LT1943
High Current Quad Output
Regulator for TFT LCD Panels
FEATURES
■
DESCRIPTIO
■
■
■
■
■
■
■
■
4 Integrated Switches: 2.4A Buck, 2.6A Boost,
0.35A Boost, 0.35A Inverter (Guaranteed Minimum
Current Limit)
Fixed Frequency, Low Noise Outputs
Soft-Start for all Outputs
Externally Programmable V
ON
Delay
Integrated Schottky Diode for V
ON
Output
PGOOD Pin for AV
DD
Output Disconnect
4.5V to 22V Input Voltage Range
PanelProtect
TM
Circuitry Disables V
ON
Upon Fault
Available in Thermally Enhanced 28-Lead TSSOP
APPLICATIO S
■
■
Large TFT-LCD Desktop Monitors
Flat Panel Televisions
The LT
®
1943 quad output adjustable switching regulator
provides power for large TFT LCD panels. The device,
housed in a low profile 28 pin thermally enhanced TSSOP
package, can generate a 3.3V or 5V logic supply along with
the triple output supply required for the TFT LCD panel.
Operating from an input range of 4.5V to 22V, a step-down
regulator provides a low voltage output V
LOGIC
with up to
2A current. A high-power step-up converter, a lower-
power step-up converter and an inverting converter pro-
vide the three independent output voltages AV
DD
, V
ON
and
V
OFF
required by the LCD panel. A high-side PNP provides
delayed turn-on of the V
ON
signal and can handle up to
30mA. Protection circuitry ensures that V
ON
is disabled if
any of the four outputs are more than 10% below the
programmed voltage.
All switchers are synchronized to an internal 1.2MHz
clock, allowing the use of low profile inductors and ce-
ramic capacitors throughout. A current mode architecture
provides excellent transient response. For best flexibility,
all outputs are adjustable. Soft-start is included in all four
channels. A PGOOD pin can drive an optional PMOS pass
device to provide output disconnect for the AV
DD
output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
PanelProtect is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
V
OFF
–5.5V
50mA
2.2µF
44.2k
SW4
NFB4
10.0k
10pF
10µH
FB4
BIAS
BOOST
0.22µF
4.7µH
V
LOGIC
3.3V
2A
16.2k
FB1
10.0k
22µF
18k
100pF
2.2nF
V
C1
V
C2
SW1
V
IN
V
IN,
8V TO 20V
0.47µF
10µF
10µH
1µF
33µH
AV
DD
12.2V
500mA
10µH
88.7k
10µF
SW3
SW2
FB2
RUN-SS
SS-234
0.015µF
0.015µF
0.047µF
PGOOD
10.0k
LT1943
C
T
PGOOD
V
ON
E3
V
ON
35V
30mA
274k
RUN-SS
2V/DIV
V
LOGIC
5V/DIV
AV
DD
10V/DIV
V
OFF
10V/DIV
V
E3
20V/DIV
V
ON
50V/DIV
I
IN(AVG)
1A/DIV
5ms/DIV
FB3
GND
SGND
V
C4
10.0k
2.2µF
V
C3
6.8k
100pF
2.2nF
27k
100pF
680pF
13k
100pF
2.2nF
0.47µF
Quad Output TFT-LCD Power Supply
1943 TA01
U
Startup Waveforms
1943fa
U
U
1
LT1943
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND
VC1
VC2
FB1
FB2
FB3
NFB4
FB4
VC3
1
2
3
4
5
6
7
8
9
29
28 SW2
27 SW2
26 V
ON
25 C
T
24 E3
23 PGOOD
22 BIAS
21 SW3
20 GND
19 SW4
18 RUN-SS
17 SS-234
16 V
IN
15 V
IN
V
IN
Voltage .............................................................. 25V
BOOST Voltage ........................................................ 36V
BOOST Voltage Above SW1 ..................................... 25V
BIAS Pin Voltage ..................................................... 18V
SW2, SW4 Pin Voltages .......................................... 40V
SW3 Voltage ............................................................ 40V
FB1, FB2, FB3, FB4 Voltages ...................................... 4V
NFB4 Voltage ................................................ +6V, –0.6V
VC1, VC2, VC3, VC4 Pin Voltages .............................. 6V
RUN-SS, SS-234 Pin Voltages ................................... 6V
PGOOD Pin Voltage ................................................. 36V
E3 Pin Voltage ......................................................... 38V
V
ON
Voltage ............................................................. 38V
C
T
Pin Voltage ........................................................... 6V
Junction Temperature ........................................... 125°C
Operating Temperature Range (Note 2) ...–40°C to 85°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LT1943EFE
VC4 10
SGND 11
BOOST 12
SW1 13
SW1 14
FE PART MARKING
1943E
FE PACKAGE
28-LEAD PLASTIC TSSOP
EXPOSED PAD (PIN 29) IS GROUND
(MUST BE SOLDERED TO PCB)
T
JMAX
= 125°C,
θ
JA
= 25°C/W,
θ
JC
= 7.5°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, RUN-SS, SS-234 = 2.5V unless otherwise noted.
