MAX17122 Evaluation Kit
Evaluates: MAX17122
4 ______________________________________________________________________________________
High-Voltage Stress Mode Input (JU3)
The MAX17122’s high-voltage stress (HVS) mode is
controlled through jumper JU3. When jumper JU3 is
installed, HVS is connected to VL and the RHVS output
is connected to AGND. When jumper JU3 is not installed,
the HVS pin is left unconnected and the RHVS output is
unconnected. See Table 2 for jumper JU3 configuration.
Thermistor Network Connection (JU4)
The 100FA current from the SET pin, together with
resistor R23 at SET determines the cold-temperature
output voltage. The network at the NTC pin controls the
transition between the warm-temperature output volt-
age (determined by FB3 resistors R5 and R6) and the
cold-temperature output voltage. As configured, the
warm-temperature output voltage is -12V, slowly transi-
tioning at approximately +25NC to the cold-temperature
output voltage level of -20V. Refer to the MAX17122 IC
data sheet for more information regarding temperature
compensation.
Jumper JU4 controls the thermistor network connected
to the NTC pin. When JU4 is installed, thermistor R8
is connected to NTC and the behavior of the GOFF2
output voltage varies with temperature. When JU4 is not
installed, NTC is connected to AGND through resistors
R7 and R9 and GOFF2 output voltage is fixed. See Table
3 for jumper JU4 configuration.
Step-Up Regulator Output-Voltage
Selection (AVDD)
The EV kit’s step-up switching-regulator output (AVDD)
is set to +15V by feedback resistors R1 and R2. To gen-
erate output voltages other than +15V, select different
external voltage-divider resistors (R1 and R2). Refer to
the Step-Up Regulator, Output Voltage Selection section
in the MAX17122 IC data sheet for more information.
Step-Down Regulator Output-Voltage
Selection (+3.3V)
The EV kit’s step-down switching regulator supports both
fixed and adjustable output voltages. By default, the EV
kit’s step-down regulator’s output (3.3V) is set to the
+3.3V fixed mode by connecting FB2 to GND through
resistor R20. For adjustable mode (+1.5V to +3.6V),
select R21 and R20 to set the desired step-down regu-
lator output voltage. Refer to the Detailed Description,
Step-Down Regulator section in the MAX17122 IC data
sheet for instructions on selecting resistors R20 and R21.
Buck-Boost Regulator Output-Voltage
Selection (VGOFF2)
The output voltage of the step-up regulator is tempera-
ture compensated. From the warm-temperature range
((3.3V - V
NTC
) > 1.65V), the output voltage is set by
connecting a resistive voltage-divider from the output
(V
GOFF2
) to the +3.3V reference, with the center tap
connected to FB3. Select R6 in the 10kI to 50kI range.
Calculate R5 with the following equation:
GOFF2_ WARM FB3
FB3
V V
R5 = R6
V 3.3V
−
×
−
where V
FB3
, the step-up regulator’s feedback set point,
is +1.65V. Place R5 and R6 close to the IC.
For cold temperatures ((3.3V - V
NTC
) < V
SET
), output
voltage is set by:
GOFF2_ COLD
SET
R6 V R5 3.3V
V
R5 R6
× + ×
=
+
If the calculated V
SET
voltage is larger than +1.65V,
then temperature compensation is disabled and the
buck-boost regulator output will be V
GOFF2_WARM
at all
temperatures.
Calculate the SET pin resister R
SET
(R23) as follows:
SET
SET
V
R
100 A
=
µ
*Default position.
*Default position.
Table 3. Jumper JU4 Function (NTC)Table 2. Jumper JU3 Function (HVS)
SHUNT
POSITION
HVS PIN RHVS OUTPUT
Installed Connected to VL
Connected to
AGND
Not
installed*
Internally pulled to
GND
Unconnected
SHUNT
POSITION
THERMISTOR
NETWORK
GOFF2 OUTPUT
Installed* Connected
Varies over
temperature
Not installed Not connected Fixed output
