19-3910; Rev 0; 1/06
KIT
ATION
EVALU
BLE
AVAILA
Low-Cost, Multiple-Output
Power Supply for LCD Monitors/TVs
Features
♦
♦
♦
♦
Optimized for 10.8V to 13.2V Input Supply
7V to 13.2V Input Supply Range
Selectable Frequency (500kHz/1MHz/1.5MHz)
Current-Mode Step-Down Regulator
14V Internal n-Channel MOSFET
1.5% Accurate Output
Current-Mode Step-Up Regulator
19V Internal n-Channel MOSFET
1% Accurate Output
True Shutdown™ (Output Goes to Zero)
180° Out-of-Phase Switching
Adjustable Positive/Negative Charge Pumps
Soft-Start and Timer Delay Fault Latch for All
Outputs
Logic-Controlled, High-Voltage Switches
Power-Up and Power-Down Sequences
Thermal-Overload Protection
General Description
The MAX8728 generates all the supply rails for thin-film
transistor (TFT) liquid-crystal display (LCD) panels in TVs
and monitors. It includes step-down and step-up regula-
tors, positive and negative charge pumps, and a dual-
mode, logic-controlled high-voltage switch control block.
The MAX8728 can operate from input voltages from 7V to
13.2V and is optimized for LCD TV panel and LCD moni-
tor applications running directly from 12V supplies.
The step-up and step-down regulators feature internal
power MOSFETs and high-frequency operation allow-
ing the use of small inductors and capacitors, resulting
in a compact solution. Both switching regulators use
fixed-frequency, current-mode control architectures,
providing fast load-transient response and easy com-
pensation. The positive and negative charge-pump reg-
ulators provide TFT gate-driver supply voltages. Both
output voltages can be adjusted with external resistive
voltage-dividers.
The MAX8728 is available in a small (5mm x 5mm), low-
profile (0.8mm), 32-pin TQFN package and operates
over the -40°C to +85°C temperature range.
MAX8728
♦
♦
♦
♦
♦
♦
♦
Applications
LCD Monitors
LCD TVs
Simplified Operating Circuit
V
IN
AV
DD
Ordering Information
V
L
PART
TEMP RANGE
PIN-
PACKAGE
PACKAGE
CODE
T3255-4
OUT1
V
L
INL
GATE
LX2
GND2
FB2
COMP
32 TQFN-EP*
MAX8728ETJ+ -40°C to +85°C
5mm x 5mm
BST
IN
LX1
GND1
+Denotes
lead-free package.
*EP
= Exposed pad.
SHDN
EN
DEL
ON/OFF
LCD ENABLE
Pin Configuration
THR
SUPP
FSEL
GON
DRN
SRC
FBN
FB2
OUT1
MAX8728
CTL
THR
MODE
FROM T
CON
TOP VIEW
24
GND2 25
LX2 26
GATE 27
EN 28
MODE 29
DEL 30
COMP 31
FB1 32
1
GND1
23
22
21
20
19
18
17
16 DRVP
15 GNDP
14 FBP
13 REF
FBI
FSEL
VL
V
CC
REF
GND
FBN
DRVN
SUPP
V
GOFF
V
IN
DRN
GON
SRC
V
GON
MAX8728
12 GND
11 SHDN
10 V
CC
9
VL
FBP
DRVP
2
OUT1
3
DRVN
4
CTL
5
IN
6
LX1
7
BST
8
INL
TQFN
True Shutdown is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Low-Cost, Multiple-Output
Power Supply for LCD Monitors/TVs
MAX8728
ABSOLUTE MAXIMUM RATINGS
IN, INL, SUPP to GND ............................................-0.3V to +14V
SUPP to IN ..........................................................................±0.3V
DRVP to GNDP.........................................-0.3V to VSUPP + 0.3V
CTL, EN,
SHDN,
OUT1, VL, VCC to GND ................-0.3V to +6V
COMP, FB1, FB2, FBN, FBP, FSEL, DEL,
THR, MODE, REF to GND ........................-0.3V to VCC + 0.3V
GND1, GND2, GNDP to GND.............................................±0.3V
BST to GND1 ..........................................................-0.3V to +20V
LX1 to BST................................................................-6V to +0.3V
LX2 to GND2 ..........................................................-0.3V to +19V
DRVN, LX1, GATE to GND1 ..........................-0.3V to VIN + 0.3V
GON, SRC to GND .................................................-0.3V to +40V
SRC to GON ...........................................................-0.3V to +40V
SRC to SUPP ..........................................................-0.3V to +30V
