Page 1
FEATURES
■
Very Low Noise: 1mV
■
–5V at 150mA from a 5V Input
■
Better Regulation Than a Charge Pump
■
Effective Output Impedance: 0.14Ω
■
Uses Tiny Capacitors and Inductors
■
Internally Compensated
■
Fixed Frequency 1.4MHz Operation
■
Low Shutdown Current: <1µA
■
Low V
■
Tiny 5-Lead SOT-23 Package
Switch: 300mV at 300mA
CESAT
Output Ripple
P–P
U
APPLICATIO S
■
MR Head Bias
■
Digital Camera CCD Bias
■
LCD Bias
■
GaAs FET Bias
■
Positive-to-Negative Conversion
LT1611
Inverting 1.4MHz Switching
Regulator in SOT-23
U
DESCRIPTIO
The LT®1611 is the industry’s first inverting 5-lead SOT-23
current mode DC/DC converter. Intended for use in small,
low power applications, it operates from an input voltage
as low as 1.1V and switches at 1.4MHz, allowing the use
of tiny, low cost capacitors and inductors 2mm or less in
height. Its small size and high switching frequency enable
the complete DC/DC converter function to consume less
than 0.25 square inches of PC board area. Capable of
generating –5V at 150mA from a 5V supply or –5V at
100mA from a 3V supply, the LT1611 replaces nonregulated
“charge pump” solutions in many applications.
The LT1611 operates in a dual inductor inverting topology
which filters the input side as well as the output side of the
DC/DC converter. Fixed frequency switching ensures a
clean output free from low frequency noise typically present
with charge pump solutions. No load quiescent current of
the LT1611 is 3mA, while in shutdown quiescent current
drops to 0.5µA. The 36V switch allows VIN to V
differential of up to 33V.
OUT
U
TYPICAL APPLICATIO
R1
29.4k
R2
10k
C2
1µF
L1B
22µH
D1
1200pF
C3
22µF
L1A
V
IN
SHDN
22µH
SW
LT1611
NFB
GND
V
IN
5V
+
C1
22µF
C1: AVX TAJB226M010
C2: TAIYO YUDEN LMK212BJ105MG
C3: TAIYO YUDEN JMK325BJ226MM (1210 SIZE)
D1: MBR0520
L1: SUMIDA CLS62-220 OR 2× MURATA LQH3C220 (UNCOUPLED)
Figure 1. 5V to –5V, 150mA Low Noise Inverting DC/DC Converter
The LT1611 is available in the 5-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Transient Response
V
OUT
–5V
150mA
LOAD CURRENT
1611 TA01
V
OUT
20mV/DIV
AC COUPLED
150mA
50mA
100µs/DIV
1611 F10
1
Page 2
LT1611
WW
W
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN Voltage .............................................................. 10V
SW Voltage ................................................–0.4V to 36V
NFB Voltage .............................................................–3V
Current into NFB Pin ............................................. ±1mA
U
U
W
PACKAGE/ORDER INFORMATION
ORDER PART
SW 1
GND 2
NFB 3
TOP VIEW
5 V
IN
4 SHDN
NUMBER
LT1611CS5
U
SHDN Voltage .......................................................... 10V
Maximum Junction Temperature .......................... 125°C
S5 PACKAGE
5-LEAD PLASTIC SOT-23
S5 PART MARKING
Operating Temperature Range
Commercial .............................................0°C to 70°C
T
= 125°C, θJA = 256°C/W
JMAX
LTES
Extended Commercial (Note 2)........... – 40°C to 85°C
Storage Temperature Range ................. –65°C to 150°C
Consult factory for Industrial and Military grade parts.
Lead Temperature (Soldering, 10 sec)..................300°C
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.5V, V
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 0.9 1.1 V
Maximum Operating Voltage 10 V
NFB Pin Bias Current V
Feedback Voltage ● –1.205 –1.23 –1.255 V
Quiescent Current V
Quiescent Current in Shutdown V
Reference Line Regulation 1.5V ≤ VIN ≤ 10V 0.02 0.2 %/V
Switching Frequency ● 1.0 1.4 1.8 MHz
Maximum Duty Cycle ● 82 86 %
Switch Current Limit (Note 3) 550 800 mA
Switch V
CESAT
Switch Leakage Current VSW = 5V 0.01 1 µA
SHDN Input Voltage High 1V
SHDN Input Voltage Low 0.3 V
SHDN Pin Bias Current V
= –1.23V ● –2.7 –4.7 –6.7 µA
NFB
= 1.5V, Not Switching 3 4.5 mA
SHDN
= 0V, VIN = 2V 0.01 0.5 µA
SHDN
= 0V, VIN = 5V 0.01 1.0 µA
V
SHDN
ISW = 300mA 300 350 mV
= 3V 25 50 µA
SHDN
V
= 0V 0 0.1 µA
SHDN
The ● denotes the specifications which apply over the full operating
= VIN unless otherwise noted.
