LINEAR TECHNOLOGY LT1614 Technical data

FEATURES

LT1614

Inverting 600kHz

Switching Regulator

U

DESCRIPTIO

■

Better Regulation Than a Charge Pump

■

0.1Ω Effective Output Impedance

■

–5V at 200mA from a 5V Input

■

600kHz Fixed Frequency Operation

■

Operates with VIN as Low as 1V

■

1mA Quiescent Current

■

Low Shutdown Current: 10µA

■

Low-Battery Detector

■

Low V

Switch: 295mV at 500mA

CESAT

U

APPLICATIO S

■

MR Head Bias

■

LCD Bias

■

GaAs FET Bias

■

Positive-to-Negative Conversion

U

TYPICAL APPLICATIO

The LT®1614 is a fixed frequency, inverting mode switch­ing reglator that operates from an input voltage as low as
1V. Utilizing a low noise topology, the LT1614 can gener­ate a negative output down to – 24V from a 1V to 5V input.
Fixed frequency switching ensures a clean output free
from low frequency noise. The device contains a low­battery detector with a 200mV reference and shuts down
to less than 10µA. No load quiescent current of the LT1614
is 1mA and the internal NPN power switch handles a
500mA current with a voltage drop of just 295mV.

High frequency switching enables the use of small induc­tors and capacitors. Ceramic capacitors can be used in
many applications, eliminating the need for bulky tanta­lum types.

The LT1614 is available in 8-lead MSOP or SO packages.

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

V

IN

5V

+

C1
33µF

C1, C2: AVX TAJB336M010
C3: TAIYO YUDEN EMK316BJ105MF
D1: MBR0520
L1, L2: MURATA LQH3C220

SHDN

V

100k

1nF

Figure 1. 5V to –5V/200mA Converter

SW

NFB

C3

1µF

69.8k

24.9k

D1

L2

22µH

C2

+

33µF

1614 TA01

V

OUT

–5V
200mA

5V to –5V Converter Efficiency

90

80

70

60

EFFICIENCY (%)

50

40

31030

LOAD CURRENT (mA)

100 300

1614 TA02

L1

22µH

V

IN

LT1614

C

GND

1

LT1614

1

2

3

4

8

7

6

5

TOP VIEW

LBO
LBI
V

IN

SW

NFB

V

C

SHDN

GND

S8 PACKAGE

8-LEAD PLASTIC SO

A

W

O

LUTEXI TIS

S

A

WUW

U

ARB

G

VIN, SHDN, LBO Voltage ......................................... 12V

SW Voltage ............................................... –0.4V to 30V

NFB Voltage ............................................................ –3V

VC Voltage ................................................................ 2V

LBI Voltage ............................................ 0V ≤ V

LBI

≤ 1V

Current into FB Pin .............................................. ±1mA

Junction Temperature...........................................125°C

WU

/

PACKAGE

NFB

1

V

2

C

3

SHDN

4

GND

8-LEAD PLASTIC MSOP

T

JMAX

O

RDER I FOR ATIO

TOP VIEW

8

LBO

7

LBI

6

V

5

SW

MS8 PACKAGE

= 125°C, θJA = 160°C/W

ORDER PART

NUMBER

LT1614CMS8
LT1614IMS8

IN

MS8 PART MARKING

LTID
LTJB

(Note 1)

Operating Temperature Range

LT1614C................................................. 0°C to 70°C

LT1614I ............................................. – 40°C to 85°C

Extended Commercial

Temperature Range (Note 2) .................. –40°C to 85°C

Storage Temperature Range ................ –65°C to 150°C

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

U

ORDER PART

NUMBER

LT1614CS8
LT1614IS8

S8 PART MARKING

T

= 125°C, θJA = 120°C/W

JMAX

1614
1614I

Consult factory for Military grade parts.