SRC to SUPP (momentary)......................................-14V to +30V
GON to SUPP ..........................................................-14V to +30V
SRC to DRN............................................................-0.3V to +40V
DRN to GND ...........................................................-0.3V to +40V
GON to DRN...........................................................-0.3V to +30V
V
L
Short Circuit to GND..............................................Momentary
REF Short Circuit to GND ...........................................Continuous
DRVN RMS Current..........................................................-400mA
DRVP RMS Current.........................................................+100mA
LX2 RMS Current ................................................................+1.6A
GND2 RMS Current ............................................................+1.6A
LX1 RMS Current .................................................................-1.6A
Continuous Power Dissipation (T
A
= +70°C)
32-Pin Thin QFN (derate 34.5mW/°C above +70°C).....2758mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(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
GENERAL
IN, INL Input Voltage Range
INL Quiescent Current
IN Standby Supply Current
Switching Frequency
For VL regulator operation
V
FB2
= V
FBP
= 2.2V, V
FBN
= 0,
LX2 not switching, LX1 switching
V
IN
= 7V to 13.2V, EN =
SHDN
= GND
FSEL = GND
FSEL = V
CC
FSEL = REF
Phase Difference Between
Step-Down/Positive and
Step-Up/Negative Regulators
VL REGULATOR
VL Output Voltage
VL Undervoltage Lockout
Threshold
REFERENCE
REF Output Voltage
REF Load Regulation
REF Sink Current
REF Undervoltage Lockout
Threshold
No external load
0 < I
REF
< 50µA
REF in regulation
Rising edge, 200mV hysteresis
0
1.5
1.98
2.00
2.02
10
10
V
mV
µA
V
7V < V
INL
< 13.2V, V
FB1
= V
FB2
= V
FBP
=
1.9V, V
FBN
= 0.5V, I
VL
= 25mA
VL rising, 2.5% hysteresis
4.8
3.8
5.0
4.0
5.1
4.1
V
V
1275
850
425
1500
1000
530
180
7.0
12.0
7
0.5
1730
1150
610
Degrees
kHz
13.2
V
mA
mA
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
Low-Cost, Multiple-Output
Power Supply for LCD Monitors/TVs
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
STEP-DOWN REGULATOR
OUT1 Voltage in Fixed Mode
FB1 Regulation Voltage in
Adjustable Modes
FB1 Adjustable Mode Threshold
Voltage
Output Voltage Adjust Range
Step-Down Regulator Fault Trip
Level
FB1 Input Leakage Current
Low-Frequency Operation
OUT1 Threshold
Low-Frequency Operation
Switching Frequency
DC Load Regulation
DC Line Regulation
LX1-to-IN Switch
On-Resistance
LX1-to-GND1 Switch
On-Resistance
Positive Current Limit
Skip Mode I
MAX
Threshold
Soft-Start Ramp Time
Maximum Duty Cycle
STEP-UP REGULATOR
Output Voltage Range
Maximum Duty Cycle
Minimum On-Time
FB2 Regulation Voltage
FB2 Fault Trip Level
FB2 Load Regulation
FB2 Line Regulation
FB2 Input Bias Current
FB2 Transconductance
FB2 Voltage Gain
LX2 Leakage Current
LX2 Current Limit
FB2 = COMP, C
COMP
= 1nF
Falling edge
0 < I
AVDD
< full, transient only
V
IN
= 10.8V to 13.2V
V
FB2
= 2V
∆I
= ±2.5µA at COMP, FB2 = COMP
FB2 to COMP
V
FB2
= 2.1V, V
LX2
= 13V
V
FB2
= 1.8V, duty cycle is 25%
1.2
-150
75
160
700
4
1.5
40
1.8
1.98
1.728
V
IN
65
75
65
2.00
1.800
-1
0.08
0.15
+150
280
17
85
100
2.02
1.872
V
%
ns
V
V
%
%/V
nA
µS
V/V
µA
A
70
EN = GND
10
2.5
0.50
Fixed mode, OUT1 falling
Adjustable mode, FB1 falling
V
FB1
= 2.1V
LX1 only
FSEL = GND
LX1 only
FSEL = V
CC
FSEL = REF
0 < I
OUT1
< 2A, EN = V
CC
7V <V
IN
< 13.2V, EN = V
CC
1.536
-100
1.3
250
167
83
0.5
0.1
200
22
2.8
0.60
1.7
77
85
300
40
3.1
0.75
%
%/V
mΩ
Ω
A
A
ms
%
kHz
V
IN
= 7.0V to 13.2V, EN = V
CC
,
I
LOAD
= 0.5A (Note 1)
20% to 35% duty cycle, EN = V
CC
,
I
LOAD
= 0.5A (Note 1)
3.25
1.97
0.10
2.0
2.640
