LTC4150
11
4150fc
APPLICATIONS INFORMATION
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 fi lter capacitor
C
F
should be placed close the C
F
+
and C
F
–
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.
4150 F07
PIN 1
TO BATTERY
TO CHARGER
LTC4150
R
SENSE
Figure 7. Kelvin Connection on SENSE Resistor
TYPICAL APPLICATIONS
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
SENSE
= 0.05V/0.5A = 0.1Ω.
With R
SENSE
= 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, I
BATT
, over a time, t, in seconds:
INT Assertions = G
VF
• I
BATT
• R
SENSE
• 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
R
L
> 2.875k. The nearest standard value is 3k.
From Equation 12, R
L
= 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.
INTSENSE
+
SENSE
–
SHDN
SHUTDOWN
R4
76.8k
R3
75k
CLR
POL
LTC4150
μP
C2
4.7μF
R
L
3k
10
9
8
7
6
1
2
5
4150 F08
V
DD
GND
R
L
3k
5.0V
POWER-DOWN
SWITCH
C
L
47μF
LOAD
C
F
+
C
F
–
3
4
C
F
4.7μF
SINGLE-CELL
Li-Ion
3.0V ~ 4.2V
R
SENSE
0.1Ω
R2
76.8k
R1
75k
+
Figure 8. Typical Application, Single Cell Lithium-Ion Battery
