DC674B - LINEAR TECHNOLOGY

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B

STANDALONE NIMH/NICD BATTERY CHARGER BOARD

LTC4011

DESCRIPTION

Demonstration circuit DC674B is a complete Fast Bat-

tery Charger capable of charging 3, 4, 8 or 10 series

connected NiMH or NiCd cells. Other cell counts can

also be charged (up to 16 cells) by installing an appro-

priate resistor on the board.

The power portion of the circuit consists of a 550kHz

synchronous step-down constant current source which

provides 2A of charge current. Other charge currents

can be selected by changing the sense resistor value,

and for higher charge current (2 to 4A), the PC board

has a dual layout for the top switch to allow a larger

FET to be used. A PowerPath™ FET is also included that

provides a low voltage drop path between the battery

and an external system load when the input power is

removed

Charge termination includes -ΔV, ΔT/Δt, peak voltage

and a safety timer. The thermistor function is set by the

NTC jumper, JP1. Battery chemistry is set by the CHEM

jumper, JP2. The number of series cells is set by the

CELLS jumper, J1. Finally, the safety timer length is set

by the TIME jumper, J2. Four LEDs indicate charger

ready, top-off charge, charging, and FAULT status.

Design files for this circuit board are available. Call

the LTC factory.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Power-

Path is a trademark of Linear Technology Corporation. All other t r ademarks are the propert y of their

respective owners.

Performance Summary

= 25°C

PARAMETER CONDITIONS / NOTES VALUE

Minimum Input Voltage 3 series cells (Default) 6.3V

4 series cells 8.3V

6 series cells 12.3V

10 series cells 20.3V

n series cells n

∙

2.0V + 0.3V

Maximum Input Voltage Limited by Input Capacitor Volt Ratings. 25V

Maximum Charge Current 2A ± 8%

−ΔV Termination CHEM=NiCd −20mV ± 2mV

CHEM=NiMH −10mV ± 1.5mV

ΔT/Δt Termination CHEM=NiCd 2°C/min ± 0.16°C Temperature Rise

CHEM=NiMH 1°C/min ± 0.14°C Temperature Rise

Precharge Current 350mV < VCELL < 900mV 400mA ± 80mA

Top Off Charge Current CHEM=NiMH, ΔT/Δt Termination Only 200mA ± 50mA

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B

STANDALONE NIMH/NICD BATTERY CHARGER BOARD

QUICK START PROCEDURE

Demonstration circuit 674B is easy to set up to eva-

luate the performance of the LTC4011. Refer to Fig-

ure 1 for proper measurement equipment setup and

follow the procedure below.

Set the jumpers according to the type and specifi-

cations of the pack under evaluation.

With all power off, connect input power supply,

and meters as shown in Figure 1.

3. Preset the system load to 0A and the input

supply to 0V, 0A current limit.

4. Turn on the supplies, setting the current limit to

2A.

5. Adjust the input voltage to the desired value, up

to 25V.

6. Connect the battery to begin charging.

Optional

1. To use a battery with a 5-pin blade connector,

use J3.

2. To use a system load up to 1A in parallel with

the charging circuit, connect to SYSTEM LOAD.

Adjust load and input supply current limit as

necessary.

For external thermistor connection, set jumper

JP1 to BAT. For the on-board thermistor, set JP1

to BRD. To remove the thermistor from the circuit,

set JP1 to OUT.

4. For custom cell count, set jumper J1 to XCELLS

and install R14 with the appropriate value.

5. For alternative timer settings, set jumper J2 as

necessary. For custom timer settings, set J2 to

4.3Hr and install R23 with the appropriate val-

ue.

Note: This value also affects Precharge and TOC

times as well.

To measure the average voltage per cell, connect a

meter to VCELL.

7. To pause the charge cycle, connect a lead from

PAUSE to GND.

Note: This pauses the timer as well, but status

outputs remain active.

Please refer to the LTC4011 datasheet for additional information.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B

STANDALONE NIMH/NICD BATTERY CHARGER BOARD

Figure 1. Proper Measurement Equipment Setup

VIN

BATTERY

−

10k NTC

*Locate

close to

battery

…

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B

STANDALONE NIMH/NICD BATTERY CHARGER BOARD

CHARGING NIMH/NICD BATTERIES

Nickel based batteries are typically charged by a

constant current source, allowing the battery vol-

tage to rise to the level it requires (within limits)

to force this current. When batteries are fast

charged (1 to 2 hours) the charge cycle must be

terminated when the battery reaches full charge.

Detecting when the battery is fully charged is

usually done by one or more methods.

1. –∆V method: Measures the battery voltage

as it is being charged with a constant current.

The voltage will rise as the battery accepts

charge. When it approaches full charge, the

battery voltage will begin rising faster, reach a

peak then begin to drop. When the battery vol-

tage drops a fixed amount of mV (depending on

battery chemistry), the battery is fully charged

and the charge cycle terminates.

2. ∆T/∆t method: Measures the rate of tempera-

ture rise vs. time. During a fast charge, the bat-

tery temperature begins to rise. When it ap-

proaches full charge, the battery temperature

will begin to rise quickly. When the rate of tem-

perature rise reaches a fixed number of

°C/minute (depending on battery chemistry) the

charge cycle terminates. NiMH batteries add a

top-off charge that continues charging at a low-

er current until the timer ends the charge cycle.

For either of these termination methods to work

correctly, the charge current must be pro-

grammed to a sufficiently high current level.

