LTC1697
1
1697f
■
PDAs
■
Handheld Computers
■
Portable Instruments
■
Handheld GPS with Map Display
■
Handheld TV/Video Monitor
■
Operates from Single Li-Ion Battery
■
2.8V to 5.5V Input Voltage Range
■
Very Low Shutdown Current: <2µA
■
Synchronous Buck Architecture for High Efficiency
■
PWM Dimming Frequency Adjustable with a Single
Capacitor
■
Accurate Lamp Current Maximizes Lamp Lifetime
■
Fixed Frequency Operation at 300kHz
■
Internal or External PWM Dimming
■
Small 10-Pin MSOP Package
The LTC
®
1697 is designed to control a single 1W cold
cathode fluorescent lamp (CCFL). An internal PWM dim-
ming system maximizes efficiency and dimming range.
Accurate lamp currents can be set with a single external
resistor.
The LTC1697 includes a synchronous current mode PWM
controller with internal 1A MOSFET switches. It contains
a 300kHz oscillator, 0.8V reference, and internal current
sense. It operates from a 2.8V to 5.5V input voltage. The
LTC1697 also has a thermal limit and a shutdown that
reduces supply current to <2µA.
The LTC1697 is available in the MSOP-10 package.
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
High Efficiency Low Power
1W CCFL Switching Regulator
, LTC and LT are registered trademarks of Linear Technology Corporation.
8.25k 0.1µF
0.022µF10µF
330Ω
65
110234
0.15µF
33µH
CCFL
LAMP
200k
V
IN
2.8V TO 5.5V
DIMMING INPUT
1V(0%) – 2V(100%)
Li-Ion
CELL
1697 TA01
27pF
1kV
+
OFF ON
V
IN
SW 0V
SEN
SHDN
V
DIM
C
DIM
R
PROG
LAMP
V
C
LTC1697
GND
R
PROG
(Ω)
4k 10k 20k6k 8k
3
2
4
5
6
7
9
8
I
CCFL
(mA)
10
1967 TA01b
ICCFL vs RPROG
Protected by U.S. Patent 6522116.
LTC1697
1697f
V
IN
Voltage .................................................. –0.5V to 6V
V
C
, OV
SEN
, C
DIM
, R
PROG
, SW
Voltages ................................... –0.5V to (V
IN
+ 0.3V)
SHDN, V
DIM
Pins ......................................... –0.5V to 6V
LAMP Pin ................................................. –0.5V to 0.5V
Operating Temperature Range (Note 5) ...–40°C to 85°C
Storage Temperature Range ..................–65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
MS PART MARKING
T
JMAX
= 125°C,
θ
JA
= 160°C/W 1 LAYER BOARD LTZR
LTC1697EMS
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Notes 1, 2)
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. 2.8V < VIN ≤ 5.5V unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Operating Supply Voltage Range (Note 2) ●2.8 5.5 V
V
UVLO
Undervoltage Lockout ●2.77 V
I
Q-SHDN
Quiescent Current - SHDN SHDN = 0V; V
DIM
= 0V 1 2 µA
I
Q-Active
Quiescent Current - Active V
C
= 0V, SHDN = V
IN
= V
DIM
= 4.2V (Note 4) 0.9 1.5 mA
I
LEAK
Switch Leakage 0.1 1 µA
R
ON
Switch On Resistance V
IN
= 4V 0.18 Ω
I
MAX
Switch Current Limit ●0.9 1.6 A
% DC Duty Cycle ●095%
f
SWITCH
Switching Frequency ●240 300 370 kHz
f
DIM
Dimming PWM Frequency C
DIM
= 0.022µF (Note 3) ●190 250 310 Hz
V
DIM
V
DIM
Input Voltage Dimming PWM Duty Cycle = 0% 1.0 V
Dimming PWM Duty Cycle = 100% 2.0 V
I
DIM
V
DIM
Input Bias Current V
DIM
= 2V ±1µA
R
LAMP
Internal R
LAMP
Resistance LAMP Pin to GND 50 60 Ω
I
L(ERROR)
Lamp Current Accuracy |1– I
LAMP(AVG)
/(32/6.4k)| • 100% (Note 6) ●26 %
I
LAMP
= 5mA
R
P(RANGE)
Programming Resistor Range (Note 10) ●6.4 16 kΩ
V
SHDN-H
SHDN Input High 1.2 V
V
SHDN-L
SHDN Input Low (Note 9) 0.4 V
I
SHDN
SHDN Input Current V
SHDN
= V
IN
●0.1 1 µA
I
OVSEN
Overvoltage Sense Protect Current (Note 7) I
LAMP
= 5mA, R
PROG
= 6.4k ●16.65 21.5 26.35 µA
V
OVSEN
Overvoltage Sense Pin Voltage ●0.95 1.2 1.5 V
V
DIM(SD-I)
Passive Shutdown Voltage (Note 8) ●0.4 V
V
DIM(SD-H)
Not in Passive Shutdown ●1.05 V
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1
2
3
4
5
CDIM
VDIM
0VSEN
SW
GND
10
9
8
7
6
SHDN
RPROG
VC
VIN
LAMP
TOP VIEW
MS PACKAGE
10-LEAD PLASTIC MSOP
LTC1697
3
1697f
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: All voltages specified with respect to GND pin.
