LINEAR TECHNOLOGY LTC1697 Technical data

FEATURES

■

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

U

APPLICATIO S

■

PDAs

■

Handheld Computers

■

Portable Instruments

■

Handheld GPS with Map Display

■

Handheld TV/Video Monitor

LTC1697

High Efficiency Low Power

1W CCFL Switching Regulator

U

DESCRIPTIO

®

The LTC
cathode fluorescent lamp (CCFL). An internal PWM dim­ming 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.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Protected by U.S. Patent 6522116.

1697 is designed to control a single 1W cold

TYPICAL APPLICATIO

110234

V

2.8V TO 5.5V

+

Li-Ion

CELL

IN

330Ω

DIMMING INPUT

1V(0%) – 2V(100%)

0.022µF10µF

OFF ON

U

65

0.15µF

33µH

VIN SW 0V

SHDN

LTC1697

V

DIM

C

DIM

R

PROG

GND

8.25k

LAMP

SEN

V

C

200k

27pF

1kV

CCFL

LAMP

0.1µF

1697 TA01

10

9
8

7

6

5

(mA)

4

CCFL

I

3

2

4k 10k 20k6k 8k

I

CCFL

vs R

R

PROG

PROG

(Ω)

1967 TA01b

1697f

1

LTC1697

1
2
3
4
5

C

DIM

V

DIM

0V

SEN

SW

GND

10
9
8
7
6

SHDN
R

PROG

V

C

V

IN

LAMP

TOP VIEW

MS PACKAGE

10-LEAD PLASTIC MSOP

WW

W

ABSOLUTE AXI U RATI GS

U

UUW

PACKAGE/ORDER I FOR ATIO

(Notes 1, 2)

VIN Voltage .................................................. –0.5V to 6V

VC, OV

Voltages ................................... –0.5V to (V

SHDN, V

, C

SEN

DIM

, R

DIM

Pins ......................................... –0.5V to 6V

PROG

, SW

+ 0.3V)

IN

ORDER PART

NUMBER

LTC1697EMS

LAMP Pin ................................................. –0.5V to 0.5V

Operating Temperature Range (Note 5) ...–40°C to 85°C

T

Storage Temperature Range ..................–65°C to 125°C

Lead Temperature (Soldering, 10 sec).................. 300°C

θ

JA

Consult LTC Marketing for parts specified with wider operating temperature ranges.

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

V

UVLO

I

Q-SHDN

I

Q-Active

I

LEAK

R

ON

I

MAX

% DC Duty Cycle ● 095%

f

SWITCH

f

DIM

V

DIM

I

DIM

R

LAMP

I

L(ERROR)

R

P(RANGE)

V

SHDN-H

V

SHDN-L

I

SHDN

I

OVSEN

V

OVSEN

V

DIM(SD-I)

V

DIM(SD-H)

Operating Supply Voltage Range (Note 2) ● 2.8 5.5 V

Undervoltage Lockout ● 2.77 V

Quiescent Current - SHDN SHDN = 0V; V

= 0V 1 2 µA

DIM

Quiescent Current - Active VC = 0V, SHDN = VIN = V

Switch Leakage 0.1 1 µA

Switch On Resistance VIN = 4V 0.18 Ω

Switch Current Limit ● 0.9 1.6 A

Switching Frequency ● 240 300 370 kHz

Dimming PWM Frequency C

V

Input Voltage Dimming PWM Duty Cycle = 0% 1.0 V

DIM

= 0.022µF (Note 3) ● 190 250 310 Hz

DIM

Dimming PWM Duty Cycle = 100% 2.0 V

V

Input Bias Current V

DIM

Internal R

Resistance LAMP Pin to GND 50 60 Ω

LAMP

Lamp Current Accuracy |1– I

= 2V ±1 µA

DIM

/(32/6.4k)| • 100% (Note 6) ● 26 %

= 5mA

I

LAMP

LAMP(AVG)

Programming Resistor Range (Note 10) ● 6.4 16 kΩ

SHDN Input High 1.2 V

SHDN Input Low (Note 9) 0.4 V

SHDN Input Current V

Overvoltage Sense Protect Current (Note 7) I

SHDN

LAMP

= V

IN

= 5mA, R

= 6.4k ● 16.65 21.5 26.35 µA

PROG

Overvoltage Sense Pin Voltage ● 0.95 1.2 1.5 V

Passive Shutdown Voltage (Note 8) ● 0.4 V

Not in Passive Shutdown ● 1.05 V

= 125°C,

JMAX

= 160°C/W 1 LAYER BOARD

= 4.2V (Note 4) 0.9 1.5 mA

DIM

● 0.1 1 µA

MS PART MARKING

LTZR

1697f

ELECTRICAL CHARACTERISTICS

LTC1697

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/C
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.

