Datasheet

ADP1607 Data Sheet
Rev. C | Page 12 of 16
APPLICATIONS INFORMATION
SETTING THE OUTPUT VOLTAGE
The ADP1607 can be configured for output voltages between
1.8 V and 3.3 V. The output voltage is set by a resistor voltage
divider, R1, from the output voltage (V
OUT
) to the 1.259 V
feedback input at FB and R2 from FB to GND (see Figure 24).
Resistances between 100 kΩ and 1 MΩ are recommended.
For larger R1 and R2 values, the voltage drop due to the FB pin
current (I
FB
) on R1 becomes proportionally significant and
needs to be factored in.
To account for the effect of I
FB
for all values of R1 and R2,
use the following equation to determine R1 and R2 for the
desired V
OUT
:
)(1 R1IV
R2
R1
V
FBFBOUT
+






+=
(1)
where:
V
FB
= 1.259 V, typical
I
FB
= 0.1 µA, typical
INDUCTOR SELECTION
The ADP1607 is designed with a 2 MHz operating frequency
enabling the use of small chip inductors ideal for use in
applications with limited solution size constraints. The
ADP1607 is designed for optimal performance with 2.2 µH
inductors, which have favorable saturation currents and lower
series resistances for their given physical size.
To ensure stable and efficient performance with the ADP1607,
care should be taken to select a compatible inductor with a
sufficient current rating, saturation current, and low dc
resistance (DCR.)
The maximum rated rms current of the inductor must be
greater than the maximum input current to the regulator.
Likewise, the saturation current of the chosen inductor must be
able to support the peak inductor current (the maximum input
current plus half the inductor ripple current) of the application.
The inductor ripple current (∆I
L
) in steady state continuous
mode can be calculated as
SW
IN
L
fL
DV
I
×
×
=∆
(2)
where:
D is the duty cycle of the application.
L is the inductor value.
f
SW
is the switching frequency of the ADP1607.
The switch duty cycle (D) is determined by the input (V
IN
) and
output (V
OUT
) voltages with the following equation:
OUT
IN
OUT
V
VV
D
−
=
(3)
Inductors with a low DCR minimize power loss and improve
efficiency. DCR values below 100 mΩ are recommended.
Table 5. Suggested Inductors
Manufacturer Part Number
Inductance
(µH)
DCR (mΩ)
Typ
Current
Rating (A)
Saturation
Current (A)
Size (L × W × H) (mm) Package
TDK MLP2016S2R2M 2.2 ± 20% 110 1.20 2.00 × 1.60 × 1.00 0806
MLP2520S2R2S 2.2 ± 20% 110 1.20 1.20 2.50 × 2.00 × 1.00 1008
VLF252012MT-2R2M 2.2 ± 20% 57 1.67 1.04 2.50 × 2.00 × 1.00 1008
VLF302510MT-2R2M 2.2 ± 20% 70 1.23 1.37 3.00 × 2.50 × 1.00
VLF302515MT-2R2M
2.2 ± 20%
42
2.71
1.57
3.00 × 2.50 × 1.40
Murata LQM2HPN2R2MG0 2.2 ± 20% 80 1.30 2.50 × 2.00 × 0.90 1008
LQH32PN2R2NNC 2.2 ± 30% 64 1.85 3.20 × 2.50 × 1.55 1210
Wurth
74479787222
2.2 ± 20%
80
1.50
0.70
2.50 × 2.00 × 1.00
1008
7440430022 2.2 ± 30% 23 2.50 2.35 4.80 × 48.0 × 2.80
Taiyo Yuden BRC2012T2R2MD 2.2 ± 20% 110 1.00 1.10 2.00 × 1.25 × 1.40 0805
Toko MDT2520-CR2R2M 2.2 ± 20% 90 1.35 2.50 × 2.00 × 1.00 1008
DEM2810C (1224AS-H-2R2M) 2.2 ± 20% 85 1.10 1.40 3.20 × 3.00 × 1.00
DEM2815C (1226AS-H-2R2M) 2.2 ± 20% 43 1.40 2.20 3.20 × 3.00 × 1.50
Coilcraft XFL3012-222 2.2 ± 20% 81 1.9 1.6 3.00 × 3.00 × 1.20 1212
XFL4020-222 2.2 ± 10% 21 8.0 3.1 4.00 × 4.00 × 2.10 1515