Evaluates: MAX1530/MAX1531
can provide at least 2A. The step-down switching regu-
lator’s switching frequency is jumper configurable
between 250kHz and 500kHz. The adjustable input
undervoltage protection (EN) protects the EV kit from
undervoltage conditions. The step-up switching regula-
tor and the source-drive regulator are protected against
overloads.
The step-down switching regulator (VOUT) generates a
+3.3V output and can provide at least 1.5A. The step-
down switching-regulator output voltage can be adjust-
ed as low as +1.24V using different feedback resistors
(see the Output Voltage Selection section).
The logic voltage supply (VLOG) is set to +2.5V using a
linear regulator controller and an external pnp bipolar
pass transistor. This logic voltage supply can provide at
least 500mA of current. The logic-voltage-supply linear
regulator’s output can be adjusted between +1.24V and
its input supply, which is the step-down regulator’s out-
put voltage (see the Output Voltage Selection section).
The source-driver supply (VSRC) is set to +10V using a
linear regulator controller and an external pnp bipolar
pass transistor. This source-driver supply can provide
at least 500mA of current. The source-drive linear regu-
lator’s output can be adjusted between +1.24V and its
input voltage, which is either the EV kit input voltage
(PIN) or the output of the MAX1522 step-up regulator,
depending on jumper JU15 (see the Output Voltage
Selection section).
The gamma reference (VGAM) is set to +9.7V using a lin-
ear regulator controller and an external pnp bipolar pass
transistor. This gamma reference can provide at least
50mA of current. The gamma linear regulator’s output
can be adjusted between +1.24V and its input voltage,
which is either the EV kit input voltage (PIN) or the output
of the MAX1522 step-up regulator, depending on jumper
JU14 (see the Output Voltage Selection section).
The TFT gate-on supply (GON) uses a two-stage posi-
tive charge pump to generate approximately +33V. The
output is postregulated to +25V using a linear regulator
controller and an external pnp bipolar pass transistor
and can provide at least 25mA. The positive linear reg-
ulator’s output can be adjusted between +1.24V and its
input, which depends on the EV kit’s input voltage and
the charge-pump configuration, jumpers JU12 and
JU13 (see the Output Voltage Selection section).
The TFT gate-off supply (GOFF) uses a negative charge
pump to generate approximately -11V. The output is
postregulated to -9V using a linear regulator controller
and an external npn bipolar pass transistor and can pro-
vide greater than 50mA. The negative linear regulator’s
output can be adjusted between 0V and its input volt-
age, which is the output of the negative charge pump
(see the Output Voltage Selection section).
The EV kit also features power-up sequencing. After EN
and SEQ go high, the logic voltage supply (VLOG) soft-
starts. The gamma reference, the gate-on supply, the
source-driver supply, and the gate-off supply can soft-
start in any sequence by setting the appropriate
jumpers (see the Power-Up Sequencing section).
The EV kit includes a current-limit circuit for the step-
down switching regulator. The current-limit threshold is
set by resistor-dividers R12, R13, and the R
DS(on)
of
MOSFET N1 (refer to the MOSFET Selection and
Current-Limit Setting section in the MAX1531 data sheet
for further detail). The EV kit also includes current over-
load protection for the source-driver supply voltage. The
MAX1531 will shut down if the source-driver supply
exceeds a current threshold. The output current over-
load threshold is set by sense resistors R35 and R36
(refer to the Overcurrent Protection Block (CSH, CSL)
section in the MAX1531 data sheet for further detail).
Jumper Selection
Enable (EN)
The MAX1531 features an enable (EN) pin that enables
or disables the MAX1531 and the EV kit’s output. The
EN pin can also be used with resistor-dividers R3 and
R4 to set the lower limit of the input voltage range (refer
to the On/Off Control (EN) section in the MAX1531 data
sheet for further detail). The 3-pin jumper JU1 provides
an option to enable, disable, or use the undervoltage
threshold feature for the MAX1531 EV kit. Table 1 lists
the selectable jumper options.
Switching Frequency Selection (FREQ)
The MAX1531 EV kit features an option to choose the
step-down switching regulator’s operating frequency
(JU2). Table 2 lists the selectable jumper options. The
EV kit is configured for 500kHz operation. Optimum
performance at 250kHz requires a larger inductor value
(refer to the Inductor Selection section in the MAX1531
data sheet).
MAX1531 Evaluation Kit
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