LT1614CMS8#TRPBF [Linear]
LT1614 - Inverting 600kHz Switching Regulator; Package: MSOP; Pins: 8; Temperature Range: 0°C to 70°C;
| 型号： | LT1614CMS8#TRPBF |
| 厂家： | 
Linear |
| 描述： | LT1614 - Inverting 600kHz Switching Regulator; Package: MSOP; Pins: 8; Temperature Range: 0°C to 70°C 稳压器 开关 |
| 文件： | 总16页 (文件大小：262K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1614
Inverting 600kHz
Switching Regulator
U
DESCRIPTIO
FEATURES
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
tolessthan10µA.NoloadquiescentcurrentoftheLT1614
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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APPLICATIO S
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.
■
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 APPLICATIO
C3
1µF
L1
22µH
L2
22µH
5V to –5V Converter Efficiency
V
IN
90
5V
V
OUT
V
SW
IN
–5V
80
70
60
50
40
+
SHDN
LT1614
C1
200mA
69.8k
24.9k
33µF
C2
33µF
D1
V
C
NFB
+
GND
100k
1nF
1614 TA01
C1, C2: AVX TAJB336M010
C3: TAIYO YUDEN EMK316BJ105MF
D1: MBR0520
L1, L2: MURATA LQH3C220
3
10
30
100
300
Figure 1. 5V to –5V/200mA Converter
LOAD CURRENT (mA)
1614 TA02
1
LT1614
ABSOLUTE AXI U 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
W W W
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(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
W
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/O
PACKAGE RDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
TOP VIEW
LT1614CS8
LT1614CMS8
NFB
1
2
3
4
8
7
6
5
LBO
LBI
NFB
1
2
3
4
8 LBO
7 LBI
LT1614IS8
LT1614IMS8
V
C
V
C
6 V
SHDN
GND
IN
5 SW
SHDN
GND
V
IN
MS8 PACKAGE
8-LEAD PLASTIC MSOP
SW
MS8 PART MARKING
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 160°C/W
LTID
LTJB
1614
1614I
TJMAX = 125°C, θJA = 120°C/W
Consult factory for Military grade parts.
The ● denotes the specifications which apply over the full operating
ELECTRICAL CHARACTERISTICS
otherwise noted.
temperature range, otherwise specifications are at TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.5V, VSHDN = VIN unless
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Quiescent Current
1
5
2
10
mA
µA
V
= 0V
SHDN
Feedback Voltage
●
●
–1.21
–2.5
–1.24
–4.5
–1.27
–7
V
NFB Pin Bias Current (Note 3)
Reference Line Regulation
V
= –1.24V
µA
NFB
1V ≤ V ≤ 2V
2V ≤ V ≤ 6V
0.6
0.3
1.1
0.8
%/V
%/V
IN
IN
Minimum Input Voltage
Maximum Input Voltage
Error Amp Transconductance
Error Amp Voltage Gain
Switching Frequency
0.92
1
6
V
V
●
∆I = 5µA
16
µmhos
V/V
100
600
●
●
500
750
kHz
Maximum Duty Cycle
73
70
80
80
%
%
Switch Current Limit (Note 4)
0.75
1.2
A
2
LT1614
ELECTRICAL CHARACTERISTICS
otherwise noted.
