Hybrid Battery Charger with Load Control for Telecom

1SLPA013A–October 2014–Revised June 2018Submit Documentation Feedback

Copyright © 2014–2018, Texas Instruments Incorporated

Hybrid Battery Charger With Load Control for Telecom Equipment

Application ReportSLPA013A–October 2014–Revised June 2018

Hybrid Battery Charger With Load Control forTelecom Equipment

ABSTRACTCommercial telecom equipment needs multiple power input systems to ensure continuous networkconnectivity. The load must be backed up to different sources. This application note describes asynchronous-buck-based reference design using MSP430, CSD87350 power blocks and the UCC27211half-bridge driver to use multiple OR’ed inputs (solar and AC/DC adaptor) to charge a 12-V SLA battery.Priority charging is used when solar energy is available. Seamless transfer between two sources ensuresbattery is always charged when inputs are available. It runs MPPT algorithms to charge while on solarinput and conventional CC/CV charging when working from an adaptor input. Multiple protection schemesensure it is a robust design.

Topic ........................................................................................................................... Page

1 Design Specifications........................................................................................... 22 Block Diagram ..................................................................................................... 33 System Explanation and Design ............................................................................ 34 Software Flow...................................................................................................... 55 Schematics........................................................................................................ 106 Test Results ...................................................................................................... 12

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Design Specifications www.ti.com

2 SLPA013A–October 2014–Revised June 2018Submit Documentation Feedback



Trademarks

1 Design Specifications

Table 1. Design Specifications

Parameter Description Value

VIN rangePanel 16.5 to 21 VAdaptor 15.5 to 16 V

Battery specifications Capacity 12 V, 100 Ah

Charging specificationsCharging current 7 AVoltage during CV mode charging 14.2 V

FSW Switch frequency 100 kHz

Output specificationsLoad current 4 AOutput voltage 10.2 to 14.2 V

Protection features

• Hot swappable load• Output short circuit• Reverse polarity protection• Two level overcurrent protection• Battery UVLO• Overtemperature protection

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100-W

12-V Solar Panel

Universal

AC Adaptor

(15 V at 7-A Capacity)

Telecom

EquipmentMicrocontroller

Oring ControlInput Current

Sense

Sync Buck

ConverterOutput Current

SenseLoad Switch

Load Current

Sense

Temp Sensor

LDO

ICS

OCS

VPANEL

LCS

VBAT

www.ti.com Block Diagram




2 Block DiagramFigure 1 shows the block level implementation of the system.

Figure 1.

3 System Explanation and Design

3.1 Power Source Control and MonitoringThe telecom equipment (load) is always powered either from a solar panel, AC/DC adaptor, or the battery.As long as solar energy from the panel is available, priority charging is used to deliver the required power(average 17 V and current sufficient enough to manage load or to charge battery). If panel voltage dropsbelow adapter (15 V), the charge controller microcontroller turns off the panel switch and turns on theAC/DC adapter switch, which also ensures no leakage of the stronger source into the weaker one. Two30-V, ultra-low RDS(on) FETs from TI (CSD17527Q5A) are selected for this purpose. The simple transistor isused for proving the drive from the microcontroller.

3.2 Synchronous Buck Power StageThe synchronous buck convertor has better efficiency and lower loss compared to asynchronous topologybecause a diode on the bottom side is replaced with a low RDS(on) value. A single 30-V, 25-A power blockfrom TI (CSD87350Q5D) is selected for this. The advantage of a power block is the smaller package andease of layout eliminating parasitics of board layout of high frequency hot nodes. The microcontrollerPWM module can generate multiple PWMs on the same timer base. Each output can be configured fordifferent output modes, for example, toggle, reset/on, reset/off, always on, and so forth. With this flexiblelogic, the user can achieve complimentary logic with required dead band. However, a half-bridge driver

