SM72441MT/NOPB - NATIONAL SEMICONDUCTOR

SM72441

SM72441 Programmable Maximum Power Point Tracking Controller for

Photovoltaic Solar Panels

Literature Number: SNOSB64F

SM72441

November 20, 2011

Programmable Maximum Power Point Tracking Controller

for Photovoltaic Solar Panels

General Description

The SM72441 is a programmable MPPT controller capable of

controlling four PWM gate drive signals for a 4-switch buck-

boost converter. Along with SM72295 (Photovoltaic Full

Bridge Driver) it creates a solution for an MPPT configured

DC-DC converter with efficiencies up to 98.5%. Integrated in-

to the chip is an 8-channel, 12 bit A/D converter used to sense

input and output voltage and current, as well as board con-

figuration. Externally programmable values include maximum

output voltage and current as well as different settings on slew

rate, and soft-start.

Features

■Renewable Energy Grade

■Programmable maximum power point tracking

■Photovoltaic solar panel voltage and current diagnostic

■Single inductor four switch buck-boost converter control

■VOUT Overvoltage protection

■Over-current protection

Package

■TSSOP-28

Block Diagram

30134202

FIGURE 1. Block Diagram

SM72441 Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar

Panels

30134201

FIGURE 2. Typical Application Circuit

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SM72441

Connection Diagram

30134203

Top View

TSSOP-28

Ordering Information

Order Number Description NSC Package Drawing Supplied As Package Top Mark

SM72441MTX TSSOP-28 MTC28 2500 Units in Tape and

Reel

S72441

SM72441MTE TSSOP-28 MTC28 250 Units in Tape and

Reel

S72441

SM72441MT TSSOP-28 MTC28 48 Units in rail S72441

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SM72441

Pin Descriptions

Pin Name Description

1 RST Active low signal. External reset input signal to the digital circuit.

2 NC1 No Connect. This pin should be grounded.

3 VDDD Digital supply voltage. This pin should be connected to a 5V supply, and bypassed to VSSD with a 0.1uF monolithic

ceramic capacitor.

4 VSSD Digital ground. The ground return for the digital supply and signals.

5 NC2 No Connect. This pin should be pulled up to the 5V supply using 10k resistor.

6 NC3 No Connect. This pin should be grounded using a 10k resistor.

7 NC4 No Connect. This pin should be grounded using a 10k resistor.

8 NC5 No Connect. This pin should be pulled up to 5V supply using 10k resistor.

9 NC6 No Connect. This pin should be pulled up to 5V supply using 10k resistor.

10 NC7 No Connect. This pin should be grounded.

11 LED LED pin outputs a pulse during normal operation.

12 VDDA Analog supply voltage. This voltage is also used as the reference voltage. This pin should be connected to a 5V supply,

and bypassed to VSSA with a 1uF and 0.1uF monolithic ceramic capacitor.

13 VSSA Analog ground. The ground return for the analog supply and signals.

14 A0 A/D Input Channel 0. Connect a resistor divider to 5V supply to set the maximum output voltage. Please refer to

application section for more information on setting the resistor value.

15 AVIN A/D Input to sense input voltage.

16 A2 A/D Input Channel 2. Connect a resistor divider to 5V supply to set MPPT update rate. Please refer to application

section for more information on setting the resistor value.

17 AVOUT A/D Input to sense the output voltage.

18 A4 A/D Input Channel 4. Connect a resistor divider to 5V supply to set the maximum output current. Please refer to

application section for more information on setting the resistor value.

19 AIIN A/D Input to sense input current.

20 A6 A/D Input Channel 6. Connect a resistor divider to 5V supply to set the maximum output voltage slew rate. Please

refer to application section for more information on setting the resistor value.

21 AIOUT A/D Input to sense the output current.

22 NC8 No Connect. This pin should be grounded using a 10k resistor.

23 NC9 No Connect. This pin should be connected with 150k pull-up resistor to 5V supply.

24 LIB Low side boost PWM output.

25 HIB High side boost PWM output.

26 HIA High side buck PWM output.

27 LIA Low side buck PWM output.

28 OVP Overvoltage Protection Pin. Active Low. SM72441 will reset once voltage on this pin drops below its threshold voltage.

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SM72441

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the Texas Instruments Sales Office/

Distributors for availability and specifications.