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.5V, VSHDN = VIN unless
PARAMETER
Switch V
CONDITIONS
MIN
TYP
MAX
UNITS
I
I
= 500mA (25°C, 0°C)
= 500mA (70°C)
295
350
400
mV
mV
CESAT
SW
SW
Shutdown Pin Current
LBI Threshold Voltage
V
V
= V
= 0V
10
–5
20
–10
µA
µA
SHDN
SHDN
IN
190
185
200
210
215
mV
mV
●
LBO Output Low
I
= 10µA
0.1
0.01
10
0.25
0.1
50
V
µA
SINK
LBO Leakage Current
V
V
= 250mV, V
= 5V
LBO
LBI
LBI
LBI Input Bias Current (Note 5)
Low-Battery Detector Gain
Switch Leakage Current
= 150mV
nA
1MΩ Load
= 5V
1000
0.01
V/V
µA
V
3
SW
Industrial Grade –40°C to 85°C. VIN = 1.5V, VSHDN = VIN unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Quiescent Current
1
5
2
10
mA
µA
V
SHDN
= 0V
Feedback Voltage
●
●
–1.21
–2
–1.24
–4.5
–1.27
–7.5
V
NFB Pin Bias Current (Note 3)
Reference Line Regulation
V
= –1.24V
µA
NFB
1V ≤ V ≤ 2V
2V ≤ V ≤ 6V
0.6
0.3
1.1
0.8
%/V
%/V
IN
IN
Minimum Input Voltage
–40°C
85°C
1.1
0.8
1.25
1.0
V
V
Maximum Input Voltage
Error Amp Transconductance
Error Amp Voltage Gain
Switching Frequency
●
6
V
µmhos
V/V
∆I = 5µA
16
100
600
80
●
●
500
70
750
kHz
Maximum Duty Cycle
%
Switch Current Limit (Note 4)
0.75
1.2
A
Switch V
I
I
= 500mA (–40°C)
= 500mA (85°C)
250
330
350
400
mV
mV
CESAT
SW
SW
Shutdown Pin Current
V
SHDN
V
SHDN
= V
= 0V
10
–5
20
–10
µA
µA
IN
LBI Threshold Voltage
LBO Output Low
●
180
200
0.1
220
0.25
0.3
mV
V
I
= 10µA
SINK
LBO Leakage Current
V
V
= 250mV, V
= 150mV
= 5V
LBO
0.1
µA
nA
V/V
µA
LBI
LBI
LBI Input Bias Current (Note 5)
Low-Battery Detector Gain
Switch Leakage Current
5
30
1MΩ Load
= 5V
1000
0.01
V
3
SW
Note 1: Absolute Maximum Ratings are those values beyond which the life
Note 3: Bias current flows out of NFB pin.
of a device may be impaired.
Note 4: Switch current limit guaranteed by design and/or correlation to
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.
static tests. Duty cycle affects current limit due to ramp generator.
Note 5: Bias current flows out of LBI pin.
3
LT1614
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Pin Bias Current vs
Input Voltage
Quiescent Current in Shutdown
LBI Bias Current vs Temperature
10
8
10
8
16
14
12
10
8
6
6
4
4
6
4
2
2
2
0
0
0
–25
0
50
0
1
2
3
4
5
0
1
2
3
4
5
–50
75
100
25
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
1614 G01
1614 G02
1614 G03
Oscillator Frequency vs
Input Voltage
Switch VCESAT vs Current
LBI Reference vs Temperature
500
210
900
800
700
600
500
400
T
= 25°C
A
208
206
204
202
200
198
196
194
192
190
25°C
85°C
400
300
200
–40°C
100
0
0
200
300
400
500
600
–50
–25
25
50
75
100
1
2
3
4
100
0
5
SWITCH CURRENT (mA)
TEMPERATURE (°C)
INPUT VOLTAGE (V)
1614 G04
1614 G05
1614 G06
Quiescent Current vs
Temperature*
NFB Pin Bias Current vs
Temperature
VNFB vs Temperature
6
5
4
3
2
1
0
6
5
4
3
2
1
0
–1.245
–1.240
–1.235
–1.230
–1.225
–1.220
–1.215
–1.210
V
= 1.25V
IN
V
= 3V
IN
V
= 5V
IN
–40 –20
0
20
40
60
80
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1614 G07
1614 G08
1614 G09
*Includes diode leakage
4
LT1614
U
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PIN FUNCTIONS
NFB(Pin1):NegativeFeedbackPin. Referencevoltageis
–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.
| VOUT | –1.24
R1=
VIN (Pin 6): Supply Pin. Must have 1µF ceramic bypass
capacitor right at the pin, connected directly to ground.
1.24
+ 4.5 •10–6
R2
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.
VC (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 VC.
LBO (Pin 8): Low-Battery Detector Output. Open collec-
tor,cansink10µA.A1MΩpull-upisrecommended.Float
this pin if not used. The low-battery detector is disabled
when SHDN is low. LBO is high-Z in this state.
