LTC4100EG#TRPBF Linear Technology, LTC4100EG#TRPBF Datasheet - Page 25

IC SMART BATTERY CHARGER 24-SSOP

LTC4100EG#TRPBF

Manufacturer Part Number
LTC4100EG#TRPBF
Description
IC SMART BATTERY CHARGER 24-SSOP
Manufacturer
Linear Technology
Datasheet

Specifications of LTC4100EG#TRPBF

Function
Charge Management
Battery Type
Smart Batteries
Voltage - Supply
6 V ~ 28 V
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
24-SSOP (0.200", 5.30mm Width)
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

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APPLICATIONS INFORMATION
Soft-Start and Undervoltage Lockout
The LTC4100 is soft-started by the 0.12μF capacitor on
the I
to 0.5V, then ramp up at a rate set by the internal 30μA
pull-up current and the external capacitor. Battery charging
current starts ramping up when I
and full current is achieved with I
capacitor, time to reach full charge current is about 2ms and
it is assumed that input voltage to the charger will reach
full value in less than 2ms. The capacitor can be increased
up to 1μF 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
computer power supply are typically supplying a fi xed
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 fi nal 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
regulators can no longer supply full load. This situation
can be prevented by utilizing the DCDIV resistor divider,
set higher than the minimum adapter voltage where full
power can be achieved.
Input and Output Capacitors
We recommend the use of high capacity low ESR/ESL X5R
type ceramic capacitors. Alternative capacitors include
OSCON or POSCAP type capacitors. Aluminum electrolytic
capacitors are not recommended for poor ESR and ESL
reasons. Solid tantalum low ESR capacitors are acceptable,
but caution must be used when tantalum capacitors are
used for input or output bypass. High input surge currents
can be created when the power adapter is hot-plugged
TH
pin. On start-up, I
TH
pin voltage will rise quickly
TH
TH
voltage reaches 0.8V
at 2V. With a 0.12μF
into the charger or when a battery is connected to the
charger. Use only “surge robust” low ESR tantalums. Re-
gardless of which type of capacitor you use, after voltage
selection, the most important thing to meet is the ripple
current requirements followed by the capacitance value.
By the time you solve the ripple current requirements,
the minimum capacitance value is often met by default.
The following equation shows the minimum C
tolerance) capacitance values for stability when used with
the compensation shown in the typical application on the
back page.
The use of aluminum electrolytic for C1, located at the
AC adapter input terminal, is helpful in reducing ringing
during the hot-plug event. Refer to Application Note 88
for more information.
In the 4A lithium battery charger (typical application on
back page), the input capacitor (C2) is assumed to absorb
all input switching ripple current in the converter, so it
must have adequate ripple current rating. Worst-case RMS
ripple current will be equal to one half of output charging
current. C2 is recommended to be equal to or greater than
C4 (output capacitor) in capacitance value.
The output capacitor (C4) is also assumed to absorb
output switching current ripple. The general formula for
capacitor current is:
For example, V
f = 300kHz, I
EMI considerations usually make it desirable to minimize
ripple current in the battery leads, and beads or induc-
tors may be added to increase battery impedance at the
300kHz switching frequency. Switching ripple current splits
between the battery and the output capacitor depending
on the ESR of the output capacitor and the battery imped-
ance. If the ESR of C3 is 0.2Ω and the battery impedance
is raised to 4Ω with a bead or inductor, only 5% of the
current ripple will fl ow in the battery.
C
I
RMS
OUT(MIN)
=
0 29
.
RMS
= 200/L1
DCIN
(
V
= 0.41A.
BAT
= 19V, V
L f
)
1
⎝ ⎜
1
BAT
V
V
DCIN
BAT
= 12.6V, L1 = 10μH, and
⎠ ⎟
LTC4100
OUT
25
(±20%
4100fb

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