34674 datasheet(20/26 Pages) FREESCALE

20 / 26 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34674

TYPICAL APPLICATIONS

INTRODUCTION

TYPICAL APPLICATIONS

INTRODUCTION

The MC34674 can be used as a regular linear charger with

the charge current set internally. However, the best way of

using this device in the travel charger application is to use this

IC together with a current-limited AC/DC regulator. Select a

version with the internally set current higher than the target

charge current and then power the charger with an AC/DC

regulator whose output current is limited to a value lower.

This section introduces how to use the MC34674 with a

current-limited AC/DC regulator. Also discussed in this

section is the application information.

CURRENT-LIMITED AC/DC REGULATOR

A current-limited AC/DC regulator has an output current

and voltage characteristics shown in Figure 24. The regulator

outputs a no load voltage, VNL, when the supply is not loaded.

As the load current increases, the output voltage remains

relatively constant. When the load current reaches the

current limit of the regulator, ILIM, the regulator output

behaves as a constant current source. Usually a current-

limited regulator output is specified in a range, as the range

limited by the dotted lines.

OPERATION WITH CURRENT-LIMITED AC/DC

REGULATOR

The operation of the MC34674 when powered by a

current-limited regulator is dependent on the battery voltage.

Figure 25 and Figure 26 assist the explanation of the

operation.

When the battery voltage is lower than the trickle-charge

threshold, the MC34674 is in the trickle mode. The trickle

mode current is typically lower than the current limit, ILIM, and

hence the AC/DC regulator output is a constant-voltage. The

MC34674 operates same as a regular linear charger.

Figure 24. AC/DC Regulator Output I/V Characteristics.

The trickle-charge mode can be illustrated both on the I/V

characteristics plot in Figure 25 and the time domain charge

curve in Figure 26. In the I/V characteristics trajectory, the

battery voltage moves from point a to point b, representing

that the current remains at the trickle mode charge current,

ITRKL while the battery voltage moves from a value below the

trickle-charge threshold, VTRKL, to the trickle-charge

threshold. The AC/DC regulator output stays at point A during

the trickle mode with no changes for its output current and

voltage.

Figure 25. AC/DC Regulator Output and MC34674

Output I/V Characteristics.

Figure 26. Charging Waveforms When Powered with

Current-Limited Regulators.

ILIM

VNL

ILIM

VNL

ITRKL

IEOC

VTRKL

4.2V

ac/dc regulator

output

MC34674

output

VIN

VBAT

IBAT

Time

ITRKL

ILIM

34674 Datasheet(PDF) 20 Page - Freescale Semiconductor, Inc

34674 Datasheet(HTML) 20 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL