Texas Instruments Battery Charger BQ24450EVM User Manual

User's Guide  
SLUU464November 2010  
bq24450EVM  
This user's guide describes the features and operation of the bq24450EVM Evaluation Module (EVM).  
This EVM assists users in evaluating the bq24450 linear battery charger. The manual includes the  
bq24450EVM bill of materials, board layout, and schematic.  
Contents  
1
Introduction .................................................................................................................. 2  
1.1  
1.2  
1.3  
1.4  
EVM Features ...................................................................................................... 2  
General Description ................................................................................................ 2  
I/O Description and Jumper Functions .......................................................................... 2  
Recommended Operating Conditions ........................................................................... 3  
2
Equipment .................................................................................................................... 3  
2.1  
2.2  
2.3  
Power Supplies ..................................................................................................... 3  
Loads ................................................................................................................ 3  
Meters ............................................................................................................... 3  
3
4
Equipment Setup ............................................................................................................ 3  
Procedure .................................................................................................................... 4  
4.1  
4.2  
4.3  
4.4  
Pre-charge .......................................................................................................... 4  
Max Charge ......................................................................................................... 4  
Charge Termination ................................................................................................ 4  
Re-Charge .......................................................................................................... 4  
5
Functions and Features .................................................................................................... 5  
5.1  
5.2  
5.3  
Changing Output Voltage and Charge Current ................................................................ 5  
Options for External Transistor ................................................................................... 6  
Other Options ....................................................................................................... 6  
6
7
PCB Layout Guideline ...................................................................................................... 6  
Bill of Materials, Board Layouts and Schematic ........................................................................ 7  
7.1  
7.2  
7.3  
Bill of Materials ..................................................................................................... 7  
Board Layout ....................................................................................................... 8  
Schematic ........................................................................................................... 9  
List of Figures  
1
2
3
4
5
6
7
Original Test Setup for HPA691 (bq24450 EVM).......................................................................  
Battery Load Circuit – PR1010-2 .........................................................................................  
Calculating the Value of ITAPER .............................................................................................  
Top Assembly Layer........................................................................................................  
Top PCB Layer..............................................................................................................  
Bottom PCB Layer ..........................................................................................................  
bq24450 EVM Schematic..................................................................................................  
List of Tables  
1
2
3
I/O Description...............................................................................................................  
Recommended Operating Conditions ....................................................................................  
Bill of Materials ..............................................................................................................  
1
SLUU464November 2010  
bq24450EVM  
© 2010, Texas Instruments Incorporated  
 
Equipment  
1.4 Recommended Operating Conditions  
Table 2. Recommended Operating Conditions  
Symbol  
Vin, J1  
Vout, J4  
Iin  
Description  
Min Typ  
Max Unit  
Supply Voltage  
9.5 10.0  
10.5  
7.5  
0.5  
0.5  
V
V
A
A
Battery Voltage (3-cell lead-acid battery)  
Supply Current  
4
0
0
Iout  
Charge Current  
2
Equipment  
2.1 Power Supplies  
Power Supply #1 (PS#1): Adjustable from 0 to 10 VDC at 1A; used for input J1.  
Power Supply #2 (PS#2): Adjustable from 0 to 10 VDC at 1.5A; used for Battery Load Board.  
2.2 Loads  
Load #1: Battery Load Circuit Board, PR1010-2, as shown in Figure 2.  
2.3 Meters  
Three Fluke 75 DMMs (equivalent or better).  
3
Equipment Setup  
The original test setup of HPA691 is shown in Figure 1.  
1. Set the PS #1 for 10V, 1A current limit and then turn off supply. Connect PS#1 across J1, J2 (VIN,  
GND).  
2. Connect a voltage meter (VM #1) across J1, J2 (VIN, GND)  
3. Set PS#2 to 5.2V and then turn off supply. Connect to the Battery Load Circuit Board (P/S+, P/S–)  
4. Connect Load #1 (BAT+, BAT–) across J4, J5 (VOUT, GND).  
5. Connect a voltage meter (VM#2) across J4, J5 (VOUT, GND).  
6. Connect a voltage meter (VM#3) across sense resistor on Load #1.  
7. Verify the jumpers are placed correctly as per, Figure 1.  
Figure 1. Original Test Setup for HPA691 (bq24450 EVM)  
3
SLUU464November 2010  
bq24450EVM  
© 2010, Texas Instruments Incorporated  
 