U

UU

DIM

(µF).

PI FU CTIO S

C

(Pin 1): Dimming Capacitor. Connect the pin to GND

DIM

with a 0.022µF capacitor (nominal). The value of capaci-
tance on the C
frequency. The transfer function of capacitance to fre­quency is 5Hz/C

V

(Pin 2): Dimming Control Pin. The V

DIM

the duty cycle of the dimming PWM. It ranges from 0% at
V

= 1V to 100% at V

DIM

<0.4V the LTC1697 will enter shutdown mode after ≈50ms.

0V

(Pin 3): Overvoltage Sense Pin. Protects the high-

SEN

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.

pin determines the dimming PWM

DIM

(µF).

DIM

pin controls

DIM

= 2V. If the V

DIM

voltage is

DIM

Note 6: I

LAMP(AVG)

positive and negative lamp current flowing into and out of the LAMP pin.
Note 7: For currents at or above I

0%.
Note 8: At V

the SHDN pin was pulled low.

Note 9: To minimize I
Note 10: 2mA ≤ I

= the average of the magnitude (absolute value) of the

, the switch duty cycle will be

the LTC1697 behaves as if

voltages below V

DIM

shutdown, pull the SHDN pin below 0.1V.

Q

≤ 5mA.

LAMP

OVSEN(ON)

DIM(SHDNON)

GND (Pin 5): Signal and Power Ground for the LTC1697.

LAMP (Pin 6): Lamp Current Feedback Pin. Connect this

pin to the CCFL lamp.

VIN (Pin 7): Input Supply Pin.

VC (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

(Pin 9): Lamp Current Programming. Connect this

PROG

pin to GND with a 6.4k 1% resistor (nominal). See Appli­cation Information section for resistor selection.

SHDN (Pin 10): Shutdown. Grounding this pin shuts down
the LTC1697. Tie to >1V to enable.

1697f

3

LTC1697

BLOCK DIAGRA

W

TO ROYER

OSCILLATOR

SHDN

10

SHUTDOWN

ANTI
SHOOTTHRU
PROTECTION

PWM

LOGIC

SW

4

N

CURRENT

LIMIT

CURRENT

COMP

200k

V

IN

7

2.8V
TO 5.5V

I

SENSE

AMP

0V

SEN

3

+

1.6A

–

TYP

–

+

+

–

Σ

TRANSFORMER

VOLTAGE

PROTECTION

V

C

8

0.8V

–

GND

PWM

+

OSC

5

DIMMING

OSC

1

C

2V
1V

0.7V

DIM

SLOPE

COMP

+

+

–

I

R

PROG

50Ω

LAMP

LAMP

FB

–

2

V

DIM

1697 BD

9

6

R

PROG

LAMP

R

P

1697f

WUUU

APPLICATIO S I FOR ATIO

LTC1697

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 life­time. Lamp drive should ideally contain zero DC compo­nent. 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 con­straints 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 Royer­class converter with efficiencies as high as 90%. The
control loop forces the CCFL PWM to modulate the aver­age inductor current to maintain constant current in the
lamp. This constant current and the resulting lamp inten­sity 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 VC 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 VIN.

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 (VC) 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
5Hz/C

pin. The dimming PWM frequency is equal to

DIM

(µF) with its duty cycle set by the voltage on the

DIM

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5

LTC1697

WUUU

APPLICATIO S I FOR ATIO

V

pin where DC = 0% at V

DIM

V

= 2V. If desired, the internal dimming PWM can be

DIM

overridden by grounding the C
input PWM signal to the V
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
lamp current. The lamp feedback circuit removes a current
from VC approximating 1/40 of the absolute value of the
current through the 50Ω resistor.

Current Programming Input (R

The I

current is set with an external resistor con-

LAMP

nected between this pin and ground. I

VC Compensation

The VC node is the point where the lamp feedback current,
the programming current, and the control for the switch­ing controller meet. A single capacitor must be connected
from the VC 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 VC capacitor should be increased until the

= 1V and DC = 100% at

DIM

pin and applying the

DIM

pin. This external PWM

DIM

)

PROG

= 32V/R

LAMP

RMS

PROG

.

line regulation becomes unacceptable. A typical value for
the VC capacitor is 0.1µF. For further information on
compensation please refer to Application Note 65 or
consult the factory.

OV

Operation

SEN

The OV

pin can be used to protect the high voltage

SEN

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
specified by V

. The duty cycle of the LTC1697 SW pin

OVSEN

will be 0% when the current flowing out of the OV
reaches I

(protect). See the manufacturers trans-

OVSEN

SEN

pin is

pin

SEN

former specifications for transformer voltage ratings.

