LINER LT3008EDC 3î¼a iq, 20ma, 45v low dropout linear regulator Datasheet

LT3008
3µA IQ, 20mA, 45V
Low Dropout Linear Regulator
FEATURES
DESCRIPTION
n
The LT®3008 is a micropower, low dropout voltage (LDO)
linear regulator. The device supplies 20mA output current
with a dropout voltage of 300mV. No-load quiescent current is 3μA. Ground pin current remains at less than 5% of
output current as load increases. In shutdown, quiescent
current is less than 1μA.
n
n
n
n
n
n
n
n
n
n
n
Ultralow Quiescent Current: 3μA
Input Voltage Range: 2.0V to 45V
Output Current: 20mA
Dropout Voltage: 300mV
Adjustable Output (VADJ = VOUT(MIN) = 600mV)
Output Tolerance: ±2% Over Load, Line and
Temperature
Stable with Low ESR, Ceramic Output Capacitors
(2.2μF minimum)
Shutdown Current: <1μA
Current Limit Protection
Reverse-Battery Protection
Thermal Limit Protection
TSOT-23 and 2mm × 2mm DFN Packages
The LT3008 is ideal for applications that require moderate
output drive capability coupled with ultralow standby power
consumption. The device is available as an adjustable
device with an output voltage range down to the 600mV
reference. The LT3008 is available in the 6-lead DFN and
8-lead TSOT-23 packages.
APPLICATIONS
n
n
n
n
n
n
The LT3008 regulator optimizes stability and transient
response with low ESR ceramic capacitors, requiring a
minimum of only 2.2μF. The LT3008 does not require
the addition of ESR as is common with other regulators.
Internal protection circuitry includes current limiting,
thermal limiting, reverse-battery protection and reversecurrent protection.
Automotive
Low Current Battery-Powered Systems
Keep-Alive Power Supplies
Remote Monitoring
Utility Meters
Low Power Industrial Applications
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
3.3V, 20mA Supply with Shutdown
Dropout Voltage/Quiescent Current
500
OUT
1μF
2.8M
1%
LT3008
SHDN
GND
2.2μF
VOUT
3.3V
20mA
ADJ
619k
1%
3008 TA01a
DROPOUT VOLTAGE (mV)
IN
6
ILOAD = 20mA
DROPOUT
VOLTAGE
400
350
5
4
300
250
IQ
3
200
2
150
100
QUIESCENT CURRENT (μA)
VIN
3.8V TO
45V
450
1
50
0
–50 –25
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
3008 TA01b
3008f
1
LT3008
ABSOLUTE MAXIMUM RATINGS
(Note 1)
IN Pin Voltage .........................................................±50V
OUT Pin Voltage ......................................................±50V
Input-to-Output Differential Voltage ........................±50V
ADJ Pin Voltage ......................................................±50V
SHDN Pin Voltage (Note 8) .....................................±50V
Output Short-Circuit Duration .......................... Indeﬁnite
Operating Junction Temperature Range (Notes 2, 3)
LT3008E .............................................–40°C to 125°C
LT3008I ..............................................–40°C to 125°C
Storage Temperature Range...................–65°C to 150°C
Lead Temperature: Soldering, 10 sec
TS8 Package Only ............................................. 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
6 GND
ADJ 1
OUT 2
7
OUT 3
SHDN
GND
GND
GND
5 SHDN
4 IN
1
2
3
4
8
7
6
5
NC
ADJ
OUT
IN
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
DC PACKAGE
6-LEAD (2mm s 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 65°C/W TO 85°C/W*
TJMAX = 125°C, θJA = 65°C/W TO 85°C/W*
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
* See Applications Information Section.
