Datasheet
13
LTC4001
4001f
where R
NOM
is the value of the bias resistor, R
HOT
and
R
COLD
are the values of R
NTC
at the desired temperature
trip points. Continuing the example from before with a
desired hot trip point of 50°C:
R
RR
k
k k is nearest
Rk
k k is nearest
NOM
COLD HOT
==
()
=
=
()
⎛
⎝
⎜
⎞
⎠
⎟
=
–
.–.
•. –.
.–.
., %
•
.
.–.
• . –. –.
., . %
2 815 0 4086
100 3 2636 0 3602
2 815 0 4086
120 8 121 1
1 100
0 4086
2 815 0 4086
3 266 0 3602 0 3602
13 3 13 3 1
The final solution is as shown if Figure 4 where R
NOM
=
121k, R1 = 13.3k and R
NTC
= 100k at 25°C.
Input and Output Capacitors
The LTC4001 uses a synchronous buck regulator to pro-
vide high battery charging current. A 10µF chip ceramic
APPLICATIO S I FOR ATIO
WUUU
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.
Figure 4. Extending the Delta Temperature
TOO COLD
LTC4001 NTC BLOCK
TOO HOT
0.29 • V
INSENSE
0.74 • V
INSENSE
R
NOM
121k
V
INSENSE
0.02 • V
INSENSE
NTC ENABLE
4001 F04
–
+
–
+
–
+
R1
13.3k
R
NTC
100k
9
NTC
11
GNDSENS
4