               
Procedure  
Replacement circuit for a 3-cell lead acid battery. BAT+ to BAT– voltage tracks the power supply input  
voltage, minus 1 diode drop  
Figure 2. Battery Load Circuit – PR1010-2  
4
Procedure  
4.1 Pre-charge  
Turn on PS #1, preset to 10 VDC. Verify voltage on VM #1.  
Turn on PS #2, preset to 5.2 VDC.  
Adjust PS #2 such that VM #2 shows 5 VDC.  
Using VM #3, measure the voltage across the current sense resistor on Load #1. Multiply this value by a  
conversion factor of 10A/V. This is the pre-charge current.  
4.2 Max Charge  
Adjust PS #2 such that VM #2 shows 6 VDC.  
Using VM #3, measure the voltage across the current sense resistor on Load #1. Multiply this value by  
a conversion factor of 10A/V. This is the max charge current.  
4.3 Charge Termination  
Adjust PS #2 such that VM #2 shows 7.5 VDC.  
There should be no charge current in this condition.  
4.4 Re-Charge  
Adjust PS #2 such that VM #2 shows 6 VDC.  
Using VM #3, measure the voltage across the current sense resistor on Load #1. Multiply this value  
by a conversion factor of 10A/V. This is the max charge current.  
4
bq24450EVM  
SLUU464November 2010  
© 2010, Texas Instruments Incorporated  
 
         
Functions and Features  
5
Functions and Features  
5.1 Changing Output Voltage and Charge Current  
This EVM is configured to charge a 3-Cell Lead Acid Battery with a maximum charge current of 450 mA.  
The EVM can be altered to charge lower or higher voltage batteries and can also be altered to have a  
lower or higher maximum charge current.  
Power Dissipation  
It is important to monitor the power dissipation in the external transistor, Q1.  
WARNING  
Q1 and the surrounding area of the PCB may become hot.  
(Power Dissipation in Q1) = (Vin – Vout – 0.25 – 0.7) × Charge Current  
With a large difference between Vin and Vbat, and/or a high charge current, there will be a significant  
amount of power dissipation in Q1. This causes both Q1 and the surrounding PCB to get hot. If any  
alterations are made to the EVM circuit, it is important to ensure a safe level of power dissipation in the  
external FET, Q1.  
Changing Output Voltage  
The output voltage may be altered by changing some on-board resistors (R7, R8, R9, R11, R12). See the  
bq24450 datasheet for information on how to size these resistors. If Vout is changed, Vin must also be  
changed. Vin should be high enough to allow for the necessary dropout (across R2, R4, Q1, and D1) and  
low enough to maintain a safe level of power dissipation.  
Changing the Maximum Charge Current  
The maximum charge current is set by sense resistor, R2. (Max Charge Current) = (0.25) / R2. Resistor  
R2 may be adjusted to set a different max charge current. However, more current will yield higher power  
dissipation in Q1. This may cause the board to become hot.  
Changing Pre-Charge Current  
Pre-Charge current is set by R10.  
Pre-Charge Current = (Vin – 2 – Vout) / R10  
Changing the value of Itaper  
As populated, ITAPER is 10% of IMax-Chg. This is because VILIM is 250mV and VISNS is 25mV and both are being  
sensed across R2. If a different value of ITAPER is desired, R4 can be populated (with a non-zero resistor)  
and JP1 and JP2 can be used to connect pins ISNSM and IFB to opposite sides of R4. See figure below.  
Figure 3. Calculating the Value of ITAPER  
5
SLUU464November 2010  
bq24450EVM  
© 2010, Texas Instruments Incorporated  
 