Analog Supply Voltage VA

(VDDA -VSSA)

-0.3 to 6.0V

Analog Supply Voltage VD

(VDDD -VSSD)

-0.3 to VA +0.3V

max 6.0V

Voltage on Any Pin to GND -0.3 to VA +0.3V

Input Current at Any Pin (Note 3) ±10 mA

Package Input Current (Note 3) ±20 mA

Storage Temperature Range -65°C to +150°C

ESD Rating (Note 2)

Human Body Model 2 kV

Recommended Operating

Conditions

Operating Temperature -40°C to 105°C

VA Supply Voltage +4.75V to +5.25V

VD Supply Voltage +4.75V to VA

Digital Input Voltage 0 to VA

Analog Input Voltage 0 to VA

Junction Temperature -40°C to 125°C

Specifications in standard typeface are for TJ = 25°C, and those in boldface type apply over the full operating junction temperature

range.(Note 3)

Symbol Parameter Conditions Min Typ Max Units

ANALOG INPUT CHARACTERISTICS

AVin, AIin

AVout, AIout Input Range - 0 to VA- V

IDCL DC Leakage Current - - ±1 µA

CINA Input Capacitance(Note 4)Track Mode - 33 - pF

Hold Mode - 3 - pF

VERR

DC Voltage Measurement

Accuracy 0.1 %

DIGITAL INPUT CHARACTERISTICS

VIL Input Low Voltage - - 0.8 V

VIH Input High Voltage 2.8 - - V

CIND

Digital Input Capacitance(Note

4) - 2 4pF

IIN Input Current - ±0.01 ±1 µA

DIGITAL OUTPUT CHARACTERISTICS

VOH Output High Voltage ISOURCE = 200 µA VA = VD = 5V VD-0.5 - - V

VOL Output Low Voltage ISINK = 200 µA to 1.0 mA VA = VD = 5V - - 0.4 V

IOZH , IOZL

Hi-Impedance Output Leakage

Current VA = VD = 5V ±1 µA

COUT

Hi-Impedance Output

Capacitance (Note 4) 2 4pF

POWER SUPPLY CHARACTERISTICS (CL = 10 pF)

VA ,VD

Analog and Digital Supply

Voltages VA ≥ VD4.75 55.25 V

IA + IDTotal Supply Current VA = VD = 4.75V to 5.25V 7 10 15 mA

PCPower Consumption VA = VD = 4.75V to 5.25V 50 78 mW

PWM OUTPUT CHARACTERISTICS

fPWM PWM switching frequency 210 kHz

tDEAD Dead time 38 ns

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation

of the device is guaranteed. Operating Ratings indicate conditions for which the device is intended to be functional, but does not guarantee specific performance

limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables.

Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 3: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical

Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL).

Note 4: Not tested. Guaranteed by design.

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SM72441

Operation Description

OVERVIEW

The SM72441 is a programmable MPPT controller capable of

outputting four PWM gate drive signals for a 4-switch buck-

boost converter. The typical application circuit is shown in

Figure 2.

The SM72441 uses an advanced digital controller to generate

its PWM signals. A maximum power point tracking (MPPT)

algorithm monitors the input current and voltage and controls

the PWM duty cycle to maximize energy harvested from the

photovoltaic module. MPPT performance is very fast. Con-

vergence to the maximum power point of the module typically

occurs within 0.01s. This enables the controller to maintain

optimum performance under fast-changing irradiance condi-

tions.

Transitions between buck, boost, and buck-boost modes are

smoothed, and advanced digital PWM dithering techniques

are employed to increase effective PWM resolution. Output

voltage and current limiting functionality are integrated into

the digital control logic. The controller is capable of handling

both shorted and no-load conditions and will recover smoothly

from both.

30134204

FIGURE 3. High Level State Diagram for Startup

STARTUP

SM72441 has a soft start feature that will ramp its output volt-

age for a fixed time of 250ms. MPPT mode will be entered

during soft start if the load current exceeded the minimum

current threshold. Otherwise, buck-boost operation is entered

after soft-start is finished where the ratio between input and

output voltage is 1:1. Refer to Figure 3 for a high level state

diagram of startup. The current threshold to transition be-

tween MPPT to standby (buck-boost) mode and vice versa

can be set by feeding the output of current sensing amplifier

(Figure 2) to the AIIN and AIOUT pin. For an appropriate volt-

age level, refer to AIIN and AIOUT section of this datasheet.

30134205

FIGURE 4. Start-Up Waveforms of Controlled Output

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SM72441

MAXIMUM OUTPUT VOLTAGE

Maximum output voltage on the SM72441 is set by resistor

divider ratio on pin A0. (Please refer to Figure 2 Typical Ap-

plication Circuit).

Where RT1 and RB1 are the resistor divider on the ADC pin

A0 and RFB1 and RFB2 are the output voltage feedback re-

sistors. A typical value for RFB2 is about 2 kΩ.

CURRENT LIMIT SETTING

Maximum output current can be set by changing the resistor

divider on A4 (pin 18). (Refer to Figure 2 ). Overcurrent at the

output is detected when the voltage on AIOUT (pin 21) equals

to the voltage on A4 (pin 18). The voltage on A4 can be set

by a resistor divider connected to 5V whereas a current sense

amplifier output can be used to set the voltage on AIOUT.

AIIN AND AIOUT PIN

These two pins are used to set current threshold from standby

(buck-boost mode) to MPPT mode and from MPPT mode into

standby mode.

