Datasheet

Data Sheet ADP2105/ADP2106/ADP2107
Rev. D | Page 17 of 36
OFF
EN
SS
LX2
FB PWIN1
AGND
OUTPUT VOLTAGE
= 0.8V TO V
IN
COMP
ON
PGND
IN
GND
GND
GND
NC
GND
LX1
PWIN2
V
IN
V
IN
INPUT VOLTAGE = 2.7V TO 5.5V
FB
C
SS
R
COMP
C
COMP
1
2
3
4
12
11
10
9
16 15 14 13
5 6 7 8
L
C
OUT
LOAD
C
IN2
C
IN1
10Ω
0.1μF
R
TOP
R
BOT
FB
NC = NO CONNECT
ADP2105/
ADP2106/
ADP2107
06079-038
Figure 38. Typical Applications Circuit for Adjustable Output Voltage Option of ADP2105/ADP2106/ADP2107(ADJ)
When R
BOT
is determined, calculate the value of the top resistor
(R
TOP
) by using the following equation:






−
=
FB
FBOUT
BOTTOP
V
VV
RR
The ADP2105/ADP2106/ADP2107(x.x V) include the resistive
voltage divider internally, reducing the external circuitry required.
For improved load regulation, connect the FB to the output
voltage as close as possible to the load.
INDUCTOR SELECTION
The high switching frequency of ADP2105/ADP2106/ADP2107
allows for minimal output voltage ripple even with small inductors.
The sizing of the inductor is a trade-off between efficiency and
transient response. A small inductor leads to larger inductor
current ripple that provides excellent transient response but
degrades efficiency. Due to the high switching frequency of
ADP2105/ADP2106/ADP2107, shielded ferrite core inductors
are recommended for their low core losses and low electromagnetic
interference (EMI).
As a guideline, the inductor peak-to-peak current ripple (ΔI
L
) is
typically set to 1/3 of the maximum load current for optimal
transient response and efficiency, as shown in the following
equations:
3
)(
)(MAXLOAD
SW
IN
OUT
IN
OUT
L
I
LfV
VVV
I ≈
××
−×
=∆
Hμ
)(5.2
)(MAX
LOAD
IN
OUT
IN
OUT
IDEAL
IV
VVV
L
×
−××
=⇒
where f
SW
is the switching frequency (1.2 MHz).
The ADP2105/ADP2106/ADP2107 use slope compensation in
the current control loop to prevent subharmonic oscillations
when operating beyond 50% duty cycle. The fixed slope compen-
sation limits the minimum inductor value as a function of
output voltage.
For the ADP2105
L > (1.12 µH/V) × V
OUT
For the ADP2106
L > (0.83 µH/V) × V
OUT
For the ADP2107
L > (0.66 µH/V) × V
OUT
Inductors 4.7 µH or larger are not recommended because they
may cause instability in discontinuous conduction mode under
light load conditions. It is also important that the inductor be
capable of handling the maximum peak inductor current (I
PK
)
determined by the following equation:






∆
+=
2
)(
L
MAXLOAD
PK
I
II
Table 6. Minimum Inductor Value for Common Output
Voltage Options for the ADP2105 (1 A)
V
OUT
V
IN
2.7 V 3.6 V 4.2 V 5.5 V
1.2 V 1.67 µH 2.00 µH 2.14 µH 2.35 µH
1.5 V 1.68 µH 2.19 µH 2.41 µH 2.73 µH
1.8 V 2.02 µH 2.25 µH 2.57 µH 3.03 µH
2.5 V 2.80 µH 2.80 µH 2.80 µH 3.41 µH
3.3 V 3.70 µH 3.70 µH 3.70 µH 3.70 µH
Table 7. Minimum Inductor Value for Common Output
Voltage Options for the ADP2106 (1.5 A)
V
OUT
V
IN
2.7 V 3.6 V 4.2 V 5.5 V
1.2 V 1.11 µH 2.33 µH 2.43 µH 1.56 µH
1.5 V 1.25 µH 1.46 µH 1.61 µH 1.82 µH
1.8 V 1.49 µH 1.50 µH 1.71 µH 2.02 µH
2.5 V 2.08 µH 2.08 µH 2.08 µH 2.27 µH
3.3 V 2.74 µH 2.74 µH 2.74 µH 2.74 µH