the sense resistor
to about -107mV ( V sub fc + 0.5 X V sub hys-fc)".
The value for the sense resistor is given as
V sub fc + 0.5 X V sub hys-fc
R = ---------------------------------
desired current
Under the conditions are that, in the "Electrical Characteristics:
Charging" chart, are Input Voltage is between 4.5V and 16.5V, Temp between
0 deg C and 45 deg C and "fast charge comparator threshold":
V sub fc has
MIN = -127mV, TYP = -121mV, and MAX = -115mV
V sub hys-fc has
MIN = 31mV, TYP = 28mV, and MAX = 25mV
In the example circuit, the current is described as being 1.07A, and the
sense resistor value is 0.1 Ohm. Input voltage is 9V. Now, this is
probably obvious to most of you (sorry) but, am I correct in assuming that
the above means, for me to find the resistor I'd need for an input of 5V
and 500mA, I'd use the following:
121mV + 0.5 X 28mV 107mV
R = ------------------------ = ----------- = 0.214 Ohm
0.5A 0.5A
??
Or do I have it mixed up?
I have a second question. There is a pin for an LED, with an associated 1k
Ohm resistor, that shows the progress/state fo the charging cycle. If I
just left off the LED and its resistor, would that cause an "imbalance" in
the rest of ti circuit? IOW, do I need to keep it in there, or can it just
be left off without mucking up the rest of the works?
Many thanks in Advance!
- Kris