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System Explanation and Design www.ti.com




with a floating high side drive is required to drive the high side and low side MOSFETs. The UCC27211,UCC2721x 120-V Boot, 4-A Peak, High-Frequency High-Side and Low-Side Driver, has high drivestrength, low propagation delays, and excellent delay matching to optimize the timing of the buck powerstage resulting in minimal switching loss. The other power stage components (inductor and capacitor)calculations are designed using standard equations of the buck converter based on the priorspecifications.• LOUT (cal) = 12.67 μH, selected LOUT = 10 μH, from Wurth Electronics• Selected COUT = 47 µF × 1; 22 µF × 2

3.3 Current Sense InputsTo ensure continuity to ground loop, a high-side sense circuit was used. A zero-drift instrumentationamplifier from TI, INA282, with a 50-V/V gain, wide common-mode input range is selected for thisapplication.

3.4 Load ManagementA simple load switch with hotswap control from TI TPS25910 is used for monitoring the load behavior. Ifthere is any short or overload, it immediately trips sending it into a hiccup mode on the load. The fast-tripcomparator of the microcontroller also quickly disables the PWM. This is second-level protection for theload. To prevent the load from discharging back into the source, a blocking FET (CSD17313Q2) from TI isused. It is controlled by the load switch.

3.5 MicrocontrollerA MSP430F5132 microcontroller is used in this application. See Section 4 for further details of thesoftware routines.

3.6 LDO and Temperature SensorA simple OR’ed supply is used as the input of the LDO to ensure that power to the controller is alwaysavailable to sense any inappropriate condition. The 3.3 V generated by the LDO (TPS73801) is used topower the MCU, LEDs, instrumentation amplifiers, and a simple thermostat TMP709, which is used fortripping the load in case there is any abnormal increase in the temperature.

3.7 Battery ManagementThe section explains the battery management software portion in the microcontroller. It checks for thestate-of-charge of the battery and applies the charging profile appropriately. This application uses a lead-acid battery. The following list shows the battery properties that are considered while charging.• Minimum 2.10 V per cell is considered as a good battery• Cells in a string are not the same strength, some are weak and some are strong.• Should not be charged above 50°C• Overcharging increases the risk of hydrogen gassing on the positive plate.• Undercharging increases sulfation on the negative plate.• Battery charge profile is in constant current mode until battery attains, for example, 70%, constant

voltage mode from 70% to 90% and float charge after that.

3.8 Maximum Power Point Tracking AlgorithmA simple MPPT algorithm known as perturb and observe is used for controlling this system. As explainedin the PWM Resolution section, every one count of PWM timer yields 0.04% of duty cycle variation, whichis “fine” enough to achieve smoother and slower tracking. With this at MPP stage, there will be 0.04%oscillation which may be negligible in a low-power application. If duty cycle variation is increased morethan 1 count, tracking is faster and reduces the variation to minimize the MPP stage oscillations. This alsoresembles incremental conductance method. It monitors battery/load current with respect to ΔV applied tothe converter, increasing the ΔV drives to MPP faster and at the MPP stage reduces the ΔV and settlessmoothly at MPP.

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http://www.ti.com/lit/ds/symlink/ucc27211.pdf

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4 Software FlowThis application uses the MSP430F5132 microcontroller. The following are key features, which enableefficient usage of resources to achieve an efficient solar power convertor.

MSP430F5132 key features supporting efficiency expectation:• Fully operates from 3.6 to 1.8 V• Only 180-µA/MHz active current, lowest current at shut down is 0.25 µA• Fast wake-up, less than 5 µs from stand by• 200 KSPS, 10-bit ADC, with just 110-µA current consumption with built-in reference• Hi-resolution timer/PWM = 4-ns minimum pulse duration, 250-µA current consumption

4.1 PWM ResolutionThe MSP430F5132 has a special hi-resolution timer, timer-D. This timer can be programmed to generatehigh switching frequency to accommodate a smaller inductor's size. This timer is clocked from thefollowing sources:• MCLK/SMCLK – Maximum range is 16 MHz• ACLK – Maximum 32 kHz• Special timer-D clock generator of the following values:

– 64 MHz– 128 MHz– 200 MHz– 256 MHZ

Effective number of bits (ENOB) is an important parameter in achieving smoother control, therebyreducing switching noise and protecting the battery from stress caused by larger voltage variations causedin a low-resolution system.

