ltc1734es6-4.2-trmpbf Linear Technology Corporation, ltc1734es6-4.2-trmpbf Datasheet - Page 11

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

APPLICATIONS
Higher charge currents require lower program resistor
values which can tolerate more capacitive loading on the
PROG pin. Maximum capacitance can be as high as 50pF
for a charge current of 50mA (R
Figure 4 is a simple test circuit for checking stability in both
the constant current and constant voltage modes. With
input power applied and a near fully charged battery
connected to the charger, driving the PROG pin with a
pulse generator will cycle the charger in and out of the
manual shutdown mode. Referring to Figure 5, after a
short delay, the charger will enter the constant current
mode first, then if the battery voltage is near the pro-
grammed voltage of 4.2V, the constant voltage mode will
begin. The resulting waveform on the PROG pin is an
indication of stability.
The double exposure photo in Figure 5 shows the effects
of capacitance on the program pin. The middle waveform
is typical while the lower waveform indicates excessive
program pin capacitance resulting in constant current
mode instability. Although not common, ringing on the
constant voltage portion of the waveform is an indication
(200pF ON PIN)
(20pF ON PIN)
TO SCOPE
GENERATOR
2.5V
0V
PROG PIN
PROG PIN
PULSE
f = 1kHz
Figure 4. Setup for AC Stability Testing
R
10k
5V
0V
2V
1V
0V
2V
1V
0V
Figure 5. Stability Waveforms
PROG
DOWN
3k
SHUT
U
DELAY
*FULLY CHARGED CELL
HORIZONTAL SCALE: 100 s/DIV
INFORMATION
PROG
U
LTC1734L
CONSTANT
CURRENT
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
BAT
PROG
W
1734 F04
+
= 7.5k).
Li-Ion*
CONSTANT
VOLTAGE
U
20 TO
200
of instability due to any combination of extremely low ESR
values, high capacitance values of the output capacitor or
very high PNP transistor beta. To minimize the effect of the
scope probe capacitance, a 10k resistor is used to isolate
the probe from the program pin. Also, an adjustable load
resistor or current sink can be used to quickly alter the
charge current when a fully charged battery is used.
Reverse Input Voltage Protection
In some applications, protection from reverse voltage on
V
series blocking diode can be used. In other cases, where
the voltage drop must be kept low, a P-channel FET as
shown in Figure 6 can be used.
V
Many types of capacitors with values ranging from 1 F to
10 F located close to the LTC1734L will provide adequate
input bypassing. However, caution must be exercised
when using multilayer ceramic capacitors. Because of the
self resonant and high Q characteristics of some types of
ceramic capacitors, high voltage transients can be gener-
ated under some start-up conditions, such as connecting
the charger input to a hot power source. To prevent these
transients from exceeding the absolute maximum voltage
rating, several ohms of resistance can be added in series
with the ceramic input capacitor.
Internal Protection
Internal protection is provided to prevent excessive DRIVE
pin currents (I
LTC1734L during a fault condition. The faults can be
generated from a shorted DRIVE pin or from excessive
DRIVE pin current to the base of the external PNP
transistor when it’s in deep saturation from a very low
V
ing of the external pass transistor. Indirectly though, self-
heating of the PNP thermally conducting to the LTC1734L
CC
CC
CE
. This protection is not designed to prevent overheat-
Bypass Capacitor
is desired. If the supply voltage is high enough, a
Figure 6. Low Loss Reverse Voltage Protection
DSHRT
*DRAIN-BULK DIODE OF FET
V
IN
) and excessive self-heating of the
*
V
LTC1734L
CC
1734 F06
LTC1734L
11
1734lf