Owner manual
MAX8728
Low-Cost, Multiple-Output
Power Supply for LCD Monitors/TVs
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
IN
= V
INL
= V
SUPP
= 12V, V
OUT1
= +3.3V, V
SRC
= 28V, GND1 = GND2 = GNDP = GND = 0, I
REF
= 0, T
A
= 0°C
to +85°C. Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
STEP-DOWN REGULATOR
OUT1 Voltage in Fixed Mode
V
IN
= 7.0V to 13.2V, EN = V
CC
,
I
LOAD
= 0.5A (Note 1)
3.25 3.30 3.35 V
FB1 Regulation Voltage in
Adjustable Modes
20% to 35% duty cycle, EN = V
CC
,
I
LOAD
= 0.5A (Note 1)
1.97 2.00 2.03 V
FB1 Adjustable Mode Threshold
Voltage
0.10 0.15 0.20 V
Output Voltage Adjust Range 2.0 3.6 V
Fixed mode, OUT1 falling 2.640
Step-Down Regulator Fault Trip
Level
Adjustable mode, FB1 falling 1.536 1.600 1.664
V
FB1 Input Leakage Current V
FB1
= 2.1V -100 +100 nA
Low-Frequency Operation
OUT1 Threshold
LX1 only 1.3 V
FSEL = GND 250
FSEL = V
CC
167
Low-Frequency Operation
Switching Frequency
LX1 only
FSEL = REF 83
kHz
DC Load Regulation 0 < I
OUT1
< 2A, EN = V
CC
0.5 %
DC Line Regulation 7V <V
IN
< 13.2V, EN = V
CC
0.1 %/V
LX1-to-IN Switch
On-Resistance
200 300 mΩ
LX1-to-GND1 Switch
On-Resistance
10 22 40 Ω
Positive Current Limit 2.5 2.8 3.1 A
Skip Mode I
MAX
Threshold EN = GND 0.50 0.60 0.75 A
Soft-Start Ramp Time 1.7 ms
Maximum Duty Cycle 70 77 85 %
STEP-UP REGULATOR
Output Voltage Range V
IN
17 V
Maximum Duty Cycle 65 75 85 %
Minimum On-Time 65 100 ns
FB2 Regulation Voltage FB2 = COMP, C
COMP
= 1nF 1.98 2.00 2.02 V
FB2 Fault Trip Level Falling edge 1.728 1.800 1.872 V
FB2 Load Regulation 0 < I
AVDD
< full, transient only -1 %
FB2 Line Regulation V
IN
= 10.8V to 13.2V 0.08 0.15 %/V
FB2 Input Bias Current V
FB2
= 2V -150 +150 nA
FB2 Transconductance ΔI = ±2.5µA at COMP, FB2 = COMP 75 160 280 µS
FB2 Voltage Gain FB2 to COMP 700 V/V
LX2 Leakage Current V
FB2
= 2.1V, V
LX2
= 13V 4 40 µA
LX2 Current Limit V
FB2
= 1.8V, duty cycle is 25% 1.2 1.5 1.8 A