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Quiescent Current
RUN-SS, SS-234 Pin Current
RUN-SS, SS-234 Threshold
BIAS Pin Voltage to Begin SS-234 Charge
BIAS Pin Current
FB Threshold Offset to Begin C
T
Charge
C
T
Pin Current Source
C
T
Threshold to Power V
ON
V
ON
Switch Drop
Maximum V
ON
Current
PGOOD Threshold Offset
PGOOD Sink Current
PGOOD Pin Leakage
Master Oscillator Frequency
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
●
MIN
TYP
MAX
4.5
22
UNITS
V
V
mA
µA
µA
V
Not Switching
RUN-SS = SS-234 = 0V
RUN-SS, SS-234 = 0.4V
2.4
90
16
1.0
●
10
35
1.7
0.8
2.8
10.5
125
20
1.1
180
30
90
200
60
125
14
45
3.15
15
160
25
1.2
240
160
1
BIAS = 3.1V, All Switches Off
(Note 3)
All FB Pins = 1.5V
All FB Pins = 1.5V
V
ON
Current = 30mA
V
E3
= 30V
V
PGOOD
= 36V
1.1
1.0
1.2
250
0.5
1.35
1.46
Foldback Switching Frequency
Frequency Shift Threshold on FB
All FB Pins = 0V
∆200kHz
1943fa
2
U
V
mA
mV
µA
V
mV
mA
mV
µA
µA
MHz
MHz
kHz
V
W
U
U
W W
W
LT1943
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, RUN-SS, SS-234 = 2.5V unless otherwise noted.
PARAMETER
SWITCH 1 (2.4A BUCK)
FB1 Voltage
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
1.23
1.22
TYP
1.25
0.01
MAX
1.27
1.27
0.03
600
UNITS
V
V
%/V
nA
V/V
µmhos
FB1 Voltage Line Regulation
FB1 Pin Bias Current
Error Amplifier 1 Voltage Gain
Error Amplifier 1 Transconductance
Switch 1 Current Limit
Switch 1 V
CESAT
Switch 1 Leakage Current
Minimum BOOST Voltage Above SW1 Pin
BOOST Pin Current
Maximum Duty Cycle (SW1)
SWITCH 2 (2.6A BOOST)
FB2 Voltage
4.5V < V
IN
< 22V
(Note 4)
∆I
= 5µA
Duty Cycle = 35% (Note 6)
I
SW
= 2A
FB1 = 1.5V
I
SW
= 1.5A (Note 7)
I
SW
= 1.5A
●
●
●
100
200
450
2.4
3.2
310
0.1
1.8
30
82
1.23
1.22
92
1.25
0.01
4.3
470
10
2.5
50
A
mV
µA
V
mA
%
●
1.27
1.27
0.03
1000
V
V
%/V
nA
V/V
µmhos
FB2 Voltage Line Regulation
FB2 Pin Bias Current
Error Amplifier 2 Voltage Gain
Error Amplifier 2 Transconductance
Switch 2 Current Limit
Switch 2 V
CESAT
Switch 2 Leakage Current
BIAS Pin Current
Maximum Duty Cycle (SW2)
SWITCH 3 (350mA BOOST)
FB3 Voltage
4.5V < V
IN
< 22V
(Note 4)
∆I
= 5µA
●
●
220
200
450
2.6
3.8
360
0.1
45
4.9
540
1
A
mV
µA
mA
%
I
SW2
= 2A
FB2 = 1.5V
I
SW2
= 2A
●
85
1.23
1.22
92
1.25
0.01
1.27
1.27
0.03
600
●
V
V
%/V
nA
V/V
µmhos
FB3 Voltage Line Regulation
FB3 Pin Bias Current
Error Amplifier 3 Voltage Gain
Error Amplifier 3 Transconductance
Switch 3 Current Limit
Switch 3 V
CESAT
Switch 3 Leakage Current
BIAS Pin Current
Maximum Duty Cycle (SW3)
4.5V < V
IN
< 22V
(Note 4)
∆I
= 5µA
●
●
100
200
450
0.35
0.5
180
0.1
14
84
83
88
700
0.7
280
1
A
mV
µA
mA
%
%
mV
I
SW3
= 0.2A
FB3 = 1.5V
I
SW3
= 0.2A
●
Schottky Diode Drop
I = 170mA
1943fa
3
LT1943
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. RUN-SS, SS-234 = 2.5V unless otherwise noted.