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3008EDC#PBF
LT3008EDC#TRPBF
LDPS
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 125°C
LT3008IDC#PBF
LT3008IDC#TRPBF
LDPS
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 125°C
LT3008ETS8#PBF
LT3008ETS8#TRPBF
LTDSX
8-Lead Plastic TSOT-23
–40°C to 125°C
LT3008ITS8#PBF
LT3008ITS8#TRPBF
LTDSX
8-Lead Plastic TSOT-23
–40°C to 125°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3008EDC
LT3008EDC#TR
LDPS
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 125°C
LT3008IDC
LT3008IDC#TR
LDPS
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 125°C
LT3008ETS8
LT3008ETS8#TR
LTDSX
8-Lead Plastic TSOT-23
–40°C to 125°C
LT3008ITS8
LT3008ITS8#TR
LTDSX
8-Lead Plastic TSOT-23
–40°C to 125°C
Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel speciﬁcations, go to: http://www.linear.com/tapeandreel/
3008f
2
LT3008
ELECTRICAL CHARACTERISTICS
The l denotes the speciﬁcations which apply over the full operating
temperature range, otherwise speciﬁcations are at TJ = 25°C. (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
45
V
600
600
606
612
mV
mV
l
2
ADJ Pin Voltage (Notes 3, 4)
VIN = 2V, ILOAD = 100μA
2V < VIN < 45V, 1μA < ILOAD < 20mA
l
594
588
Line Regulation (Note 3)
ΔVIN = 2V to 45V, ILOAD = 1mA
l
0.6
3
mV
Load Regulation (Note 3)
VIN = 2V, ILOAD = 1μA to 10mA
VIN = 2V, ILOAD = 1μA to 20mA
l
l
0.4
0.5
2
5
mV
mV
Dropout Voltage
VIN = VOUT(NOMINAL) (Notes 5, 6)
ILOAD = 100μA
ILOAD = 100μA
l
115
180
250
mV
mV
ILOAD = 1mA
ILOAD = 1mA
l
170
250
350
mV
mV
ILOAD = 10mA
ILOAD = 10mA
l
270
340
470
mV
mV
ILOAD = 20mA
ILOAD = 20mA
l
300
365
500
mV
mV
ILOAD = 0μA
ILOAD = 0μA
l
6
μA
μA
GND Pin Current
VIN = VOUT(NOMINAL) + 0.5V (Notes 6, 7)
ILOAD = 0μA
ILOAD = 100μA
ILOAD = 1mA
ILOAD = 10mA
ILOAD = 20mA
l
l
l
l
l
6
12
50
500
1200
μA
μA
μA
μA
μA
Output Voltage Noise (Note 9)
COUT = 2.2μF, ILOAD = 20mA, BW = 10Hz to 100kHz
Operating Voltage
Quiescent Current (Notes 6, 7)
3
3
6
21
160
350
92
μVRMS
l
–10
0.4
10
nA
VOUT = Off to On
VOUT = On to Off
l
l
0.67
0.61
1.5
0.25
V
V
VSHDN = 0V, VIN = 45V
VSHDN = 45V, VIN = 45V
l
l
±1
2
μA
μA
Quiescent Current in Shutdown
VIN = 6V, VSHDN = 0V
l
<1
μA
Ripple Rejection (Note 3)
VIN – VOUT = 1.5V, VRIPPLE = 0.5VP-P,
fRIPPLE = 120Hz, ILOAD = 20mA
Current Limit
VIN = 45V, VOUT = 0
VIN = VOUT(NOMINAL) + 1V, ΔVOUT = – 5%
l
Input Reverse Leakage Current
VIN = –45V, VOUT = 0
l
Reverse Output Current
VOUT = 1.2V, VIN = 0
ADJ Pin Bias Current
Shutdown Threshold
SHDN Pin Current
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT3008 is tested and speciﬁed under pulse load conditions
such that TJ ≅ TA. The LT3008E is 100% tested at TA=25°C. Performance
at – 40°C and 125°C is assured by design, characterization and correlation
with statistical process controls. The LT3008I is guaranteed over the full
– 40°C to 125°C operating junction temperature range.
Note 3: The LT3008 adjustable version is tested and speciﬁed for these
conditions with the ADJ pin connected to the OUT pin.
0.65
58
70
dB
75
mA
mA
22
1
30
μA
0.6
10
μA
Note 4: Operating conditions are limited by maximum junction
temperature. The regulated output voltage speciﬁcation will not apply
for all possible combinations of input voltage and output current. When
operating at the maximum input voltage, the output current range must be
limited. When operating at the maximum output current, the input voltage
must be limited.
Note 5: Dropout voltage is the minimum input to output voltage differential
needed to maintain regulation at a speciﬁed output current. In dropout, the
output voltage equals (VIN – VDROPOUT).
3008f
3
LT3008
ELECTRICAL CHARACTERISTICS
The l denotes the speciﬁcations which apply over the full operating
temperature range, otherwise speciﬁcations are at TJ = 25°C. (Note 2)
Note 6: To satisfy minimum input voltage requirements, the LT3008
adjustable version is tested and speciﬁed for these conditions with an
external resistor divider (61.9k bottom, 280k top) which sets VOUT to 3.3V.
The external resistor divider adds 9.69μA of DC load on the output. This
external current is not factored into GND pin current.
Note 7: GND pin current is tested with VIN = VOUT(NOMINAL) + 0.5V and a
current source load. GND pin current will increase in dropout. See the GND
Pin Current curves in the Typical Performance Characteristics section.
Note 8: The SHDN pin can be driven below GND only when tied to the IN
pin directly or through a pull-up resistor. If the SHDN pin is driven below
GND by more than –0.3V while IN is powered, the output will turn on.
Note 9: Output noise is listed for the adjustable version with the ADJ pin
connected to the OUT pin. See the RMS Output Noise vs Load Current
curve in the Typical Performance Characteristics Section.
TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Voltage
Minimum Input Voltage
450
2
400
400
1.8
TJ = 125°C
350
300
TJ = 25°C
250
200
150
100
350
20mA
300
10mA
250
200
1mA
100
50
0
0
2
4
100μA
150
50
0
6 8 10 12 14 16 18 20
OUTPUT CURRENT (mA)
1.4
–50 –25
0
25
50
75
1
0.8
0.6
0.4
–50 –25
0
25
50
75
100 125 150
TEMPERATURE (°C)
3008 G02
3008 G03
ADJ Pin Bias Current
IL = 100μA
Quiescent Current
6
8
0.604
0.602
0.600
0.598
0.596
0.594
0.592
5
6
QUIESCENT CURRENT (μA)
ADJ PIN BIAS CURRENT (nA)
0.606
4
2
0
–2
–4
–6
4
3
2
1
–8
0.590
0.588
–50 –25
1.2
0
100 125 150
10
0.608
ADJ PIN VOLTAGE (mV)
1.6
TEMPERATURE (°C)
ADJ Pin Voltage
0.610
ILOAD = 20mA
0.2
3008 G01
0.612
MINIMUM INPUT VOLTAGE (V)
450
DROPOUT VOLTAGE (mV)
DROPOUT VOLTAGE (mV)
Dropout Voltage
TJ = 25°C, unless otherwise noted.
–10
0
25
50
75
100 125 150
–50 –25
0
25
50
75
100 125 150
TEMPERATURE (°C)
TEMPERATURE (°C)
3008 G04
0
–50 –25
0
25
50
75
100 125 150
TEMPERATURE (°C)
3008 G05
3008 G06
3008f
4
LT3008
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
GND Pin Current
VOUT = 3.3V
VOUT = 3.3V
ILOAD = 1μA
20mA (RLOAD = 165Ω)
350
24
18
15
12
9
250
200
10mA (RLOAD = 330Ω)
150
100
6
3
0
0
2
4
6
8
10
12
0
1
2
3
4
5
6
7
8
1
0.001
10
2
1.8
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
1.4
1.2
1
5
10
15 20 25 30 35
SHDN PIN VOLTAGE (V)
3008 G10
0.6
0.4
0
–50 –25
45
VIN = 2V
30
20
0
Input Ripple Rejection
OUT = ADJ = 1.2V
IN = SHDN = GND
35
30
25
20
15
ADJ
10
25 50 75 100 125 150
TEMPERATURE (°C)
3008 G13
0
–50 –25
OUT
0
VIN = 2.1V + 50mVRMS
VOUT = 600mV
ILOAD = 20mA
80
40
5
10
25 50 75 100 125 150
TEMPERATURE (°C)
90
INPUT RIPPLE REJECTION (dB)
REVERSE OUTPUT CURRENT (μA)
90
50
0
3008 G12
Reverse Output Current
50
40
40 45
3008 G11
Current Limit
60
VSHDN = 45V
0.8
0.2
0
100
100
1.6
0
25 50 75 100 125 150
TEMPERATURE (°C)
VIN = 45V
10
SHDN Pin Input Current
2
0.2
70
1
3008 G09
SHDN PIN INPUT CURRENT (μA)
SHDN PIN INPUT CURRENT (μA)
ON TO OFF
80
0.1
LOAD (mA)
SHDN Pin Input Current
OFF TO ON
0
0.01
3008 G08
SHDN Pin Thresholds
SHDN PIN THRESHOLD (V)
9
INPUT VOLTAGE (V)
3008 G07
0
–50 –25
10
1mA (RLOAD = 3.3k)
INPUT VOLTAGE (V)
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–50 –25
100
100μA (RLOAD = 33k)
50
0
VIN = 3.8V
VOUT = 3.3V
300
GND PIN CURRENT (μA)
21
GND CURRENT (μA)
27
QUIESCENT CURRENT (μA)
GND Pin Current vs ILOAD
1000
400
30
CURRENT LIMIT (mA)
TJ = 25°C, unless otherwise noted.
