SM72445_15 Datasheet, PDF (10/20 Pages) Texas Instruments – SM72445 Programmable Maximum Power Point Tracking Controller With Adjustable PWM Frequency

SM72445
SNVS795 – MARCH 2012
www.ti.com
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 provided 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 frequency 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 whenever 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 11.
40V
30V
Fast
No Slew
20 - 40ms
(Frequency
dependent)
Slow
'V = 10V
600 ms
1200 ms
Figure 10. Slew Rate Limitation Circuit
Pulse High
SM72445
10V
VCC OUT_A
0.47 PF
OUT_B
Square Wave
SM72482
PM PM_OUT
IN_A
IN_B
VEE
10k
499 0.47 PF
2.00k
PV (+) Panel Mode FETs VOUT (+)
499
150 pF ^10k
Figure 11. Sample Application for Panel Mode Operation
RESET PIN
When the reset pin is pulled low, the chip will cease its normal operation and turn-off all of its PWM outputs
including the output of PM_OUT pin. Below is an oscilloscope capture of a forced reset condition.
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