SHDN
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: C grade device specifications are guaranteed over the 0°C to 70°C
temperature range. In addition, C grade device specifications are assured
over the –40°C to 85°C temperature range by design or correlation, but
are not production tested.
2
Note 3: Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
Page 3
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency, V
85
OUT
= –5V
–1.245
vs Temperature
NFB
LT1611
NFB Pin Bias Current vs
TemperatureV
6
80
75
70
65
EFFICIENCY (%)
60
55
50
0
Switch V
700
TA = 25°C
600
500
400
(mV)
300
CESAT
V
200
100
0
0 100 200 300 400 500 600 700
50 75 100 125 150
25
LOAD CURRENT (mA)
CESAT
SWITCH CURRENT (mA)
VIN = 5V
VIN = 3V
vs Switch Current Switch Current Limit vs Duty CycleSHDN Pin Bias Current vs V
Oscillator Frequency vs
Temperature
2.00
1.75
1.50
1.25
1.00
0.75
0.50
SWITCHING FREQUENCY (MHz)
0.25
VIN = 5V
VIN = 1.5V
0
–50 –25 0 25 50 75 100
TEMPERATURE (°C)
1611 G01
1611 G04
1611 G07
–1.240
–1.235
–1.230
(V)
NFB
V
–1.225
–1.220
–1.215
–1.210
–50 0 50–25 25 75 100
50
40
30
20
10
SHDN PIN BIAS CURRENT (µA)
0
012345
TEMPERATURE (°C)
SHDN PIN VOLTAGE (V)
No-Load Operating Quiescent
Current vs Temperature*
6.0
5.5
5.0
4.5
4.0
3.5
3.0
OPERATING CURRENT (mA)
2.5
2.0
–50 0 50–25 25 75 100
TEMPERATURE (°C)
1611 G02
SHDN
1611 G05
1611 G08
5
4
3
2
NFB PIN BIAS CURRENT (µA)
1
0
–50 0 50–25 25 75 100
900
TA = 25°C
800
700
600
500
400
300
200
SWITCH CURRENT LIMIT (mA)
100
0
10
TEMPERATURE (°C)
20 30 40 50 60 70 80
DUTY CYCLE (%)
Switch Current Limit vs
Temperature (Duty Cycle = 30%)
900
800
700
600
500
400
300
200
SWITCH CURRENT LIMIT (mA)
100
0
–25 0 25 50 75 100
–50
TEMPERATURE (°C)
1611 G03
1611 G06
1611 G09
* Includes bias current through R1, R2 and Schottky leakage current at T ≥ 75°C
3
Page 4
LT1611
UUU
PIN FUNCTIONS
SW (Pin 1): Switch Pin. Minimize trace area at this pin to
keep EMI down.
GND (Pin 2): Ground. Tie directly to local ground plane.
NFB (Pin 3): Negative Feedback Pin. Minimize trace area.
Reference voltage is –1.23V. Connect resistive divider tap
here. The suggested value for R2 is 10k. Set R1 and R2
according to:
W
BLOCK DIAGRAM
V
IN
R6
40k
+
A1
g
m
–
Q2
x10
R3
30k
R4
140k
3
NFB
R
C
C
C
C
(OPTIONAL)
V
5
IN
R5
40k
Q1
V
OUT
PL
R1
(EXTERNAL)
NFB
R2
(EXTERNAL)
V
R
1
=
123
.
R
2
OUT
+
−
45
.•
123
.
10
6
−
SHDN (Pin 4): Shutdown Pin. Tie to 1V or more to enable
device. Ground to shut the device down.
VIN (Pin 5): Input Supply Pin. Must be locally bypassed.
1
SW
Q3
+
0.15Ω
–
2
GND
1611 BD
RAMP
GENERATOR
1.4MHz
OSCILLATOR
SHDN
4
Σ
COMPARATOR
–
A2
+
SHUTDOWN
FF
RQ
S
A = 3
DRIVER
Figure 2
U
OPERATIO
The LT1611 combines a current mode, fixed frequency
PWM architecture with a –1.23V reference to directly
regulate negative outputs. Operation can be best understood 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
the summation of a signal representing switch current and
a ramp generator (introduced to avoid subharmonic oscillations at duty factors greater than 50%) exceeds the V
signal, comparator A2 changes stage, resetting the flip-
C
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.
Frequency compensation is provided internally by RC and
CC. Transient response can be optimized by the addition of
a phase lead capacitor, CPL, in parallel with R1 in applications where large value or low ESR output capacitors are
used.
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.
The LT1611 can work in either of two topologies. The
simpler topology appends a capacitive level shift to a
4
Page 5
OPERATIO
LT1611
U
boost converter, generating a negative output voltage,
which is directly regulated. The circuit schematic is detailed 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
LT1611’s internal switch is off.
If D2 is replaced by an inductor, as shown in Figure 4, a
higher performance solution results. This converter topology 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
the output. Abrupt changes in output capacitor current are
eliminated because the output inductor delivers current to
the output during both the off-time and the on-time of the
LT1611 switch. With proper layout and high quality output
capacitors, output ripple can be as low as 1mV
P–P
.
The operation of Cuk’s topology is shown in Figures 5
and␣ 6. During the first switching phase, the LT1611’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 R
L2 and C3. The voltage at node SW is V
SWX the voltage is –(VIN + |V
|). Q1 must conduct both
OUT
is supplied by
LOAD
and at node
CESAT
L1 and L2 current. C2 functions as a voltage level shifter,
with an approximately constant voltage of (VIN + |V
OUT
|)
across it.
When Q1 turns off during the second phase of switching,
the SW node voltage abruptly increases to (VIN + |V
OUT
|).
The SWX node voltage increases to VD (about 350mV).
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.
An important layout issue arises due to the chopped
nature of the currents flowing in Q1 and D1. If they are both
tied directly to the ground plane before being combined,
switching noise will be introduced into the ground plane.
It is almost impossible to get rid of this noise, once present
in the ground plane. The solution is to tie D1’s cathode to
the ground pin of the LT1611 before the combined currents 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
riding on V
. Ripple magnitude equals the ripple current
OUT
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.
C2
V
IN
+
C1
Figure 3. Direct Regulation of Negative Output
Using Boost Converter with Charge Pump
L1
V
IN
LT1611
GND
1µF
SW
R1
NFBSHDNSHUTDOWN
R2
10k
D2
D1
+
–V
C3
1611 F03
OUT
C2
SW
NFB
1µF
R1
R2
10k
D1
–V
OUT
C3
+
1611 F04
V
IN
+
C1
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
L1 L2
V
IN
LT1611
GND
5
Page 6
LT1611
OPERATIO
V
IN
U
+ V
V
CESAT
L1 L2
–(V
IN
C2
SW SWX
OUT
)
–V
OUT
+
C1 C3 R
Q1
D1
+
1611 F05
LOAD
Figure 5. Switch-On Phase of Inverting Converter. L1 and L2 Current Have Positive dI/dt
+ V
V
IN
V
IN
L1 L2
+
C1 C3 R
+ V
OUT
D
SW SWX
Q1
V
D
C2
–V
OUT
D1
+
LOAD
Figure 6. Switch-Off Phase of Inverting Converter. L1 and L2 Current Have Negative dI/dt
Transient Response
The inverting architecture of the LT1611 can generate a
very low ripple output voltage. Recently available high
value ceramic capacitors can be used successfully in
LT1611 designs with the addition of a phase lead capacitor, CPL (see Figure 7). Connected in parallel with feedback
resistor R1, this capacitor reduces both output perturba-
6
1611 F06
tions due to load steps and output ripple voltage to very
low levels. To illustrate, Figure 7 shows an LT1611 inverting converter with resistor loads R
and RL2. RL1 is
L1
connected across the output, while RL2 is switched in
externally via a pulse generator. Output voltage waveforms are pictured in subsequent figures, illustrating the
performance of output capacitor type and the effect of C
PL
connected across R1.
Page 7
OPERATIO
LT1611
U
R1
R2
10k
C2
1µF
C
PL
L1A
V
IN
SHDN
22µH
LT1611
GND
V
IN
5V
+
C1
C1: AVX TAJB226M010
C2: TAIYO YUDEN LMK212BJ105MG
C3: SEE TEXT
D1: MBR0520
L1A, L1B: SUMIDA CLS62-220
SW
NFB
Figure 7. Switching RL2 Provides 50mA to 150mA
Load Step for LT1611 5V to –5V Converter
V
OUT
50mV/DIV
AC COUPLED
D1
L1B
22µH
Figure 8 shows the output voltage with a 50mA to 150mA
load step, using an AVX TAJ “B” case 22µF tantalum
–V
OUT
R
L1
C3
100Ω
+
capacitor at the output. Output perturbation is approximately 100mV as the load changes from 50mA to 150mA.
R
L2
Steady-state ripple voltage is 20mV
50Ω
, due to L1’s ripple
P–P
current and C3’s ESR. Step response can be improved by
adding a 3.3nF capacitor (CPL) as shown in Figure 9.
Settling time improves from 150µs to 40µs, although
1611 F07
steady-state ripple voltage does not improve. Figure 10
pictures the output voltage and switch pin voltage at
200ns per division. Note the absence of high frequency
spikes at the output. This is easily repeatable with proper
layout, described in the next section.
V
OUT
20mV/DIV
AC COUPLED
LOAD CURRENT
150mA
50mA
100µs/DIV
Figure 8. Load Step Response of LT1611
with 22µF Tantalum Output Capacitor
V
OUT
10mV/DIV
SWITCH VOLTAGE
5V/DIV
LOAD = 150mA 200ns/DIV
Figure 10. 22µF “B” Case Tantalum Capacitor (AVX TAJ “B” Series)
Has ESR Resulting in 20mV
LOAD CURRENT
1611 F08
Figure 9. Addition of CPL to Figure 7’s Circuit
Improves Load Step Response. CPL = 3.3nF
Voltage Ripple at Output
P–P
150mA
50mA
1611 F10
20µs/DIV
1611 F09
7
Page 8
LT1611
OPERATIO
U
In Figure 11 (also shown on the first page), output capacitor C3 is replaced by a ceramic unit. These large value
ceramic capacitors have ESR of about 2mΩ and result in
very low output ripple. At the 20mV/division scale, output
voltage ripple cannot be seen. Figure 12 pictures the
output and switch nodes at 200ns per division. The output
voltage ripple is approximately 1mV
. Again, good
P–P
layout is mandatory to achieve this level of performance.
V
OUT
20mV/DIV
AC COUPLED
LOAD CURRENT
150mA
50mA
100µs/DIV
Figure 11. Replacing C3 with 22µF Ceramic Capacitor
(Taiyo Yuden JMK325BJ226MM) Improves Output
Noise. CPL = 1200pF Results in Best Phase Margin
1611 F11
Layout
The LT1611 switches current at high speed, mandating
careful attention to layout for best performance.
not get advertised performance with careless layout.
You will
Figure␣ 13
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 11 and 12’s oscillographs. Input
bypass capacitor C1 should be placed close to the LT1611
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.
V
OUT
5mV/DIV
AC COUPLED
SWITCH VOLTAGE
5V/DIV
LOAD = 150mA 200ns/DIV
Figure 12. 22µF Ceramic Capacitor at
Output Reduces Ripple to 1mV
. Proper
P–P
Layout Is Essential to Achieve Low Noise
1611 F12
8
L1A
C1
+
V
IN
1
2
3
R2
5
4
R1
SHUTDOWN
1611 F13
–V
OUT
GND
L1B
D1
C2
C3
+
Figure 13. Suggested Component Placement. Note Cut in Ground Copper at D1’s Cathode
Page 9
OPERATIO
LT1611
U
Start-Up/Soft-Start
The LT1611, starting from V
= 0V, reaches final voltage
OUT
in approximately 450µs after SHDN is pulled high, with
C
= 22µF, VIN = 5V and V
OUT
= – 5V. Charging the output
OUT
capacitor at this speed requires an inrush current of over
1A. If a longer start-up time is acceptable, a soft-start
circuit consisting of RSS and CSS, as shown in Figure 14,
can be used to limit inrush current to a lower value. Figure
15 pictures V
and input current, starting into a 33Ω
OUT
load, with RSS of 33kΩ and CSS of 33nF. Input current,
V
SS
V
IN
5V
R
SS
33k
D2
1N4148
C
33nF/0.1µF
CURRENT
PROBE
+
C1
22µF
SS
C1: AVX TAJB226M010
C2: TAIYO YUDEN LMK212BJ105MG
V
C3: TAIYO YUDEN JMK325BJ226MM (1210 SIZE)
OUT
D1: MBR0520
L1: SUMIDA CLS62-220 OR 2× MURATA LQH3C220 (UNCOUPLED)
V
IN
SHDN
L1A
22µH
SW
LT1611
NFB
GND
measured at VIN, is limited to a peak value of 450mA as the
time required to reach final value increases to 700µs. In
Figure 16, CSS is increased to 0.1µF, resulting in a lower
peak input current of 240mA with a V
ramp time of
OUT
2.1ms. CSS can be increased further for an even slower
ramp, if desired. Diode D2 serves to quickly discharge C
SS
when VSS is driven low to shut down the device. D2 can be
omitted, resulting in a “soft-stop” slow discharge of the
output capacitor.