1.600
1.664
+100
3.30
2.00
0.15
3.35
2.03
0.20
3.6
V
V
V
V
V
nA
V
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8728
_______________________________________________________________________________________
3
Low-Cost, Multiple-Output
Power Supply for LCD Monitors/TVs
MAX8728
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
Current-Sense Transresistance
LX2 On-Resistance
Soft-Start Period
POSITIVE CHARGE-PUMP REGULATOR
FBP Regulation Voltage
FBP Line Regulation Error
FBP Input Bias Current
DRVP p-Channel MOSFET
On-Resistance
DRVP n-Channel MOSFET
On-Resistance
FBP Fault Trip Level
Positive Charge-Pump Soft-Start
Period
NEGATIVE CHARGE-PUMP REGULATOR
FBN Regulation Voltage
FBN Input Bias Current
FBN Line Regulation
DRVN p-Channel MOSFET
On-Resistance
DRVN n-Channel MOSFET
On-Resistance
FBN Fault Trip Level
Negative Charge-Pump
Soft-Start Period
SEQUENCE CONTROL
SHDN
Input Low Voltage
SHDN
Input High Voltage
SHDN
Input Current
EN Charge Current
EN Turn-On Threshold
DEL Capacitor Charge Current
DEL Turn-On Threshold
GATE Output Sink Current
GATE On Voltage
GATE Done Threshold
GATE Pullup Resistance
EN = high, GATE = IN
EN = high
EN = high, V
GATE
_
DONE
- V
GATE
_
ON
EN = low, V
GATE
= V
IN
- 5V
During startup, V
DEL
= 1.0V
During startup, V
EN
= 1.0V
4
0.95
4
0.95
8
V
IN
- 6
0
5
1.00
5
1.00
11
V
IN
- 5
1
1
2
1
6
1.05
6
1.05
14
V
IN
- 4
0.4
V
V
µA
µA
V
µA
V
µA
V
V
kΩ
Rising edge
V
REF
- V
FBN
V
FBN
= 250mV
V
IN
= 10.8V to 13.2V
4
1
600
3
1.727
-50
1.750
1.773
+50
6
V
nA
mV
Ω
Ω
mV
ms
Falling edge
1.536
V
IN
= V
SUPP
= 10.8V to 13.2V
V
FBP
= 2.1V
-50
4
1
1.600
3
1.664
1.98
2.00
2.02
6
+50
V
mV
nA
Ω
Ω
V
ms
CONDITIONS
MIN
0.6
TYP
1.2
0.5
3
MAX
1.8
1.0
UNITS
V/A
Ω
ms
4
_______________________________________________________________________________________
Low-Cost, Multiple-Output
Power Supply for LCD Monitors/TVs
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
DEL, EN Discharge Switch
On-Resistance
FBN Discharge Switch
On-Resistance
CTL Input Low Voltage
CTL Input High Voltage
CTL Input Leakage Current
CTL-to-GON Rising Propagation
Delay
1kΩ from DRN to GND, 1.5nF from GON to
GND
2.0
-1
100
250
38
V
MODE
= V
REF
, V
DEL
= V
CTL
= 3V
V
MODE
= V
REF
, V
DEL
= 3V, V
CTL
= 0
V
MODE
= V
REF
, V
DRN
= 8V, V
DEL
= 3V,
V
GON
> V
DRN
, V
CTL
= 0
V
MODE
= V
REF
, V
DEL
= V
CTL
= 3V
V
MODE
= V
REF
, V
DEL
= V
CTL
= 3V,
V
SRC
- V
GON
> 5V
V
MODE
= V
REF
, V
DEL
= 3V, V
CTL
= 0, V
GON
= 28V, V
THR
= 1.4V
V
MODE
= V
REF
, V
DEL
= 3V, V
CTL
= 0, V
GON
= 28V, V
THR
= 1.4V, V
GON
- V
DRN
> 5V
SHDN
= GND
MODE rising
Operating mode 2, V
MODE
= 0.7V
Enabling DRN switch control in mode 2
1.2
40
0.8
9.4
1.5
0.14
0
15
260
25
100
1
1.4
50
1.0
10.0
50
15°C typical hysteresis
FSEL = V
CC
(1MHz)
FSEL Input Levels
FSEL Input Current
FSEL = REF (0.5MHz)
FSEL = GND (1.5MHz)
Forced to V
CC
10
V
CC
- 0.4
1.65
2.35
0.5
µA
V
+160
1.6
60
1.2
10.6
50
2.0
0.20
1
30
+1
CONDITIONS
SHDN
= low or fault tripped
EN = low or fault tripped
MIN
TYP
20
5
MAX
UNITS
Ω
kΩ
MAX8728
POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHES
0.6
V
V
µA
ns
ns
V
mA
µA
Ω
mA
Ω
mA
kΩ
V
µA
V
V/V
ms
°C
CTL-to-GON Falling Propagation 1kΩ from DRN to GND, 1.5nF from GON to
Delay
GND
SRC Input Voltage Range
SRC Input Current
DRN Input Current
SRC Switch On-Resistance
SRC Switch Saturation Current
DRN Switch
On-Resistance
DRN Switch Saturation Current
MODE Switch On-Resistance
MODE Current-Source Stop
Voltage Threshold
MODE Charge Current
MODE Voltage Threshold
THR to GON Voltage Gain
FAULT DETECTION
Duration to Trigger Fault
Thermal Shutdown Threshold
SWITCHING-FREQUENCY SELECTION
_______________________________________________________________________________________
5
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