Note 3: The dimming PWM frequency is set by the equation 5Hz/CDIM(µF).
Note 4: Actual operating current will be higher due to lamp operating
current.
Note 5: The LTC1697 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 6: I
LAMP(AVG)
= the average of the magnitude (absolute value) of the
positive and negative lamp current flowing into and out of the LAMP pin.
Note 7: For currents at or above I
OVSEN(ON)
, the switch duty cycle will be
0%.
Note 8: At V
DIM
voltages below V
DIM(SHDNON)
the LTC1697 behaves as if
the SHDN pin was pulled low.
Note 9: To minimize I
Q
shutdown, pull the SHDN pin below 0.1V.
Note 10: 2mA ≤ I
LAMP
≤ 5mA.
C
DIM
(Pin 1): Dimming Capacitor. Connect the pin to GND
with a 0.022µF capacitor (nominal). The value of capaci-
tance on the C
DIM
pin determines the dimming PWM
frequency. The transfer function of capacitance to fre-
quency is 5Hz/C
DIM
(µF).
V
DIM
(Pin 2): Dimming Control Pin. The V
DIM
pin controls
the duty cycle of the dimming PWM. It ranges from 0% at
V
DIM
= 1V to 100% at V
DIM
= 2V. If the V
DIM
voltage is
<0.4V the LTC1697 will enter shutdown mode after ≈50ms.
0V
SEN
(Pin 3): Overvoltage Sense Pin. Protects the high-
voltage transformer from the overvoltage condition that
occurs when the lamp is open or not present. This pin is
connected through a resistor to the emitters of the drive
transistors of the Royer oscillator.
SW (Pin 4): Switch Pin. Connect the inductor and optional
Schottky diode here. Minimize trace length to keep EMI
and high frequency ringing down.
GND (Pin 5): Signal and Power Ground for the LTC1697.
LAMP (Pin 6): Lamp Current Feedback Pin. Connect this
pin to the CCFL lamp.
V
IN
(Pin 7): Input Supply Pin.
V
C
(PIN 8): Compensation Node. Connect this pin to GND
through a 0.1µF capacitor. See Application Information
section. A frequency compensation network is connected
to this pin to compensate the loop. See the section “V
C
Compensation” for guidelines.
R
PROG
(Pin 9): Lamp Current Programming. Connect this
pin to GND with a 6.4k 1% resistor (nominal). See Appli-
cation Information section for resistor selection.
SHDN (Pin 10): Shutdown. Grounding this pin shuts down
the LTC1697. Tie to >1V to enable.