LTC recommends between C/2 and 2C rates,

but charging at 2C may result in excessive cell

temperature, especially for small, low capacity

NiMH cells. Rates lower than C/2 will be too dif-

ficult to detect for LTC4011 termination algo-

rithm.

“C rate” is a measure of cell capacity in mAHr.

For example, to charge an 1800mAHr battery at

1C would require a charge current of 1.8A.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B

STANDALONE NIMH/NICD BATTERY CHARGER BOARD

DIFFERENCES BETWEEN NICD & NIMH BATTERIES

NiCd batteries exhibit very little temperature rise

during most of the charge cycle. The tempera-

ture rise mainly occurs near the end of the

charge cycle.

Whereas, NiMH battery temperature rise occurs

throughout the charge cycle and accelerates

near the end of the charge cycle.

The -∆V that occurs when charging a NiMH bat-

tery is less than a NiCd. This makes -∆V termina-

tion somewhat more difficult to detect for a NiMH

battery, therefore it is also recommended to in-

clude a thermistor in the NiMH battery packs.

Figure 2. NiMH Charge Profile (1C Charge Rate)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B

STANDALONE NIMH/NICD BATTERY CHARGER BOARD

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURE / PART #

Required Circuit Components

1 2 C1, C2 Capacitor, X5R, 10μF, 20% 25V 1210 Taiyo Yuden, TMK325BJ106MM

2 3 C3, C4, C5 Capacitor, X5R, 0.1μF, 25V 0603 AVX, 06033D104KAT2A

3 1 D6 Diode Schottky, 1A, 40V POWERMITE Micro Semi., UPS140

4 1 L1 Inductor, 10μH Toko, 919AS-100M

5 1 Q1 MOSFET, Dual P-Channel SuperSOT-8 Fairchild, FDS6975P

6 1 Q2 MOSFET, Single P-Channel SuperSOT-6 Fairchild, FDC658AP

7 1 Q3 MOSFET, N-Channel, 30V Vishay, SI3434DV

8 1 R6 Resistor, 0.05Ω, 1/2W, 1% 1206 Panasonic, ERJ-L08KJ50MV

9 1 R7 Resistor, 9.76k, 1/16W, 1% 0402 Vishay, CRCW04029K76FKED

10 1 R8 Resistor, 20k, 1/16W, 5% 0402 Vishay, CRCW040220K0JNED

11 2 R9, R18 Resistor, 10.0k, 1/16W, 1% 0402 Vishay, CRCW040210K0FKED

12 1 R10 Resistor, 20.0k, 1/16W 1% 0402 Vishay, CRCW040220K0FKED

13 1 R15 Resistor, 24.9k, 1/16W 1% 0402 Vishay, CRCW040224K9FKED

14 1 R21 Resistor, 28.0k, 1/16W 1% 0402 Vishay, CRCW040228K0FKED

15 1 U1 I.C. Battery Charger TSSOP-20 Linear Technology LTC4011EFE#PBF

Additional Demo Board Circuit Components

1 0 C6, C7 OPT.

2 1 D1 Diode, Zener, 18V SOD-323 Diode Inc., MMSZ5248BS-7

3 1 D2 LED, Green Rohm, SML-010FTT86L

4 2 D3, D4 LED, Orange Rohm, SML-010DTT86L

5 1 D5 LED, Red Rohm, SML-010VTT86L

6 1 R1 Resistor, 47K, 1/16W, 5% 0402 Vishay, CRCW040247K0JNED

7 4 R2-R5 Resistor, 3K, 1/16W, 5% 0402 Vishay, CRCW04023K00JNED

8 1 R11 Resistor, 30.1K, 1/16W, 1% 0402 Vishay, CRCW040230K1FKED

9 2 R12, R16 Resistor, 49.9K, 1/16W, 1% 0402 Vishay, CRCW040249K9FKED

10 1 R13 Resistor, 90.9K, 1/16W, 1% 0402 Vishay, CRCW040290K9FKED

11 0 R14, R23 OPT.

12 1 R17 Resistor, 100K, 1/16W, 1% 0402 Vishay, CRCW0402100KFKED

13 1 R19 Resistor, 28.0K, 1/16W, 1% 0402 Vishay, CRCW040228K0FKED

14 1 R20 Resistor, 10K, 1/4W, 5% 1206 Vishay, CRCW120610K0JNEA

15 1 R22 Resistor, 0Ω, 1/16W, 0402 Vishay, CRCW04020000Z0ED

Hardware/Components (For Demo Board Only)

1 1 JP1 Jumper, 0.079"CC, 4 Pin Sullins, NRPN041PAEN

2 1 JP2 Jumper, 0.079"CC, 3 Pin Sullins, NRPN031PAEN

3 1 J1 Header, 10 Pin, 2 Row, .079CC Samtech, TMM-105-02-L-D

4 1 J2 Header, 8 Pin, 2 Row, .079CC Sullins, NRPN042PAEN

5 1 J3 Header, Right Angle TE Connectivity, 5787441-1

6 4 JP1, JP2, J1, J2 Shunt Samtec, 2SN-BK-G

7 9 E1-E9 Turret, Test Pin, .095" Mill-Max 2501-2-00-80-00-00-07-0

8 4 Hardware Screw, #4-40, 1/4" Any

9 4 Standoff, #4-40, 1/4" Micro Plastics 14HTSP101

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B

STANDALONE NIMH/NICD BATTERY CHARGER BOARD