25 50 75 100 125 150
TEMPERATURE (°C)
3008 G14
70
60
50
40
10μF
30
20
2.2μF
10
0
10
100
1000
10000
100000 1000000
FREQUENCY (Hz)
3008 G15
3008f
5
LT3008
TYPICAL PERFORMANCE CHARACTERISTICS
5
70
4.5
50
40
30
20
10
$IL = 1μA to 20mA
VOUT = 600mV
VIN = 2V
4
60
0
3.5
3
2.5
2
1.5
1
VIN = VOUT (NOMINAL) + 2V + 0.5VP-P
RIPPLE AT f = 120Hz
ILOAD = 20mA
0
–50 –25
Output Noise Spectral Density
OUTPUT NOISE SPECTRAL DENSITY (μV Hz)
Load Regulation
80
LOAD REGULATION (mV)
INPUT RIPPLE REJECTION (dB)
Input Ripple Rejection
0.5
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
25 50 75 100 125 150
TEMPERATURE (°C)
RMS Output Noise
vs Load Current
450
COUT = 2.2μF
ILOAD = 20mA
5V
3.3V
2.5V
1.8V
1.5V
1V
0.6V
10
1
0.1
10
100
1k
10k
FREQUENCY (Hz)
100k
3008 G18
Transient Response
COUT = 10μF
5V
IOUT = 1mA TO 20mA
VIN = 5.5V
VOUT = 5V
COUT = 2.2μF
400
OUTPUT NOISE (μVRMS)
100
3008 G17
3008 G16
500
TJ = 25°C, unless otherwise noted.
350
VOUT
50mV/DIV
3.3V
300
2.5V
250
1.8V
200
1.5V
150
100
1.2V
50
0.6V
0
0.001
0.01
0.1
1
10
IOUT
20mA/DIV
500μs/DIV
3008 G21
100
ILOAD (mA)
3008 G19
Transient Response (Load Dump)
Transient Response
IOUT = 1mA TO 20mA
VIN = 5.5V
VOUT = 5V
COUT = 10μF
VOUT
50mV/DIV
VOUT
50mV/DIV
45V
VOUT = 5V
IOUT = 20mA
COUT = 4.7μF
VIN
10V/DIV
IOUT
20mA/DIV
500μs/DIV
3008 G22
1ms/DIV
12V
3008 G23
3008f
6
LT3008
PIN FUNCTIONS
(TSOT-23/DFN)
SHDN (Pin 1/Pin 5): Shutdown. Pulling the SHDN pin
low puts the LT3008 into a low power state and turns the
output off. If unused, tie the SHDN pin to VIN. The LT3008
does not function if the SHDN pin is not connected. The
SHDN pin cannot be driven below GND unless tied to the
IN pin. If the SHDN pin is driven below GND while IN is
powered, the output will turn on. SHDN pin logic cannot
be referenced to a negative rail.
GND (Pins 2, 3, 4/Pin 6): Ground. Connect the bottom
of the resistor divider that sets output voltage directly to
GND for the best regulation.
IN (Pin 5/Pin 4): Input. The IN pin supplies power to the
device. The LT3008 requires a bypass capacitor at IN if
the device is more than six inches away from the main
input ﬁlter capacitor. In general, the output impedance of
a battery rises with frequency, so it is advisable to include
a bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 0.1μF to 10μF will sufﬁce. The
LT3008 withstands reverse voltages on the IN pin with respect to ground and the OUT pin. In the case of a reversed
input, which occurs with a battery plugged in backwards,
the LT3008 acts as if a blocking diode is in series with its
input. No reverse current ﬂows into the LT3008 and no
reverse voltage appears at the load. The device protects
both itself and the load.
OUT (Pin 6/Pins 2, 3): Output. This pin supplies power
to the load. Use a minimum output capacitor of 2.2μF
to prevent oscillations. Large load transient applications
require larger output capacitors to limit peak voltage
transients. See the Applications Information section for
more information on output capacitance and reverse
output characteristics.
ADJ (Pin 7/Pin 1): Adjust. This pin is the error ampliﬁer’s
inverting terminal. Its 400pA typical input bias current
ﬂows out of the pin (see curve of ADJ Pin Bias Current vs
Temperature in the Typical Performance Characteristics
section). The ADJ pin voltage is 600mV referenced to GND
and the output voltage range is 600mV to 44.5V.
NC (Pin 8, TSOT-23 Package Only): No Connect. Pin 8
is an NC pin in the TSOT-23 package. This pin is not tied
to any internal circuitry. It may be ﬂoated, tied to VIN or
tied to GND.
Exposed Pad (Pin 7, DFN Package Only): Ground. The
Exposed Pad (backside) of the DFN package is an electrical connection to GND. To ensure optimum performance,
solder Pin 7 to the PCB and tie directly to Pin 6.
3008f
7
LT3008
APPLICATIONS INFORMATION
The LT3008 is a low dropout linear regulator with ultralow quiescent current and shutdown. Quiescent current is
extremely low at 3μA and drops well below 1μA in shutdown. The device supplies up to 20mA of output current.
Dropout voltage at 20mA is typically 300mV. The LT3008
incorporates several protection features, making it ideal for
use in battery-powered systems. The device protects itself
against both reverse-input and reverse-output voltages.
In battery backup applications, where a backup battery
holds up the output when the input is pulled to ground,
the LT3008 acts as if a blocking diode is in series with its
output and prevents reverse current ﬂow. In applications
where the regulator load returns to a negative supply, the
output can be pulled below ground by as much as 50V
without affecting startup or normal operation.
Typical Performance Characteristics.
Speciﬁcations for output voltages greater than 0.6V are
proportional to the ratio of the desired output voltage to
0.6V: VOUT/0.6V. For example, load regulation for an output
current change of 100μA to 20mA is –0.5mV typical at
VOUT = 0.6V. At VOUT = 5V, load regulation is:
5V
• (− 0 . 5mV) = − 4 . 17mV
0 . 6V
Table 1 shows resistor divider values for some common output voltages with a resistor divider current of
about 1μA.
Table 1. Output Voltage Resistor Divider Values
Adjustable Operation
The LT3008 has an output voltage range of 0.6V to 44.5V.
Figure 1 shows that output voltage is set by the ratio of two
external resistors. The IC regulates the output to maintain
the ADJ pin voltage at 600mV referenced to ground. The
current in R1 equals 600mV/R1 and the current in R2 is
the current in R1 minus the ADJ pin bias current. The
ADJ pin bias current, typically 400pA at 25°C, ﬂows out
of the pin. Calculate the output voltage using the formula
in Figure 1. An R1 value of 619k sets the divider current
to 0.97μA. Do not make R1’s value any greater than 619k
to minimize output voltage errors due to the ADJ pin bias
current and to insure stability under minimum load conditions. In shutdown, the output turns off and the divider
current is zero. Curves of ADJ Pin Voltage vs Temperature
and ADJ Pin Bias Current vs Temperature appear in the
VOUT = 600mV • (1 + R2/R1) – (IADJ • R2)
VADJ = 600mV
IADJ = 0.4nA at 25°C
OUTPUT RANGE = 0.6V to 44.5V
VOUT
R1
R2
1V
604k
402k
1.2V
590k
590k
1.5V
590k
887k
1.8V
590k
1.18M
2.5V
590k
1.87M
3V
590k
2.37M
3.3V
619k
2.8M
5V
590k
4.32M
Because the ADJ pin is relatively high impedance (depending on the resistor divider used), stray capacitances
at this pin should be minimized. Special attention should
be given to any stray capacitances that can couple external signals onto the ADJ pin producing undesirable
output transients or ripple.
