Final Electrical Specifications
LT1614
Inverting 600kHz
Switching Regulator
July 1998
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTION
The LT
®
1614 is a fixed frequency, inverting mode switch-
ing reglator that operates from an input voltage as low as
1V. Utilizing a low noise topology, the LT1614 can gener-
ate 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 low-
battery 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 induc-
tors and capacitors. Ceramic capacitors can be used in
many applications, eliminating the need for bulky tanta-
lum types.
The LT1614 is available in 8-lead MSOP or SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Better Regulation Than a Charge Pump
0.1
Ω
Effective Output Impedance
– 5V at 200mA from a 5V Input
600kHz Fixed Frequency Operation
Operates with V
IN
as Low as 1V
1mA Quiescent Current
Low Shutdown Current: 10µA
Low-Battery Detector
Low V
CESAT
Switch: 295mV at 500mA
APPLICATIONS
s
s
s
s
MR Head Bias
LCD Bias
GaAs FET Bias
Positive-to-Negative Conversion
TYPICAL APPLICATION
5V to – 5V Converter
L1
22µH
C3
1µF
L2
22µH
5V to – 5V Converter Efficiency
90
V
IN
5V
80
SHDN
LT1614
V
C
NFB
GND
EFFICIENCY (%)
+
V
IN
C1
33µF
100k
1nF
C1, C2: AVX TAJB336M010
C3: AVX 1206CY106
D1: MBR0520
L1, L2: MURATA LQH3C220
SW
69.8k
D1
24.9k
V
OUT
– 5V
200mA
C2
33µF
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
+
U
U
1
LT1614
ABSOLUTE
AXI U
RATI GS
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
V
IN
, SHDN, LBO Voltage ......................................... 12V
SW Voltage ............................................... – 0.4V to 30V
NFB Voltage ............................................................ – 3V
V
C
Voltage ................................................................ 2V
LBI Voltage ............................................ 0V
≤
V
LBI
≤
1V
Current into FB Pin ..............................................
±1mA
Junction Temperature ........................................... 125°C
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
NFB
V
C
SHDN
GND
1
2
3
4
8
7
6
5
LBO
LBI
V
IN
SW
TOP VIEW
LT1614CMS8
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 160°C/W
MS8 PART MARKING
LTEJ
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
Commercial Grade 0°C to 70°C. V
IN
= 1.5V, V
SHDN
= V
IN
, T
A
= 25°C unless otherwise noted.
PARAMETER
Quiescent Current
V
SHDN
= 0V
Feedback Voltage
NFB Pin Bias Current (Note 2)
Reference Line Regulation
Minimum Input Voltage
Maximum Input Voltage
Error Amp Transconductance
Error Amp Voltage Gain
Switching Frequency
Maximum Duty Cycle
q
q
q
q
CONDITIONS
V
NFB
= –1.24V
1V
≤
V
IN
≤
2V
2V
≤
V
IN
≤
6V
∆I
= 5µA
500
73
70
0.75
Switch Current Limit (Note 3)
2
U
U
W
W W
U
W
ORDER PART
NUMBER
NFB 1
V
C
2
SHDN 3
GND 4
8
7
6
5
LBO
LBI
V
IN
SW
LT1614CS8
LT1614IS8
S8 PACKAGE
8-LEAD PLASTIC SO
S8 PART MARKING
1614
1614I
T
JMAX
= 125°C,
θ
JA
= 120°C/W
MIN
TYP
1
5
MAX
2
10
– 1.27
–7
1.1
0.8
1
6
UNITS
mA
µA
V
µA
%/V
%/V
V
V
µmhos
V/V
– 1.21
– 2.5
– 1.24
– 4.5
0.6
0.3
0.92
16
100
600
80
80
1.2
q
750
kHz
%
%
A
LT1614
ELECTRICAL CHARACTERISTICS
Commercial Grade 0°C to 70°C. V
IN
= 1.5V, V
SHDN
= V
IN
, T
A
= 25°C unless otherwise noted.
PARAMETER
Switch V
CESAT
Shutdown Pin Current
LBI Threshold Voltage
q
CONDITIONS
I
SW
= 500mA (25°C, 0°C)
I
SW
= 500mA (70°C)
V
SHDN
= V
IN
V
SHDN
= 0V
MIN
TYP
295
10
–5
MAX
350
400
20
– 10
210
215
0.25
0.1
50
3
UNITS
mV
mV
µA
µA
mV
mV
V
µA
nA
V/V
µA
190
185
200
0.1
0.01
10
1000
0.01
LBO Output Low
LBO Leakage Current
LBI Input Bias Current (Note 4)
Low-Battery Detector Gain
Switch Leakage Current
I
SINK
= 10µA
V
LBI
= 250mV, V
LBO
= 5V
V
LBI
= 150mV
1MΩ Load
V
SW
= 5V
Industrial Grade – 40°C to 85°C. V
IN
= 1.5V, V
SHDN
= V
IN
unless otherwise noted.
