LCD Panel Power Supplies
Power-Up Sequence and Shutdown Control
When the MAX8710/MAX8711/MAX8712/MAX8761 are
powered up, REF rises with the voltage on IN. After REF
reaches regulation and if SHDN is logic high, the linear
regulator, operational amplifier, and negative charge-
pump regulator are enabled and begin their respective
soft-start routines. After the soft-start routines are com-
pleted, the fault-protection circuits for the linear regulator
and the negative charge-pump regulator are activated.
When the linear regulator is enabled, the positive
charge-pump-regulator delay block is enabled. An
internal current source starts charging the DLP capaci-
tor. The voltage on DLP linearly rises because of the
constant charging current. When VDLP goes above
VREF / 2, the switch control block is enabled, and the
positive charge-pump regulator begins its soft-start.
After the positive charge-pump regulator’s soft-start is
completed, the fault protection of the positive charge-
pump regulator is also enabled.
The MAX8710/MAX8711/MAX8712/MAX8761 enter into
shutdown when SHDN is pulled low or REF falls below
4.5V. In shutdown, OUTL and OUTB are internally
pulled to ground with 1kΩ resistors, FBN and FBP are
internally pulled to ground with 10Ω resistors, and DLP
is pulled to GND through a 10Ω resistor, discharging
CDLP. In the MAX8710 only, GON is pulled to GND
through a 1kΩ resistor. REF remains on in shutdown.
Pulling SHDN high when REF is above 4.5V reactivates
the IC. Output fault protection and thermal-overload
protection can also turn off the IC’s outputs. See the
respective sections for details.
Output Fault Protection
During steady-state operation, if the output of the linear
regulator or any of the charge-pump regulator outputs
does not exceed its respective fault-detection thresh-
old, the MAX8710/MAX8711/MAX8712/MAX8761 acti-
vate an internal fault timer. If any condition or the
combination of conditions indicates a continuous fault for
the fault-timer duration (44ms typ), the MAX8710/
MAX8711/MAX8712/MAX8761 set the fault latch, shutting
down all the outputs except the reference. Once the fault
condition is removed, cycle the input voltage or toggle
SHDN to clear the fault latch and reactivate the device.
Each regulator’s fault-detection circuit is disabled during
the regulator’s soft-start time.
The thermal-overload protection prevents excessive
power dissipation from overheating the IC. When the
junction temperature exceeds +160°C, a thermal sensor
immediately activates the fault protection, which shuts
down all the outputs except the reference, allowing the
device to cool down. Once the device cools down by
approximately 15°C, the IC restarts automatically.
Switch Control (MAX8710/MAX8761)
The MAX8710/MAX8761s' switch-control block (Figures
6 and 7) consists of a high-voltage p-channel MOSFET
Q1 between SRC and GON, and a common-source-con-
nected p-channel MOSFET pair Q2 between GON and
DRN. The MAX8710 switch control block is enabled
when VDLP goes above VREF / 2 and for MAX8761 VDLP
has no control on switch control block. Both the
MAX8710 and MAX8761 have two different modes of
Activate the first mode by connecting MODE to REF.
When CTL is logic high, Q1 turns on and Q2 turns off,
connecting GON to SRC. When CTL is logic low, Q1
turns off and Q2 turns on, connecting GON to DRN.
GON can then be discharged through a resistor con-
nected between DRN and GND or OUTL. Q2 turns off
and stops discharging GON when VGON reaches 10
times the voltage on THR.
When VMODE is less than 0.9 x VREF, the switch-control
block works in the second mode. The rising edge of VCTL
turns on Q1 and turns off Q2, connecting GON to SRC.
An internal n-channel MOSFET Q5 between MODE and
GND is also turned on to discharge an external capacitor
between MODE and GND. The falling edge of VCTL turns
off Q5, and an internal 50µA current source starts charg-
ing the MODE capacitor. Once VMODE exceeds 0.5 x
VREF, the switch-control block turns off Q1 and turns on
Q2, connecting GON to DRN. GON can then be dis-
charged through a resistor connected between DRN and
GND or OUTL. Q2 turns off and stops discharging GON
when VGON reaches 10 times the voltage on THR.