ENOB = Log2(Module clock / Output frequency) (1)

This application requires 100-kHz switching frequency. Therefore, the following settings provide,

Module clock = 256 MHz

Output frequency = 100 kHz

ENOB = 11.36 bitsVOUT = D × VIN

where• D = Duty cycle or on-time of the switch• VIN = Input voltage (from battery, solar panel, or ACDC adapter)• VOUT = Output voltage (2)

Consider the converter to be 100% efficient. Therefore, no loss factor is taken into account in thiscalculation. For a single bit change in D varies by approximately 4 ns in a 100-kHz period wave, which is0.038% of VIN; if a VIN of 17, VOUT varies by 0.00646 V.

4.2 ADC ModuleThis device has 10-bit SAR ADC, speed can be configured for 50ksps for low power or 200ksps for fasterprocessing. This application can go slow, which helps to conserve additional power loss caused by theADC module itself (refer to the data sheet for power consumption data). This module can be operatedindependently without sharing the CPU clock. Hence, the CPU can be placed in low-power mode,enabling only the ADC to function.

A special ADC DMA can be configured to scan all channels and interrupt the CPU when data is availableat the RAM for further processing. This application requires 6 channels: battery current, panel current,battery voltage, panel voltage, load current, and temperature sensor. Therefore, a 6-channel conversion isrequired every loop, until then the CPU can be put in IDLE to conserve power.

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Source

S1

Panel V x I

Source

S2

Adapter V x I

S1 S2≥Select S2,

Turn OFF S1

Select S1,

Turn OFF S2

Power on/

Reset

Init ADC

Init PWM

Init Comparator for Tripping

Start Control Loop

Software Flow www.ti.com




4.3 ADC Measurement RangeThis MCU has a 10-bit SAR ADC, input voltage range is 0 V to AVCC, which can be up to 3.6 V (refer todata sheet for more electrical data). Hence, input signal strength can be from 3.3 mV per count of ADCuntil 3.3 V (1023 counts) can be sensed. Sense resistors are 5 mΩ. Hence, minimum current sensiblefrom panel/load/battery with a gain of 50 is about 13 mA.

Figure 2. Initialization Flow Chart

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ADC Interrupt every

100 ms

SAMPLE

• Panel Voltage (P_V)

• Panel Current (P_I)

• Battery Voltage(B_V)

• Battery Current(B_I)

• Adaptor Voltage (A_V)

• Load Current(A_I)

B_V > P_V

&&

B_V > A_V

P_V < A_V

&&

P_I ~= 0*

P_V > A_V

&&

P_I > Lowest

Threshold*

P_V > B_V

&&

P_I > Threshold

• Disable Battery Charging Algorithm

• Only Load Management Thread

• Turn OFF Panel and Adaptor Indicator LEDs

Wait for ADC

Interrupt

• Panel Switch OFF, Adaptor switch ON

• Turn OFF Panel LED and Turn ON Adaptor

Indicator LED

• Load Management and CC/CV Mode

• Adaptor Switch OFF, Panel switch ON

• Turn OFF Adaptor LED and Turn ON Panel

Indicator LED

• Call Current Control (MPPT) and Load

Management

• Load Management

Yes

Yes

Yes

No

Yes





Figure 3. Control Loop Flow Chart

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State of Charge

Fast Charge

CC Mode

Topping Charge

CV ModeFloat Charge

Safety Test

Temp

Short

Open

Charge < 20%

Charge > 70%

Charge > 95%

Fault Wait

Current Control

Loop Start

(MPPT)

Sample Battery Current

I_B(n)

I_B(n) >

I_B(n-1)

