34674 datasheet(13/26 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34674

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

Figure 18. 34674 Functional Internal Block Diagram

INTEGRATED SUPPLY

INTERNAL SUPPLY AND REFERENCE

The internal supply and reference block steps down the

high input voltage to a lower voltage to power all the internal

control blocks. In addition, this block generates the reference

voltages for other functional blocks.

SENSING AND CONTROL

VIN MONITOR

The VIN monitor block monitors the input voltage for two

thresholds, power-on-reset (POR) and over-voltage

protection (OVP). If the input is lower than the POR or higher

than the OVP threshold, this block outputs a logic signal to

disable the charger.

CHARGE CONTROL

The charge-control block controls the gate voltage of the

power MOSFET to regulate the charge current, the battery

voltage, or the die temperature. It can also completely turn off

the power MOSFET to stop the current flow between the

input and the battery.

EOC (END OF CHARGE)

The EOC block monitors the charge current and the

battery voltage for the EOC conditions. Once the EOC

conditions are reached, this block outputs a logic signal to

indicate the end of the charge.

VIN-BAT COMPARATOR

The VIN-BAT comparator monitors the voltage difference

between the input voltage VIN and the battery voltage VBAT,

as shown in Figure 2. The input voltage has to be higher than

the battery voltage for the charger to be enabled. If the input

voltage falls below the battery voltage, this block outputs a

signal to disable the charger to prevent the leakage current

from the battery to the input. Due to the intrinsic input offset

voltage of the VIN-BAT comparator, a small voltage, VOS, is

added. The added VOS guarantees that the power MOSFET

is turned off when the input voltage is lower than the battery

voltage.

DIE TEMPERATURE FEEDBACK

The die temperature feedback block monitors the die

temperature. Once the die temperature reaches a threshold

of 110°C, the charge-control block can reduce the charge

current to prevent further temperature rise.

NTC INTERFACE

The NTC interface block offers an interface to an external

NTC thermistor circuit to monitor the battery temperature and

to set the charge temperature window.

MC34674 - Functional Block Diagram

Integrated Supply

Sensing & Control

MOSFET

Power MOSFET

Logic

Integrated Supply

Internal Supply & Reference

Sensing & Control

Logic

Die Temperature Feedback

Status Indication

VIN - BAT Compare

VIN Monitor

Charge Control

Logic Control

NTC Thermistor Interface

End of Charge

34674 Datasheet(PDF) 13 Page - Freescale Semiconductor, Inc

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