SLEA004
4
Extending Battery Life With the TPS61040 White Light LED Driver
Table 1 provides resistor values for different bias voltages and different current sense voltages.
Table 2 shows the operating parameters of the circuit under various conditions. The values
shown in the Vcs=2 V column were measured using the circuit in Figure 1, and Vin=3.6 V. All
other data are taken with the circuit in Figure 2. Note that although the efficiency of the circuit is
essentially the same under all conditions, the battery current is reduced when the full-scale
voltage drop across the current sense resistor is reduced. The battery life is calculated using a
1000-mA/hr Li-Ion battery.
Table 1.
Calculated Resistor Values
Vcs (V)
0.5
0.5
0.5
0.25
0.25
0.25
Vbias (V)
3.3
5
12.7
3.3
5
12.7
Rbias (k
Ω
)
499
499
499
499
499
499
R2 (k
Ω
)
1466
804
264
3430
1882
618
R3 (k
Ω
)
222
122
40
260
143
47
R4 (
Ω
)
25
25
25
12.5
12.5
12.5
Table 2.
Measured Data Shows Extended Battery Life
Vcs (V)
2
0.5
0.5
0.25
0.25
Vbias (V)
N/A
5
Vout (1)
5
Vout (2)
Iout (mA)
20
20
20
20
20
Vout (V)
14.77
13.17
13.17
12.92
12.92
Iin (mA)
95.8
84.9
85
83.1
83.4
Effic (%)
85.6
86.2
86.2
86.3
86.1
Battery Life at
100% duty (Hours)
10.4
11.8
11.8
12
12
(1) Vout is approximately 13.17V
(2) Vout is approximately 12.92V
References
1. TPS61040 – Low Power DC/DC Boost Converter in SOT-23 Package (SLVS413)
2. TPS61040EVM-002 White Light LED Bias Supply Evaluation Module (SLVU068)
15.4% Increase