LECTRICAL C CHARA TERIST

E

temperature range, otherwise specifications are at TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.5V, V
otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Quiescent Current 12mA

Feedback Voltage ● –1.21 –1.24 –1.27 V
NFB Pin Bias Current (Note 3) V
Reference Line Regulation 1V ≤ VIN ≤ 2V 0.6 1.1 %/V

Minimum Input Voltage 0.92 1 V
Maximum Input Voltage ● 6V
Error Amp Transconductance ∆I = 5µA16µmhos
Error Amp Voltage Gain 100 V/V
Switching Frequency ● 500 600 750 kHz
Maximum Duty Cycle 73 80 %

Switch Current Limit (Note 4) 0.75 1.2 A

The ● denotes the specifications which apply over the full operating

ICS

= VIN unless

SHDN

V

= 0V 5 10 µA

SHDN

= –1.24V ● –2.5 –4.5 –7 µA

NFB

2V ≤ V

≤ 6V 0.3 0.8 %/V

IN

● 70 80 %

2

LT1614

LECTRICAL C CHARA TERIST

E

temperature range, otherwise specifications are at TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.5V, V
otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Switch V

Shutdown Pin Current V

LBI Threshold Voltage 190 200 210 mV

LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 5) V
Low-Battery Detector Gain 1MΩ Load 1000 V/V
Switch Leakage Current VSW = 5V 0.01 3 µA

CESAT

ICS

The ● denotes the specifications which apply over the full operating

= VIN unless

SHDN

ISW = 500mA (25°C, 0°C) 295 350 mV

= 500mA (70°C) 400 mV

I

SW

= V

SHDN

IN

= 0V –5 – 10 µA

V

SHDN

● 185 215 mV

= 10µA 0.1 0.25 V

SINK

= 250mV, V

LBI

= 150mV 10 50 nA

LBI

= 5V 0.01 0.1 µA

LBO

10 20 µA

Industrial Grade –40°C to 85°C. VIN = 1.5V, V

PARAMETER CONDITIONS MIN TYP MAX UNITS

Quiescent Current 12mA

Feedback Voltage ● –1.21 –1.24 –1.27 V
NFB Pin Bias Current (Note 3) V
Reference Line Regulation 1V ≤ VIN ≤ 2V 0.6 1.1 %/V

Minimum Input Voltage – 40°C 1.1 1.25 V

Maximum Input Voltage ● 6V
Error Amp Transconductance ∆I = 5µA16µmhos
Error Amp Voltage Gain 100 V/V
Switching Frequency ● 500 600 750 kHz
Maximum Duty Cycle ● 70 80 %
Switch Current Limit (Note 4) 0.75 1.2 A
Switch V

Shutdown Pin Current V

LBI Threshold Voltage ● 180 200 220 mV
LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 5) V
Low-Battery Detector Gain 1MΩ Load 1000 V/V
Switch Leakage Current VSW = 5V 0.01 3 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: The LT1614C is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and expected to meet these
extended temperature limits, but is not tested at –40°C and 85°C. The
LT1614I is guaranteed to meet the extended temperature limits.

CESAT

= VIN unless otherwise noted.

SHDN

= 0V 5 10 µA

V

SHDN

= –1.24V ● –2 – 4.5 –7.5 µA

NFB

≤ 6V 0.3 0.8 %/V

2V ≤ V

IN

85°C 0.8 1.0 V

ISW = 500mA (–40°C) 250 350 mV

= 500mA (85°C) 330 400 mV

I

SW

= V

SHDN

IN

= 0V –5 – 10 µA

V

SHDN

= 10µA 0.1 0.25 V

SINK

= 250mV, V

LBI

= 150mV 5 30 nA

LBI

Note 3: Bias current flows out of NFB pin.
Note 4: Switch current limit guaranteed by design and/or correlation to

static tests. Duty cycle affects current limit due to ramp generator.
Note 5: Bias current flows out of LBI pin.

