Texas Instruments BQ24450EVM User Manual
User's Guide
SLUU464–November 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 EVM Features ...................................................................................................... 2
1.2 General Description ................................................................................................ 2
1.3 I/O Description and Jumper Functions .......................................................................... 2
1.4 Recommended Operating Conditions ........................................................................... 3
2 Equipment .................................................................................................................... 3
2.1 Power Supplies ..................................................................................................... 3
2.2 Loads ................................................................................................................ 3
2.3 Meters ............................................................................................................... 3
3 Equipment Setup ............................................................................................................ 3
4 Procedure .................................................................................................................... 4
4.1 Pre-charge .......................................................................................................... 4
4.2 Max Charge ......................................................................................................... 4
4.3 Charge Termination ................................................................................................ 4
4.4 Re-Charge .......................................................................................................... 4
5 Functions and Features .................................................................................................... 5
5.1 Changing Output Voltage and Charge Current ................................................................ 5
5.2 Options for External Transistor ................................................................................... 6
5.3 Other Options ....................................................................................................... 6
6 PCB Layout Guideline ...................................................................................................... 6
7 Bill of Materials, Board Layouts and Schematic ........................................................................ 7
7.1 Bill of Materials ..................................................................................................... 7
7.2 Board Layout ....................................................................................................... 8
7.3 Schematic ........................................................................................................... 9
List of Figures
1 Original Test Setup for HPA691 (bq24450 EVM)....................................................................... 3
2 Battery Load Circuit – PR1010-2 ......................................................................................... 4
3 Calculating the Value of I
4 Top Assembly Layer........................................................................................................ 8
5 Top PCB Layer.............................................................................................................. 8
6 Bottom PCB Layer.......................................................................................................... 9
7 bq24450 EVM Schematic.................................................................................................. 9
1 I/O Description............................................................................................................... 2
2 Recommended Operating Conditions.................................................................................... 3
3 Bill of Materials.............................................................................................................. 7
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............................................................................................. 5
TAPER
List of Tables
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1
Introduction
1 Introduction
1.1 EVM Features
• Evaluation module for bq24450 (HPA691)
• Charge controller for lead-acid batteries
• Constant current and constant voltage modes
• Accommodates external transistor in DPAK or TO-220 package
• Programmable charge current
• Pre-Charge for deeply discharged batteries
1.2 General Description
The bq24450 contains all the necessary circuitry to optimally control the charging of lead-acid batteries.
The IC controls the charging current as well as the charging voltage to safely and efficiently charge the
battery, maximizing battery capacity and life. Depending on the application, the IC can be configured as a
simple constant-voltage float charge controller or a dual-voltage float-cum-boost charge controller.
The built-in precision voltage reference is especially temperature-compensated to track the characteristics
of lead-acid cells, and maintains optimum charging voltage over an extended temperature range without
using any external components. The low current consumption of the IC allows for accurate temperature
monitoring by minimizing self-heating effects.
The IC can support a wide range of battery capacities and charging currents, limited only by the selection
of the external pass transistor. The versatile driver for the external pass transistor provides at least 25mA
of base drive.
In addition to the voltage- and current-regulating amplifiers, the IC features comparators that monitor the
charging voltage and current. These comparators feed into an internal state machine that sequences the
charge cycle. Some of these comparator outputs are made available as status signals at external pins of
the IC. These status and control pins can be connected to a processor, or they can be connected up in
flexible ways for standalone applications.
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1.3 I/O Description and Jumper Functions
Table 1. I/O Description
Header Description
J1 – Vin Power Supply Positive
J2 – GND Power Supply Negative
J3 – GND Ground
J4 – Vout Connected to Battery/System Load
J5 – GND Ground
spacer
Jumper Description See Functions and Features section for more information.
JP1 Connects I
resistor, R4.
JP2 Connects IFBfor current sense for I
JP3 Selects the topology for the external transistor. The external transistor can be configured for
either Common-Emitter topology or Quasi-Darlington topology.
for current sense for I
SNSM
. It can connect I
TAPER
It can connect IFBto either side of the sense resistor, R4.
MAX.
to either side of the sense
SNSM
2
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1.4 Recommended Operating Conditions
Table 2. Recommended Operating Conditions
Symbol Description Min Typ Max Unit
Vin, J1 Supply Voltage 9.5 10.0 10.5 V
Vout, J4 Battery Voltage (3-cell lead-acid battery) 4 7.5 V
Iin Supply Current 0 0.5 A
Iout Charge Current 0 0.5 A
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
Equipment
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)
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3
Procedure
Replacement circuit for a 3-cell lead acid battery. BAT+ to BAT– voltage tracks the power supply input
voltage, minus 1 diode drop
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.
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Figure 2. Battery Load Circuit – PR1010-2
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
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