UC3906 VT

qi james

Prodigy 10 points

Other Parts Discussed in Thread: BQ24450, UC3906

Hello Sir,

For 12 V lead-acid battery charge.

What is the Value:Vt

Ra = (Rsum + Rx ) (1 -2.3V /Vt)
where: Rx = Rc*Rd / (Rc + Rd)

Thanks

James

over 13 years ago

0 Chris Glaser over 13 years ago

TI__Guru**** 150930 points

Vt stands for trickle voltage. It is explained on page 6 of this app note: http://www.ti.com/lit/an/slua115/slua115.pdf

Ra sets the voltage at which the IC switches between trickle charge and fast charge. If you will notice, it is this voltage on pin 12 that activates the trickle charge current on pin 11.

I would encourage you to use the bq24450 as its datasheet is newer and easier to read.

0 Matthew Day over 13 years ago

TI__Mastermind 36110 points

The term "Vt" in the UC3906 lead acid battery charger datasheet refers to a customer chosen value. Application note U-104, http://www.ti.com/lit/an/slua115/slua115.pdf, has a very detailed explanation of the UC3906 IC and states that "when the battery voltage is below the resulting threshold, Vt, the driver on the UC3809 is disabled and the trickle bias output goes high." Vt is the customer chosen value for the battery voltage where they want to ensure they charge it with the trickle current.

Power management

Power management forum

UC3906 VT