PARAMETER
SWITCH 4 (350mA INVERTER)
FB4 Voltage
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
1.23
1.22
TYP
1.25
0.01
MAX
1.27
1.27
0.03
600
1.275
1.275
0.03
600
UNITS
V
V
%/V
nA
V
V
%/V
nA
V/V
µmhos
FB4 Voltage Line Regulation
FB4 Pin Bias Current
NFB4 Voltage (V
FB4
-V
NFB4
)
4.5V < V
IN
< 22V
(Note 4)
●
●
100
1.215
1.205
1.245
0.01
100
200
450
NFB4 Voltage Line Regulation
NFB4 Pin Bias Current
Error Amplifier 4 Voltage Gain
Error Amplifier 4 Transconductance
Switch 4 Current Limit
Switch 4 V
CESAT
Switch 4 Leakage Current
BIAS Pin Current due to SW4
Maximum Duty Cycle (SW4)
4.5V < V
IN
< 22V
(Note 5)
∆I
= 5µA
●
0.35
0.5
260
0.1
15
0.7
390
1
A
mV
µA
mA
%
%
I
SW4
= 0.3A
FB4 = 1.5V
I
SW4
= 0.3A
●
84
83
88
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1943E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization, and correlation
with statistical process controls.
Note 3:
The C
T
pin is held low until FB1, FB2, FB3 and FB4 all ramp above
the FB threshold offset.
Note 4:
Current flows into FB1, FB2, FB3 and FB4 pins.
Note 5:
Current flows out of NFB4 pin.
Note 6:
Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at high duty cycle.
Note 7:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Output Current
for V
LOGIC
= 3.3V
2.8
5
T
A
= 25°C
2.6
4
2.4
4.0
L1 = 4.7µH
2.2
L1 = 3.3µH
2.0
1.8
1.6
1.4
1.2
0
0
5
10
INPUT VOLTAGE (V)
1943 G01
V
LOGIC
MAXIMUM OUTPUT CURRENT (A)
SW1 CURRENT (A)
3
SW1 CURRENT (A)
80
100
1943 G02
15
4
U W
20
SW1 Current Limit vs Duty Cycle
4.5
T
A
= 25°C
SW1 Current Limit
TYPICAL
3.5
2
MINIMUM
1
3.0
0
20
40
60
DUTY CYCLE (%)
2.5
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1943 G03
1943fa
LT1943
TYPICAL PERFOR A CE CHARACTERISTICS
MINIMUM Input Voltage to Start,
V
LOGIC
= 3.3V
6.0
T
A
= 25°C
5.5
BOOST PIN CURRENT (mA)
INPUT VOLTAGE (V)
5.0
4.5
4.0
3.5
3.0
SW2 CURRENT (A)
0
20
40
60
80
LOAD CURRENT (mA)
SW3 Current Limit
0.8
0.7
SW3 CURRENT (A)
SW4 CURRENT (A)
SW1 VOLTAGE DROP (mV)
0.6
0.5
0.4
0.3
0.2
–50 –25
50
25
75
0
TEMPERATURE (°C)
600
500
SW2 V
CESAT
T
A
= 25°C
SW3 VOLTAGE DROP (mV)
SW2 VOLTAGE DROP (mV)
400
300
200
100
0
SW4 VOLTAGE DROP (mV)
0
0.5
1.0
1.5
2.0
SW2 CURRENT (A)
U W
1943 G04
BOOST Pin Current
100
T
A
= 25°C
80
4.5
5.0
SW2 Current Limit
60
4.0
40
3.5
20
3.0
0
100
0
0.5
1.0
1.5
2.0
SW1 CURRENT (A)
2.5
3.0
1943 G05
2.5
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1943 G06
SW4 Current Limit
0.8
0.7
0.6
0.5
0.4
0.3
0.2
–50 –25
600
SW1 V
CESAT
T
A
= 25°C
500
400
300
200
100
0
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
0
0.5
1.0
1.5
2.0
SW1 CURRENT (A)
2.5
3.0
1943 G09
1943 G07
1943 G08
SW3 V
CESAT
500
T
A
= 25°C
400
400
500
SW4 V
CESAT
T
A
= 25°C
300
300
200
200
100
100
0
2.5
3.0
1943 G10
0
0.1
0.2
SW3 CURRENT (A)
0.3
0
0.4
1943 G11
0
0.1
0.2
SW4 CURRENT (A)
0.3
0.4
1943 G12
1943fa
5
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