LINER LT1614IS8

Final Electrical Specifications
LT1614
Inverting 600kHz
Switching Regulator
July 1998
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DESCRIPTION
FEATURES
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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.
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 VCESAT Switch: 295mV at 500mA
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APPLICATIONS
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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.
MR Head Bias
LCD Bias
GaAs FET Bias
Positive-to-Negative Conversion
The LT1614 is available in 8-lead MSOP or SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
5V to – 5V Converter
C3
1µF
L1
22µH
VIN
5V
5V to – 5V Converter Efficiency
90
L2
22µH
C1
33µF
100k
SHDN
LT1614
VC
NFB
GND
69.8k
D1
24.9k
+
+
VOUT
– 5V
200mA
SW
C2
33µF
1nF
C1, C2: AVX TAJB336M010
C3: AVX 1206CY106
D1: MBR0520
L1, L2: MURATA LQH3C220
EFFICIENCY (%)
80
VIN
70
60
50
1614 TA01
40
3
100
10
30
LOAD CURRENT (mA)
300
1614 TA02
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.
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LT1614
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ABSOLUTE
RATI GS
VIN, SHDN, LBO Voltage ......................................... 12V
SW Voltage ............................................... – 0.4V to 30V
NFB Voltage ............................................................ – 3V
VC Voltage ................................................................ 2V
LBI Voltage ............................................ 0V ≤ VLBI ≤ 1V
Current into FB Pin .............................................. ±1mA
Junction Temperature ........................................... 125°C
Operating Temperature Range
LT1614C ................................................. 0°C to 70°C
LT1614I ............................................. – 40°C to 85°C
Extended Commercial
Temperature Range (Note 1) .................. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
TOP VIEW
NFB
VC
SHDN
GND
1
2
3
4
8
7
6
5
LBO
LBI
VIN
SW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
LT1614CMS8
MS8 PART MARKING
TJMAX = 125°C, θJA = 160°C/W
LTEJ
NFB 1
8
LBO
VC 2
7
LBI
SHDN 3
6
VIN
GND 4
5
SW
LT1614CS8
LT1614IS8
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
1614
1614I
TJMAX = 125°C, θJA = 120°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
Commercial Grade 0°C to 70°C. VIN = 1.5V, VSHDN = VIN, TA = 25°C unless otherwise noted.
PARAMETER
CONDITIONS
MIN
Quiescent Current
VSHDN = 0V
Feedback Voltage
NFB Pin Bias Current (Note 2)
VNFB = –1.24V
Reference Line Regulation
1V ≤ VIN ≤ 2V
2V ≤ VIN ≤ 6V
Error Amp Transconductance
2
2
10
mA
µA
– 1.21
– 1.24
– 1.27
V
– 2.5
– 4.5
–7
µA
0.6
0.3
1.1
0.8
%/V
%/V
0.92
1
V
6
V
●
∆I = 5µA
16
µmhos
100
V/V
●
500
600
●
73
70
80
80
%
%
0.75
1.2
A
Maximum Duty Cycle
Switch Current Limit (Note 3)
1
5
UNITS
●
Error Amp Voltage Gain
Switching Frequency
MAX
●
Minimum Input Voltage
Maximum Input Voltage
TYP
750
kHz
LT1614
ELECTRICAL CHARACTERISTICS
Commercial Grade 0°C to 70°C. VIN = 1.5V, VSHDN = VIN, TA = 25°C unless otherwise noted.
PARAMETER
CONDITIONS
TYP
MAX
UNITS
Switch VCESAT
ISW = 500mA (25°C, 0°C)
ISW = 500mA (70°C)
MIN
295
350
400
mV
mV
Shutdown Pin Current
VSHDN = VIN
VSHDN = 0V
10
–5
20
– 10
µA
µA
200
210
215
mV
mV
LBI Threshold Voltage
●
190
185
LBO Output Low
ISINK = 10µA
0.1
0.25
V
LBO Leakage Current
VLBI = 250mV, VLBO = 5V
0.01
0.1
µA
LBI Input Bias Current (Note 4)
VLBI = 150mV
10
50
nA
Low-Battery Detector Gain
1MΩ Load
1000
Switch Leakage Current
VSW = 5V
0.01
3
V/V
TYP
MAX
1
5
2
10
µA
Industrial Grade – 40°C to 85°C. VIN = 1.5V, VSHDN = VIN unless otherwise noted.
