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19-1308; Rev 1; 10/98

MAX1660 Evaluation Kit

General Description

The MAX1660 evaluation kit (EV kit) is an assembled

surface-mount demonstration board. The EV kit embod-

ies the typical application circuit shown in Figure 8 of

the MAX1660 data sheet. Additional circuitry allows an

IBM-compatible personal computer to use its parallel

port to emulate an Intel System Management Bus

(SMBus™) interface.

4A Max Current, 1% Accuracy

Proven PC Board Layout

Convenient Test Points Provided On-Board

Data-Logging Software

Fully Assembled and Tested

Features

Measures 4A Currents to 1% Accuracy

Evaluates: MAX1660

Ordering Information

PART

MAX1660EVKIT

TEMP. RANGE

0°C to +70°C

IC PACKAGE

16 QSOP

Component List

DESIGNATION QTY

C6*

D1, D20, D21,

D22

D23–D26

DESCRIPTION

0.33µF, 6V ceramic capacitor

10nF, 6V ceramic capacitor

0.1µF, 6V ceramic capacitor

4.7nF, 6V ceramic capacitor

10nF, 6V ceramic capacitor

0.33µF ceramic capacitor (option)

1N4148-type SOT23 signal diodes

1N5233B-type, 6V, 500mW, axial-

leaded zener diodes

DB25 male right-angle connector

Smart battery connector

AMP 787259-1 (10.8V key on left)

Uninsulated, nickel-plated standard

banana jacks

E. F. Johnson 108-0740

Unstuffed

Red light-emitting diode

Logic-level, P-channel, SO-8, single

power MOSFET

International Rectifier IRF7205

R2, R30–R33

R3, R5

R4, R6

R7, R8

R9, R10, R20,

R21, R24,

R25, R26

R11

R12*

R22, R23,

R27, R28,

R29, R35

R34

SW1

*User

option

DESIGNATION QTY

Q20, Q21,

Q22

DESCRIPTION

2N3904 NPN equivalent, SOT23

0.030Ω, 1%, 1W sense resistor

IRC LR2512-01-R030-F or

Dale WSL-2512 0.030Ω

100Ω, 5%, 1/16W resistors

910kΩ, 1%, 1/16W resistors

75kΩ, 1%, 1/16W resistors

470kΩ, 5%, 1/16W resistors

10kΩ, 5%, 1/16W resistors

1MΩ, 5%, 1/16W resistor

51Ω, 5%, 1/16W resistor (option)

100kΩ, 5%, 1/16W resistors

680Ω, 5%, 1/16W resistor

Slide switch

Maxim MAX1660EEE

74HC14 hex Schmitt trigger, SO-14

J3, J4

JU1

LED1

M1, M2

SMBus is a trademark of Intel Corp.

________________________________________________________________

Maxim Integrated Products

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.

For small orders, phone 1-800-835-8769.

MAX1660 Evaluation Kit

Evaluates: MAX1660

Component Suppliers

SUPPLIER

Dale

Sense Resistors

International

Rectifier

IRC

PHONE

(402) 564-3131

(310) 322-3331

(512) 992-7900

FAX

(402) 563-6418

(310) 322-3332

(512) 992-3377

3) The MAX1660.EXE software program can be run

from the floppy or from a hard drive. Simply use the

Windows program manager to run the program. If

desired, you may use the INSTALL.EXE program to

copy the files and create icons for them in the

Windows 3.1 Program Manager (or the Windows 95

Start Menu).

4) Start the MAX1660 program by opening its icon in

the Program Manager (or Start Menu).

5) The program prompts you to select the correct paral-

lel port. An auto-detect routine attempts to identify the

correct port and highlights it as the default choice.

6) Apply the load or charger and observe the charge

or discharge current readings on the main window

display.

*Please

indicate that you are using the MAX1660 when

contacting these suppliers.