     
PCB Layout Guideline  
5.2 Options for External Transistor  
Using a Transistor in a TO-220 package  
The EVM is populated with a DPAK transistor for Q1. However, if desired, a TO-220 transistor can be  
used instead. Three holes have been placed in the PCB in parallel with the DPAK pad. Remove the DPAK  
transistor and replace it with a TO-220 transistor. The top hole is the base, the middle hole is the collector,  
and the bottom hole is the emitter.  
Using a P-channel FET  
The EVM is populated with a PNP transistor for Q1. However, if desired, a P-channel MOSFET may be  
used instead. In order to use a P-FET, a resistor must be populated on R5. Pin 16 of the BQ24450 will  
sink current through R5 and generate a negative gate to source voltage for the P-FET. By varying the sink  
current (and subsequently Vgs), the IC can accurately control the charge current. A 1kΩ resistor is  
suitable for R5.  
Changing the topology  
The EVM is configured with the Common-Emitter PNP topology. However, it can also be configured for  
the PNP in a Quasi-Darlington as described on page 13 of the datasheet. To make this change, the  
following steps should be taken:  
1. Place jumper on JP3 such that it connects Pin 15 of the IC to the collector of Q1.  
2. Remove R6 and replace with Rp as calculated on page 13 of the data sheet.  
5.3 Other Options  
Disabling Pre-Charge Mode  
The EVM is populated to perform pre-charge on a deeply depleted battery. If pre-charge mode is not  
desired, it can be disabled by performing the steps below.  
1. Populate R1 = 0 Ω  
2. Remove R11 and R12  
3. Populate R14 = R11 + R12 (For example: If R11 = 75kΩ and R12 = 16.9kΩ, R14 = 91.9kΩ)  
PGOOD  
As populated, the EVM uses PGOOD as part of the feedback divider (explained on page 11 of data  
sheet). If desired, PGOOD can be used to indicate the supply status on pin 5.  
1. Remove R8 and place it on R15 pad.  
2. Populate R13 with a pull-up resistor.  
6
PCB Layout Guideline  
It is important to pay special attention to the printed-circuit board (PCB) layout. The following provides  
some guidelines:  
1. All low-current GND connections must be kept separate from the high-current charge or discharge  
paths from the battery. Use a single-point ground technique incorporating both the small signal ground  
path and the power ground path.  
2. The high current charge paths into IN pin and from the OUT pin must be sized appropriately for the  
maximum charge current in order to avoid voltage drops in these traces.  
6
bq24450EVM  
SLUU464November 2010  
© 2010, Texas Instruments Incorporated  
 
