Datasheet

Buck

Boost

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SM72445 Evaluation Module Design Specification

Modifications to the configuration can be performed by changing the resistor settings. The change in

configuration will only happen at start-up and during reset of the IC.

“Panel Mode” Operation

The board is configured to use “Panel Mode” FETs to reach the highest possible efficiency at a 1:1

conversion ratio. The SM72445 will disconnect the DC/DC converter and turn on this switch whenever it

detects that the panel is matched to the load. The detail of this operation can be found in the SM72445

datasheet. Alternatively, the SM72445 can be configured to run the DC/DC converter in a Panel-Mode

behavior instead, driving the high-side FETs of the converter in a mostly ONstate (Figure 2) and achieving

the same function as the dedicated Panel-Mode FETs. This option optimizes the component count and the

cost of the solution but slightly reduces the efficiency of the system in the band close to a 1:1 conversion

ratio. To configure the board in this mode, the resistor couple R29 and R39 can be changed to modify the

voltage at pin A2. In addition, T1 should be removed. Check the Prog Max Pwr Point Tracking Cntrl w/

Adjustable PWM Frequency (SNVS795) data sheet for additional details on the different configuration

settings.

Figure 2. Panel Mode Operation Using Converter's FET (“Boost” waveform is taken at drain of Q3,

“Buck” waveform was taken at drain of Q4.)

“SOFT” Output Voltage Limit

The soft output voltage limit of “Soft OVP” is designed to prevent the output voltage from reaching

dangerous level when the system is running the converter in boost mode. This mechanism works by

reducing the duty cycle of the converter when the voltage at pin AVOUT is increasing above the voltage at

pin A0.

Slew Rate Limit

The slew rate limit is designed to limit the rate of rise of the output voltage when and only when the

converter is running in boost mode. The rise of the duty cycle will be limited to ensure that the output

voltage will rise in a controlled manner, especially during transients such as when the load is reduced or

gets removed (before the SM72445 returns in stand-by mode). To test the slew rate limit, start-up the

system with a current load at 1.5A and with an input that has a maximum power point above 3A. The

output voltage will increase very rapidly until it reaches the input voltage. The output voltage will then

increase slowly above the input voltage as limited by the slew rate setting programmed.

SNVA649A–May 2012–Revised May 2013 AN-2241 SM72445 Evaluation Board

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