LTC4150 Linear Technology, LTC4150 Datasheet - Page 10

• Manufacturer Part Number: LTC4150
• Description: Coulomb Counter/ Battery Gas Gauge
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC4150
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 C
should be placed close the C
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
SENSE
powered load, see Figure 7.
Figure 8 shows a typical application designed for a single
cell lithium-ion battery and 500mA maximum load current.
Use Equation 1 to calculate R
With R
corresponds to 0.085mAh. Equation 14, derived from
Equation 2, gives the number of INT assertions for average
battery current, I
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.
10
TYPICAL APPLICATIO S
INT Assertions = G
SENSE
–
pins and longer force lines to the battery pack and
= 0.1Ω, Equation 7 shows that each interrupt
BATT
U
, over a time, t, in seconds:
VF
SINGLE-CELL
3.0V ~ 4.2V
• I
U
BATT
R
Li-Ion
SENSE
F
0.1Ω
SENSE
+
and C
+
• R
Figure 8. Typical Application, Single Cell Lithium-Ion Battery
4.7µF
U
= 0.05V / 0.5A = 0.1Ω.
SENSE
C
F
W
F
–
pins and should be
1
2
3
4
5
• t
SENSE
SENSE
C
C
SHDN
F
F
+
–
LTC4150
+
–
U
+
GND
CLR
V
POL
INT
DD
(14)
and
10
9
8
7
6
R4
76.8k
R3
75k
F
SHUTDOWN
C2
4.7µF
With a microcontroller supply = 5V, Equation 11 gives
R
From Equation 12, R
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.
L
> 2.875k. The nearest standard value is 3k.
R
3k
L
R2
76.8k
R1
75k
Figure 7. Kelvin Connection on SENSE Resistor
R
SENSE
R
3k
TO CHARGER
TO BATTERY
L
5.0V
µP
L
C
47µF
= 3k gives R1 + R2 equal to 150.5k.
L
POWER-DOWN
SWITCH
PIN 1
LTC4150
LOAD
4150 F08
4150 F07
4150fa