DS273 데이터 시트보기 (PDF) - Maxim Integrated

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DS273

Cache-Memory Battery-Backup Management IC

Maxim Integrated 

Cache-Memory Battery-Backup Management IC

I

PRECHARGE

MODE

CHARGE

BEGIN

CONSTANT-CURRENT

MODE

ICHARGE

V

V

CONSTANT-VOLTAGE

MODE

CHARGE

END

VPK

I

10% x ICHARGE

VMIN

5% x ICHARGE

t

CHARGE TERMINATION

Figure 4. Li+ Battery Charging Characteristics

Constant-Current (CC) Mode

CC mode is entered either directly from initiate or after

precharge. Current is regulated based on the voltage

drop across an external 50mΩ sense resistor and an

internal feedback circuit. The CC charge rate is set by

the RSET pin. It can be calculated by the following

formula:

ICHARGE = 2500/R

Where R is the value of the resistor connected to RSET.

The charge current can range from 0.5A to 1.5A.

The safety timer begins when CC mode is entered. If it

expires during CC mode, the charger enters a fault

state. If the current-sense feedback or RSET resistor is

shorted, the charger clamps current at IOVERCURRENT.

Li+ Charger CC Operation

Detailed Description

In CC mode, the CCCV charger regulates current by

monitoring the voltage drop across the SNS resistor.

The differential voltage measurement provides feed-

back that controls the switching of the high-side and

low-side FETs. Inside the DS2731 CHG1 and CHG2

pins are a high-side p-channel MOSFET (Q1) and a

low-side n-channel MOSFET (Q2). Q1 and Q2 alternate

on and off, either supplying current to the load and

inductor or providing a current loop for the inductor to

supply the load. The inductor charges during Q1 ON

and discharges during Q2 ON. The Q1 and Q2 switch-

ing is controlled by the voltage across RSNS.

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