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LTC1733EMSE#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
LTC1733
7
sn1733 1733fs
SI PLIFIED
W
BLOCK DIAGRA
W
Figure 1.
2.485V
–
+
–
+
–
+
–
+
–
+
1733 F01
HOT COLD DISABLE
STOP
FAULT
CHARGE
OSCILLATOR
COUNTER
TIMER
C
TIMER
NTC
NTC
CHRG
ACPR
FAULT
25µA
2.485V
TO BAT
REF
–
+
C/10
ACPR
TA
CA
C2
–
+
C1
C3
VA
MA
PROG
BAT
V
CC
GND
R1
R4
R5
R6
R7
R2
R3
30µA
2.5µA
1.5V
2.15V
0.15V
105°C
T
DIE
D1
D2
D3
M2
×1
M1
×1000
MP
R
PROG
SHDN
LOGIC
SEL
2
6
1
10
3
475
8
9
LTC1733
8
sn1733 1733fs
The LTC1733 is a linear battery charger designed primarily
for charging single cell lithium-ion batteries. Featuring an
internal P-channel power MOSFET, the charger uses a
constant-current/constant-voltage charge algorithm with
programmable current and a programmable timer for
charge termination. Charge current can be programmed
up to 1.5A with a final float voltage accuracy of ±1%. No
blocking diode or sense resistor is required thus dropping
the external component count to three for the basic
charger circuit. The CHRG, ACPR, and FAULT open-drain
status outputs provide information regarding the status of
the LTC1733 at all times. An NTC thermistor input
provides the option of charge qualification using battery
temperature.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 105°C. This feature protects
the LTC1733 from excessive temperature, and allows the
user to push the limits of the power handling capability of
a given circuit board without risk of damaging the LTC1733
or the external components. Another benefit of the LTC1733
thermal limit is that charge current can be set according to
typical, not worst-case, ambient temperatures for a given
application with the assurance that the charger will auto-
matically reduce the current in worst-case conditions.
The charge cycle begins when the voltage at the V
CC
pin
rises above the UVLO level and a program resistor is
connected from the PROG pin to ground. At the beginning
of the charge cycle, if the battery voltage is below 2.48V,
the charger goes into trickle charge mode to bring the cell
voltage up to a safe level for charging. The charger goes
into the fast charge constant-current mode once the
voltage on the BAT pin rises above 2.48V. In constant-
current mode, the charge current is set by R
PROG
.
When the battery approaches the final float voltage, the
charge current begins to decrease as the LTC1733 switches
to constant-voltage mode. When the current drops to 10%
of the full-scale charge current, an internal comparator
latches off the MOSFET at the CHRG pin and connects a
weak current source to ground to indicate a near end-of-
charge (C/10) condition. The C/10 latch can be cleared by
momentarily pulling the PROG pin above the 2.15V
shutdown threshold, or momentarily removing and reap-
plying V
CC
.
An external capacitor on the TIMER pin sets the total
charge time. When this time elapses the charge cycle
terminates and the CHRG pin assumes a high impedance
state. To restart the charge cycle, simply remove the input
voltage and reapply it, or force the PROG pin above the
2.15V shutdown threshold (note: simply floating the PROG
pin will not restart the charging cycle.
For lithium-ion and similar batteries that require accurate
final float potential, the internal reference, voltage ampli-
fier and the resistor divider provide regulation with ±1%
(max) accuracy.
When the input voltage is not present, the charger goes
into a sleep mode, dropping battery drain current, I
BAT
, to
less than 5µA. This greatly reduces the current drain on the
battery and increases the standby time. The charger can be
shut down (I
CC
= 0.9mA) by forcing the PROG pin above
2.15V.
OPERATIO
U
LTC1733
9
sn1733 1733fs
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
CC
rises above the undervoltage lockout threshold. The UVLO
circuit has a built-in hysteresis of 150mV. Furthermore, to
protect against reverse current in the power MOSFET, the
UVLO circuit keeps the charger in shutdown mode if V
CC
falls to within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown until V
CC
rises 60mV above the battery voltage.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage is
low (below 2.48V) the charger goes into trickle charge
reducing the charge current to 10% of the full-scale
current. If the low battery voltage persists for one quarter
of the total charge time, the battery is assumed to be
defective, the charge cycle is terminated, the CHRG pin
output assumes a high impedance state, and the FAULT
pin latches low. The fault can be cleared by toggling V
CC
,
temporarily forcing the PROG pin above 2.15V, or tempo-
rarily forcing the BAT pin voltage above 2.48V.
Shutdown
The LTC1733 can be shutdown (I
CC
= 0.9mA) by pulling
the PROG pin above the 2.15V shutdown threshold volt-
age. In shutdown the internal linear regulator is turned off,
and the internal timer is reset.
Recharge
The LTC1733 has the ability to recharge a battery
assuming that the battery voltage has been charged above
4.05V (SEL = 5V) or 3.95V (SEL = 0V). Once above these
thresholds, a new charge cycle will begin if the battery
voltage drops below 4V (SEL = 5V) or 3.9V (SEL = 0V) due
to either a load on the battery or self-discharge. The
recharge circuit integrates the BAT pin voltage for a few
milliseconds to prevent a transient from restarting the
charge cycle.
If the battery voltage remains below 2.48V during trickle
charge for 1/4 of the programmed time, the battery may be
defective and the charge cycle will end. In addition, the
recharge comparator is disabled and a new charge cycle
will not begin unless the input voltage is toggled, the PROG
pin is pulled above the 2.15V shutdown threshold, or the
BAT pin is pulled above the 2.48V trickle charge threshold.
Programming Charge Current
The formula for the battery charge current (see Figure 1)
is:
I
CHG
= (I
PROG
) • 1000
= (1.5V / R
PROG
) • 1000 or
R
PROG
= 1500/I
CHG
where R
PROG
is the total resistance from the PROG pin to
ground. Under trickle charge conditions, this current is
reduced to 10% of the full-scale value.
For example, if 500mA charge current is required,
calculate:
R
PROG
= 1500/0.5A = 3kΩ
For best stability over temperature and time, 1% metal-
film resistors are recommended.
If the charger is in constant-temperature or constant-
voltage mode, the battery current can be monitored by
measuring the PROG pin voltage as follows:
I
CHG
= (V
PROG
/ R
PROG
) • 1000
Programming the Timer
The programmable timer is used to terminate the charge
cycle. The timer duration is programmed by an external
capacitor at the TIMER pin. The total charge time is:
Time (Hours) = (3 Hours) • (C
TIMER
/ 0.1µF) or
C
TIMER
= 0.1µF • Time (Hours)/3 (Hours)
The timer starts when an input voltage greater than the
undervoltage lockout threshold level is applied and the
program resistor is connected to ground. After a time-out
occurs, the charge current stops, and the CHRG output
assumes a high impedance state to indicate that the
charging has stopped. Connecting the TIMER pin to ground
disables the timer function.
APPLICATIO S I FOR ATIO
WUU
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P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LTC1733EMSE#TRPBF

Mfr. #:
Buy LTC1733EMSE#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Battery Management Mono Lin Lithium-Ion Bat Chr w/ Thermal
Lifecycle:
New from this manufacturer.
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