PARAMETER
CONDITIONS
MIN
Quiescent Current
VSHDN = 0V
Feedback Voltage
●
– 1.21
– 1.24
– 1.27
●
–2
UNITS
mA
µA
V
NFB Pin Bias Current (Note 2)
VNFB = – 1.24V
– 4.5
– 7.5
µA
Reference Line Regulation
1V ≤ VIN ≤ 2V
2V ≤ VIN ≤ 6V
0.6
0.3
1.1
0.8
%/V
%/V
Minimum Input Voltage
– 40°C
85°C
1.1
0.8
1.25
1.0
V
V
6
V
Maximum Input Voltage
Error Amp Transconductance
●
∆I = 5µA
µmhos
16
Error Amp Voltage Gain
100
Switching Frequency
●
500
600
Maximum Duty Cycle
●
70
80
Switch Current Limit (Note 3)
0.75
V/V
750
kHz
%
1.2
A
Switch VCESAT
ISW = 500mA (– 40°C)
ISW = 500mA (85°C)
250
330
350
400
mV
mV
Shutdown Pin Current
VSHDN = VIN
VSHDN = 0V
10
–5
20
– 10
µA
µA
200
220
mV
LBI Threshold Voltage
●
180
LBO Output Low
ISINK = 10µA
0.1
0.25
V
LBO Leakage Current
VLBI = 250mV, VLBO = 5V
0.1
0.3
µA
LBI Input Bias Current (Note 4)
VLBI = 150mV
5
30
nA
Low-Battery Detector Gain
1MΩ Load
1000
Switch Leakage Current
VSW = 5V
0.01
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: 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.
V/V
µA
3
Note 2: Bias current flows out of NFB pin.
Note 3: Switch current limit guaranteed by design and/or correlation to
static tests. Duty cycle affects current limit due to ramp generator.
Note 4: Bias current flows out of LBI pin.
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LT1614
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PIN FUNCTIONS
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:
R1 =
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.
| VOUT | – 1.24
1.24 
+ 4.5 • 10 – 6
R2 
VIN (Pin 6): Supply Pin. Must have 1µF ceramic bypass
capacitor right at the pin, connected directly to ground.
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.
LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between ground and
700mV. Float this pin if not used.
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.
LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 10µA. A 1MΩ pull-up is recommended. Float
this pin if not used.
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BLOCK DIAGRAM
VIN
6
VIN
R5
40k
R6
40k
+
SHDN
VC
gm
2
ERROR
AMPLIFIER
+
SHUTDOWN
–
Q1
Q2
×10
LBI
BIAS
–
R4
140k
NFB
LBO
8
A1
–
200mV
A4
SW
COMPARATOR
–
1
VOUT
+
7
ENABLE
R3
30k
RAMP
GENERATOR
R1
(EXTERNAL)
+
Σ
+
DRIVER
FF
A2
5
Q3
Q
R
+
S
+
NFB
R2
(EXTERNAL)
3
A=3
600kHz
OSCILLATOR
0.15Ω
–
4
GND
4
1614 BD
LT1614
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APPLICATIONS INFORMATION
Shutdown Pin
3.3V
R1
The LT1614 has a Shutdown pin (SHDN) that must be
grounded to shut the device down or tied to a voltage equal
or greater than VIN to operate. The shutdown circuit is
shown in Figure 1.
VIN
LBI
LT1614
1M
+
LBO
R2
100k
Note that allowing SHDN to float turns on both the startup current (Q2) and the shutdown current (Q3) for VIN >
2VBE. The LT1614 doesn’t know what to do in this situation
and behaves erratically. SHDN voltage above VIN is allowed. This merely reverse-biases Q3’s base emitter junction, a benign condition.
