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LTC4095EDC#TRMPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
LTC4095
7
4095fa
SIMPLIFIED BLOCK DIAGRAM
–
+
–
+
6
+
–
RECHRG
CHRGR
ON
TEMP
FAULT
TERMINATE
CHARGE
BAD
BAT
TRICKLE
2.9V
M1
BAT
4.105V
NTC
3
CHRG
NTC
TRICKLE
CHARGE
TEMP FAULT
CONTROL
LOGIC
BLINK
LOGIC
COUNTER
2.25MHz CLOCK
CONSTANT CURRENT/
CONSTANT VOLTAGE
CHARGE
CURRENT
CONTROL
RECHARGE
–
+
C/10
100mV
PROG
I
BAT
ENABLE
I
BAT
800
T
REF
HPWR
T
DIE
5
IN
THERMAL
AMP
BAT
BAT
IN
4V
8
1
–
+
–
+
SUSP
4095 F01
4
7
GND
2
IN
DUVLO
UVLO
Figure 1. LTC4095 Block Diagram
OPERATION
Introduction
The LTC4095 is a linear battery charger designed to
charge single-cell lithium-ion batteries. The charger uses
a constant-current/constant-voltage charge algorithm
with a charge current programmable up to 950mA. Ad-
ditional features include automatic recharge, an internal
termination timer, low-battery trickle charge conditioning,
bad-battery detection, and a thermistor sensor input for
out of temperature charge pausing.
Futhermore, the LTC4095 is capable of operating from a
USB power source. In this application, charge current can
be programmed to a maximum of 100mA or 500mA per
USB power specifi cations.
Input Current vs Charge Current
The LTC4095 regulates the total current delivered to the
BAT pin; this is the charge current. To calculate the total
input current (i.e., the total current drawn from the IN pin),
it is necessary to sum the battery charge current, charger
quiescent current and PROG pin current.
Undervoltage Lockout (UVLO)
The undervoltage lockout circuit monitors the input volt-
age (IN) and disables the battery charger until IN rises
above V
UVLO
(typically 4V). 200mV of hysteresis prevents
oscillations around the trip point. In addition, a differential
undervoltage lockout circuit disables the battery charger
when IN falls to within V
DUVLO
(typically 40mV) of the
BAT voltage.
Suspend Mode
The LTC4095 can also be disabled by pulling the SUSP
pin above 1.2V. In suspend mode, the battery drain cur-
rent is reduced to 1.3µA and the input current is reduced
to 8.5µA.
LTC4095
8
4095fa
OPERATION
Charge Cycle Overview
When a battery charge cycle begins, the battery charger
fi rst determines if the battery is deeply discharged. If the
battery voltage is below V
TRKL
, typically 2.9V, an automatic
trickle charge feature sets the battery charge current to
10% of the full-scale value.
Once the battery voltage is above 2.9V, the battery charger
begins charging in constant-current mode. When the bat-
tery voltage approaches the 4.2V required to maintain a full
charge, otherwise known as the fl oat voltage, the charge
current begins to decrease as the LTC4095 switches into
constant-voltage mode.
Trickle Charge and Defective Battery Detection
Any time the battery voltage is below V
TRKL
, the charger
goes into trickle charge mode and reduces the charge
current to 10% of the full-scale current. If the battery
voltage remains below V
TRKL
for more than 1/2 hour, the
charger latches the bad-battery state, automatically termi-
nates, and indicates via the
⎯
C
⎯
H
⎯
R
⎯
G pin that the battery was
unresponsive. If for any reason the battery voltage rises
above V
TRKL
, the charger will resume charging. Since the
charger has latched the bad-battery state, if the battery
voltage then falls below V
TRKL
again but without rising past
V
RECHRG
fi rst, the charger will immediately assume that
the battery is defective. To reset the charger (i.e., when
the dead battery is replaced with a new battery), simply
remove the input voltage and reapply it or put the part in
and out of suspend mode.
Charge Termination
The battery charger has a built-in safety timer that sets
the total charge time for 4 hours. Once the battery voltage
rises above V
RECHRG
(typically 4.105V) and the charger
enters constant-voltage mode, the 4-hour timer is started.
After the safety timer expires, charging of the battery will
discontinue and no more current will be delivered.
Automatic Recharge
After the battery charger terminates, it will remain off,
drawing only microamperes of current from the battery.
If the portable product remains in this state long enough,
the battery will eventually self discharge. To ensure that the
battery is always topped off, a charge cycle will automati-
cally begin when the battery voltage falls below V
RECHRG
(typically 4.105V). In the event that the safety timer is
running when the battery voltage falls below V
RECHRG
, it
will reset back to zero. To prevent brief excursions below
V
RECHRG
from resetting the safety timer, the battery voltage
must be below V
RECHRG
for more than 1.7ms. The charge
cycle and safety timer will also restart if the IN UVLO or
DUVLO cycles low and then high (e.g., IN is removed
and then replaced) or the charger enters and then exits
suspend mode.
Programming Charge Current
The PROG pin serves both as a charge current program
pin, and as a charge current monitor pin. By design, the
PROG pin current is 1/800th of the battery charge current.