Thermal Shutdown

This IC includes overtemperature protection that is in­tended to protect the device during momentary overload
conditions. Junction temperature will exceed 125°C when
overtemperature protection is active. Continuous opera­tion 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
be pulled below V

DIM(SD-I)

for more than approximately

SHDN-1

, or the V

DIM

pin can

50mS. For normal operation, both pins must be pulled
high. The SHDN pin must be pulled above V
V

pin must be pulled above V

DIM

DIM (SD-H)

SHDN-H

, and the

.

1697f

PACKAGE DESCRIPTIO

U

MS Package

10-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1661)

0.889 ± 0.127

± .005)

(.035

LTC1697

5.23

(.206)

MIN

0.305

± 0.038
± .0015)

(.0120

TYP

RECOMMENDED SOLDER PAD LAYOUT

0.254
(.010)

GAUGE PLANE

0.18

(.007)

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

3.20 – 3.45

(.126 – .136)

DETAIL “A”

DETAIL “A”

0.50

(.0197)

BSC

° – 6° TYP

0

0.53 ± 0.152
(.021 ± .006)

SEATING

PLANE

3.00 ± 0.102
(.118 ± .004)

(NOTE 3)

4.90 ± 0.152

(.193 ± .006)

(.043)

0.17 – 0.27

(.007 – .011)

TYP

1.10

MAX

12

0.50

(.0197)

BSC

8910

3

7

6

45

0.497 ± 0.076

(.0196 ± .003)

REF

3.00 ± 0.102

(.118 ± .004)

(NOTE 4)

0.86

(.034)

REF

0.127 ± 0.076
(.005 ± .003)

MSOP (MS) 0603

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 represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

1697f

7

LTC1697

TYPICAL APPLICATIO

U

External PWM Dimming

RELATED PARTS

V

IN

2.8V TO 5.5V

+

Li-Ion

CELL

1V TO 2V

C1
10µF

C1: TAIYO YUDEN JMK212BJ106MM
C2: PANASONIC ECH-U1H154JC9
L1:SUMIDA CDRH6D28-330NC

110234

R1

330Ω

0V

OFF ON

150Hz TO

500Hz

Q1 Q2

33µH

8.25k

Q1, Q2: ZETEX FMMT-617
R1: 330Ω,1206 PKG
T1: SUMIDA CLQ122-S-227-5316

65

T1

C2

0.15µF

L1

VIN SW 0V

SHDN

LTC1697

V

DIM

C

DIM

R

PROG

GND

LAMP

SEN

V

200k

C

C3

27pF

1kV

CCFL

LAMP

C4

0.1µF

1697 TA02

PART NUMBER DESCRIPTION COMMENTS

LT1170/LT1170HV 5A, 100kHz High Efficiency Switching Regulator VIN: 3V to 40V/60V, V

I

= <50µA, N8, S16, TO220-5, DD Packages

SD

LT1182/LT1183 CCFL/LCD Contrast Switching Regulators, CCFL VIN: 3V to 30V, V

OUT(MAX)

Switch: 1.25A, LCD Switch: 625mA SO-16 Package

LT1184/LT1184F 1.25A, 200kHz, CCFL Current Mode Switching Regulator VIN: 3V to 30V, V

OUT(MAX)

SO-16 Package

LT1186/LT1186F 1.25A, 100kHz, DAC Programmable CCFL VIN: 4.5V to 30V, V

OUT(MAX)

Current Mode Switching Regulator SO-16 Package

LT1372/LT1372HV/ 1.5A, 500kHz/1MHz, High Efficiency Switching Regulator VIN: 2.7V to 30V, V

OUT(MAX)

LT1377 N8, S8 Packages

LT1373/LT1373HV 1.5A, 250kHz High Efficiency Switching Regulator VIN: 0.5V to 5V, V

OUT(MAX)

can Regulate Positive or Negative Outputs N8, S8 Packages

LT1768 High Power CCFL Controller for Wide Dimming Range VIN: 8V to 24V, V

OUT(MAX)

and Maximum Lamp Lifetime SSOP-16 Package

LT1786F 1.25A, 200kHz, SMBus Controlled CCFL Switching Regulator VIN: 4.5V to 30V, V

OUT(MAX)

Precision 100mA Full Scale Current SO-16 Package

= 65V/75V, IQ = 6mA,

OUT(MAX)

= 60V, IQ = 6mA, ISD = 35µA,

= 60V, IQ = 6mA, ISD = 35µA,

= 60V, IQ = 6mA, ISD = 35µA

= 35V, IQ = 4mA, ISD = <12µA

= 35V, IQ = 1mA, ISD = <12µA

= 28V, IQ = 7mA, ISD = 65µA

= 60V, IQ = 6mA, ISD = 150µA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone] ● www.linear.com

1697f

LT/TP 1004 1K • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2004