sm72441mtx National Semiconductor Corporation, sm72441mtx Datasheet - Page 6

• Manufacturer Part Number: sm72441mtx
• Description: Programmable Maximum Power Point Tracking Controller For Photovoltaic Solar Panels
• Manufacturer: National Semiconductor Corporation

www.national.com
Operation Description
OVERVIEW
The SM72441 is a programmable MPPT controller capable of
outputting four PWM gate drive signals for a 4-switch buck-
boost converter. The typical application circuit is shown in
Figure
The SM72441 uses an advanced digital controller to generate
its PWM signals. A maximum power point tracking (MPPT)
algorithm monitors the input current and voltage and controls
the PWM duty cycle to maximize energy harvested from the
STARTUP
SM72441 has a soft start feature that will ramp its output volt-
age for a fixed time of 250ms. MPPT mode will be entered
during soft start if the load current exceeded the minimum
current threshold. Otherwise, buck-boost operation is entered
after soft-start is finished where the ratio between input and
output voltage is 1:1. Refer to
diagram of startup. The current threshold to transition be-
tween MPPT to standby (buck-boost) mode and vice versa
can be set by feeding the output of current sensing amplifier
(Figure
age level, refer to AIIN and AIOUT section of this datasheet.
2.
2) to the AIIN and AIOUT pin. For an appropriate volt-
Figure 3
FIGURE 3. High Level State Diagram for Startup
for a high level state
6
photovoltaic module. MPPT performance is very fast. Con-
vergence to the maximum power point of the module typically
occurs within 0.01s. This enables the controller to maintain
optimum performance under fast-changing irradiance condi-
tions.
Transitions between buck, boost, and buck-boost modes are
smoothed, and advanced digital PWM dithering techniques
are employed to increase effective PWM resolution. Output
voltage and current limiting functionality are integrated into
the digital control logic. The controller is capable of handling
both shorted and no-load conditions and will recover smoothly
from both.
FIGURE 4. Start-Up Waveforms of Controlled Output
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