LTC4150CMS(RevA) Просмотр технического описания (PDF) - Linear Technology

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LTC4150CMS
(Rev.:RevA)

Coulomb Counter/Battery Gas Gauge

Linear Technology 

LTC4150

APPLICATIO S I FOR ATIO

PC BOARD LAYOUT SUGGESTIONS

Keep all traces as short as possible to minimize noise and

inaccuracy. The supply bypass capacitor C2 should be

placed close to the LTC4150. The 4.7µF filter capacitor CF

should be placed close the CF+ and CF– pins and should be

a low leakage, unpolarized type. Use a 4-wire Kelvin sense

connection for the sense resistor, locating it close to the

LTC4150 with short sense traces to the SENSE+ and

SENSE– pins and longer force lines to the battery pack and

powered load, see Figure 7.

TO CHARGER

RSENSE

PIN 1

LTC4150

TO BATTERY

4150 F07

Figure 7. Kelvin Connection on SENSE Resistor

TYPICAL APPLICATIO S

Figure 8 shows a typical application designed for a single

cell lithium-ion battery and 500mA maximum load current.

Use Equation 1 to calculate RSENSE = 0.05V / 0.5A = 0.1Ω.

With RSENSE = 0.1Ω, Equation 7 shows that each interrupt

corresponds to 0.085mAh. Equation 14, derived from

Equation 2, gives the number of INT assertions for average

battery current, IBATT, over a time, t, in seconds:

INT Assertions = GVF • IBATT • RSENSE • t

(14)

Loading the battery so that 51.5mA is drawn from it over

600 seconds results in 100 INT assertions. For an 800mAh

battery, this is (51.5mA • 1/6h) / 800mAh = 11% of the

battery’s capacity.

With a microcontroller supply = 5V, Equation 11 gives

RL > 2.875k. The nearest standard value is 3k.

From Equation 12, RL = 3k gives R1 + R2 equal to 150.5k.

A single cell lithium-ion battery can discharge as low as

2.7V.

From Equation 13, select R1 = 75k; the nearest standard

value for R2 is 76.8k.

Also from Equation 13, we choose R3 = 75k and R4 =

76.8k.

POWER-DOWN

SWITCH

5.0V

CL

47µF

LOAD

RSENSE

0.1Ω

SINGLE-CELL +

Li-Ion

3.0V ~ 4.2V

CF

4.7µF

1 SENSE+

10

INT

LTC4150 CLR 9

2 SENSE–

8

VDD

3 CF+

7

GND

4 CF–

5

SHDN

6

POL

RL

RL

3k

3k

R2

76.8k

C2

4.7µF R1

75k

µP

SHUTDOWN

R4

76.8k

10

R3

75k

4150 F08

Figure 8. Typical Application, Single Cell Lithium-Ion Battery

4150fa

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