DC/DC converter
Panel Mode
Bi-directional switch
SM72445
SM72295
Curr.
Sense amp.
Comparator
Temp. sensor
PV
Panel
L
O
A
D
PWM signal
Gate Drive
Current
sense
Input
Current
sense
Input voltage
sense
Output voltage
sense
Protection trigger
Out current sense
Protection
trigger
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Introduction
1
Introduction
The SM72445 is designed to maximize the energy production of a photovoltaic panel through the control
of a four switch buck-boost converter as well as an optional FET bi-directional switch (two FETs) designed
to maximize the efficiency at 1:1 conversion ratios. The maximum voltage and power transferred depend
on the component choice (driver, passive components, FET, and so forth). The SM72445 performs
optimization of the operating point of the solar panel through a high speed Perturb&Observe algorithm.
The input voltage and current are sampled at a high rate and digitally filtered while the algorithm updates
the output PWM waveform at a rate up to 1.2ms/step. The PWM waveforms include dead-time and can be
directly fed to the drivers controlling the DC/DC converter’s switches. The SM72445 is designed to
operate at 110kHz, 137kHz and 220kHz depending on the operating mode set. The SM72445 includes
and I2C slave module with 8 address settings to communicate monitoring information and to allow remote
shut-down and configuration modifications.
The SolarMagic™ SM72445 Evaluation Board is based off of the SM3320-1A1 power optimizer, and
shares all of its best-in-class power optimization features. This includes its ability to mitigate real-world
mismatch, its 99.5% peak efficiency, and its Panel-Mode operation. In addition, the same ultra-low profile
form factor of the original SM3320-1A1 is maintained so that it can be integrated into the same junction
box designs.
This Evaluation module is fully operational and can be used with panels from 15V up to 50V (absolute)
operating voltage and up to 300W of power. Proper heat-sinking of the Power FETs must be achieved for
power levels above 50W at room temperature.
The absolute maximum output voltage is 50V. The maximum operating current is 11A
2
System Overview
Figure 1
depicts how the SM72445 design would be implemented in its intended application. In this
example, the SM72445 senses the input and output voltages and currents, filters them digitally and
calculates power. It then issues four PWM pulses to the gate drivers to control the converter's switches.
The SM72445 also operates an additional switch (called Panel-Mode or PM switch) to optimize efficiency
when operating close to a 1:1 conversion ratio. Optionally, the switch can be omitted for reduced cost. The
SM72445 then utilizes the converter at a 1:1 conversion ratio and increases efficiency by reducing the
switching frequency of the converter
Figure 6
shows the detailed schematic with component references.
Figure 1. Evaluation Board Simplified Diagram
5
SNVA649 – May 2012
AN-2241 SM72445 Evaluation Board
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