PARAMETER
Quiescent Current
V
SHDN
= 0V
Feedback Voltage
NFB Pin Bias Current (Note 2)
Reference Line Regulation
Minimum Input Voltage
Maximum Input Voltage
Error Amp Transconductance
Error Amp Voltage Gain
Switching Frequency
Maximum Duty Cycle
Switch Current Limit (Note 3)
Switch V
CESAT
Shutdown Pin Current
LBI Threshold Voltage
LBO Output Low
LBO Leakage Current
LBI Input Bias Current (Note 4)
Low-Battery Detector Gain
Switch Leakage Current
I
SINK
= 10µA
V
LBI
= 250mV, V
LBO
= 5V
V
LBI
= 150mV
1MΩ Load
V
SW
= 5V
I
SW
= 500mA (– 40°C)
I
SW
= 500mA (85°C)
V
SHDN
= V
IN
V
SHDN
= 0V
q
q
q
q
CONDITIONS
MIN
TYP
1
5
MAX
2
10
– 1.27
– 7.5
1.1
0.8
1.25
1.0
6
UNITS
mA
µA
V
µA
%/V
%/V
V
V
V
µmhos
V/V
– 1.21
–2
– 1.24
– 4.5
0.6
0.3
1.1
0.8
V
NFB
= – 1.24V
1V
≤
V
IN
≤
2V
2V
≤
V
IN
≤
6V
– 40°C
85°C
q
q
∆I
= 5µA
500
70
0.75
16
100
600
80
1.2
250
330
10
–5
180
200
0.1
0.1
5
1000
0.01
3
350
400
20
– 10
220
0.25
0.3
30
750
kHz
%
A
mV
mV
µA
µA
mV
V
µA
nA
V/V
µA
The
q
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.
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.
3
LT1614
PIN FUNCTIONS
NFB (Pin 1):
Negative Feedback Pin. Reference voltage is
– 1.24V. Connect resistive divider tap here. The sug-
gested value for R2 is 24.9k. Set R1 and R2 according to:
R1
=
| V
OUT
| – 1.24
1.24
+
4.5 • 10
– 6
R2
V
C
(Pin 2):
Compensation Pin for Error Amplifier. Con-
nect a series RC from this pin to ground. Typical values
are 100kΩ and 1nF. Minimize trace area at V
C
.
SHDN (Pin 3):
Shutdown. Ground this pin to turn off
switcher. Must be tied to V
IN
(or higher voltage) to enable
switcher. Do not float the SHDN pin.
BLOCK DIAGRAM
V
IN
6
R5
40k
Q1
V
OUT
R1
(EXTERNAL)
NFB
R2
(EXTERNAL)
NFB
RAMP
GENERATOR
600kHz
OSCILLATOR
4
+
+
Σ
+
–
W
U
U
U
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.
V
IN
(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 refer-
ence. Voltage on LBI must stay between ground and
700mV. Float this pin if not used.
LBO (Pin 8):
Low-Battery Detector Output. Open collec-
tor, can sink 10µA. A 1MΩ pull-up is recommended. Float
this pin if not used.
V
IN
R6
40k
+
g
m
V
C
2
LBI
SHDN
SHUTDOWN
3
–
Q2
×10
R3
30k
R4
140k
1
ERROR
AMPLIFIER
+
ENABLE
BIAS
7
+
–
A4
LBO
8
–
A1
200mV
COMPARATOR
FF
R
A2
S
Q
DRIVER
SW
5
Q3
+
A=3
0.15Ω
–
4
GND
1614 BD
LT1614
APPLICATIONS INFORMATION
Shutdown Pin
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 V
IN
to operate. The shutdown circuit is
shown in Figure 1.
Note that allowing SHDN to float turns on both the start-
up current (Q2) and the shutdown current (Q3) for V
IN
>
2V
BE
. The LT1614 doesn’t know what to do in this situation
and behaves erratically. SHDN voltage above V
IN
is al-
lowed. This merely reverse-biases Q3’s base emitter junc-
tion, a benign condition.
V
IN
Q3
R2
400k
SHDN
200k
START-UP
CURRENT
Q2
Q1
1614 F01
SHUTDOWN
CURRENT
Figure 1. Shutdown Circuit
Low-Battery Detector
The LT1614’s low-battery detector is a simple PNP input
gain stage with an open collector NPN output. The nega-
tive 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 refer-
ence can also be accessed as shown in Figure 3.
100k
1nF
24.9k
C1, C2: AVX TAJB336M010
C3: AVX 1206CY106
D1: MBR0520
L1: COILTRONICS CTX10-1
Figure 4. 5V to – 5V Converter with Coupled Inductor
+
U
W
U
U
3.3V
R1
LBI
R2
100k
V
IN
LT1614
1M
LBO
TO PROCESSOR
+
–
200mV
INTERNAL
REFERENCE
GND
1614 F02
R1 =
V
LB
– 200mV
2µA
Figure 2. Setting Low-Battery Detector Trip Point
200k
2N3906
V
REF
200mV
10k
LBO
V
IN
LT1614
+
10µF
LBI
GND
1614 F03
Figure 3. Accessing 200mV Reference
Coupled Inductors
The applications shown in this data sheet use two un-
coupled 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
C3
1µF
L1B
10µH
V
IN
5V
•
SW
69.8k
•
+
V
IN
C1
33µF
SHDN
LT1614
V
C
NFB
GND
V
OUT
– 5V
200mA
D1
C2
33µF
1614 F04
5
无线连接
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