SHDN (Pin 3): Shutdown. Ground this pin to turn off
switcher. MustbetiedtoVIN (orhighervoltage)toenable
switcher. Do not float the SHDN pin.
W
BLOCK DIAGRAM
V
IN
6
V
IN
+
–
R5
40k
R6
40k
SHDN
V
C
SHUTDOWN
3
g
m
2
LBI
7
ERROR
AMPLIFIER
A1
+
–
+
–
LBO
8
Q1
Q2
ENABLE
200mV
×10
BIAS
R3
30k
A4
R4
140k
SW
5
COMPARATOR
–
+
1
DRIVER
FF
RAMP
NFB
GENERATOR
V
OUT
Q3
R
Q
+
Σ
S
R1
A2
+
(EXTERNAL)
+
A = 3
–
NFB
0.15Ω
R2
600kHz
OSCILLATOR
(EXTERNAL)
4
GND
1614 BD
Figure 2. Block Diagram
5
LT1614
U
OPERATIO
The LT1614 combines a current mode, fixed frequency
PWM architecture with a –1.23V reference to directly
regulate negative outputs. Operation can be best under-
stood by referring to the block diagram of Figure 2. Q1 and
Q2 form a bandgap reference core whose loop is closed
around the output of the converter. The driven reference
point is the lower end of resistor R4, which normally sits
at a voltage of –1.23V. As the load current changes, the
NFB pin voltage also changes slightly, driving the output
of gm amplifier A1. Switch current is regulated directly on
a cycle-to-cycle basis by A1’s output. The flip-flop is set at
the beginning of each cycle, turning on the switch. When
thesummationofasignalrepresentingswitchcurrentand
a ramp generator (introduced to avoid subharmonic oscil-
lations at duty factors greater than 50%) exceeds the VC
signal, comparator A2 changes stage, resetting the flip-
flop and turning off the switch. Output voltage decreases
(the magnitude increases) as switch current is increased.
The output, attenuated by external resistor divider R1 and
R2, appears at the NFB pin, closing the overall loop.
Frequencycompensationisprovidedexternallybyaseries
RC connected from the VC pin to ground. Typical values
are 100k and 1nF. Transient response can be tailored by
adjustment of these values.
The LT1614 can work in either of two topologies. The
simpler topology appends a capacitive level shift to a
boost converter, generating a negative output voltage,
which is directly regulated. The circuit schematic is de-
tailed in Figure 3. Only one inductor is required, and the
two diodes can be in a single SOT-23 package. Output
noise is the same as in a boost converter, because current
is delivered to the output only during the time when the
LT1614’s internal switch is on.
If D2 is replaced by an inductor, as shown in Figure 4, a
higherperformancesolutionresults.Thisconvertertopol-
ogy was developed by Professor S. Cuk of the California
Institute of Technology in the 1970s. A low ripple voltage
results with this topology due to inductor L2 in series with
theoutput. Abruptchangesinoutputcapacitorcurrentare
eliminated because the output inductor delivers current to
the output during both the off-time and the on-time of the
LT1614switch. Withproperlayoutandhighqualityoutput
capacitors, output ripple can be as low as 1mVP–P
.
The operation of Cuk’s topology is shown in Figures 5
and 6. During the first switching phase, the LT1614’s
switch, represented by Q1, is on. There are two current
loops in operation. The first loop begins at input capacitor
C1, flows through L1, Q1 and back to C1. The second loop
flows from output capacitor C3, through L2, C2, Q1 and
back to C3. The output current from RLOAD is supplied by
L2 and C3. The voltage at node SW is VCESAT and at node
SWX the voltage is –(VIN + |VOUT|). Q1 must conduct both
L1 and L2 current. C2 functions as a voltage level shifter,
with an approximately constant voltage of (VIN + |VOUT|)
As load current is decreased, the switch turns on for a
shorter period each cycle. If the load current is further
decreased, the converter will skip cycles to maintain
output voltage regulation.
across it.