In order to transition from standby to MPPT mode, the follow-

ing conditions have to be satisfied:

1) AIIN and AIOUT voltage > 0.488V

2) Iout < Iout_max

On the other hand, in order to transition from MPPT to standby

mode, the following condition have to be satisfied:

1) AIIN and AIOUT voltage < 0.293V

2) Iout < Iout_max

Current limit is triggered when AIOUT (pin 21) voltage is equal

to A4 (pin 18).

AVIN PIN

AVIN pin is an A/D input to sense the input voltage of

SM72441. A resistor divider can be used to scale the max

voltage to about 4V, which is 80% of the full scale of the A/D

input.

CONFIGURABLE SETTINGS

The voltage on A0 sets the max output voltage; whereas the

voltage on A2 enables MPPT update rate and limits the max

boost ratio when output current is below the standby thresh-

old. Output current limit is set by the voltage on A4 and output

voltage slew rate limit is set on A6. In order to set a slew rate

limit of 125V/sec, the ratio of the two resistors in A6 should

be 9:1.

The low current condition is detected if the voltage on AIIN is

less than 0.488V (rising) and 0.293 (falling) + ΔI or if the volt-

age on AIOUT is less than 0.488 V (rising) and 0.293 (falling)

+ ΔI. If low current is detected, the converter operates in

standby mode and limit the maximum duty cycle to either a 1

(buck-boost), 1.15 (boost) or 1.25 (boost) conversion ratio

(programmable). In this case no MPPT will be performed.

The actual value of current will depend on the gain of the cur-

rent sensing amplifier circuitry that feeds the AIIN and AIOUT

pins.

For more complete information on the various settings based

on the voltage level of A2, please refer to Table 1 below. Vfs

denotes the full scale voltage of the ADC which is equal to

VDDA where VDDA is a reference voltage to analog ground.

A typical value for top configuration resistors (RT1 to RT4)

should be 20 kΩ.

TABLE 1. List of configurable modes on ADC Channel 2

ADC Channel 2 MPPT Update Time Slew Rate

Detection

Low Current

Detection

Initial Boost Ratio Delta I

0 < VADC2 < Vfs/16 1.2 ms Disabled Disabled N/A N/A

1Vfs/16 < VADC2 <2Vfs/16 38 ms Disabled Disabled N/A N/A

2Vfs/16 < VADC2 <3Vfs/16 77 ms Disabled Disabled N/A N/A

3Vfs/16 < VADC2 <4Vfs/16 38 ms Enabled Disabled N/A N/A

4Vfs/16 < VADC2 <5Vfs/16 38 ms Enabled Enabled 1.15 60 (0.3 A)

5Vfs/16 < VADC2 <6Vfs/16 38 ms Enabled Enabled 1.15 90 (0.45 A)

6Vfs/16 < VADC2 <7Vfs/16 38 ms Enabled Enabled 1.15 120(0.6 A)

7Vfs/16 < VADC2 <8Vfs/16 38 ms Enabled Enabled 1.25 60

8Vfs/16 < VADC2 <9Vfs/16 38 ms Enabled Enabled 1.25 90

9Vfs/16 < VADC2 <10Vfs/16 38 ms Enabled Enabled 1.25 120

10Vfs/16 < VADC2 <11Vfs/16 77 ms Enabled Enabled 1.15 60

11Vfs/16 < VADC2 <12Vfs/16 77 ms Enabled Enabled 1.15 90

12Vfs/16 < VADC2 <13Vfs/16 77 ms Enabled Enabled 1.15 120

13Vfs/16 < VADC2 <14Vfs/16 77 ms Enabled Enabled 1.25 60

14Vfs/16 < VADC2 <15Vfs/16 77 ms Enabled Enabled 1.25 90

15Vfs/16 < VADC2 <16Vfs/16 77 ms Enabled Enabled 1.25 120

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SM72441

RESET PIN

When the reset pin is pulled low, the chip will cease its normal

operation and turn-off all of its PWM outputs. Below is an os-

cilloscope capture of a forced reset condition.

30134208

FIGURE 5. Reset Operational Behavior

As seen in Figure 5, 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 de-

creases 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 6. Diode D1 and D2 provide ESD protection

for the analog inputs. The operating range for the analog in-

puts is 0V to VA. Going beyond this range will cause the ESD

diodes to conduct and result in erratic operation.

The capacitor C1 in Figure 6 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 typ-

ically 500Ω. Capacitor C2 is the ADC sampling capacitor; itis

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.

30134209

FIGURE 6. Equivalent Input Circuit

DIGITAL INPUTS and OUTPUTS

The digital input signals have an operating range of 0V to

VA, where VA = VDDA - VSSA. They are not prone to latch-

up and may be asserted before the digital supply VD, where

VD = VDDD - VSSD, without any risk. The digital output sig-

nals operating range is controlled by VD. The output high

voltage is VD – 0.5V (min) while the output low voltage is 0.4V

(max).

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SM72441

Physical Dimensions inches (millimeters) unless otherwise noted

NS Package Drawing MTC28

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SM72441

Notes

SM72441 Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar

Panels

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