R1
29.4k
R2
10k
C2
1µF
C
P
1200pF
D1
L1B
22µH
V
–5V
C3
22µF
1611 F14
OUT
Figure 14. RSS and CSS at SHDN Pin Provide Soft-Start to LT1611 Inverting Converter
V
OUT
2V/DIV
I
IN
200mA/DIV
V
S
5V/DIV
LOAD = 150mA 500µs/DIV
Figure 15. RSS = 33k, CSS = 33nF; V
OUT
–5V in 750µs; Input Current Peaks at 450mA
Reaches
1611 F15
V
OUT
2V/DIV
I
IN
200mA/DIV
V
S
5V/DIV
LOAD = 150mA 500µs/DIV
Figure 16. RSS = 33k, CSS = 0.1µF; V
OUT
–5V in 2.1ms; Input Current Peaks at 240mA
1611 F16
Reaches
9
Page 10
LT1611
OPERATIO
U
Output Current
The LT1611 will deliver 150mA at –5V from a 5V ±10%
input supply. If a higher voltage supply is available, more
output current can be obtained. Figure 17’s schematic
shows how to get more current. Although the LT1611’s
maximum voltage allowed at VIN is 10V, the SW pin can
handle higher voltage (up to 36V). In Figure 17, the VIN pin
of the LT1611 is driven from a 5V supply, while input
inductor L1A is driven from a separate 12V supply. Figure
18’s graph shows maximum recommended output current as the voltage on L1A is varied. Up to 300mA can be
delivered when driving L1A from a 12V supply.
COMPONENT SELECTION
Inductors
Each of the two inductors used with the LT1611 should
have a saturation current rating (where inductance is
approximately 70% of zero current inductance) of approximately 0.25A or greater. If the device is used in
“charge pump” mode, where there is only one inductor,
then its rating should be 0.5A or greater. DCR of the
inductors should be 0.5Ω or less. A value of 22µH is
suitable if using a coupled inductor such as Sumida
CLS62-220 or Coiltronics CTX20-1. If using two separate
inductors, increasing the value to 47µH will result in the
same ripple current. Inductance can be reduced if operating from a supply voltage below 3V. Table 1 lists several
inductors that will work with the LT1611, although this is
not an exhaustive list. There are many magnetics vendors
whose components are suitable.
V
L
(SEE TEXT)
350
300
250
200
OUTPUT CURRENT (mA)
MAXIMUM RECOMMENDED
150
100
5 6 7 8 9 10 11 12
34
VL (V)
1611 F18
5V
V
IN
SHDN
C1
1µF
C1, C2: TAIYO YUDEN LMK212BJ105MG
C3: TAIYO YUDEN JMK325BJ226MM
D1: MBR0520
L1A, L1B: SUMIDA CLS62-220
LT1611
GND
SW
NFB
L1A
22µH
29.4k
10k
C2
1µF
1200pF
D1
L1B
22µH
V
OUT
–5V
UP TO 300mA
C3
22µF
1611 F17
Figure 17. Increase Output Current By Driving L1A from a Higher Voltage Figure 18. Output Current Increases to
300mA When Driving VL from 12V Supply
10
Page 11
OPERATIO
LT1611
U
Capacitors
As described previously, ceramic capacitors can be used
with the LT1611 provided loop stability is considered. For
lower cost applications, small tantalum units can be used.
A value of 22µF is acceptable, although larger capacitance
values can be used. ESR is the most important parameter
in selecting an output capacitor. 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 critical, and either tantalum or
Table 1. Inductor Vendors
VENDOR PHONE URL PART COMMENT
Sumida (847) 956-0666 www.sumida.com CLS62-22022 22µH Coupled
Murata (404) 436-1300 www.murata.com LQH3C-220 22µH, 2mm Height
Coiltronics (407) 241-7876 www.coiltronics.com CTX20-1 20µH Coupled, Low DCR
Table 2. Capacitor Vendors
VENDOR PHONE URL PART COMMENT
Taiyo Yuden (408) 573-4150 www.t-yuden.com Ceramic Caps X5R Dielectric
AVX (803) 448-9411 www.avxcorp.com Ceramic Caps
Murata (404) 436-1300 www.murata.com Ceramic Caps
ceramic can be used with little trade-off in circuit performance. Some capacitor types appropriate for use with the
LT1611 are listed in Table 2.