C2
C2
1µF
1µF
D2
L1
L1
L2
V
V
IN
IN
D1
D1
+
V
IN
SW
V
IN
SW
C1
+
–V
OUT
–V
OUT
LT1614
LT1614
C1
R1
R1
SHUTDOWN
SHDN
SHUTDOWN
SHDN
V
C
NFB
V
C
NFB
C3
C3
+
+
GND
GND
R2
10k
R2
10k
10Ok
1nF
10Ok
1nF
1614 F03
1614 F04
Figure 3. Direct Regulation of Negative Output
Using Boost Converter with Charge Pump
Figure 4. L2 Replaces D2 to Make Low Output Ripple
Inverting Topology. Coupled or Uncoupled Inductors Can
Be Used. Follow Phasing If Coupled for Best Results
6
LT1614
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OPERATIO
When Q1 turns off during the second phase of switching,
theSWXnodevoltageabruptlyincreasesto(VIN +|VOUT|).
TheSWnodevoltageincreasestoVD (about350mV).Now
current in the first loop, begining at C1, flows through L1,
C2, D1 and back to C1. Current in the second loop flows
from C3 through L2, D1 and back to C3. Load current
continues to be supplied by L2 and C3.
rents are dumped into the ground plane as drawn in
Figures 4, 5 and 6. This single layout technique can
virtually eliminate high frequency “spike” noise so often
present on switching regulator outputs.
Output ripple voltage appears as a triangular waveform
ridingonVOUT. Ripplemagnitudeequalstheripplecurrent
of L2 multiplied by the equivalent series resistance (ESR)
of output capacitor C3. Increasing the inductance of L1
and L2 lowers the ripple current, which leads to lower
output voltage ripple. Decreasing the ESR of C3, by using
ceramic or other low ESR type capacitors, lowers output
ripple voltage. Output ripple voltage can be reduced to
arbitrarily low levels by using large value inductors and
low ESR, high value capacitors.
An important layout issue arises due to the chopped
natureofthecurrentsflowinginQ1andD1.Iftheyareboth
tied directly to the ground plane before being combined,
switching noise will be introduced into the ground plane.
Itisalmostimpossibletogetridofthisnoise,oncepresent
in the ground plane. The solution is to tie D1’s cathode to
the ground pin of the LT1614 before the combined cur-
V
–(V
+
V
OUT
)
CESAT
IN
C2
L1
L2
SW
SWX
V
IN
–V
OUT
D1
Q1
+
C1
C3
R
LOAD
+
1614 F05
Figure 5. Switch-On Phase of Inverting Converter. L1 and L2 Current Have Positive dI/dt
V
+
V
+ V
V
D
IN
OUT
D
C2
L1
L2
SW
SWX
V
–V
OUT
IN
D1
Q1
+
C1
C3
R
LOAD
+
1614 F06
Figure 6. Switch-Off Phase of Inverting Converter. L1 and L2 Current Have Negative dI/dt
7
LT1614
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OPERATIO
Transient Response
In Figure 10, output capacitor C3 is replaced by a ceramic
unit.TheselargevaluecapacitorshaveESRof2mΩorless
and result in very low output ripple. A 1nF capacitor, CPL,
connected across R1 reduces output perburbation due to
load step. This keeps the output voltage within 5% of
steady-state value. Figure 11 pictures the output and
switch nodes at 500ns per division. Output ripple is about
5mVP-P. Again, goodlayoutisessentialtoachievethislow
noise performance.
The inverting architecture of the LT1614 can generate a
very low ripple output voltage. Recently available high
value ceramic capacitors can be used successfully in
LT1614 designs. The addition of a phase lead capacitor,
CPL, reduces output perturbations due to load steps when
lower value ceramic capacitors are used and connected in
parallel with feedback resistor R1. Figure 7 shows an
LT1614 inverting converter with resistor loads RL1 and
RL2. RL1 is connected across the output, while RL2 is
switched in externally via a pulse generator. Output volt-
age waveforms are pictured in subsequent figures, illus-
trating the performance of output capacitor type.
Layout
The LT1614 switches current at high speed, mandating
careful attention to layout for best performance. You will
not get advertised performance with careless layout. Figure 12
shows recommended component placement. Follow this
closely in your printed circuit layout. The cut ground
copper at D1’s cathode is essential to obtain the low noise
achieved in Figures 10 and 11’s oscillographs. Input
bypass capacitor C1 should be placed close to the LT1614
as shown. The load should connect directly to output
capacitor C2 for best load regulation. You can tie the local
ground into the system ground plane at C3’s ground
terminal.
