Charging a lead acid battery

AN3971

12/28

Doc ID 022119 Rev 2

The voltage reference, along with one op amp, is the core of the voltage control loop; the

current sensing circuit and the other op amp make up the current control loop.

The external components needed to complete the two control loops are:

●

A resistor divider that senses the output of the power supply and fixes the voltage

regulation set-point at the specified value

●

A sense resistor that feeds the current sensing circuit with a voltage proportional to the

DC output current, setting the current regulation set-point (it must be adequately rated

in terms of power dissipation)

●

The frequency compensation components (R-C networks) for both loops.

Please refer to the SEA05 datasheet for further details.

3.3

Interaction between the SPV1020 and SEA05

The SPV1020 usually sets the duty cycle according to the MPPT algorithm except when

even one of the protection or regulation thresholds is triggered.

voltage feedback loop enters regulation, implying an upper limit to the duty cycle computed

by the MPPT. The higher the voltage on the Vout_sns pin, the lower the upper limit on the

< 1.04 V. If the 1.04 V threshold is triggered then the overvoltage protection forces the burst

mode.

The stability of the regulation loop can be externally regulated by connecting a resistor and a

capacitor (pole-zero compensation) between the PZ_OUT pin and SGND pin.

The PZ_OUT pin may have two different roles:

●

To perform compensation loop to control the Vout_sns behavior

●

To force an imposed duty cycle proportional to its voltage on the pin.

Figure 11.

Internal duty cycle reference

The final duty cycle results from the minimum value between the one due to MPPT

algorithm, and the second one imposed by the PZ_OUT external voltage.

The SEA05 provides two independent internal thresholds designed to separately control

battery voltage and current control.

If one of the two thresholds is triggered, the common output is proportionally forced low, and

the internal duty cycle imposed is proportional too.

Therefore, the output behavior of the SEA05 is perfectly compatible with the PZ_OUT pin of

the SPV1020.