UU
U
PI FU CTIO S
ELECTRICAL CHARACTERISTICS
LTC1697
1697f
BLOCK DIAGRA
W
–
+
–
+
–
+
PWM
LOGIC
ANTI
SHOOTTHRU
PROTECTION
CURRENT
COMP
CURRENT
LIMIT
I
SENSE
AMP
Σ
1.6A
TYP
PWM
OSC
DIMMING
OSC
SLOPE
COMP
–
+
–+
2V
1V
0.7V
4
1
5
10
2
7
3
8
9
6
SHDN SHUTDOWN
TRANSFORMER
VOLTAGE
PROTECTION
R
PROG
R
PROG
50Ω
LAMP
V
DIM
V
C
C
DIM
I
LAMP
LAMP
FB
0.8V
V
IN
2.8V
TO 5.5V
0V
SEN
SW
TO ROYER
OSCILLATOR
200k
N
–+
GND
1697 BD
R
P
LTC1697
5
1697f
APPLICATIO S I FOR ATIO
WUUU
Background
Current generation handheld computers and instruments
typically use backlit liquid crystal displays (LCDs). Cold
cathode fluorescent lamps (CCFLs) provide the highest
available efficiency for backlighting the display, where
providing the most light out for the least amount of input
power is the most important goal. These lamps require
high voltage AC to operate, mandating an efficient high
voltage DC/AC converter. The lamps operate from DC, but
migration effects damage the lamp and shorten its life-
time. Lamp drive should ideally contain zero DC compo-
nent. In addition to good efficiency, the converter should
deliver the lamp drive in the form of a sine wave. This
minimizes EMI and RF emissions, which can interfere with
other devices and degrade overall operating efficiency.
Sinusoidal CCFL drive also maximizes current-to-light
conversion in the lamp. The circuit also permits lamp
intensity control from zero to full brightness with no
hysteresis or “pop-on.”
The small size and battery-powered operation associated
with LCD-equipped apparatus dictate low component
count and high efficiency for these circuits. Size con-
straints place severe limitations on circuit architecture and
long battery life is usually a priority. Handheld portable
computers offer an excellent example. The CCFL and its
power supply can be responsible for almost 50% of the
total battery drain.
The CCFL regulator drives an inductor that acts as a
switch-mode current source for a current-driven Royer-
class converter with efficiencies as high as 90%. The
control loop forces the CCFL PWM to modulate the aver-
age inductor current to maintain constant current in the
lamp. This constant current and the resulting lamp inten-
sity is programmable. Lamp intensity is further controlled
by modulating the current to the Royer converter at 150Hz
to 500Hz.
Operation
The LTC1697 is a fixed frequency, current mode regulator.
Such a switcher controls switch duty cycle directly by
switch current rather than by output voltage. Referring to
the block diagram for the LTC1697, the NMOS switch
turns ON at the start of each oscillator cycle. The NMOS
switch turns back OFF when switch current reaches a
predetermined level.
Current Sensing
Lossless current sensing converts the peak current signal
to a voltage which is summed with the internal slope
compensation. This summed signal is compared to V
C
to
provide a peak current control command for the PWM.
Current Limit
The current limit amplifier will shut the NMOS switch off
once the current exceeds the current limit threshold. The
current amplifier delay to the output is typically 50ns.
Synchronous Rectifier
The LTC1697 operates as a synchronous converter. When
the NMOS switch turns OFF as mentioned above, the
PMOS switch turns ON. This gives a low resistance current
path for the inductor current back to V
IN
.
Dimming PWM
An on-chip PWM dimming circuit enables and disables the
current mode regulator for each dimming cycle. It also
disconnects the feedback network from the compensation
node (V
C
) to reduce slew time at the next enable time. The
oscillator for the dimming PWM produces a triangle wave
whose frequency is determined by an external capacitor
on the C
DIM
pin. The dimming PWM frequency is equal to
5Hz/C
DIM
(µF) with its duty cycle set by the voltage on the
LTC1697
1697f
V
DIM
pin where DC = 0% at V
DIM
= 1V and DC = 100% at
V
DIM
= 2V. If desired, the internal dimming PWM can be
overridden by grounding the C
DIM
pin and applying the
input PWM signal to the V
DIM
pin. This external PWM
signal should be in the range of 150Hz to 500Hz.
