SM72445 Datasheet, PDF (9/19 Pages) Texas Instruments – Programmable Maximum Power Point Tracking Controller With Adjustable PWM Frequency

A2
1.56 V
0.94 V
0.31 V
PWM Frequency
setting
LOW
MED.
HIGH
Panel Mode Operation
Uses dedicated PM
switch
Uses dedicated PM
switch
Uses dedicated PM
switch
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 lim-
ited in Buck mode (output voltage lower than input voltage).
The user can also select the output voltage slew rate, mini-
mum current threshold and duration of Panel Mode after the
TABLE 2 Programmable Settings on Pin A6
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
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
Starting Panel
Mode Time
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 con-
stant 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 out-
put voltage will be held for 120ms for every 1V increase. (See
Figure 6).
Starting PM Time: After initial power-up or reset, the output
soft-starts and then enters Panel Mode for this amount of
time.
MPPT Exit Threshold and MPPT Start Threshold: These
are the hysteretic thresholds for Iout_th read on pin AIOUT.
The values are expressed as a fraction of the voltage at pin
VDDA. AIOUT is the output current sensing pin and should
be connected to the output of a current sense amplifier. For
example, with a current sense amplification of 0.5V/A provid-
ed by an external current sense resistor and amplifier and
assuming VDDA=5V and A6=0.94V, the output current
threshold to bring the device out of stand-by mode will be
0.39A.
Starting Boost Ratio: This is the end-point of the soft-start
voltage ramp expressed as a ratio of VOUT/VIN. 1:1 ratio
means it stops when Vout = Vin, whereas a 1:1.2 ratio means
it stops when Vout = 1.2 x Vin.
DEAD-TIME
The dead time of the switches to avoid cross conduction of
the buck FETs and boost FETs depends on the switching fre-
quency set: it is equal to (3/256) x 1/f_SWITCH. When the IC is
programmed for 215 kHz operation, the dead time between
HIA and LOA and between HIB and LOB will be 55ns.
PANEL MODE PIN (PM)
The SM72445 can be forced into Panel Mode by pulling the
PM pin low. One sample application is to connect this pin to
the output of an external temperature sensor; therefore when-
ever an over-temperature condition is detected the chip will
enter Panel Mode.
Once Panel Mode is enabled, either when the unit is running
in MPPT mode with a 1:1 conversion ratio or when PM is
pulled low, the PM_OUT pin will output a 440 kHz square
wave signal. Using a gate driver and transformer, this square
wave signal can then be used to drive a Panel Mode FET as
shown in Figure 7.
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