LTC4001-1 Linear Technology, LTC4001-1 Datasheet - Page 13

• Manufacturer Part Number: LTC4001-1
• Description: 2A Synchronous Buck Li-Ion Charger
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
where R
R
trip points. Continuing the example from before with a
desired hot trip point of 50°C:
The fi nal solution is as shown if Figure 4 where R
121k, R1 = 13.3k and R
Input and Output Capacitors
The LTC4001-1 uses a synchronous buck regulator to
provide high battery charging current. A 10μF chip ceramic
R
R1= 100k •
COLD
NOM
= 13.3k, 13.3k is nearest 1%
=
= 120.8k, 121k is nearest 1%
are the values of R
2.815 – 0.4086
NOM
R
COLD
2.815 – 0.4086
is the value of the bias resistor, R
– R
0.4086
HOT
=
NTC
100k • 3.2636 – 0.3602
NTC
= 100k at 25°C.
• 3.266 – 0.3602
(
at the desired temperature
2.815 – 0.4086
(
R
121k
R1
13.3k
GNDSENS
NOM
V
R
100k
INSENSE
Figure 4. Extending the Delta Temperature
NTC
NTC
11
9
4
)
– 0.3602
HOT
)
0.74 • V
0.29 • V
0.02 • V
NOM
and
INSENSE
INSENSE
INSENSE
=
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
connecting 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 fl ow in the battery. Similar
techniques may also be applied to minimize EMI from
the input leads.
–
+
–
+
+
–
LTC4001-1 NTC BLOCK
TOO COLD
TOO HOT
NTC ENABLE
40011 F04
LTC4001-1
13
40011fa