Datasheet

ADP2105/ADP2106/ADP2107 Data Sheet
Rev. D | Page 16 of 36
APPLICATIONS INFORMATION
ADIsimPower DESIGN TOOL
The ADP2105/ADP2106/ADP2107 is supported by
ADIsimPower design tool set. ADIsimPower is a collection
of tools that produce complete power designs optimized for a
specific design goal. The tools enable the user to generate a
full schematic, bill of materials, and calculate performance in
minutes. ADIsimPower can optimize designs for cost, area,
efficiency, and parts count while taking into consideration
the operating conditions and limitations of the IC and all
real external components. For more information about
ADIsimPower design tools, refer to www.analog.com/
ADIsimPower. The tool set is available from this website, and
users can also request an unpopulated board through the tool.
EXTERNAL COMPONENT SELECTION
The external component selection for the ADP2105/ADP2106/
ADP2107 application circuits shown in Figure 37 and Figure 38
depend on input voltage, output voltage, and load current
requirements. Additionally, trade-offs between performance
parameters like efficiency and transient response can be made
by varying the choice of external components.
SETTING THE OUTPUT VOLTAGE
The output voltage of ADP2105/ADP2106/ADP2107(ADJ) is
externally set by a resistive voltage divider from the output
voltage to FB. The ratio of the resistive voltage divider sets the
output voltage, and the absolute value of those resistors sets the
divider string current. For lower divider string currents, the
small 10 nA (0.1 μA maximum) FB bias current is to be taken
into account when calculating resistor values. The FB bias
current can be ignored for a higher divider string current, but
this degrades efficiency at very light loads.
To limit output voltage accuracy degradation due to FB bias
current to less than 0.05% (0.5% maximum), ensure that the
divider string current is greater than 20 μA. To calculate the
desired resistor values, first determine the value of the bottom
divider string resistor (R
BOT
) using the following equation:
STRING
FB
BOT
I
V
R =
where:
V
FB
= 0.8 V, the internal reference.
I
STRING
is the resistor divider string current.
OFF
EN
SS
LX2
AGND
OUTPUT VOLTAGE = 1.2V, 1.5V, 1.8V, 3.3V
COMP
ON
PGND
GND
GND
GND
NC
LX1
PWIN2
V
IN
V
IN
INPUT VOLTAGE = 2.7V TO 5.5V
V
OUT
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
NC = NO CONNECT
ADP2105/
ADP2106/
ADP2107
06079-065
V
OUT
FB PWIN1INGND
Figure 37. Typical Applications Circuit for Fixed Output Voltage Options of ADP2105/ADP2106/ADP2107(x.x V)