Figure 8 shows the output voltage with a 50mA to 200mA
load step, using an AVX TAJ “B” case 33µF tantalum
capacitor at the output. Output perturbation is approxi-
mately 250mV as the load changes from 50mA to 200mA.
Steady-state ripple voltage is 40mVP–P, due to L1’s ripple
current and C3’s ESR. Figure 9 pictures the output voltage
and switch pin voltage at 500ns per division. Note the
absence of high frequency spikes at the output. This is
easily repeatable with proper layout, described in the next
section.
COMPONENT SELECTION
Inductors
C2
1µF
L1
22µH
L2
22µH
V
IN
5V
Each of the two inductors used with the LT1614 should
have a saturation current rating (where inductance is
approximately 70% of zero current inductance) of ap-
proximately 0.4A or greater. If the device is used in
“charge pump” mode, where there is only one inductor,
then its rating should be 0.75A or greater. DCR of the
inductors should be 0.4Ω or less. 22µH inductors are
called out in the applications schematics because these
Murata units are physically small and inexpensive. In-
creasing the inductance will lower ripple current, increas-
ing available output current. A coupled inductor of 33µH,
such as Coiltronics CTX33-2, will provide 290mA at –5V
from a 5V input. Inductance can be reduced if operating
from a supply voltage below 3V. Table 1 lists several
inductors that will work with the LT1614, although this is
not an exhaustive list. There are many magnetics vendors
whose components are suitable.
D1
–V
OUT
V
SW
IN
SHDN
R
C
PL
1nF
L2
33Ω
R1
+
LT1614
GND
69.8k
R
L1
100Ω
C1
V
C
NFB
C
C3
+
R2
24.9k
R
C
C
C1: AVX TAJB226M010
C2: TAIYO YUDEN LMK212BJ105MG
C3: AVX TAJB336M006 OR MURATA (SEE TEXT)
D1: MBR0520
L1, L2: MURATA LQH3C220
1614 F07
Figure 7. Switching RL2 Provides 50mA to 200mA
Load Step for LT1614 5V to –5V Converter
8
LT1614
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OPERATIO
VOUT
100mV/DIV
AC COUPLED
VOUT
20mV/DIV
AC COUPLED
VSW
5V/DIV
200mA
ILOAD
50mA
500µs/DIV
1614 F08
500ns/DIV
1614 F09
Figure 8. Load Step Response of LT1614
with 33µF Tantalum Output Capacitor
Figure 9. 33µF “B” Case Tantalum Capacitor Has ESR Resulting
in 40mVP-P Voltage Ripple at Output with 200mA Load
VOUT
100mV/DIV
AC COUPLED
VOUT
10mV/DIV
AC COUPLED
VSW
5V/DIV
200mA
ILOAD
50mA
500µs/DIV
1614 F10
500ns/DIV
1614 F11
Figure 10. Replacing C3 with 22µF Ceramic Capacitor
Lowers Output Voltage Ripple. 1nF Phase-Lead Capacitor
in Parallel with R1 Lowers Transient Excursion
Figure 11. 22µF Ceramic Capacitor at
Output Reduces Output Ripple Voltage
C1
+
SHUTDOWN
V
IN
1
8
R
C
C
R1
R2
2
3
4
7
6
5
L1
C
D1
GND
C3
C2
1614 F12
L2
V
OUT
Figure 12. Suggested Component Placement. Note: Cut in Ground Copper at D1’s Cathode
9
LT1614
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OPERATIO
Capacitors
critical, and either tantalum or ceramic can be used with
little trade-off in circuit performance. Some capacitor
types appropriate for use with the LT1614 are listed in
Table 2.
As described previously, ceramic capacitors can be used
with the LT1614. For lower cost applications, small tanta-
lum units can be used. A value of 22µF is acceptable,
althoughlargercapacitancevaluescanbeused. ESRisthe
most important parameter in selecting an output capaci-
tor. The “flying” capacitor (C2 in the schematic figures)
should be a 1µF ceramic type. An X5R or X7R dielectric
should be used to avoid capacitance decreasing severely
with applied voltage. The input bypass capacitor is less
Diodes
ASchottkydiodeisrecommendedforusewiththeLT1614.
