LT1947
Adjustable Output TFT-LCD
Triple Switching Regulator
FEATURES
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DESCRIPTIO
Complete Solution Under 1.2mm
Develops Three Outputs from a 3.3V or 5V Supply
Externally Programmable V
ON
Delay
Fixed Frequency Low Noise Outputs
All Ceramic Capacitors
3MHz Switching Frequency
Fast Transient Response
Few External Components Required
2.7V to 8V Input Range
Adjustable AV
DD
and V
ON
Voltages
Tiny 10-Lead MSOP and Thermally Enhanced
10-Lead MSOP Packages
APPLICATIO S
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TFT-LCD Notebook Display Panels
TFT-LCD Desktop Monitor Display Panels
Digital Cameras
Handheld Computers
The LT
®
1947 is a highly integrated multiple output DC/DC
converter designed for use in TFT-LCD panels. The device
contains two independent switching regulators. The main
regulator has an adjustable output voltage with an internal
1.1A switch that can generate a boosted voltage as high as
30V. The second regulator’s output is also adjustable up
to 30V and can deliver 10mA for positive bias. A simple
level-shift charge pump off the main switch node gener-
ates the negative bias voltage. An external capacitor sets
the delay time from AV
DD
’s final value to the rising edge at
the V
ON
pin. The 3MHz switching frequency allows the use
of tiny low profile chip inductors and capacitors through-
out, providing a low noise, low cost total solution with all
components under 1.2mm in height. The device operates
from an input range of 2.7V to 8V and is available in
10-lead MSOP and thermally enhanced 10-lead MSOP
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
D3
D4
L1
3.3µH
V
IN
L2
4.7µH
C1
2.2µF
CERAMIC
C6
0.68µF
D1
V
IN
SW2
SW1
FB1
C4
0.68µF
CERAMIC
AV
DD
8V
200mA
R1
53.6k
C2
3.3µF
CERAMIC
×2
V
SHDN
5V/DIV
V
ON
20V/DIV
V
OFF
–8V
10mA
D2
V
O2
C3
220nF
R3
182k
FB2
R4
10k
SHDN C
T
C5
10nF
D1: MBRM120LT3
D2: CMDSH-3
D3, D4: BAT54S DUAL DIODE
L1: SUMIDA CLQ4D103R3
L2: TAIYO YUDEN LB2012B4R7M
V
ON
GND
LT1947
R2
10k
V
ON
24V
10mA
AV
DD
10V/DIV
SHUTDOWN
V
OFF
10V/DIV
1947 F01
C1: TAIYO YUDEN LMK316BJ225MD
C2: TAIYO YUDEN LMK325BJ335MD
×2
C3: AVX 0.22µF 25V X7R
C4, C6: TAIYO YUDEN LMK107BJ684MA
Figure 1. 3.3V Powered TFT-LCD Bias Generator
1947fa
U
Start-Up Waveforms
2ms/DIV
1947 TA01.tif
U
U
1
LT1947
ABSOLUTE
(Note 1)
AXI U
RATI GS
FB1, FB2 .................................................................... 3V
SHDN......................................................................... 8V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Lead Temperature (Soldering, 10 sec).................. 300°C
V
IN
Voltage ................................................................ 8V
C
T
Voltage.................................................................. 6V
SW1, SW2 Voltage .................................................. 36V
V
ON
, V
O2
Voltage ..................................................... 30V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
FB1
FB2
C
T
SW1
GND
1
2
3
4
5
10
9
8
7
6
V
ON
V
02
SHDN
SW2
V
IN
ORDER PART
NUMBER
LT1947EMSE
FB1
FB2
C
T
SW1
GND
1
2
3
4
5
11
MSE PACKAGE
10-LEAD PLASTIC MSOP
EXPOSED PAD (PIN 11) IS GND
MUST BE SOLDERED TO PCB
MSE PART MARKING
LTBQW
T
JMAX
= 125°C,
θ
JA
= 40°C/W
Order Options
Tape and Reel: Add #TR, Lead Free: Add #PBF, Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
Input Voltage Range
Supply Current
FB1 Voltage
SHDN = 2.4V
SHDN = 0V
CONDITIONS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
SHDN
= 3.3V unless otherwise specified.
MIN
2.7
9.5
1.240
1.225
1.225
1.210
1.26
1.26
0.01
TYP
MAX
8
12.5
1
1.280
1.295
1.295
1.310
0.05
UNITS
V
mA
µA
V
V
V
V
%/V
FB2 Voltage
●
Reference Line Regulation
V
IN
= 2.7V to 8V
2
U
U
W
W W
U
W
TOP VIEW
10
9
8
7
6
V
ON
V
O2
SHDN
SW2
V
IN
ORDER PART
NUMBER
LT1947EMS
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 120°C/W
MS PART MARKING
LTUE
●
1947fa
LT1947
ELECTRICAL CHARACTERISTICS
SYMBOL
Error Amplifier Voltage Gain
C
T
Current Source
C
T
Threshold to Turn On Q3
FB1 Voltage to Begin C
T
Charge
SW1 Current Limit
SW2 Current Limit
SW1 Saturation Voltage
SW2 Saturation Voltage
SW1 Maximum Duty Cycle
SW2 Maximum Duty Cycle
Oscillator Frequency
V
ON
Switch Drop
SW1 Leakage Current
SW2 Leakage Current
SHDN Pin Bias Current
SHDN Pin High
SHDN Pin Low
I
Q3
= 7mA
(Note 3)
(Note 3)
I
SW1
= 800mA
I
SW2
= 300mA
CONDITIONS
EA1 and EA2
V
FB1
= 1.3V
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
SHDN
= 3.3V unless otherwise specified.
