Datasheet
Multi-Output Power Supplies with VCOM Amplifier
and High-Voltage Gamma Reference for LCD TVs
MAX17126/MAX17126A
26 _____________________________________________________________________________________
Power-Up Sequence
The step-down regulator starts up when the MAX17126/
MAX17126As’ internal reference voltage (REF) is above
its undervoltage lockout (UVLO) threshold. Once the
step-down regulator soft-start is done, the FB2 fault-
detection circuit and the negative charge pump are
enabled. Negative charge-pump fault protection is
enabled after its own soft-start is done.
When EN goes to logic-high, a 10µA current source
starts to pull down on GD, turning on the external GD_I-
AVDD PMOS switch. When V
GD
reaches GD-done
threshold (V
GD_I
- 6V), the step-up regulator is enabled.
Gamma reference is enabled at the same time.
The MAX17126/MAX17126A simplify system design
by including an internal 12ms soft-start for the step-up
regulator. When the capacitor on the SS pin is less than
200pF, the internal 12ms soft-start is in place. This saves
one capacitor from system design. If an external capaci-
tor greater than 200pF is used, a 5µA current source
charges the SS capacitor pin and when the SS voltage
reaches 1.25V, soft-start is done. The FB1 fault-detection
circuit is enabled after this soft-start is done.
The positive charge pump is also enabled after the
step-up regulator finishes its soft-start. After the positive
charge pump’s soft-start is done, the FBP fault-detection
circuit is enabled, as well as the high-voltage switch
delay block. C
DLY1
is charged with an internal 10µA
current source and V
DLY1
rises linearly. When V
DLY1
reaches REF, the high-voltage switch block is enabled.
Figure 7. Power-Up Sequence
BOOST
FAULT BLANK
NEGATIVE CHARGE-PUMP FAULT BLANK
POSITIVE CHARGE -PUMP FAULT BLANK
BUCK FAULT BLANK
DLY1
TIME
TIME
POSITIVE
CHARGE-PUMP
REGULATOR
OUTPUT
NEGATIVE
CHARGE-PUMP
REGULATOR
OUTPUT
VL
REF
IN/INVL
BUCK
OUTPUT
EN
INVL UVLO
AVDD
GD
DONE
GD
REF
TIME
VGHM UNCONNECTED
VGHM DEPENDS
ON GVOFF
REF
SS
VGHM
TIME
REF
UVLO
VL
UVLO
GREF
TIME
PGOOD
t
SS
t
SS
t
SS
t
SS