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

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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

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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

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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

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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

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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.

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