LTC4001EUF datasheet(13/20 Pages) LINER

13 / 20 page

LTC4001

4001f

where RNOM is the value of the bias resistor, RHOT and

RCOLD are the values of RNTC at the desired temperature

trip points. Continuing the example from before with a

desired hot trip point of 50

°C:

k is nearest

NOM

COLD

HOT

()

⎛

⎝⎜

⎞

⎠⎟

–

.– .

•.

– .

.– .

•

.– .

•

–.

2 815 0 4086

100

3 2636 0 3602

2 815 0 4086

120 8 121

1 100

0 4086

2 815 0 4086

3 266 0 3602

0 3602

13 3 13 3

The final solution is as shown if Figure 4 where RNOM =

121k, R1 = 13.3k and RNTC = 100k at 25°C.

Input and Output Capacitors

The LTC4001 uses a synchronous buck regulator to pro-

vide high battery charging current. A 10

µF chip ceramic

APPLICATIO S I FOR ATIO

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 0.1

Ω and the battery

impedance is raised to 2

Ωwithabeadorinductor,only5%

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 • VINSENSE

0.74 • VINSENSE

RNOM

121k

VINSENSE

0.02 • VINSENSE

NTC ENABLE

4001 F04

–

13.3k

RNTC

100k

NTC

GNDSENS

LTC4001EUF Datasheet(PDF) 13 Page - Linear Technology

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