ltc4001 Linear Technology Corporation, ltc4001 Datasheet - Page 13

• Manufacturer Part Number: ltc4001
• Description: 2a Synchronous Buck Li-ion Charger
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
where R
R
trip points. Continuing the example from before with a
desired hot trip point of 50°C:
The final solution is as shown if Figure 4 where R
121k, R1 = 13.3k and R
Input and Output Capacitors
The LTC4001 uses a synchronous buck regulator to pro-
vide high battery charging current. A 10µF chip ceramic
R
R
COLD
NOM
1 100
=
=
13 3 13 3
=
=
are the values of R
. ,
120 8 121
NOM
2 815 0 4086
k
R
k
.
•
COLD
⎛
⎜
⎝
. ,
2 815 0 4086
is the value of the bias resistor, R
k
.
.
– .
k is nearest
–
0 4086
R
.
HOT
U
– .
k is nearest
NTC
=
U
NTC
100
1
= 100k at 25°C.
• .
%
(
k
at the desired temperature
3 266 0 3602
2 815 0 4086
• .
1
.
(
%
R
121k
R1
13.3k
3 2636 0 3602
GNDSENS
NOM
W
V
R
100k
INSENSE
NTC
NTC
11
– .
– .
9
4
Figure 4. Extending the Delta Temperature
– .
0.74 • V
0.29 • V
0.02 • V
)
U
– .
0 3602
HOT
INSENSE
INSENSE
INSENSE
)
NOM
and
⎞
⎟
⎠
=
–
–
–
+
+
+
capacitor is recommended for both the input and output
capacitors because it provides low ESR and ESL and can
handle the high RMS ripple currents. However, some high
Q capacitors may produce high transients due to self-
resonance under some start-up conditions, such as con-
necting the charger input to a hot power source. For more
information, refer to Application Note 88.
EMI considerations usually make it desirable to minimize
ripple current in the battery leads, and beads or inductors
may be added to increase battery impedance at the 1.5MHz
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 impedance.
If the ESR of the output capacitor is 0.1Ω and the battery
impedance is raised to 2Ω with a bead or inductor, only 5%
of the ripple current will flow in the battery. Similar
techniques may also be applied to minimize EMI from the
input leads.
LTC4001 NTC BLOCK
TOO COLD
TOO HOT
NTC ENABLE
4001 F04
LTC4001
13
4001f