Hi all,
For charging 12V 7.2Ah lead acid batteries, I choose to use the bq24450 charger.
I made a test pcb with the schematic of figure 8 in the datasheet (with Dext added, and common-emitter pnp external trasistor)
These are the values of the resistors I use:
Rc: 47900E, Rd: 592k, Ra: 214k6, Rb: 20k, Rt: 350E, Risns: 0.33E, and 1D4001 for Dext, and TIP30C for Qext.
Rp: 100E
These are my expected values:
Vth: 10.5 V , Vboost: 14.1 V , Vfloat: 13.5 , Imax is 280mA (due to Rp being 100E)
I have a high efficienty led connected with its kathode to STAT2, with a 4k7 resistor, from Vin.
The problem is, whenever I touch Vfb, or CE (directly on the IC, or on a resistor) the IC toggles between Boost and Float states. Either I touch it with my finger/hand, or with a measurement probe, it switches states.
When in float mode, the battery voltage = 13.5, and Vfb = 2.3V, and Ichg slowly increases.
Then a touch appears, and the LED lights up, battery voltage = 14V, and Vfb is around 2.0 - 2.2V
How can this appear?
And how can I make sure the charger boosts, and then floats when full?
Thank you in advance!
M Nijkamp