The Motorola MBR0520 is a very good choice. Where the
input to output voltage differential exceeds 20V, use the
MBR0530 ( a 30V diode).
Table 1. Inductor Vendors
VENDOR
PHONE
URL
PART
COMMENT
Sumida
(847) 956-0666
www.sumida.com
CLS62-22022
CD43-470
22µH Coupled
47µH
Murata
(404) 436-1300
(407) 241-7876
www.murata.com
LQH3C-220
CTX20-1
22µH, 2mm Height
Coiltronics
www.coiltronics.com
20µH Coupled, Low DCR
Table 2. Capacitor Vendors
VENDOR
Taiyo Yuden
AVX
PHONE
URL
PART
COMMENT
(408) 573-4150
(803) 448-9411
www.t-yuden.com
www.avxcorp.com
Ceramic Caps
X5R Dielectric
Ceramic Caps
Tantalum Caps
Murata
(404) 436-1300
www.murata.com
Ceramic Caps
10
LT1614
U
W U U
APPLICATIONS INFORMATION
Shutdown Pin
3.3V
R1
V
IN
LT1614
LBO
The LT1614 has a Shutdown pin (SHDN) that must be
groundedtoshutthedevicedownortiedtoavoltageequal
or greater than VIN to operate. The shutdown circuit is
shown in Figure 13.
1M
LBI
+
–
TO PROCESSOR
R2
100k
200mV
V
LB
– 200mV
2µA
Note that allowing SHDN to float turns on both the start-
up current (Q2) and the shutdown current (Q3) for VIN >
2VBE.TheLT1614doesn’tknowwhattodointhissituation
and behaves erratically. SHDN voltage above VIN is al-
lowed. This merely reverse-biases Q3’s base emitter junc-
tion, a benign condition. The low-battery detector is dis-
abled when SHDN is low.
R1 =
INTERNAL
REFERENCE
GND
1614 F14
Figure 14. Setting Low-Battery Detector Trip Point
V
IN
200k
V
IN
2N3906
REF
LBO
LBI
Q3
LT1614
R2
V
SHUTDOWN
CURRENT
400k
200mV
+
SHDN
GND
10k
10µF
200k
1614 F15
START-UP
CURRENT
Figure 15. Accessing 200mV Reference
Q2
Q1
Coupled Inductors
1614 F13
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 16. Be sure to
get the phasing right.
Figure 13. 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 14
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-
encecanalsobeaccessedasshowninFigure15. Thelow-
battery detect is not operative when the device is shut
down.
C3
1µF
L1A
10µH
L1B
10µH
V
•
•
IN
5V
V
OUT
V
SW
IN
–5V
+
SHDN
C1
33µF
200mA
69.8k
LT1614
C2
33µF
D1
V
C
NFB
+
GND
24.9k
100k
1nF
1614 F16
C1, C2: AVX TAJB336M010
C3: AVX 1206CY106
D1: MBR0520
L1: COILTRONICS CTX10-1
Figure 16. 5V to –5V Converter with Coupled Inductor
11
LT1614
TYPICAL APPLICATIO S
U
5V to –15V/80mA DC/DC Converter
C1
1µF
L1
22µH
L2
22µH
V
IN
5V
V
OUT
V
SW
IN
–15V
+
SHDN
80mA
255k
22µF
LT1614
10µF
25V
D1
NFB
V
C
+
GND
24.9k
100k
1nF
1614 TA05
C1: 25V, Y5V
D1: MBR0520
L1, L2: MURATA LQH3C220
5V to –15V Converter Efficiency
80
75
70
65
60
55
50
1
10
100
LOAD CURRENT (mA)
1614 TA06
12
LT1614
U
TYPICAL APPLICATIO S
3.3V to –3.1V/200mA DC/DC Converter
C1
1µF
L1
22µH
L2
22µH
V
IN
3.3V
V
OUT
V
SW
FB
IN
–3.1V
SHDN
+
200mA
18.7k
LT1614
22µF
D1
V
C
22µF
+
GND
12.7k
100k
1nF
1614 TA03
C1: AVX1206CY106
D1: MBR0520
L1, L2: MURATA LQH3C220
3.3V to –3.1V Converter Efficiency
80
70
60
50
40
30
