SM72442 Datasheet, PDF (7/14 Pages) National Semiconductor (TI) – Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar Panels

STARTUP
SM72442 has a soft start feature that will ramp its output volt-
age for a fixed time of 250ms.
If no output current is detected during soft-start time, the chip
will then be in Panel Mode for 60 seconds. A counter will start
once the minimum output current threshold is met (set by ADC
input channel 4). During these 60 seconds, any variation on
the output power will not cause the chip to enter MPPT mode.
Once 60 seconds have elapsed, at a certain power level vari-
ation at the output (set by ADC input channel 2) will engage
the chip in MPPT mode.
If the output current exceeded the current threshold set at
A/D Channel 6 (A6) during soft-start, the chip will then engage
in MPPT mode.
30134305
FIGURE 5. Startup Sequence
MAXIMUM OUTPUT VOLTAGE
Maximum output voltage on the SM72442 is set by resistor
divider ratio on pin A0. (Please refer to Figure 2 Typical Ap-
plication Circuit).
CURRENT LIMIT SETTING
Maximum output current can be set by changing the resistor
divider on A4 (pin 18). Refer to Figure 2. Overcurrent at the
output is detected when the voltage on AIOUT (pin 21) equals
the voltage on A4 (pin 18). The voltage on A4 can be set by
a resistor divider connected to 5V whereas the voltage on
AIOUT can be set by a current sense amplifier.
AVIN PIN
AVIN is an A/D input to sense the input voltage of the
SM72442. A resistor divider can be used to scale max voltage
to about 4V, which is 80% of the full scale of the A/D input.
CONFIGURABLE SETTINGS
A/D pins A0, A2, A4, and A6 are used to configure the be-
havior of the SM72442 by adjusting the voltage applied to
them. One way to do this is through resistor dividers as shown
in Figure 2, where RT1 to RT4 should be in the range of 20
kΩ.
Different conditions to enter and exit Panel Mode can be set
on the ADC input channel 2. Listed below are different con-
ditions that a user can select on pin A2. “1:1”refers to the state
in which the DC/DC converter operates with its output voltage
equal to its input voltage (also referred to as “Buck-Boost”
mode on Figure 4.)
A2
4.69 V
4.06 V
3.44 V
2.81 V
2.19 V
1.56 V
0.94 V
0.31 V
Entering Panel Mode
2s in 1:1 Mode
1s in 1:1 Mode
0.4s in 1:1 Mode
0.2s in 1:1 Mode
2s in 1:1 Mode
1s in 1:1 Mode
0.4s in 1:1 Mode
0.2s in 1:1 Mode
Exiting Panel Mode
3.1% power variation
3.1% power variation
3.1% power variation
3.1% power variation
1.6% power variation
1.6% power variation
1.6% power variation
1.6% power variation
The user can also select the output voltage slew rate, mini-
mum current threshold and duration of Panel Mode after the
soft-start period has finished, by changing the voltage level
on pin A6 which is the input of ADC channel 6.
Where RT1 and RB1 are the resistor divider on the ADC pin
A0 and RFB1 and RFB2 are the output voltage sense resis-
tors. A typical value for RFB2 is about 2 kΩ
A6
4.69 V
4.06 V
3.44 V
2.81 V
2.19 V
1.56 V
0.94 V
0.31 V
Output Voltage
Slew Rate Limit
Slow
Slow
Slow
Slow
Slow
Slow
Fast
No slew rate limit
Starting Panel
Mode Time
Not applicable
60s
0s
120s
Not applicable
60s
60s
60s
MPPT Exit
Threshold
0 mA
75mA
300mA
300mA
300mA
300mA
300mA
300mA
MPPT Start
Threshold
0 mA
125mA
500mA
500mA
500mA
500mA
500mA
500mA
Starting boost ratio
1:1
1:1
1:1
1:1
1:1.2
1:1
1:1
1:1
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