ADP2442-EVALZ Analog Devices, ADP2442-EVALZ Datasheet - Page 19

• Manufacturer Part Number: ADP2442-EVALZ
• Description: Power Management IC Development Tools Eval board
• Manufacturer: Analog Devices
• Type: DC/DC Converters, Regulators & Controllersr
• Series: ADP2442r

Specifications of ADP2442-EVALZ

• Rohs: yes
• Tool Is For Evaluation Of: ADP2442
• Factory Pack Quantity: 1

Data Sheet
APPLICATIONS INFORMATION
ADIsimPOWER DESIGN TOOL
The
set. ADIsimPower is a collection of tools that produce complete
power designs optimized to a specific design goal. These tools
allow 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. The ADIsimPower tool
can be found at
request an unpopulated board through the tool.
SELECTING THE OUTPUT VOLTAGE
The output voltage is set using a resistor divider connected between
the output voltage and the FB pin (see Figure 57). The resistor
divider divides down the output voltage to the 0.6 V FB regulation
voltage. The output voltage can be set to as low as 0.6 V and as
high as 90% of the power input voltage.
The ratio of the resistive voltage divider sets the output voltage,
and the absolute value of the resistors sets the divider string
current. When calculating the resistor values for lower divider
string currents, take into account the small 50 nA (0.1 μA maxi-
mum) FB bias current. The FB bias current can be ignored for a
higher divider string current; however, using small feedback
resistors degrades efficiency at very light loads.
To limit degradation of the output voltage accuracy due to FB
bias current to less than 0.005% (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
resistor, R
where:
V
I
Next, calculate the value of the top resistor, R
STRING
REF
ADP2442
is the internal reference and equals 0.6 V.
R
R
is the resistor divider string current.
TOP
BOTTOM
BOTTOM
=
R
R
BOTTOM
=
BOTTOM
is supported by the ADIsimPower design tool
www.analog.com/adisimpower
, as follows:
R
I
TOP
V
STRING
V
REF
OUT
Figure 57. Voltage Divider
×




V
EXTERNAL
OUT
PGOOD
SUPPLY
FB
V
REF
−
R
V
ADP2442
FREQ
REF
FREQ




TOP
and the user can
, as follows:
Rev. 0 | Page 19 of 36
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Table 6. Output Voltage Selection
Voltage (V)
12
5
3.3
1.2
SETTING THE SWITCHING FREQUENCY
The choice of the switching frequency depends on the required
dc-to-dc conversion ratio and is limited by the minimum and
maximum controllable duty cycle, as shown in Figure 58. This
limitation is due to the requirement of minimum on time and
minimum off time for current sensing and robust operation.
However, the choice is also influenced by whether there is a need
for small external components. For example, higher switching
frequencies are required for small, area limited power solutions.
Calculate the value of the frequency resistor by using the
following equation:
where R
Table 7 and Figure 59 provide examples of frequency resistor
values that are based on the switching frequency.
Table 7. Frequency Resistor Selection
R
308 kΩ
132 kΩ
92.5 kΩ
FREQ
100
R
90
80
70
60
50
40
30
20
10
FREQ
0
FREQ
0
=
is in kΩ and f
Figure 58. Duty Cycle vs. Switching Frequency
92
f
200
,
SW
500
R
190
73
45
10
400
TOP
FREQUENCY (kHz)
SW
D
D
(kΩ)
MAX
MIN
is in kHz.
600
Frequency
300 kHz
700 kHz
1 MHz
800
R
10
10
10
10
BOTTOM
1000
ADP2442
(kΩ)
1200
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