20
3
10
30
100
300
LOAD CURRENT (mA)
1614 TA04
13
LT1614
U
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
0.040 ± 0.006
(1.02 ± 0.15)
0.034 ± 0.004
(0.86 ± 0.102)
0.007
(0.18)
0° – 6° TYP
0.118 ± 0.004**
(3.00 ± 0.102)
SEATING
PLANE
0.193 ± 0.006
(4.90 ± 0.15)
0.012
(0.30)
REF
0.021 ± 0.006
(0.53 ± 0.015)
0.006 ± 0.004
(0.15 ± 0.102)
0.0256
(0.65)
BSC
MSOP (MS8) 1098
1
2
3
4
* 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
14
LT1614
U
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
7
5
8
6
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
3
4
2
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.050
(1.270)
BSC
0.014 – 0.019
(0.355 – 0.483)
TYP
*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
SO8 1298
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
15
LT1614
TYPICAL APPLICATIO S
U
5V to –5V Converter Uses All Ceramic Capacitors
C3
1µF
L1
22µH
L2
22µH
V
IN
3V TO 5V
V
OUT
V
SW
IN
–5V
200mA
SHDN
C1
1nF
69.8k
24.9k
LT1614
4.7µF
C2
10µF
D1
V
C
NFB
GND
100k
1nF
1614 TA07
C1: TAIYO YUDEN LMK316BJ475ML
C2: TAIYO YUDEN JMK316BJ106ML
C3: TAIYO YUDEN EMK316BJ105MF
D1: MOTOROLA MBR0520
L1, L2: MURATA LQH3C220 OR SUMIDA CD43-220
Efficiency vs Load Current
80
75
70
65
60
55
50
45
40
V
V
= 3V
IN
OUT
= –5V
1
10
LOAD CURRENT (mA)
100
1614 TA08
RELATED PARTS
PART NUMBER
LTC®1174
LT1307
DESCRIPTION
COMMENTS
High Efficiency Step-Down and Inverting DC/DC Converter
Single Cell Micropower 600kHz PWM DC/DC Converter
Single Cell High Current Micropower 600kHz Boost Converter
Micropower Boost DC/DC Converter
Selectable I
= 300mA or 600mA
PEAK
3.3V at 75mA from 1 Cell, MSOP Package
5V at 1A from a Single Li-Ion Cell, SO-8 Package
Programmable Peak Current Limit, MSOP Package
2 Cells to 3.3V at 200mA, MSOP Package
LT1308
LT1316
LT1317
Micropower 600kHz PWM DC/DC Converter
LTC1474
LT1610
Low Quiescent Current High Efficiency DC/DC Converter
1.7MHz Single Cell Micropower DC/DC Converter
Inverting 1.4MHz Switching Regulator in 5-Lead SOT-23
1.4MHz Switching Regulator in 5-Lead SOT-23
I = 10µA, Programmable Peak Current Limit, MSOP
Q
5V at 200mA from 3.3V, MSOP Package
LT1611
–5V at 150mA from 5V Input, Tiny SOT-23 Package
5V at 200mA from 3.3V Input, Tiny SOT-23 Package
20V at 12mA from 2.5V, Tiny SOT-23 Package
–15V at 12mA from 2.5V, Tiny SOT-23 Package
LT1613
LT1615
Micropower Constant Off-Time DC/DC Converter in 5-Lead SOT-23
Micropower Inverting DC/DC Converter in 5-Lead SOT-23
1.2MHz Boost DC/DC Converter in 5-Lead SOT-23
1.2MHz Inverting DC/DC Converter in 5-Lead SOT-23
LT1617
LT1930
5V at 480mA from 3.3V Input, V
Up to 34V
OUT
LT1931
–5V at 350mA from 5V Input, 1mV Output Ripple
P-P
sn1614 1614fs LT/TP 1000 4K • PRINTED IN THE USA
LINEAR TECHNOLOGY CORPORATION 1998
16 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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