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MC33340

Battery Fast Charge Controllers

ON Semiconductor 

MC33340, MC33342

INTRODUCTION

Nickel Cadmium and Nickel Metal Hydride batteries

require precise charge termination control to maximize cell

capacity and operating time while preventing overcharging.

Overcharging can result in a reduction of battery life as well

as physical harm to the end user. Since most portable

applications require the batteries to be charged rapidly, a

primary and usually a secondary or redundant charge sensing

technique is employed into the charging system. It is also

desirable to disable rapid charging if the battery voltage or

temperature is either too high or too low. In order to address

these issues, an economical and flexible fast charge controller

was developed.

The MC33340/342 contains many of the building blocks

and protection features that are employed in modern high

performance battery charger controllers that are specifically

designed for Nickel Cadmium and Nickel Metal Hydride

batteries. The device is designed to interface with either

primary or secondary side regulators for easy implementation

of a complete charging system. A representative block diagram

in a typical charging application is shown in Figure 8.

The battery voltage is monitored by the Vsen input that

internally connects to a voltage to frequency converter and

counter for detection of a negative slope in battery voltage. A

timer with three programming inputs is available to provide

backup charge termination. Alternatively, these inputs can be

used to monitor the battery pack temperature and to set the

over and undertemperature limits also for backup charge

termination.

Two active low open collector outputs are provided to

interface this controller with the external charging circuit.

The first output furnishes a gating pulse that momentarily

interrupts the charge current. This allows an accurate method

of sampling the battery voltage by eliminating voltage drops

that are associated with high charge currents and wiring

resistances. Also, any noise voltages generated by the

charging circuitry are eliminated. The second output is

designed to switch the charging source between fast and

trickle modes based upon the results of voltage, time, or

temperature. These outputs normally connect directly to a

linear or switching regulator control circuit in non−isolated

primary or secondary side applications. Both outputs can be

used to drive optoisolators in primary side applications that

require galvanic isolation. Figure 9 shows the typical charge

characteristics for NiCd and NiMh batteries.

Regulator

DC

Input

Charge

Status

Reg Control

R2

R1

MC33340 or MC33342

VCC 8

Internal Bias

Undervoltage

Lockout

Vsen

Voltage to

Frequency

1

Converter

Over

Temp

Ck

High

F/V R

Over

Latch

R

Q

2.0 V

S

Battery

Temp

Detect

Detect

1.0 V

Low

Under

t1

−DV Detect

Counter

Vsen

Timer

Gate

t2

2

Vsen

Gate

t3

3

VCC

2.9 V

30 mA

30 mA

30 mA

Fast/

Trickle

F/T

t/T

Time/

Temp

Select

ǒ Ǔ R2 + R1

VBatt

Vsen

–

1

Gnd

4

VCC

0.7 V

Figure 8. Typical Battery Charging Application

T

RNTC

Battery

Pack

t1/Tref High

7

SW1

R3

t2/Tsen

6

SW2

t3/Tref Low

5

SW3

R4

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