MIN
4
1.25
1.17
1.1
0.35
TYP
100
5.5
1.28
1.2
1.4
0.6
0.230
0.3
82
85
●
MAX
6.5
1.30
1.23
2
1
0.280
0.36
UNITS
V/V
µA
V
V
A
A
V
V
%
%
2.3
3
160
0.01
0.01
10
3.5
200
5
5
25
0.4
MHz
mV
µA
µA
µA
V
V
Switch Off, SW1 = 3.3V
Switch Off, SW2 = 3.3V
V
SHDN
= 2.4V
Active Mode
Shutdown Mode
2.4
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1947 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:
Switch current limit guaranteed by design and/or correlation to
static tests.
TYPICAL PERFOR A CE CHARACTERISTICS
3.3V TFT-LCD Converter Efficiency
85
80
75
EFFICIENCY (%)
V
IN
= 3.3V
SUPPLY CURRENT (mA)
65
60
55
50
45
40
35
0
25
50 75 100 125 150 175 200
AV
DD
LOAD CURRENT (mA)
1947 G01
8
C
T
CURRENT (µA)
70
V
IN
= 3V
U W
V
IN
= 2.7V
Supply Current
12
SHDN = 2.4V
10
–4
–2
C
T
Current Source
–6
6
–8
4
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1947 G02
–10
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1947 G03
1947fa
3
LT1947
TYPICAL PERFOR A CE CHARACTERISTICS
SW1 Current Limit
1.8
1.6
SW1 CURRENT (A)
1.4
SW2 CURRENT (A)
–25
0
25
50
TEMPERATURE (°C)
75
100
1947 G04
1.2
1.0
0.8
–50
Switch 1 Saturation Voltage
500
SWITCH 1 SATURATION VOLTAGE (mV)
SWITCH 2 SATURATION VOLTAGE (mV)
400
25°C
300
90°C
200
–45°C
100
0
0
0.2
0.4 0.6 0.8
1
SWITCH CURRENT (A)
1.2
1.4
SW1 Maximum Duty Cycle
100
3.2
90
OSCILLATOR FREQUENCY (MHz)
SW1 DUTY CYCLE (%)
80
70
60
50
–50
–25
0
25
50
TEMPERATURE (°C)
4
U W
SW2 Current Limit
1.0
0.8
0.6
0.4
0.2
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1947 G05
Switch 2 Saturation Voltage
800
25°C
600
90°C
400
–45°C
200
0
0
0.1
0.2
0.3
0.4
SWITCH CURRENT (A)
0.5
0.6
1947 G07
1947 G06
Oscillator Frequency
3.0
2.8
2.6
2.4
75
100
1947 G08
2.2
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1947 G09
1947fa
LT1947
PI FU CTIO S
FB1 (Pin 1):
Feedback Pin for First Switcher. Connect
resistor divider tap here. Set AV
DD
according to:
AV
DD
= 1.26V(1 + R1/R2).
FB2 (Pin 2):
Feedback Pin for Second Switcher. Connect
resistor divider 2 here and set V
ON
using:
V
ON
= 1.26V (1 + R3/R4) – 160mV.
C
T
(Pin 3):
Timing Capacitor Pin. Connect a 10nF capacitor
from C
T
to ground to program a 2.3ms delay from FB1
reaching 1.26V to V
ON
turning on.
SW1 (Pin 4):
AV
DD
Switch Node. Connect L1 and D1 here
(see Figure 1). Minimize trace area at this pin to keep EMI
down.
GND (Pin 5):
Ground. Connect directly to local ground
plane.
V
IN
(Pin 6):
Input Supply Pin. Must be bypassed with a
ceramic capacitor close to the pin.
SW2 (Pin 7):
V
O2
Switch Node. Connect L2 and D2 here.
Minimize trace area at this pin to keep EMI down.
SHDN (Pin 8):
Pull this pin low for shutdown mode. For
normal operation, tie to a voltage between 2.4V and 8V.
V
O2
(Pin 9):
SW2 Output. This node is also internally
connected to the emitter of Q3 (see Block Diagram), the
high side switch between V
O2
and V
ON
.
V
ON
(Pin 10):
This is the delayed output for second
Switcher. V
ON
reaches its programmed voltage after the
internal timer times out.
Exposed Pad (Pin 11):
Ground (MSE package only). The
exposed pad must be soldered to the PCB and electrically
connected to ground.
U
U
U
1947fa
5
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