10 20 µA

= 5V 0.1 0.3 µA

LBO

3

LT1614

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Shutdown Pin Bias Current vs
Input Voltage

10

8

6

4

QUIESCENT CURRENT (µA)

2

0

012345

INPUT VOLTAGE (V)

500

400

300

(mV)

CESAT

200

V

100

Switch V

TA = 25°C

0

0

100

vs Current

CESAT

200 300 400

SWITCH CURRENT (mA)

500 600

1614 G01

1614 G04

10

8

6

4

SHDN BIAS CURRENT (µA)

2

0

012345

INPUT VOLTAGE (V)

210
208
206
204
202
200
198
196

REFERENCE VOLTAGE (mV)

194
192
190

–50

–25

0

TEMPERATURE (°C)

25 50

LBI Bias Current vs TemperatureQuiescent Current in Shutdown

16

14

12

10

8

6

LBI BIAS CURRENT (nA)

4

2

0

1614 G02

–25 0 50

–50

TEMPERATURE (°C)

25

75

100

1614 G03

Oscillator Frequency vs
Input VoltageLBI Reference vs Temperature

900

800

700

600

FREQUENCY (kHz)

500

100

75

1614 G05

400

1

2

25°C

85°C

–40°C

3

INPUT VOLTAGE (V)

4

5

1614 G06

Quiescent Current vs
Temperature*

6

5

4

3

2

QUIESCENT CURRENT (mA)

1

0

–40–200 20406080

TEMPERATURE (°C)

*Includes diode leakage

VIN = 1.25V

VIN = 3V

4

VIN = 5V

1614 G07

NFB Pin Bias Current vs
Temperature

6

5

4

3

2

NFB PIN BIAS CURRENT (µA)

1

0

–50 0 50–25 25 75 100

TEMPERATURE (°C)

1614 G08

V

vs Temperature

NFB

–1.245

–1.240

–1.235

–1.230

(V)

NFB

V

–1.225

–1.220

–1.215

–1.210

–50 0 50–25 25 75 100

TEMPERATURE (°C)

1614 G09

UUU

PIN FUNCTIONS

LT1614

NFB (Pin 1): Negative Feedback Pin. Reference voltage is
–1.24V. Connect resistive divider tap here. The sug­gested value for R2 is 24.9k. Set R1 and R2 according to:

||–.

V

.

124

R

2

OUT

+

R

1

=

124



.•

45 10



6

–




VC (Pin 2): Compensation Pin for Error Amplifier. Con­nect a series RC from this pin to ground. Typical values
are 100kΩ and 1nF. Minimize trace area at VC.

SHDN (Pin 3): Shutdown. Ground this pin to turn off
switcher. Must be tied to VIN (or higher voltage) to enable
switcher. Do not float the SHDN pin.

W

BLOCK DIAGRAM

GND (Pin 4): Ground. Connect directly to local ground
plane.

SW (Pin 5): Switch Pin. Minimize trace area at this pin to
keep EMI down.

VIN (Pin 6): Supply Pin. Must have 1µF ceramic bypass
capacitor right at the pin, connected directly to ground.

LBI (Pin 7): Low-Battery Detector Input. 200mV refer­ence. Voltage on LBI must stay between ground and
700mV. Float this pin if not used.

LBO (Pin 8): Low-Battery Detector Output. Open collec­tor, can sink 10µA. A 1MΩ pull-up is recommended. Float
this pin if not used. The low-battery detector is disabled
when SHDN is low. LBO is high-Z in this state.

V

IN

6

V

OUT

R1
(EXTERNAL)

R2
(EXTERNAL)

NFB

V

IN

NFB

1

Q2
×10

R6
40k

R3
30k

R4
140k

+

g

m

–

ERROR

AMPLIFIER

A1

RAMP

GENERATOR

600kHz

OSCILLATOR

V

C

2

LBI

+

ENABLE

BIAS

–

COMPARATOR

–

+

Σ

+

+

A2

7

200mV

FF

R

S

SHUTDOWN

+

–

A4

DRIVER

Q

A = 3

SHDN

3

LBO

8

SW

5

Q3

+

0.15Ω

–

4

1614 BD

GND

R5
40k

Q1

Figure 2. Block Diagram

5