Analog Devices MAX77859 Manual page 7

MAX77859 Evaluation Kit
Output Voltage Configuration
By default, the EV kit is configured to use internal feedback resistors with a 5V default startup output voltage and an
output voltage range from 3.2V to 16V. To achieve a different default startup output voltage other than 5V, or to achieve
a lower minimum output voltage range down to 3V or a higher maximum output voltage range up to 20V, external feedback
resistors are required. To change the EV kit to an external feedback configuration, replace the feedback resistor R
(R10) and R (R11) with appropriate value resistors (use resistors with 1% tolerance or better) and adjust R
BOT
accordingly to select the external feedback option. If V
forward capacitor on C9 when using external feedback.
To select appropriate external feedback resistor values, first chose R
calculate the value of R
BOT
Where V is 0.30518V and V
REF
maximum output voltage of 20V. The recommended external feedback resistor values for common output voltages are
listed in Table 3.
After startup, the output voltage can be adjusted dynamically using the I
section for more information. When using internal feedback, output voltage ranges are between 3.2V and 16V in 20mV
steps. When using external feedback, output voltage range and step size vary based on the external feedback resistor
values. To calculate the output voltage range, use the following equation and plug in the minimum V
maximum V of 0.97656V:
REF
Output voltage step size can be calculated with the following equation:
Programmable output voltage ranges and output voltage step sizes for each recommended feedback resistor pair are
listed in Table 3.
Table 3. Feedback Resistor Value Recommendations
DEFAULT
V (V) R10 (kΩ)
REF
0.30518
*Default EV kit configuration
High-Temperature Testing
The MAX77859 is rated for operation under junction temperatures up to +125°C. Note that not all components on the EV
kit are rated for temperatures this high. Some ceramic capacitors experience extra leakage when put under temperatures
higher than they are rated for and supply current readings for the IC might be larger than expected. The
MAXUSB_INTERFACE# is also not rated for +125°C. Double-check the components on the EV kit if testing at +125°C
www.analog.com
(R11) for a desired startup output voltage with the following equation:
is the desired startup output voltage. Note that the output voltage cannot exceed the
OUT
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R R
TOP BOT
R11 (kΩ)
205 23.2
162 16.5
Internal feedback resistors*
160 5.62
182 4.75
180 3.74
330 5.11
is 6V or below, it is also recommended to install a 10pF feed-
OUT
(R10) to be between 150kΩ and 330kΩ. Then
TOP
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STARTUP PROGRAMMABLE V
V (V)
OUT
3
3.3
5
9
12
15
20
Evaluates: MAX77859 (WLP)
2
C serial interface. See the
)
OUT
RANGE (V)
3.0 to 9.61
3.0 to 10.56
3.2 to 16
5.76 to 20
7.68 to 20
9.6 to 20
12.81 to 20
TOP
(R9)
SEL
EV Kit Software
of 0.19531V and
REF
V STEP SIZE
OUT
(mV)
12
13.2
20
36
48
60
80
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