_________________________Quick Start

Equipment Required

Before you begin, you will need the following equip-

ment:

•

A battery pack

An appropriate charger

An appropriate load

An IBM PC-compatible computer running Windows

3.1™ or Windows 95™

A spare parallel printer port (this is a 25-pin socket

on the back of the computer)

A standard 25-pin, straight-through, male-to-female

cable to connect the computer’s parallel port to the

Maxim EV kit (optional). Or, the EV kit can be

plugged directly into the parallel printer port.

Detailed Description

_________________________of Software

The battery pack can be charged and discharged

through the PACK+ and PACK- terminals. When a load

is connected across the PACK+ and PACK- terminals,

the discharge current is measured and displayed. If the

load current exceeds the overcurrent trip threshold,

MOSFET M1 turns off, disconnecting the load.

Main Display

The charge and discharge counters are automatically

displayed in either decimal or hexadecimal, along with

the corresponding charge count and the calculated

current values. The

Clear Counters

button commands

the MAX1660 to clear its charge and discharge coun-

ters, and it also restarts the integration timer.

The display is automatically updated at the rate select-

ed by the

Integration Time

control. This automatic

update can be turned off by unchecking the

Automatically Update Displays

check-box.

The

INT

signal is checked several times per second,

and the

Interrupt

box indicates if it is low. To clear the

interrupt, click on the

Clear Interrupt

button.

When the

Fuel Gauge Off

control is activated, the soft-

ware automatically activates

Disconnect Battery

and

Disconnect Load

to protect the battery. Unchecking

either

Disconnect Battery

Disconnect Load

auto-

matically unchecks

Fuel Gauge Off.

The

Calibrate

check-box controls the OFFSETMEAS bit

in the configuration word. When active, the Coulomb

counter is disconnected from the sense resistor, reveal-

ing the offset voltage (which appears as an offset cur-

rent in this display.)

Procedure

1) Connect the battery pack to the board at connector

J2. Total battery-pack voltage should be within the

4V to 28V range accepted by the MAX1660. The

battery cells may be of any rechargeable chemistry,

such as NiCd, NiMH, or Li-Ion. The battery pack will

later be charged and discharged through the

PACK+ and PACK- terminals; however, leave

PACK+ unconnected until the software is started.

Powering the EV kit with a power supply that is not

isolated from the computer creates a ground loop,

degrading measurement accuracy by 50% or more.

2) Connect the board to the computer’s parallel printer

port. The parallel port is typically labeled LPT or

PRINTER.

To avoid damaging the EV kit or your

computer, make sure you are using the parallel

printer port and not a 25-pin SCSI port or any

other connector that is physically similar to the

25-pin parallel printer port.

Windows 3.1 and Windows 95 are trademarks of Microsoft Corp.

_______________________________________________________________________________________

MAX1660 Evaluation Kit

The MAX1660 register values can be displayed in

32-bit binary format by selecting

Registers

from the

MAX1660 menu. This command opens a window that

updates five times per second, independent of the

main display’s integration time control. The

Compare

group in the main window selects the charge

or discharge register.

Accuracy Limitations under DOS

To allow evaluation of the MAX1660 without the current-

measurement errors caused by Windows, use the

DOS1660 program. This menu-driven program pro-

vides rudimentary access to the MAX1660, with stable

timing. An oscilloscope can be used to observe a read

diagnostic strobe that appears on pins 5 and 13 of the

parallel port. To start the DOS1660 program, click on

the DOS1660 menu item, or exit Windows and run

DOS1660.EXE.

Evaluates: MAX1660

Sense-Resistor Value

The effect of different current-sense resistors can be

shown by selecting the

Sense Resistor

command from

the MAX1660 menu. This command opens a window

that displays the assumed sense resistor value, as well

as the conversion gain calculations resulting from that

value. For correct current display, the sense-resistor

value should match the actual value of R

(which is

R1 on the EV kit board).

Detailed Description

________________________of Hardware

U1, the MAX1660, is a digitally controlled fuel-gauge

interface that accurately monitors charge and dis-

charge currents. C6 and C1 bypass the power supply.

R1 is the noninductive current-sense resistor. It is

Kelvin connected to reduce error at high currents.

