sm72441mtx National Semiconductor Corporation, sm72441mtx Datasheet - Page 7

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

10Vfs/16 < VADC2 <11Vfs/16
11Vfs/16 < VADC2 <12Vfs/16
12Vfs/16 < VADC2 <13Vfs/16
13Vfs/16 < VADC2 <14Vfs/16
14Vfs/16 < VADC2 <15Vfs/16
15Vfs/16 < VADC2 <16Vfs/16
9Vfs/16 < VADC2 <10Vfs/16
1Vfs/16 < VADC2 <2Vfs/16
2Vfs/16 < VADC2 <3Vfs/16
3Vfs/16 < VADC2 <4Vfs/16
4Vfs/16 < VADC2 <5Vfs/16
5Vfs/16 < VADC2 <6Vfs/16
6Vfs/16 < VADC2 <7Vfs/16
7Vfs/16 < VADC2 <8Vfs/16
8Vfs/16 < VADC2 <9Vfs/16
MAXIMUM OUTPUT VOLTAGE
Maximum output voltage on the SM72441 is set by resistor
divider ratio on pin A0. (Please refer to
plication Circuit).
Where RT1 and RB1 are the resistor divider on the ADC pin
A0 and RFB1 and RFB2 are the output voltage feedback re-
sistors. A typical value for RFB2 is about 2 kΩ.
CURRENT LIMIT SETTING
Maximum output current can be set by changing the resistor
divider on A4 (pin 18). (Refer to
output is detected when the voltage on AIOUT (pin 21) equals
to the voltage on A4 (pin 18). The voltage on A4 can be set
by a resistor divider connected to 5V whereas a current sense
amplifier output can be used to set the voltage on AIOUT.
AIIN AND AIOUT PIN
These two pins are used to set current threshold from standby
(buck-boost mode) to MPPT mode and from MPPT mode into
standby mode.
In order to transition from standby to MPPT mode, the follow-
ing conditions have to be satisfied:
On the other hand, in order to transition from MPPT to standby
mode, the following condition have to be satisfied:
1) AIIN and AIOUT voltage > 0.488V
2) Iout < Iout_max
1) AIIN and AIOUT voltage < 0.293V
2) Iout < Iout_max
0 < VADC2 < Vfs/16
ADC Channel 2
MPPT Update Time
Figure 2
TABLE 1. List of configurable modes on ADC Channel 2
1.2 ms
38 ms
77 ms
38 ms
38 ms
38 ms
38 ms
38 ms
38 ms
38 ms
77 ms
77 ms
77 ms
77 ms
77 ms
77 ms
Figure 2
). Overcurrent at the
Typical Ap-
Slew Rate
Detection
Disabled
Disabled
Disabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
7
Current limit is triggered when AIOUT (pin 21) voltage is equal
to A4 (pin 18).
AVIN PIN
AVIN pin is an A/D input to sense the input voltage of
SM72441. A resistor divider can be used to scale the max
voltage to about 4V, which is 80% of the full scale of the A/D
input.
CONFIGURABLE SETTINGS
The voltage on A0 sets the max output voltage; whereas the
voltage on A2 enables MPPT update rate and limits the max
boost ratio when output current is below the standby thresh-
old. Output current limit is set by the voltage on A4 and output
voltage slew rate limit is set on A6. In order to set a slew rate
limit of 125V/sec, the ratio of the two resistors in A6 should
be 9:1.
The low current condition is detected if the voltage on AIIN is
less than 0.488V (rising) and 0.293 (falling) + ΔI or if the volt-
age on AIOUT is less than 0.488 V (rising) and 0.293 (falling)
+ ΔI. If low current is detected, the converter operates in
standby mode and limit the maximum duty cycle to either a 1
(buck-boost), 1.15 (boost) or 1.25 (boost) conversion ratio
(programmable). In this case no MPPT will be performed.
The actual value of current will depend on the gain of the cur-
rent sensing amplifier circuitry that feeds the AIIN and AIOUT
pins.
For more complete information on the various settings based
on the voltage level of A2, please refer to
denotes the full scale voltage of the ADC which is equal to
VDDA where VDDA is a reference voltage to analog ground.
A typical value for top configuration resistors (RT1 to RT4)
should be 20 kΩ.
Low Current
Detection
Disabled
Disabled
Disabled
Disabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Initial Boost Ratio
1.15
1.15
1.15
1.25
1.25
1.25
1.15
1.15
1.15
1.25
1.25
1.25
N/A
N/A
N/A
N/A
Table 1
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below. Vfs
90 (0.45 A)
120(0.6 A)
60 (0.3 A)
Delta I
N/A
N/A
N/A
N/A
120
120
120
60
90
60
90
60
90