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ADP1653
EXTERNAL COMPONENT SELECTION
Selecting the Inductor
The ADP1653 step-up converter increases the battery voltage to
allow driving one, two, or three LEDs, whose combined voltage
drop is higher than the battery voltage plus the 0.32 V (typical)
current source headroom voltage. This allows the converter to
regulate the HPLED current over the entire battery voltage range
and with a wide variation of LED forward voltage.
The inductor saturation current should be greater than the sum
of the dc input current and half the inductor ripple current.
A reduction in the effective inductance due to saturation increases
the inductor current ripple but improves loop stability, reducing
the amount of output capacitance required. Ensure that the peak
inductor current (dc + 1/2 of inductor ripple) is less than the
LX minimum current limit (1.8 A).
Table 9. Recommended Inductors
Users should choose an inductor value such that the inductor
ripple current is approximately 2/5th of the maximum dc input
load current. In general, lower inductance values have higher
saturation current and lower series resistance for a given physical
size. For most applications, an inductor in the range of 1.5 μH
to 3.3 μH works well.
To determine the inductor ripple current, users should first
Vendor
Toko
Toko
Toko
Coilcraft
Coilcraft
Value
(μH)
2.2
2.0
3.3
2.2
2.2
Part No.
FDSE0312
DE2812C
FDSE0312
LPS3010
LPS3314
DCR
(mΩ)
145
67
199
220
100
ISAT
(A)
3.1
1.8
2.6
1.4
1.5
Dimensions
L × W × H (mm)
3 × 3 × 1.2
2.8 × 2.8 × 1.2
3 × 3 × 1.2
3 × 3 × 1.0
3 × 3 × 1.4
calculate the switch duty cycle for the step-up converter, which
is determined by the input voltage (V IN ), output voltage (V OUT ),
and Schottky forward voltage (V F ). V OUT equals the LED voltage
drop plus 320 mV (typical) overhead for the HPLED current
regulator.
Selecting the Input Capacitor
The ADP1653 requires an input bypass capacitor to supply
transient currents while maintaining constant input and output
voltage. The input capacitor carries the input ripple current,
allowing the input power source to supply only the dc current.
V IN
V OUT + V F
= 1 ? D
(14)
Use an input capacitor with sufficient ripple current rating to
handle the inductor ripple. A 4.7 μF X5R/X7R ceramic capacitor
D = 1 ?
V + V F ? V IN
Solving for D
V IN
V OUT + V F
= OUT
V OUT + V F
rated for 6.3 V is the minimum recommended input capacitor.
Increased input capacitance reduces the amplitude of the switching
frequency ripple on the battery. Because of the dc bias charac-
teristics of ceramic capacitors, a 0603, 6.3 V X5R/X7R, 10 μF
The HPLED (output) current is regulated as low as 50 mA
(torch mode) and as high as 500 mA (flash mode). The
maximum dc input current is related to the maximum dc
output current by the following equation:
ceramic capacitor is preferable.
Table 10. Recommended Input Capacitors
Dimensions
L×W×H
I IN ( MAX ) = I OUT ( MAX ) × ? ? OUT
? 1
? η
? V
? V IN
? ×
?
(15)
Vendor
Murata
TDK
Value
10 μF, 6.3 V
10 μF, 6.3 V
Part No.
GRM188R60J106ME47
C1608JB0J106K
(mm)
1.6 × 0.8 × 0.8
1.6 × 0.8 × 0.8
where η is efficiency (assume η ≈ 0.80 in the two-LED case).
Choose the initial inductor value by using the equation
Selecting the Diode
The ADP1653 is a nonsynchronous boost and, as such, requires
? V OUT + V F ? V IN
?
?
?
L =
V IN
Δ I L × f SW
?
? V OUT + V F
?
?
(16)
an external Schottky rectifier to conduct the inductor current to
the output capacitor and HPLEDs when the LX switch is off.
Ensure that the Schottky peak current rating is greater than the
where:
L is the inductor value (reduce L to reduce solution size).
f SW is the switching frequency.
ΔI L is the inductor ripple current, typically 2/5th of the
maximum dc input current.
maximum inductor current. Choose a diode with an average
current rating that is significantly larger than the maximum
LED current. To prevent thermal runaway, derate the Schottky
rectifier to ensure reliable operation at high junction temperatures.
To achieve the best efficiency, select a Schottky diode with a low V F .
V F is the forward voltage of the Schottky diode.
Rev. B | Page 18 of 24
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