LT1769CGN#TR Linear Technology, LT1769CGN#TR Datasheet - Page 10

• Manufacturer Part Number: LT1769CGN#TR
• Description: IC CHARGER BATT CONST V/I 28SSOP
• Manufacturer: Linear Technology

Specifications of LT1769CGN#TR

• Function: Charge Management
• Battery Type: Lead Acid, Li-Ion, NiCd, NiMH
• Voltage - Supply: 8 V ~ 25 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.150", 3.95mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LT1769
APPLICATIONS
V
V
Example: With R6 = 5k, V
R5 = 5k (12V – 6.7V)/6.7V = 4k
The resistor divider should be connected directly to the
adapter output as shown, not to the V
battery drain with no adapter voltage. If the UV pin is not
used, connect it to the adapter output (not V
connect a resistor no greater than 5k to ground. Floating
this pin will cause reverse battery current to increase from
3 A to 200 A.
If connecting the unused UV pin to the adapter output is not
possible, it can be grounded. Although it would seem that
grounding the pin creates a permanent lockout state, the
UV circuitry is arranged for phase reversal with low volt-
ages on the UV pin to allow the grounding technique to work.
Adapter Current Limiting
An important feature of the LT1769 is the ability to
automatically adjust charge current to a level which avoids
overloading the wall adapter. This allows the product to
operate at the same time the batteries are being charged
without complex load management algorithms. Addition-
ally, batteries will automatically be charged at the maximum
possible rate of which the adapter is capable.
This is accomplished by sensing total adapter output
current and adjusting the charge current downward if a
preset adapter current limit is exceeded. True analog
control is used, with closed-loop feedback ensuring that
10
UV
IN
= Charger input voltage that will sustain full load power
= Rising lockout threshold on the UV pin
CL1
LT1769
Figure 2. Adapter Input Current Limiting
+
–
100mV
+
U
CLP
CLN
V
UV
CC
*R
UV
INFORMATION
S4
U
= 6.7V and setting V
=
+
ADAPTER CURRENT LIMIT
1 F
100mV
W
R
S4
CC
*
500
pin, to prevent
U
IN
CC
AC ADAPTER
at 12V;
OUTPUT
R5
R6
1769 F02
) and
V
IN
adapter load current remains below the limit. Amplifier
CL1 in Figure 2 senses the voltage across R
between the CLP and CLN pins. When this voltage exceeds
100mV, the amplifier will override the programmed charge
current to limit adapter current to 100mV/R
filter formed by 500
switching noise. If the input current limit is not used, both
CLP and CLN pins should be connected to V
Charge Current Programming
The basic formula for charge current is (see Block
Diagram):
where R
For the sense amplifier CA1 biasing purpose, R
have the same value as R
directly to the sense resistor (R
Diagram.
For example, 2A charge current is needed. For low power
dissipation on R
CA1, let R
to 0.2W. Let R
Charge current can also be programmed by pulse width
modulating I
higher than a few kHz (Figure 3). Charge current will be
proportional to the duty cycle of the switch with full current
at 100% duty cycle.
Lithium-Ion Charging
The 2A Lithium-Ion Battery Charger (Figure 1) charges at
a constant 2A until battery voltage reaches a limit set by R3
and R4. The charger will then automatically go into a
constant-voltage mode with current decreasing to near
zero over time as the battery reaches full charge. This is the
normal regimen for lithium-ion charging, with the charger
I
R
=
BAT
S2
(2A)(5k)(0.05)
= R
PROG
= I
2.465V
S1
PROG
S3
PROG
= 100mV/2A = 0.05 . This limits R
is the total resistance from PROG pin to ground.
=
PROG
S1
(I
R
R
with a switch Q1 to R
BAT
and enough signal to drive the amplifier
S2
S1
= 5k, then:
)(R
= 200
=
2.465V
and 1 F is required to eliminate
S2
PROG
2.465V
R
and SPIN should be connected
PROG
)(R
S1
) as shown in the Block
S1
)
R
R
PROG
S2
S1
S4
at a frequency
S4
CC
, connected
. A lowpass
.
S3
S1
should
power
1769fa