LT1614
Inverting 600kHz
Switching Regulator
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
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
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.
APPLICATIO S
s
s
s
s
MR Head Bias
LCD Bias
GaAs FET Bias
Positive-to-Negative Conversion
TYPICAL APPLICATIO
L1
22µH
C3
1µF
V
IN
5V
L2
22µH
5V to – 5V Converter Efficiency
90
+
V
IN
C1
33µF
100k
1nF
SW
69.8k
D1
24.9k
EFFICIENCY (%)
C1, C2: AVX TAJB336M010
C3: TAIYO YUDEN EMK316BJ105MF
D1: MBR0520
L1, L2: MURATA LQH3C220
Figure 1. 5V to – 5V/200mA Converter
+
SHDN
LT1614
V
C
NFB
GND
V
OUT
– 5V
200mA
C2
33µF
80
70
60
1614 TA01
50
40
3
100
10
30
LOAD CURRENT (mA)
300
1614 TA02
U
U
U
1
LT1614
ABSOLUTE
AXI U
RATI GS
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
LT1614IMS8
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 160°C/W
MS8 PART MARKING
LTID
LTJB
Consult factory for Military grade parts.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. Commercial Grade 0°C to 70°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 3)
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
ELECTRICAL CHARACTERISTICS
CONDITIONS
V
NFB
= –1.24V
1V
≤
V
IN
≤
2V
2V
≤
V
IN
≤
6V
∆I
= 5µA
500
73
70
0.75
Switch Current Limit (Note 4)
2
U
U
W
W W
U
W
(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
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
T
JMAX
= 125°C,
θ
JA
= 120°C/W
S8 PART MARKING
1614
1614I
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
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. Commercial Grade 0°C to 70°C. V
IN
= 1.5V, V
SHDN
= V
IN
unless
otherwise noted.
PARAMETER
Switch V
CESAT
Shutdown Pin Current
LBI Threshold Voltage
q
ELECTRICAL CHARACTERISTICS
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 5)
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 3)
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 4)
Switch V
CESAT
Shutdown Pin Current
LBI Threshold Voltage
LBO Output Low
LBO Leakage Current
LBI Input Bias Current (Note 5)
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
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.
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.
3
LT1614
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current in Shutdown
10
10
QUIESCENT CURRENT (µA)
SHDN BIAS CURRENT (µA)
8
LBI BIAS CURRENT (nA)
6
4
2
0
0
1
2
3
INPUT VOLTAGE (V)
Switch V
CESAT
vs Current
500
T
A
= 25°C
210
208
REFERENCE VOLTAGE (mV)
400
V
CESAT
(mV)
300
202
200
198
196
194
192
FREQUENCY (kHz)
200
100
0
0
100
500
200
300
400
SWITCH CURRENT (mA)
Quiescent Current vs
Temperature*
6
5
4
3
V
IN
= 3V
2
1
0
–40
V
IN
= 1.25V
NFB PIN BIAS CURRENT (µA)
QUIESCENT CURRENT (mA)
V
NFB
(V)
–20
0
20
40
TEMPERATURE (°C)
*Includes diode leakage
4
U W
4
5
1614 G01
Shutdown Pin Bias Current vs
Input Voltage
16
14
8
12
10
8
6
4
2
0
0
1
2
3
INPUT VOLTAGE (V)
4
5
1614 G02
LBI Bias Current vs Temperature
6
4
2
0
–50
–25
50
25
TEMPERATURE (°C)
0
75
100
1614 G03
LBI Reference vs Temperature
900
Oscillator Frequency vs
Input Voltage
206
204
800
85°C
700
25°C
–40°C
600
500
600
190
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
1614 G05
400
1
2
3
INPUT VOLTAGE (V)
4
5
1614 G06
1614 G04
NFB Pin Bias Current vs
Temperature
6
5
4
3
2
–1.220
1
0
–50
–1.215
–1.245
–1.240
–1.235
–1.230
–1.225
V
NFB
vs Temperature
V
IN
= 5V
60
80
1614 G07
–25
0
25
50
TEMPERATURE (°C)
75
100
1614 G08
–1.210
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1614 G09
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:
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. The low-battery detector is disabled
when SHDN is low. LBO is high-Z in this state.
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
Figure 2. Block Diagram
+
+
Σ
+
–
W
U
U
U
V
IN
R6
40k
+
g
m
V
C
2
LBI
SHDN
SHUTDOWN
3
–
Q2
×10
R3
30k
R4
140k
1
ERROR
AMPLIFIER
A1
BIAS
+
ENABLE
7
+
–
A4
LBO
8
–
200mV
COMPARATOR
FF
R
A2
S
Q
DRIVER
SW
5
Q3
+
A=3
0.15Ω
–
4
GND
1614 BD
5
FPGA/CPLD
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