SM72445_15 Datasheet, PDF (13/20 Pages) Texas Instruments – SM72445 Programmable Maximum Power Point Tracking Controller With Adjustable PWM Frequency

SM72445
www.ti.com
reg4 Register Description
Bits
Field
Reset Value
R/W
55:32
RSVD
24'd0
R/W
31:24
Vout offset
8'h0
R/W
23:16
Iout offset
8'h0
R/W
15:8
Vin offset
8'h0
R/W
7:0
Iin offset
8'h0
R/W
SNVS795 – MARCH 2012
Bit Field Description
Reserved
Voltage out offset
Current out offset
Voltage in offset
Current in offset
reg5 Register Description
Bits
Field
Reset Value
R/W
55:40
RSVD
15'd0
R/W
39:30
iin_hi_th
10'd40
R/W
29:20
iin_lo_th
10'd24
R/W
19:10
iout_hi_th
10'd40
R/W
9:0
iout_lo_th
10'd24
R/W
Bit Field Description
Reserved
Current in high threshold for start
Current in low threshold for start
Current out high threshold for start
Current out low threshold for start
The open loop operation allows the user to set a fixed operating duty cycle (buck or boost) on the converter. The
unit will not sense current or voltage in this mode and will perform an internal reset when exiting open loop
mode.
The bb_reset bit performs a limited reset of the IC. While this bit is set high, the unit will not output any driving
signal and will not sense any input. When this bit is transited back to zero, the unit will go through its initialization
phase according to the programming mode set and possible I2C overrides. The IC will NOT perform a sample of
the A0–A6 input when the bb_reset bit is cleared.
To change the PWM frequency options the first time after power up, the following programming sequence must
be used :
• set bb_reset bit (reg3[2]), set over-ride bit (reg3[46]), set to the desired PWM code (reg3[42:40])
• reset bb_reset bit, keep over-ride bit, keep the desired PWM code
To change PWM options subsequent to an earlier programming :
• set bb_reset bit, reset over-ride bit, set to the desired PWM code
• reset bb_reset bit, reset over-ride bit, keep the desired PWM code
• set bb_reset bit, set over-ride bit, keep the desired PWM code
• reset bb_reset bit, keep over-ride bit, keep the desired PWM code
The switching frequency will be returned to the default external resistor setting after each hard reset of the IC.
The “tdoff” and” tdon” (REG3[14:19]) parameters allow modification of the dead time. the dead time for the
turning on of the synchronous rectifier (affecting buck and boost mode) will be set by (td_on/256)*(1/f_switch).
The default parameter for td_on is 3.
The dead time for the turning on of the main switch after the synchronous rectifier as turned off (affecting buck
and boost mode) will be set by (td_off/256)*(1/f_switch). The default parameter for td_off is 3. The dead time
parameters are returned to their default value after each hard reset of the IC.
The offsets are 8 bit signed numbers which are added or substracted to the results of the A/D converter and
affect the sensed values displayed in Register 0 as well as the thresholds.
Using the I2C port, the user will be able to control the duty cycle of the PWM signal. Input and output voltage and
current offsets can also be controlled using I2C on register 4. Control registers are available for additional
flexibility.
The thresholds iin_hi_th, iin_lo_th, iout_hi_th, iout_lo_th, in reg5 are compared to the values read in by the ADC
on the AIIN and AIOUT pins. Scaling is set by the scaling of the analog signal fed into AIIN and AIOUT. These
10–bit values determine the entry and exit conditions for MPPT. The startup high thresholds set the voltages at
pin AIIN and AIOUT above which the unit will begin transition from PM_Startup state to MPPT state. The low
thresholds set the voltage below which the unit will transition back to PM_Startup (stand-by). The initial
thresholds are a function of the value programmed in A6. As determined by Table 2, if A6 was between 0 and
1.56V at start-up, the thresholds will be 0.023*VDDA and 0.039*VDDA.
Copyright © 2012, Texas Instruments Incorporated
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