     
Bill of Materials, Board Layouts and Schematic  
7
Bill of Materials, Board Layouts and Schematic  
7.1 Bill of Materials  
Table 3. Bill of Materials  
Reference  
Value  
Description  
Size  
Part Number  
MFR  
Designator  
C1, C4  
C2, C5  
C3  
Open  
Capacitor, Ceramic  
1206  
603  
Std  
Std  
Std  
Std  
1.0µF  
Capacitor, Ceramic, 25V, X5R, 10%  
Capacitor, Ceramic, 25V, X7R, 10%  
Diode  
Std  
0.1µF  
603  
Std  
D1  
ES2AA-13-F  
SMA  
ES2AA-13-F  
Diodes,  
Inc.  
Q1  
MJD32CT4  
Open  
Transistor, PNP  
DPAK  
603  
MJD32CT4  
Std  
ST  
R1, R5, R13, R14,  
R15  
Resistor, Chip, 1/16W, 1%  
Std  
R2  
0.56Ω  
0Ω  
Resistor, Chip, 1/2W, 1%  
Resistor, Chip, 1/16W  
2010  
603  
STD  
STD  
Std  
Vishay  
Std  
Std  
Std  
Std  
Std  
Std  
Std  
TI  
R3, R6  
R4  
Std  
0Ω  
Resistor, Chip, 1/2W  
2010  
603  
CRCW20100000Z0EF  
R7  
475kΩ  
46.4kΩ  
453Ω  
Resistor, Chip, 1/16W, 1%  
Resistor, Chip, 1/16W, 1%  
Resistor, Chip, 1/16W, 1%  
Resistor, Chip, 1/10W, 1%  
Resistor, Chip, 1/16W, 1%  
Resistor, Chip, 1/16W, 1%  
Resistor, Chip, 1/16W, 1%  
Std  
R8  
603  
Std  
R9  
603  
Std  
R10  
R11  
R12  
R16  
U1  
187Ω  
603  
Std  
75.0kΩ  
16.9kΩ  
10.0kΩ  
BQ24450D  
603  
Std  
603  
Std  
603  
Std  
IC, INTEGRATED CHARGE  
CONTROLLER  
SO-16  
BQ24450D  
FOR LEAD-ACID BATTERIES  
7
SLUU464November 2010  
bq24450EVM  
© 2010, Texas Instruments Incorporated  
 
     
Bill of Materials, Board Layouts and Schematic  
7.2 Board Layout  
Figure 4. Top Assembly Layer  
Figure 5. Top PCB Layer  
8
bq24450EVM  
SLUU464November 2010  
© 2010, Texas Instruments Incorporated  
 
     
Bill of Materials, Board Layouts and Schematic  
Figure 6. Bottom PCB Layer  
7.3 Schematic  
Figure 7. bq24450 EVM Schematic  
9
SLUU464November 2010  
bq24450EVM  
© 2010, Texas Instruments Incorporated  
 
     
Evaluation Board/Kit Important Notice  
Texas Instruments (TI) provides the enclosed product(s) under the following conditions:  
This evaluation board/kit is intended for use for ENGINEERING DEVELOPMENT, DEMONSTRATION, OR EVALUATION  
PURPOSES ONLY and is not considered by TI to be a finished end-product fit for general consumer use. Persons handling the  
product(s) must have electronics training and observe good engineering practice standards. As such, the goods being provided are  
not intended to be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations,  
including product safety and environmental measures typically found in end products that incorporate such semiconductor  
components or circuit boards. This evaluation board/kit does not fall within the scope of the European Union directives regarding  
electromagnetic compatibility, restricted substances (RoHS), recycling (WEEE), FCC, CE or UL, and therefore may not meet the  
technical requirements of these directives or other related directives.  
Should this evaluation board/kit not meet the specifications indicated in the User’s Guide, the board/kit may be returned within 30  
days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY  
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This evaluation board/kit is intended for use for ENGINEERING DEVELOPMENT, DEMONSTRATION, OR EVALUATION  
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EVM Warnings and Restrictions  
It is important to operate this EVM within the input voltage range of 9.5 V to 10.5 V and the output voltage range of 4 V to 7.5 V .  
Exceeding the specified input range may cause unexpected operation and/or irreversible damage to the EVM. If there are  
questions concerning the input range, please contact a TI field representative prior to connecting the input power.  
Applying loads outside of the specified output range may result in unintended operation and/or possible permanent damage to the  
EVM. Please consult the EVM User's Guide prior to connecting any load to the EVM output. If there is uncertainty as to the load  
specification, please contact a TI field representative.  
During normal operation, some circuit components may have case temperatures greater than 75° C. The EVM is designed to  
operate properly with certain components above 75° C as long as the input and output ranges are maintained. These components  
include but are not limited to linear regulators, switching transistors, pass transistors, and current sense resistors. These types of  
devices can be identified using the EVM schematic located in the EVM User's Guide. When placing measurement probes near  
these devices during operation, please be aware that these devices may be very warm to the touch.  
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Copyright © 2010, Texas Instruments Incorporated  
 
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