ltc1734es6-4.2 Linear Technology Corporation, ltc1734es6-4.2 Datasheet - Page 7

• Manufacturer Part Number: ltc1734es6-4.2
• Description: Ltc1734-4.2 - Lithium-ion Linear Battery Charger In Thinsot
• Manufacturer: Linear Technology Corporation

APPLICATIONS
Manual Shutdown
Floating the program resistor allows an internal 3 A
current source (I
2.15V shutdown threshold (V
the charger. In this mode, the LTC1734 continues to draw
some current from the supply (I
gible leakage current is delivered to the battery (I
Shutdown can also be accomplished by pulling the other-
wise grounded end of the program resistor to a voltage
greater than 2.25V (V
1.5V, but the internal battery voltage resistor divider will
draw about 34 A from the battery until shutdown is
entered. Figure 1 illustrates a microcontroller configura-
tion that can either float the resistor or force it to a voltage.
The voltage should be no more than 8V when high and
have an impedance to ground of less than 10% of the
program resistor value when low to prevent excessive
charge current errors. To reduce errors the program
resistor value may be adjusted to account for the imped-
ance to ground. The programming resistor will prevent
potentially damaging currents if the PROG pin is forced
above V
down by other circuitry or be shorted to ground. If V
not shorted to ground the current through the resistor will
pull V
Another method is to directly switch the PROG pin to a
voltage source when shutdown is desired (Caution: pull-
ing the PROG below 1.5V with V
excessive and uncontrolled charge currents). The volt-
age source must be capable of sourcing the resulting
current through the program resistor. This has the ad-
vantage of not adding any error to the program resistor
during normal operation. The voltage on the PROG pin
must be greater than 2.25V (V
CC
CC
up somewhat.
Figure 1. Interfacing with a Microcontroller
. Under this condition V
POLE OUTPUT
OPEN DRAIN
OR TOTEM
ADC INPUT
PROGPU
C
U
MSDT
) to pull the PROG pin above the
INFORMATION
R
Max). Charging will cease above
PROG
U
MSDT
SHDN
CC
MSDT(MAX)
PROG
CC
), thus shutting down
W
LTC1734
may float, be loaded
), but only a negli-
applied will cause
1734 F01
) to ensure
U
BMS
CC
).
is
entering shutdown, but no more than 0.3V above V
prevent damaging the LTC1734 from excessive PROG
pin current. An exception is if V
no other circuitry loading V
current will be low, it is allowable to have the PROG pin
shutdown voltage applied. A three-state logic driver with
sufficient pull-up current can be used to perform this
function by enabling the high impedance state to charge
or enabling the pull-up device to enter shutdown.
An NPN transistor or a diode can also be utilized to
implement shutdown from a voltage source. These have
the advantage of blocking current when the voltage source
goes low, thus automatically disconnecting the voltage
source for normal charging operation. The use of an NPN
allows for use of a weak voltage source due to the current
gain of the transistor. For an NPN connect the collector to
V
PROG pin. For a diode, connect the anode to the voltage
source and cathode to the PROG pin. An input high level
ranging from 3.3V to V
shutdown while a low level of 0.5V or less should allow for
normal charging operation. Use of inexpensive small
signal devices such as the 2N3904 or 1N914 is recom-
mended to prevent excessive capacitive loading on the
PROG pin (see Stability section).
Sleep Mode
When the input supply is disconnected, the IC enters the
sleep mode. In this mode, the battery drain current (I
is a negligible leakage current, allowing the battery to re-
main connected to the charger for an extended period of
time without discharging the battery. The leakage current
is due to the reverse-biased B-E junction of the external
PNP transistor.
Undervoltage Lockout
Undervoltage lockout (UVLO) keeps the charger off until
the input voltage exceeds a predetermined threshold level
(V
hysteresis is built in to prevent oscillation around the
threshold level. In undervoltage lockout, battery drain
current is very low (< 1 A).
CC,
UVLOI
the base to the voltage source and the emitter to the
) that is typically 4.56V. Approximately 150mV of
CC
should be adequate to enter
CC
down. Then, because the
CC
is allowed to float with
LTC1734
CC
BSL
7
to
)