Increment PWM

Duty Cycle Count

Decrement PWM

Duty Cycle Count

Yes No

Software Flow www.ti.com




Figure 4. MPPT Algorithm Flow Chart

Figure 5. Battery Management Flow Chart

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ADC InterruptEvery 100 ms

Run MPPT

Charging Loop

if Solar Panel

Powered

Run CC/CV

Charging Loop

if Adapter

Powered

Run Load

Management Loop

Run Battery

Management

Loop

CPU Idle

State





Figure 6. Control Loop Logic

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PANEL CURRENT SENSE

CONVERTER OUTPUT CURRENT SENSE

LOAD CURRENT SENSE

BATTERY CHARGER CIRCUITPANEL CONNECTOR

ADAPTOR CONNECTOR

IND_74436xxxx

3.01

CONN-RMC-2PIN

CONN-RMC-2PIN

R603

2512

2512

QFN5X6MM

R603

R603

SOT23

CONN-RMC-2PIN

CONN-RMC-2PIN

R603

R603

R603

SOT23

QFN5X6MM

QFN5X6MM_DUAL

C603 C603

C603

C603

CAP_EEUCF CAP_EEUCF C603 C603 C603

2512

2512

SO8

SO8

SO8

R603

R603

R603

C603

C603

C603

R603

DNP

R603

R603

SOT-23

R603

R603

SOT-23

PANEL AND ADAPTOR VOLTAGE SENSE

VP P+

V3V3

IP_SNS

BAT+

CONV_OUT

V3V3

IBAT_SNS

VLOAD BAT+

V3V3

ILOAD_SNS

BAT+

CONV_OUT

BUCK_PWM

SYNCB_PWM

P+

BAT+

PAN_SW

BAT+

AC_SW

VP

BAT+

VP

P+

VP_SNSV

3V

3

P-

ADP-

P-

VP

VADP_SNS

V3V

3

ADP-

L110 Hµ

12

U13INA28xAID

REF23

NC4

-IN1

GND2

OUT5V+6REF17+IN8

R4810 kΩ

R5510 kΩ

Q3CSD17527Q5A

5

4

123

C324.7 µF

R141206

R4774 kΩ

Q82N2907A

Q92N2907A

J2CONN-RMC-2PIN

1

2

R39

10 kΩ

C18

0.01 µF

U11INA28xAID

REF23

NC4

-IN1

GND2

OUT5V+6REF17+IN8

R42DNP

D10

MMBZ5237

R5670 kΩ

D12

BAT54S

S

A C

C190.22 uF

Q5MMBT2222ALT1

B

CE

C33

100 p

C171 µF

D7

LED

AK

R321 kΩ

U15INA28xAID

REF23

NC4

-IN1

GND2

OUT5V+6REF17+IN8

R45 2 kΩ

R171 kΩ

Q6CSD17527Q5A

5

4

123

R1310 mΩ

1 2

L210 µH

12

R1210 mΩ

1 2

R46 2 kΩ

R44

1 kΩ

R151206

C142.2 nF

R270 Ω

R341 kΩ

R43DNP

C1622 Fµ

R261 kΩ

+ C1247 µF

C1522 Fµ

J3CONN-RMC-2PIN

1

2

R5110 kΩ

C34

100 p

R3810 kΩ

C1322 Fµ

R280 Ω

U7UCC27211_D_8

HO3

HS4

VDD1

HB2

HI5LI6VSS7LO8

R30

10 mΩ

1 2

C260.1 Fµ

+C1147 µF

R5410 kΩ

R3720 kΩ

C240.1 Fµ

R5374 kΩ

D11

BAT54S

S

A C

Q7MMBT2222ALT1

B

CE

R31

10 mΩ

1 2

Q4CSD87350Q5D

3TG

1 VIN1

4

TGR

5

BG

6VSW1

7VSW2

8VSW3

9

PGND

R5270 kΩ

+C311000 µF

C280.1 Fµ

R161206

R290 Ω

Schematics www.ti.com




5 Schematics

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LOAD CURRENT CONTROL

TEMPERATURE SENSOR

LOAD CONNECTOR

BATTERY CONNECTOR

CONTROLLER SECTION

12 V at 4.5 A

CONN-RMC-2PIN

CONN-RMC-2PIN

CONN-RMC-2PIN

CONN-RMC-2PIN

