LTC1325 View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC1325 Datasheet PDF : 24 Pages
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WU
W
TI I G DIAGRA
MSB-FIRST DATA (MSBF = 1)
CS
CLK
START
DIN
DOUT HI-Z
MSBF
COMMAND WORD
NULL
D9
MSB-FIRST DATA (MSBF = 0)
CS
CLK
START
DIN
DOUT HI-Z
COMMAND WORD
NOTE: THE TIMING DIAGRAM SHOWS TWO POSSIBLE COMMAND WORDS.
REFER TO FUNCTIONAL DESCRIPTION FOR INFORMATION ON HOW TO
CONSTRUCT THE COMMAND WORD
VR1
NULL
D9
LTC1325
BATP
D1 D0
FS
HI-Z
ADC DATA
STATUS WORD
D1 D0 D1
ADC DATA
BATP
D9
FS
STATUS WORD
HI-Z
LTC1325 • TD
FUNCTIONAL DESCRIPTIO
GENERAL DESCRIPTION
During normal operation, a command word is shifted into
the chip via the serial interface, then an ADC measurement
is made and the 10-bit reading and chip status word are
shifted out. The command word configures the LTC1325
and forces it into one of five modes: power shutdown, idle,
discharge, charge or gas gauge mode.
In the power shutdown mode, the analog section is turned
off and the supply current drops to 30µA. The voltage
regulator, which provides power to the internal analog
circuitry and external bias networks, is shut down. The
voltage divider across the battery is disconnected and only
the voltage regulator for the serial interface logic is left on.
During the idle mode, the chip is fully powered but the
discharge, charge, and gas gauge circuits are off. The chip
may be placed in the idle mode momentarily while charg-
ing the battery, allowing an ADC measurement to be made
without any switching noise from the PWM current source
affecting the accuracy of the reading. The mode command
bits are picked off as they appear at DIN, allowing the
charging loop to turn off and settle while the remainder of
the command word is being shifted in.
During the discharge mode, the battery is discharged by
an external transistor and series resistor. The battery is
monitored for fault conditions.
In the charge mode, the µP monitors the battery’s voltage,
temperature and ambient temperature via the 10-bit ADC.
Termination methods such as –∆VBAT, ∆VBAT/∆Time,
∆TBAT, ∆TBAT/∆Time, ∆(TBAT – TA), maximum tempera-
ture, maximum voltage and maximum charge time may be
accurately implemented in software. The LTC1325 also
monitors the battery for fault conditions.
In the gas gauge mode, the average voltage across the
sense resistor can be measured to determine the average
battery load current. The sense voltage is filtered by an RC
circuit, multiplied by an inverting gain of four, then con-
verted by the ADC. The µP can then accumulate the ADC
measurements and do a time average to determine the
total charge leaving the battery. The RC circuit consists of
an internal 1k resistor RF and an external capacitor CF
connected to the Filter pin.
9
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