Therefore, connecting a resistor from PROG to ground
programs the charge current while measuring the PROG pin
voltage allows the user to calculate the charge current.
Full-scale charge current is defi ned as 100% of the con-
stant-current mode charge current programmed by the
PROG resistor. In constant-current mode, the PROG pin
servos to 1V if HPWR is high, which corresponds to charg-
ing at the full-scale charge current, or 200mV if HPWR
is low, which corresponds to charging at 20% of the full-
scale charge current. Thus, the full-scale charge current
and desired program resistor for a given full-scale charge
current are calculated using the following equations:
I
V
R
R
V
I
CHG
PROG
PROG
CHG
=
=
800
800
LTC4095
9
4095fa
OPERATION
In any mode, the actual battery current can be determined
by monitoring the PROG pin voltage and using the follow-
ing equation:
I
PROG
R
BAT
PROG
= •800
Thermal Regulation
To prevent thermal damage to the IC or surrounding
components, an internal thermal feedback loop will
automatically decrease the programmed charge current
if the die temperature rises to approximately 115°C.
Thermal regulation protects the LTC4095 from excessive
temperature due to high power operation or high ambient
thermal conditions and allows the user to push the limits
of the power handling capability with a given circuit board
design without risk of damaging the LTC4095 or external
components. The benefi t of the LTC4095 thermal regula-
tion loop is that charge current can be set according to
actual conditions rather than worst-case conditions with
the assurance that the battery charger will automatically
reduce the current in worst-case conditions.
Charge Status Indication
The
⎯
C
⎯
H
⎯
R
⎯
G pin indicates the status of the battery charger.
Four possible states are represented by
⎯
C
⎯
H
⎯
R
⎯
G: charging,
not charging, unresponsive battery and battery temperature
out of range.
The signal at the
⎯
C
⎯
H
⎯
R
⎯
G pin can be easily recognized as one
of the above four states by either a human or a micropro-
cessor. The
⎯
C
⎯
H
⎯
R
⎯
G pin, which is an open-drain output, can
drive an indicator LED through a current limiting resistor
for human interfacing, or simply a pull-up resistor for
microprocessor interfacing.
To make the
⎯
C
⎯
H
⎯
R
⎯
G pin easily recognized by both humans
and microprocessors, the pin is either a DC signal of
ON for charging, OFF for not charging, or it is switched
at high frequency (35kHz) to indicate the two possible
faults: unresponsive battery and battery temperature out
of range.
When charging begins,
⎯
C
⎯
H
⎯
R
⎯
G is pulled low and remains
low for the duration of a normal charge cycle. When the
charge current has dropped to below 10% of the full-scale
current, the
⎯
C
⎯
H
⎯
R
⎯
G pin is released (high impedance). If a
fault occurs after the
⎯
C
⎯
H
⎯
R
⎯
G pin is released, the pin re-
mains high impedance. However, if a fault occurs before
the
⎯
C
⎯
H
⎯
R
⎯
G pin is released, the pin is switched at 35kHz.
While switching, its duty cycle is modulated between a high
and low value at a very low frequency. The low and high
duty cycles are disparate enough to make an LED appear
to be on or off thus giving the appearance of “blinking”.
Each of the two faults has its own unique “blink” rate for
human recognition as well as two unique duty cycles for
microprocessor recognition.
Table 1 illustrates the four possible states of the
⎯
C
⎯
H
⎯
R
⎯
G
pin when the battery charger is active.
Table 1.
⎯
C
⎯
H
⎯
R
⎯
G Output Pin
STATUS FREQUENCY
MODULATION
(BLINK)
FREQUENCY DUTY CYCLE
Charging 0Hz 0 Hz (Lo-Z) 100%
I
BAT
< C/10 0Hz 0 Hz (Hi-Z) 0%
NTC Fault
35kHz
1.5Hz at 50% 6.25% to 93.75%
Bad Battery
35kHz
6.1Hz at 50% 12.5% to 87.5%
An NTC fault is represented by a 35kHz pulse train whose
duty cycle varies between 6.25% and 93.75% at a 1.5Hz
rate. A human will easily recognize the 1.5Hz rate as a
“slow” blinking which indicates the out of range battery
temperature while a microprocessor will be able to decode
either the 6.25% or 93.75% duty cycles as an NTC fault.
If a battery is found to be unresponsive to charging (i.e.,
its voltage remains below V
TRKL
for over 1/2 hour), the
⎯
C
⎯
H
⎯
R
⎯
G pin gives the battery fault indication. For this fault,
a human would easily recognize the frantic 6.1Hz “fast”
blinking of the LED while a microprocessor would be able
to decode either the 12.5% or 87.5% duty cycles as a bad
battery fault.
Although very improbable, it is possible that a duty cycle
reading could be taken at the bright-dim transition (low
duty cycle to high duty cycle). When this happens the
duty cycle reading will be precisely 50%. If the duty cycle
reading is 50%, system software should disqualify it and
take a new duty cycle reading.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LTC4095EDC#TRMPBF

Mfr. #:
Buy LTC4095EDC#TRMPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Battery Management Standalone 950mA USB Li-Ion/Polymer Battery Charger in DFN
Lifecycle:
New from this manufacturer.
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