SMA

CAP_EEUCF

C603 R603

RSA-16

R603

R603

SON_2X2MM

C603

C603 CAP_EEUCF

SOT23

R603 R603

R603

DBV_5 C603

R603

2010

2010

D_SOD123

R603

R603 C603

DNP

SOT-23

R603

R603

C603

C603

R603 R603

BAT_CHRG

LOW_BAT

DA_38P

AC_CHRG

R603

C603

DNP

R603

C603

R603

C603

R603

C603

SOT-23

C603 C603

R603

DCQ

R603

R603

C603 C603

BATTERY VOLTAGE SENSE

BAT+

LOAD_ENABLE

VLOAD

VOUT

AGND

V3V3

LOAD_ENABLE

VLOAD

V3V3

V3V3

V3V3

V3V3

BAT+

VBAT_SNS

BAT+

VP

AC_SWPAN_SW

V3V3

LOAD_ENABLE

VBAT_SNS

IBAT_SNS

VP_SNS

IP_SNS

ILOAD_SNS

SYNCB_PWMBUCK_PWM

V3V

3

ILOAD_SNSVADP_SNS

D1SMAJ20A

AK

R96.8k

R400 Ω

+ C347 µF

R251 kΩ

C2100 nF

U3TPS738xxDCQR

IN1

EN5

OUT2

FB4

GND3

GN

D1

6

D6BAT54C

C

A2

A1

R8200 kΩ

R3310 mΩ

R7100 kΩ

U2TMP709

VCC5

GND2

OT3

HYST4

SET1

J1CONN-RMC-2PIN

1

2

C10.1 µF

R410 Ω

R61 kΩ

C5DNP

C90.1uF

C1010 µF

R241 kΩ

R1846.8 kΩ

J5CONN-RMC-2PIN

1

2

D4

LED

AK

R231 kΩ

D3

LED

AK

C222.2 nF

C302.2 nF

R360 Ω

R510 kΩ

C292.2 nF

C40.1 µF

R3547k

R30 Ω

C2510 nF

D9

BAT54S

S

A C

D2MBR130

AK

R104k

R426 kΩ

C21

0.1 µF

C232.2nF

R140.2 kΩ

U5MSP430F5132IDAR

AVCC1

PJ.4/XOUT2

PJ.5/XIN3

AVSS4

P1.05

P1.26

P1.17

P1.38

P1.49

P1.510

PJ.011

PJ.112

PJ.213

PJ.314

P1.615

P1.716

P2.017

P2.118

P2.219

P2.320DVIO21DVSS122P2.423P2.524P2.625P2.726P3.027P3.128VCORE29DVSS230DVCC31PJ.632P3.233P3.334SBWTCK/TEST35NMI/SBWTDIO_RST36P3.537P3.638

+

C6DNP

C20 470 nF

R2247 kΩ

R220 kΩ

C810uF

C7

0.1 µF

Q2MMBT2222ALT1

B

CE

R1910 kΩ

J4CONN-4P-TOPENTRY

4

3

2

1

R1110 mΩ

Q1CSD17313Q2

1

3

74 2

568

D5

LED

AK

U1TPS25910RSA

VIN11

VIN22

VIN33

GATE4

GND15

GND26

ILIM7

GND38

GND49

OUT10

OUT111

OUT212

GND513

GND614

FLT15

EN16

PW

PD

17

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Test Results www.ti.com




6 Test Results

Figure 7. Variation of the Duty Cycle from the Controller

Figure 8. Seamless Transfer from Panel to Adaptor

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Figure 9. Output PWM Pulses from UCC27211

Figure 10. Load Switch Response to Short Circuit

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Revision History www.ti.com



Revision History

Figure 11. MSP430 Fast Trip Comparator Response to Load Short Circuit (EN)

Revision HistoryNOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Original (October 2014) to A Revision .................................................................................................... Page

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