LT1505CG Linear Technology, LT1505CG Datasheet - Page 11

• Manufacturer Part Number: LT1505CG
• Description: IC BATT CHARGER CONST I/V 28SSOP
• Manufacturer: Linear Technology

Specifications of LT1505CG

• Function: Charge Management
• Battery Type: Li-Ion, NiCd, NiMH
• Voltage - Supply: 11 V ~ 24 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
EMI considerations usually make it desirable to minimize
ripple current in the battery leads. Beads or inductors may
be added to increase battery impedance at the 200kHz
switching frequency. Switching ripple current splits be-
tween the battery and the output capacitor depending on
the ESR of the output capacitor and the battery imped-
ance. If the ESR of C
is raised to 4 with a bead or inductor, only 5% of the
ripple current will flow in the battery.
Soft Start and Undervoltage Lockout
The LT1505 is soft started by the 0.33 F capacitor on the
V
0.5V, then ramp up at a rate set by the internal 45 A pull-
up current and the external capacitor. Battery charge
current starts ramping up when V
and full current is achieved with V
capacitor, time to reach full charge current is about 10ms
and it is assumed that input voltage to the charger will
reach full value in less than 10ms. The capacitor can be
increased up to 1 F if longer input start-up times are
needed.
In any switching regulator, conventional timer-based soft
starting can be defeated if the input voltage rises much
slower than the time out period. This happens because the
switching regulators in the battery charger and the com-
puter power supply are typically supplying a fixed amount
of power to the load. If input voltage comes up slowly
compared to the soft start time, the regulators will try to
deliver full power to the load when the input voltage is still
well below its final value. If the adapter is current limited,
it cannot deliver full power at reduced output voltages and
the possibility exists for a quasi “latch” state where the
adapter output stays in a current limited state at reduced
output voltage. For instance, if maximum charger plus
computer load power is 30W, a 15V adapter might be
current limited at 2.5A. If adapter voltage is less than
(30W/2.5A = 12V) when full power is drawn, the adapter
voltage will be pulled down by the constant 30W load until
it reaches a lower stable state where the switching regu-
lators can no longer supply full load. This situation can be
prevented by setting undervoltage lockout higher than the
minimum adapter voltage where full power can be achieved.
C
pin. On start-up, the V
OUT
U
is 0.2 and the battery impedance
INFORMATION
C
U
pin voltage will rise quickly to
C
C
at 1.1V. With a 0.33 F
W
voltage reaches 0.7V
U
A resistor divider is used to set the desired V
voltage as shown in Figure 2. A typical value for R6 is 5k
and R5 is found from:
V
V
Example: With R6 = 5k, V
R5 = 5k (16V – 6.7V)/6.7V = 6.9k
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
the pin will cause reverse battery current to increase from
10 A to 200 A.
Adapter Current Limiting
(Not Applicable for the LT1505-1)
An important feature of the LT1505 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 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.
UV
IN
R5 =
= Charger input voltage that will sustain full load power
= Rising lockout threshold on the UV pin
CL1
R6(V – V )
LT1505
+
–
V
Figure 2. Adapter Current Limiting
IN
UV
92mV
+
UV
CLP
CLN
V
UV
CC
*R
UV
S4
= 6.7V and setting V
=
+
ADAPTER CURRENT LIMIT
C
1 F
IN
R
92mV
S4
500
*
CC
pin to prevent
LT1505
CC
IN
AC ADAPTER
CC
11
OUTPUT
lockout
R5
R6
1505 F02
at 16V;
) and
1505fc
V
IN