Diodes
A Schottky diode is recommended for use with the LT1611.
The Motorola MBR0520 is a very good choice. Where the
input to output voltage differential exceeds 20V, use the
MBR0530 ( a 30V diode). If cost is more important than
efficiency, a 1N4148 can be used, but only at low current
loads.
CD43-470 47µH
Tantalum Caps
U
TYPICAL APPLICATIO S
3.3V
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.
“Charge Pump” Inverting DC/DC Converter
SW
NFB
C2
1µF
29.4k
10k
D1
C3
22µF
1611 TA02
L1
10µH
V
IN
SHDN
C1
1µF
C1, C2: TAIYO YUDEN LMK212BJ105MG
C3: TAIYO YUDEN JMK325BJ226MM
D1, D2: MBR0520
L1: MURATA LQH3C-100
LT1611
GND
D2
–5V
70mA
11
Page 12
LT1611
U
TYPICAL APPLICATIO S
4-Cell to –10V Inverting Converter
L1A
V
IN
+
C1
22µF
C1: AVX TAJB226M010 (803) 946-0362
C2: TAIYO YUDEN LMK212BJ105MG
C3: AVX TAJA685M016
D1: MOTOROLA MBR0520 (800) 441-2447
L1: SUMIDA CL562-150 (847) 956-0666
15µH
V
IN
LT1611
GND
C2
1µF
SW
68.1k
NFBSHDNSHUTDOWN
10k
PACKAGE DESCRIPTION
2.60 – 3.00
(0.102 – 0.118)
1.50 – 1.75
(0.059 – 0.069)
4-Cell to –10V Inverting Converter Efficiency
85
80
75
70
65
EFFICIENCY (%)
60
55
50
0
VIN = 3.6V
25 50 75 100 125 150
LOAD CURRENT (mA)
D1
L1B
15µH
V
OUT
–10V/60mA
C3
+
6.8µF
1611 TA03
U
Dimensions in inches (millimeters) unless otherwise noted.
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.80 – 3.00
0.00 – 0.15
(0.00 – 0.006)
0.90 – 1.45
(0.035 – 0.057)
(0.110 – 0.118)
(NOTE 3)
VIN = 6.5V
VIN = 5V
1611 TA04
0.35 – 0.55
(0.014 – 0.022)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DIMENSIONS ARE INCLUSIVE OF PLATING
3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
4. MOLD FLASH SHALL NOT EXCEED 0.254mm
5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.35 – 0.50
(0.014 – 0.020)
FIVE PLACES (NOTE 2)
0.90 – 1.30
(0.035 – 0.051)
1.90
(0.074)
REF
0.95
(0.037)
REF
S5 SOT-23 0599
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LT1307 Single Cell Micropower DC/DC with Low Battery Detector 3.3V/75mA from 1V, 600kHz Fixed Frequency
LT1316 Burst ModeTM Operation DC/DC with Programmable Current Limit 1.5V Minimum VIN, Precise Control of Peak Switch Current
LT1317 2-Cell Micropower DC/DC with Low Battery Detector 3.3V/200mA from Two Cells, 600kHz Fixed Frequency
LT1370/LT1371 500kHz High Efficiency DC/DC Converter 42V, 6A/3A Internal Switch, Negative Feedback Regulation
LT1610 Single Cell Micropower DC/DC 3V/30mA from 1V, 1.7MHz Fixed Frequency, 30µA I
LT1613 1.4MHz SOT-23 Step-Up DC/DC Converter 5V at 200mA from 3.3V Input
LT1614 Inverting Mode Switching Regulator with Low-Battery Detector –5V at 200mA from 5V Input in MSOP
LT1615 Micropower SOT-23 Step-Up DC/DC Converter 20µA Quiescent Current, V
LT1617 Micropower SOT-23 Inverting Regulator V
Up to –34V, 20µA Quiescent Current
OUT
Up to 34V
OUT
Burst Mode is a trademark of Linear Technology Corporation.
1611f LT/TP 0999 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear-tech.com
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