Datasheet

MAX17103/AUO-P1721.14
DC-DC Converter with Integrated Scan Driver,
VGL Controller, Op Amp, and LDO for TFT LCD
______________________________________________________________________________________ 17
Undervoltage Lockout (UVLO)
The UVLO circuit compares the input voltage at IN with
the UVLO threshold (2.0V typ) to ensure that the input
voltage is high enough for reliable operation. The
150mV (typ) hysteresis prevents supply transients from
causing a restart. Once the input voltage exceeds the
UVLO rising threshold, startup begins. When the input
voltage falls below the UVLO falling threshold, the con-
troller turns off the main step-up regulator, the refer-
ence, the operational amplifier, and negative linear-
regulator controller.
Overcurrent Protection
The step-up regulator features an adjustable cycle-by-
cycle current limit. The inductor current is sensed
through the LX switch during the LX switch on-time. If
the peak inductor current rises above the current-limit
threshold set by R
ENA
, the LX switch immediately turns
off until the next switching cycle, effectively limiting the
peak inductor current each cycle.
Soft-Start
The soft-start feature effectively limits the inrush current
during startup by linearly ramping up the step-up regu-
lator’s peak switch current limit. The soft-start period ter-
minates when either the output voltage reaches
regulation or full current limit is reached. The soft-start
capacitor (C
SS
) is charged with a 4mA (typ) current
source such that a full current limit is reached when volt-
age across C
SS
reaches 1.24V.
Fault Protection
The MAX17103 monitors OPAS for an overvoltage condi-
tion. If the OPAS voltage is above 17V (typ), the
MAX17103 disables the gate driver of the step-up regula-
tor and prevents the internal MOSFET from switching. The
OPAS overvoltage condition does not set the fault latch.
Anytime after the boost soft-start period, if V
FB
falls
below 1.1V (typ) or if V
FBN
rises above 420mV (typ) for
more than 160ms (typ), the controller turns off all out-
puts, except LDOO and REF, until the input voltage is
cycled off then on again.
SOFT-
START
OSCILLATOR
1.24V
FB
LX
ILIM
COMPARATOR
I
LIMIT
CURRENT
SENSE
PGND
COMP
CLOCK
ERROR AMP
PWM
COMPARATOR
SLOPE COMPENSATION
LOGIC AND DRIVER
Figure 3. Step-Up Regulator Block Diagram