Lamp Feedback
In a typical application, the LAMP pin is connected to the
low voltage side of the lamp. The lamp pin is internally
connected to ground by a ~50Ω resistor. This resistor will
limit the voltage on the LAMP pin to ±0.35V for a 5mA
RMS
lamp current. The lamp feedback circuit removes a current
from V
C
approximating 1/40 of the absolute value of the
current through the 50Ω resistor.
Current Programming Input (R
PROG
)
The I
LAMP
current is set with an external resistor con-
nected between this pin and ground. I
LAMP
= 32V/R
PROG
.
V
C
Compensation
The V
C
node is the point where the lamp feedback current,
the programming current, and the control for the switch-
ing controller meet. A single capacitor must be connected
from the V
C
pin to ground to compensate the feedback
loop. Careful consideration should be given to the value of
capacitance used. A large value (1µF) will give excellent
stability at high lamp currents but will result in degraded
line regulation. On the other hand, a small value (10nF) will
result in overshoot and poor load regulation. The value
chosen will depend on the maximum load current and
dimming range. After these parameters are decided upon,
the value of the V
C
capacitor should be increased until the
line regulation becomes unacceptable. A typical value for
the V
C
capacitor is 0.1µF. For further information on
compensation please refer to Application Note 65 or
consult the factory.
OV
SEN
Operation
The OV
SEN
pin can be used to protect the high voltage
transformer from an overvoltage condition that can occur
when the lamp is open or not present. Connect this pin
through a resistor to the emitters of the drive transistors
of the Royer oscillator. The voltage at the OV
SEN
pin is
specified by V
OVSEN
. The duty cycle of the LTC1697 SW pin
will be 0% when the current flowing out of the OV
SEN
pin
reaches I
OVSEN
(protect). See the manufacturers trans-
former specifications for transformer voltage ratings.
Thermal Shutdown
This IC includes overtemperature protection that is in-
tended to protect the device during momentary overload
conditions. Junction temperature will exceed 125°C when
overtemperature protection is active. Continuous opera-
tion above the specified maximum operating junction
temperature may result in device degradation or failure.
Shutdown Operation
There are two ways to place the LTC1697 in shutdown. The
SHDN pin can be pulled below V
SHDN-1
, or the V
DIM
pin can
be pulled below V
DIM(SD-I)
for more than approximately
50mS. For normal operation, both pins must be pulled
high. The SHDN pin must be pulled above V
SHDN-H
, and the
V
DIM
pin must be pulled above V
DIM (SD-H)
.
APPLICATIO S I FOR ATIO
WUUU
LTC1697
7
1697f
PACKAGE DESCRIPTIO
U
MSOP (MS) 0603
0.53 ± 0.152
(.021 ± .006)
SEATING
PLANE
0.18
(.007)
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
0.127 ± 0.076
(.005 ± .003)
0.86
(.034)
REF
0.50
(.0197)
BSC
12345
4.90 ± 0.152
(.193 ± .006)
0.497 ± 0.076
(.0196 ± .003)
REF
8910 76
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.254
(.010) 0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ± 0.127
(.035 ± .005)
RECOMMENDED SOLDER PAD LAYOUT
0.305 ± 0.038
(.0120 ± .0015)
TYP
0.50
(.0197)
BSC
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC1697
1697f
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2004
LT/TP 1004 1K • PRINTED IN USA
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External PWM Dimming
V
IN
SW 0V
SEN
SHDN
V
DIM
C
DIM
R
PROG
LAMP
V
C
LTC1697
GND
8.25k
C4
0.1µF
C1
10µF
T1
R1
330Ω
65
110234
C2
0.15µF
Q1 Q2
L1
33µH
CCFL
LAMP
200k
V
IN
2.8V TO 5.5V
Li-Ion
CELL
1697 TA02
C3
27pF
1kV
C1: TAIYO YUDEN JMK212BJ106MM
C2: PANASONIC ECH-U1H154JC9
L1:SUMIDA CDRH6D28-330NC
+
OFF ON
Q1, Q2: ZETEX FMMT-617
R1: 330Ω,1206 PKG
T1: SUMIDA CLQ122-S-227-5316
1V TO 2V
0V 150Hz TO
500Hz
