SM72445_15 Datasheet, PDF (11/20 Pages) Texas Instruments – SM72445 Programmable Maximum Power Point Tracking Controller With Adjustable PWM Frequency

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SM72445
SNVS795 – MARCH 2012
Figure 12. Forced Reset Condition
As seen in Figure 12, the initial value for output voltage and load current are 28V and 1A respectively. After the
reset pin is grounded both the output voltage and load current decreases immediately. MOSFET switching on the
buck-boost converter also stops immediately. VLOB indicates the low side boost output from the SM72295.
ANALOG INPUT
An equivalent circuit for one of the ADC input channels is shown in Figure 13. Diode D1 and D2 provide ESD
protection for the analog inputs. The operating range for the analog inputs is 0V to V_A. Going beyond this range
will cause the ESD diodes to conduct and result in erratic operation.
The capacitor C1 in Figure 13 has a typical value of 3 pF and is mainly the package pin capacitance. Resistor R1
is the on resistance of the multiplexer and track / hold switch; it is typically 500Ω. Capacitor C2 is the ADC
sampling capacitor; it is typically 30 pF. The ADC will deliver best performance when driven by a low-impedance
source (less than 100Ω). This is especially important when sampling dynamic signals. Also important when
sampling dynamic signals is a band-pass or low-pass filter which reduces harmonic and noise in the input. These
filters are often referred to as anti-aliasing filters.
VDDA
Ax
C₁
3 pF
D₁
R₁
C₂
30 pF
D₂
Conversion Phase: Switch Open
Track Phase: Switch Close
Figure 13. Equivalent Input Circuit
DIGITAL INPUTS and OUTPUTS
The digital input signals have an operating range of 0V to V_A, where V_A = VDDA – VSSA. They are not prone to
latch-up and may be asserted before the digital supply V_D, where V_D = VDDD – VSSD, without any risk. The
digital output signals operating range is controlled by V_D. The output high voltage is V_D – 0.5V (min) while the
output low voltage is 0.4V (max).
SCL and SDA
SCL is an input, and SDA is bidirectional with an open-drain output. SCL and SDA do not have internal pull-ups.
A “high” level will not be observed on this pin until pull-up current is provided by some external source, typically a
pull-up resistor. The choice of resistor value depends on many system factors such as load capacitance and
trace length. A typical value of pull-up resistor for SM72445 ranges from 2 kΩ to 10 kΩ. For more information,
refer to the I2C Bus specification for selecting the pull-up resistor value. The SCL and SDA outputs can operate
while being pulled up to 5V and 3.3V.
Copyright © 2012, Texas Instruments Incorporated
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