LTC4100EG#TRPBF Linear Technology, LTC4100EG#TRPBF Datasheet - Page 22

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

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

LTC4100
APPLICATIONS INFORMATION
I
I
current as requested over the SMBus. If you deviate
from the resistance values shown in Table 9, it will lead
to charge current gain errors. The requested current and
the actual charge current applied to the battery will not
be the same.
Table 9. Recommended Resistor Values
Warning
DO NOT CHANGE THE VALUE OF R
TION. The value must remain fi xed and track the R
value at all times. Changing the current setting can result
in currents that greatly exceed the requested value and
potentially damage the battery or overload the wall adapter
if no input current limiting is provided.
Inductor Selection
Higher operating frequencies allow the use of smaller
inductor and capacitor values. A higher frequency gener-
ally results in lower effi ciency because of MOSFET gate
charge losses. In addition, the effect of inductor value
on ripple current and low current operation must also be
considered. The inductor ripple current ΔI
higher frequency and increases with higher V
Accepting larger values of ΔI
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is ΔI
maximum ΔI
inductor value also has an effect on low current operation.
22
MAX
MAX
ΔI
I
MAX
1.023
2.046
3.068
4.092
value that is still above your expected battery charge
is the full-scale charge current. Chose the lowest
L
(A)
=
( )( )
f L
1
L
occurs at the maximum input voltage. The
R
SENSE
V
OUT
0.100
0.025
0.025
0.05
(Ω) 1%
⎛
⎜
⎝
1
−
V
V
L
OUT
IN
= 0.4(I
R
L
⎞
⎟
⎠
SENSE
0.25
0.25
allows the use of low
0.5
0.5
ILIM
MAX
(W)
). Remember the
DURING OPERA-
L
decreases with
R
ILIM
IN
Open
.
10k
33k
(Ω) 1%
0
SENSE
The transition to low current operation begins when the
inductor current reaches zero while the bottom MOSFET
is on. Lower inductor values (higher ΔI
to occur at higher load currents, which can cause a dip in
effi ciency in the upper range of low current operation. In
practice 10μH is the lowest value recommended for use.
Table 10. Recommended Inductor Values
Charger Switching Power MOSFET
and Diode Selection
Two external power MOSFETs must be selected for use
with the charger: a P-channel MOSFET for the top (main)
switch and an N-channel MOSFET for the bottom (syn-
chronous) switch.
The peak-to-peak gate drive levels are set internally. This
voltage is typically 6V. Consequently, logic-level threshold
MOSFETs must be used. Pay close attention to the BV
specifi cation for the MOSFETs as well; many of the logic
level MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFETs include the
on-resistance R
transfer capacitance C
output current. The charger is operating in continuous
mode so the duty cycles for the top and bottom MOSFETs
are given by:
Maximum Average
Main Switch Duty Cycle = V
Synchronous Switch Duty Cycle = (V
Current (A)
1
1
2
2
3
3
4
4
DS(ON)
Input Voltage (V)
, total gate capacitance Q
RSS
≤20
>20
≤20
>20
≤20
>20
≤20
>20
, input voltage and maximum
OUT
/V
Minimum Inductor Value
IN
L
IN
) will cause this
40 ± 20%
56 ± 20%
20 ± 20%
30 ± 20%
15 ± 20%
20 ± 20%
10 ± 20%
15 ± 20%
– V
(μH)
OUT
G
, reverse
)/V
IN
4100fb
DSS