SM72445_15 Datasheet, PDF (9/20 Pages) Texas Instruments – SM72445 Programmable Maximum Power Point Tracking Controller With Adjustable PWM Frequency

SM72445
www.ti.com
SNVS795 – MARCH 2012
CONFIGURABLE SETTINGS
A/D pins A0, A2, A4, and A6 are used to configure the behavior of the SM72445 by adjusting the voltage applied
to them through resistor dividers as shown in Figure 2, where RT1 to RT4 should be in the range of 20 kΩ.
The voltages of the configuration pins are read and the operating mode is then set at start-up and after each
reset of the device.
Three different frequencies for the PWM operation of the H-bridge as well as two different implementations of the
Panel Mode switch can be set on the ADC input channel 2 (pin A2). The table below lists the different conditions
that a user can select on pin A2. Each frequency has a different associated dead time for the operation of the
synchronous switches. When dedicated PM switch modes are used, the unit will stop switching the converter
upon entering PM mode and the PM_OUT pin will switch at a high frequency to provide activation of a dedicated
Panel Mode switch. When the H-bridge modes are used, the unit will keep the H-bridge switching at half the
operating frequency (to reduce switching losses) and with a total input to output ratio of 1. The dead times are
unchanged during this phase.
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
Table 1. Programmable Settings on Pin A2
PWM Frequency setting
HIGH
HIGH
LOW
MED.
HIGH
LOW
MED.
HIGH
Panel Mode Operation
Uses dedicated PM switch
Uses dedicated PM switch
Uses H-bridge for PM operation
Uses H-bridge for PM operation
Uses H-bridge for PM operation
Uses dedicated PM switch
Uses dedicated PM switch
Uses dedicated PM switch
The user can also select the output voltage slew rate, minimum 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. The slew rate limiter takes control of the duty cycle if the output voltage rises faster than the programmed limit
while the unit is running in Boost mode (output voltage higher than input voltage). The device will control the duty
cycle so that the output voltage stays within the allowed slew rate. The slew rate is never limited in Buck mode
(output voltage lower than input voltage).
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
Table 2. Programmable Settings on Pin A6
Output Voltage Starting Panel Mode
Slew Rate Limit
Time
10V/1.2s
10V/1.2s
10V/1.2s
10V/1.2s
10V/1.2s
10V/1.2s
10V/0.6s
No slew rate limit
Not applicable
60s
0s
120s
Not applicable
60s
60s
60s
MPPT Exit
Threshold (on
AIOUT or AIIN)
0V
0.006xVDDA
0.023xVDDA
0.023xVDDA
0.006xVDDA
0.023xVDDA
0.023xVDDA
0.023xVDDA
MPPT Start
Threshold (on
AIOUT)
0V
0.010xVDDA
0.039xVDDA
0.039xVDDA
0.010xVDDA
0.039xVDDA
0.039xVDDA
0.039xVDDA
Starting boost ratio
N/A
1:1
1:1
1:1
1:1.2
1:1
1:1
1:1
PARAMETER DEFINITIONS
Output Voltage Slew Rate Limit Settling Time: Time constant of the internal filter used to limit output voltage
change. At the fast slew rate, the output voltage will be held for 60 ms for every 1V increase, whereas in the slow
slew rate, the output voltage will be held for 120ms for every 1V increase. (See Figure 10).
Starting PM Time: After initial power-up or reset, the output soft-starts and then enters Panel Mode for this
amount of time.
Copyright © 2012, Texas Instruments Incorporated
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