SM3320-BATT-EV-NOPB Datasheet, PDF (5/21 Pages) Texas Instruments – AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design

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DC/DC Converter
5 DC/DC Converter
The DC/DC converter stage is a step up/step down four switch converter as shown in Figure 4. This stage
transfers the power from the PV panel to the load.
Figure 4. DC/DC Converter Stage
C18, R11, and D15 as shown in the system schematic in Figure 20, form a snubber to reduce ripple on
the switch node on the “Buck” side of the converter. C19,R14 and D14 form a snubber circuit to reduce
ripple on the switch node of the “Boost” side of the converter.
When the circuit operates in Buck mode, the Boost switch node will issue small pulses at a lower
frequency in order to recharge the Bootstrap capacitor of Q2. Likewise, in Boost mode, the Buck switch
node will pulse to recharge the bootstrap capacitor of Q1.
Specific design guidelines for the DC/DC converter can be found in the AN-2124 Power Circuit Design for
SolarMagic SM3320 Application Report (SNOSB84) for power optimizers.
Specific timings related to the switches can be found in SM72442 Programmable Maximum Power Point
Tracking Controller for Photovoltaic Solar Panels (SNVS689) and SM72295 Photovoltaic Full Bridge Driver
(SNVS688).
The waveforms in Figure 5 through Figure 8 are examples of the switching signals of the DC/DC converter
stage.
If the system is to be used at elevated power levels causing high temperature increases in MOSFETs Q1,
Q2, Q3, and/or Q4, we recommend the use of a proper heatsink for the MOSFETs, especially at higher
ambient temperatures. Care must be taken to prevent electrical contact between the drains of the
MOSFETs in the process of proper heatsinking.
Figure 5. Buck Gate Drive Signals From SM72442
Figure 6. Switch Nodes in Buck Mode
SNOSB76C – December 2010 – Revised May 2013
AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference
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