Datasheet

Step-Up, Step-Down Regulator, Gate-On Charge Pump,
and Boost-Buck Regulator for TV TFT LCD Display
MAX17122
______________________________________________________________________________________ 23
Soft-Start
The boost-buck regulator includes a 7-bit soft-start
DAC that steps its internal reference voltage from 3.3V
to the reference voltage determined by temperature-
compensation logic in 128 steps. The soft-start period
is 3ms (typ) and FB3 fault detection is disabled dur-
ing this period. The soft-start feature effectively limits
the inrush current during startup (see the Boost-Buck
Regulator Soft-Start Waveforms in the Typical Operating
Characteristics).
Linear Regulator (VL)
The MAX17122 includes an internal linear regulator. IN is
the input of the linear regulator. The input voltage range
is between 8V and 16.5V. The output voltage is set to 5V.
The regulator powers the internal MOSFET drivers, PWM
controllers, charge-pump regulators, and logic circuitry.
The total external load capability is 25mA. Bypass VL to
AGND with a minimum 1FF ceramic capacitor.
Figure 4. Switching Frequency vs. R
FOSC
Figure 5. Compensation Network
+
-
+
-
-
+
3.3V
REFERENCE
R
R
R4
3.3V GOFF2
R3
R
SET
NTC
10kI
1.65V
SETNTC
100µA 100µA
1.65V
1.65V
FB3
EA
1.65V TO
0.1V
+
-
MAX17122
0
-5
-10
-15
-20
-25
2.94
2.40
1.85
1.31
0.76
0.22
-50
-25
0 25
TEMPERATURE (°C)
GOFF2(FB3) VOLTAGE
vs. TEMPERATURE
50 75 100
GOFF2 VOLTAGE (V)
FB3 VOLTAGE (V)
TRANSITION LEVEL
(FB3 = 3.3V - NTC VOLTAGE)
COLD LEVEL
(FB3 = SET VOLTAGE)
WARM LEVEL
(FB3 = 1.65V)