TO PROCESSOR
–
200mV
INTERNAL
REFERENCE
GND
R1 =
VLB – 200mV
2µA
1614 F02
Figure 2. Setting Low-Battery Detector Trip Point
VIN
200k
Q3
R2
400k
SHDN
VIN
2N3906
SHUTDOWN
CURRENT
LBO
LT1614
VREF
200mV
200k
10k
START-UP
CURRENT
LBI
+
GND
10µF
1614 F03
Q2
Figure 3. Accessing 200mV Reference
Q1
1614 F01
Coupled Inductors
Low-Battery Detector
The LT1614’s low-battery detector is a simple PNP input
gain stage with an open collector NPN output. The negative input of the gain stage is tied internally to a 200mV
reference. The positive input is the LBI pin. Arrangement
as a low-battery detector is straightforward. Figure 2
details hookup. R1 and R2 need only be low enough in
value so that the bias current of the LBI pin doesn’t cause
large errors. For R2, 100k is adequate. The 200mV reference can also be accessed as shown in Figure 3.
The applications shown in this data sheet use two uncoupled inductors because the Murata units specified are
small and inexpensive. This topology can also be used
with a coupled inductor as shown in Figure 4. Be sure to
get the phasing right.
L1A
10µH
VIN
5V
+
VIN
C1
33µF
100k
C3
1µF
•
•
L1B
10µH
VOUT
– 5V
200mA
SW
SHDN
LT1614
VC
NFB
GND
69.8k
D1
24.9k
+
Figure 1. Shutdown Circuit
C2
33µF
1nF
C1, C2: AVX TAJB336M010
C3: AVX 1206CY106
D1: MBR0520
L1: COILTRONICS CTX10-1
1614 F04
Figure 4. 5V to – 5V Converter with Coupled Inductor
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LT1614
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TYPICAL APPLICATION
5V to – 15V/80mA DC/DC Converter
C1
1µF
L1
22µH
VIN
+
100k
VOUT
–15V
80mA
SW
SHDN
LT1614
NFB
VC
22µF
L2
22µH
GND
255k
D1
+
VIN
5V
24.9k
10µF
25V
1nF
C1: 25V, Y5V
D1: MBR0520
L1, L2: MURATA LQH3C220
1614 TA05
5V to – 15V Converter Efficiency
80
EFFICIENCY (%)
75
70
65
60
55
50
1
10
LOAD CURRENT (mA)
100
1614 TA06
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LT1614
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PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 ± 0.004*
(3.00 ± 0.102)
8
7 6
5
0.118 ± 0.004**
(3.00 ± 0.102)
0.192 ± 0.004
(4.88 ± 0.10)
1
2 3
4
0.040 ± 0.006
(1.02 ± 0.15)
0.007
(0.18)
0.034 ± 0.004
(0.86 ± 0.102)
0° – 6° TYP
SEATING
PLANE 0.012
(0.30)
0.0256
REF
(0.65)
TYP
0.021 ± 0.006
(0.53 ± 0.015)
0.006 ± 0.004
(0.15 ± 0.102)
MSOP (MS8) 1197
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
8
7
6
5
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
2
3
4
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
SO8 0996
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LT1614
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TYPICAL APPLICATION
3.3V to – 3.1V/200mA DC/DC Converter
C1
1µF
L1
22µH
VIN
SHDN
LT1614
VC
+
22µF
100k
VOUT
– 3.1V
200mA
SW
18.7k
D1
FB
GND
22µF
+
VIN
3.3V
L2
22µH
12.7k
1nF
C1: AVX1206CY106
D1: MBR0520
L1, L2: MURATA LQH3C220
1614 TA03
3.3V to – 3.1V Converter Efficiency
80
EFFICIENCY (%)
70
60
50
40
30
20
3
10
30
100
LOAD CURRENT (mA)
300
1614 TA04
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Low Quiescent Current High Efficiency DC/DC Converter
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Linear Technology Corporation
1614i LT/GP 0798 4K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1998