lt3651-4.2 Linear Technology Corporation, lt3651-4.2 Datasheet - Page 13

• Manufacturer Part Number: lt3651-4.2
• Description: Monolithic 4a High Voltage Li-ion Battery Charger Features
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
System Input Current Limit
The LT3651 contains a PowerPath  control feature to
help manage supply load currents. The charger adjusts
charger output current in response to a system load so as
to maintain a constant input supply load. If overall input
supply current exceeds the programmed maximum value
the charge current is diminished in an attempt to keep
supply current constant. One application where this is
helpful is if you have a current limited input supply. Setting
the maximum input current limit below the supply limit
prevents supply collapse.
A resistor, R
system and charger loads as shown in Figure 3.
The LT3651 sources 50µA from the I
is developed by simply connecting a resistor to ground.
The voltage on the I
Figure 3. Input Current Limit Configuration
Figure 2. Inductance (L) vs Maximum V
2
1
0
4
3
CL
5
, is placed between the input supply and the
LT3651-4.2
10
LIM
CLN
CLP
I
V
LIM
pin corresponds to 11.5 times the
IN
V
15
IN(MAX)
SUPPLY
INPUT
I
f
25% TO 35% RIPPLE
R
R
MAX
OSC
365142 F03
LIM
CL
(V)
20
SYSTEM LOAD
= 1MHz
= 4A
25
LIM
36512 F02
pin, so a voltage
30
IN
maximum voltage across the input sense resistor (R
Input current limit is defined by:
The programming range for I
than 1V have no effect on the maximum input current. The
default maximum sense voltage is 95mV and is obtained
if R
For example, say you want a maximum input current of
2A and the charger is designed for 4A maximum average
charge current, which is 1A V
cycle). Using the full I
across R
When the system load exceeds 1A (= 2A – 1A) charge
current is reduced such that the total input current stays
at 2A. When the system load is 2A the charge current is 0.
This feature only controls charge current so if the system
load exceeds the maximum limit and no other limitation
is designed, the input current exceeds the maximum
desired, though the charge current reduces to 0A. When
the input limiter reduces charge current it does not impact
the internal system timer if used. See Figure 4.
If reduced voltage overhead or better efficiency is required
then reduce the maximum voltage across R
instance, a 10k R
43mV. This reduction comes at the expense of slightly
increased limit variation.
I
INPUT MAX
ILIM
Figure 4. Input Current Limit for 4A Maximum Charger
and 6A System Current Limit
is greater than 20k or if the pin is left open.
(
CL
is 95mV. So R
2
1
0
3
0
)
=
11 5
ILIM
SYSTEM LOAD CURRENT (A)
V
. •
ILIM
sets the maximum R
1
INPUT CURRENT
LIM
R
CL
CL
range, the maximum voltage
LIM
is set at 95mV/2A = 48mΩ.
=
CHARGE
CURRENT
(V
IN
is 0V to 1V. Voltages higher
IN
50
11 5
REFERRED)
2
referred (4A time duty
µA R
. •
LT3651-4.2
•
365142 F04
R
ILIM
CL
CL
voltage to
CL
. So for

365142f
CL
).