R3–R6 set the overcurrent trip thresholds. MOSFETs

M1 and M2 are used by the overcurrent protection cir-

cuitry to interrupt the discharge and charge paths,

respectively. D1 and R11 would typically be used by a

microcontroller to implement a hard-shutdown mode.

Refer to the MAX1660 data sheet for more discussion

of the standard application circuit.

The SMBus interface circuitry consists of J1, D20–D26,

LED1, Q20, Q21, Q22, R20–R35, and U2. This part of

the circuit provides the 2-wire clock and data interface,

as well as a GPIO output (used for shutdown control)

and an interrupt input. When the board is not plugged

into an IBM PC parallel port, the clock and data lines

can be driven externally, and the GPIO output is con-

trolled by switch SW1. The LED lights up whenever the

interrupt signal is at a logic-low level.

If desired, the EV kit can be driven with a user-supplied

SMBus 2-wire interface. Connect it to the DGND, SCL,

and SDA pads on the board.

SMBus Menu

The SMBus menu allows individual SMBus operations

to be performed. The main window continues indepen-

dently performing its own SMBus transactions unless

the

Automatic Update Displays

box is unchecked.

The SMBus dialog boxes accept numeric data in bina-

ry, decimal, or hexadecimal. Hexadecimal numbers

should be prefixed by $ or 0x. Binary numbers must be

exactly 8 or 16 digits.

Accuracy Limitations under Windows

Charge or discharge current can be measured by sam-

pling the counter value at intervals and calculating:

Current = (increase in counter value) / (time interval

in seconds x conversion gain)

When calculating charge or discharge current, there is

an inherent measurement error of one count or less in

each integration period, due to fractional counts during

the integration period. There is also a processor-

dependent measurement uncertainty in the integration

time. A crystal-controlled microcontroller with no other

tasks can easily have less than 1µs of uncertainty,

whereas the EV kit software under Windows has an

uncertainty of 10,000µs. Longer integration time

reduces this measurement error. The current measure-

ment error due to timing jitter is displayed in the main

window under the heading “uncertainty”.

To accurately measure load current, the program must

accurately measure the time interval between counter

reads. The counter value is latched on the falling edge

of the ACK clock pulse during the SMBusReadWord

(address 0x83, command 0x82). Refer to the MAX1660

data sheet.

___________________Interface Details

A complete smart-battery solution is far beyond the

scope of this manual; however, there are a few details

that the software designer must know in order to suc-

cessfully use this device.

Reading 32-Bit Counters

To accurately measure supply current, the program

must accurately measure the time interval between

counter reads. During the read-word protocol, begin

the integration time at the falling edge of the ninth clock

pulse of the command byte. Not counting the start con-

dition, this is the 18th falling edge of the clock during

SMBusReadWord (address 0x8e, command 0x82).

_______________________________________________________________________________________

MAX1660 Evaluation Kit

Evaluates: MAX1660

When reading the 32-bit charge or discharge counter

value, read the low word first (command 0x82) followed

by the high word (command 0x83). This sequence

latches the counter value and prevents the data from

being corrupted if there is a 16-bit carry during the

read operation. See Listing 1.

battery or the load connected with the fuel gauge off

can destroy the FETs if a short-circuit condition occurs.

See Listing 2.

Optional Offset Calibration

The MAX1660’s input offset is quite low; however, it can

be measured by setting OFFSETMEAS = 1. When off-

set-measurement mode is active, the charge and dis-

charge currents cannot be monitored, so disconnect

the battery (OCHI = 1, OCLO = 0) and the load (ODHI

= 1, ODLO = 0). See Listing 3.

Soft Shutdown

When turning the fuel gauge off (SOFTSHDN = 1), dis-

connect the battery (OCHI = 1, ODLO = 0) and the load

(ODHI = 1, ODLO = 0). When the fuel gauge is inactive,

the overcurrent protection is disabled. Leaving the

Listing 1. Reading 32-Bit Counters

Listing 2. Soft Shutdown

_______________________________________________________________________________________

MAX1660 Evaluation Kit

Evaluates: MAX1660

Listing 3. Measuring Offset

_______________________________________________________________________________________

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