IN
VIN
VOUT
OUT
LT3008
SHDN
GND
R2
ADJ
R1
3008 F01
Figure 1. Adjustable Operation
3008f
8
LT3008
APPLICATIONS INFORMATION
Extra care should be taken in assembly when using high
valued resistors. Small amounts of board contamination
can lead to signiﬁcant shifts in output voltage. Appropriate
post-assembly board cleaning measures should be
implemented to prevent board contamination. If the
board is to be subjected to humidity cycling or if board
cleaning measures cannot be guaranteed, consideration
should be given to using resistors an order of magnitude
smaller than in Table 1 to prevent contamination from
causing unwanted shifts in the output voltage.
Output Capacitance and Transient Response
The LT3008 is stable with a wide range of output capacitors. The ESR of the output capacitor affects stability, most
notably with small capacitors. Use a minimum output
capacitor of 2.2μF with an ESR of 3Ω or less to prevent
oscillations. The LT3008 is a micropower device and output
load transient response is a function of output capacitance.
Larger values of output capacitance decrease the peak
deviations and provide improved transient response for
larger load current changes.
Give extra consideration to the use of ceramic capacitors.
Manufacturers make ceramic capacitors with a variety of
20
dielectrics, each with different behavior across temperature
and applied voltage. The most common dielectrics are
speciﬁed with EIA temperature characteristic codes of
Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics
provide high C-V products in a small package at low cost,
but exhibit strong voltage and temperature coefﬁcients as
shown in Figures 2 and 3. When used with a 5V regulator,
a 16V 10μF Y5V capacitor can exhibit an effective value
as low as 1μF to 2μF for the DC bias voltage applied and
over the operating temperature range. The X5R and X7R
dielectrics yield more stable characteristics and are more
suitable for use as the output capacitor. The X7R type has
better stability across temperature, while the X5R is less
expensive and is available in higher values. One must still
exercise care when using X5R and X7R capacitors; the
X5R and X7R codes only specify operating temperature
range and maximum capacitance change over temperature.
Capacitance change due to DC bias with X5R and X7R
capacitors is better than Y5V and Z5U capacitors, but can
still be signiﬁcant enough to drop capacitor values below
appropriate levels. Capacitor DC bias characteristics tend
to improve as component case size increases, but expected
capacitance at operating voltage should be veriﬁed.
40
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
20
X5R
CHANGE IN VALUE (%)
CHANGE IN VALUE (%)
0
–20
–40
–60
Y5V
–80
–100
–20
–40
2
4
8
6
10 12
DC BIAS VOLTAGE (V)
14
16
3008 F02
Figure 2. Ceramic Capacitor DC Bias Characteristics
Y5V
–60
–80
0
X5R
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
–100
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3008 F03
Figure 3. Ceramic Capacitor Temperature Characteristics
3008f
9
LT3008
APPLICATIONS INFORMATION
Voltage and temperature coefﬁcients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor, the stress can be
induced by vibrations in the system or thermal transients.
The resulting voltages produced can cause appreciable
amounts of noise, especially when a ceramic capacitor is
used for noise bypassing. A ceramic capacitor produced
Figure 4’s trace in response to light tapping from a pencil.
Similar vibration induced behavior can masquerade as
increased output voltage noise.
VOUT = 0.6V
COUT = 22μF
ILOAD = 10μA
VOUT
500μV/DIV
100ms/DIV
3008 F04
Figure 4. Noise Resulting from Tapping
on a Ceramic Capacitor
Thermal Considerations
The LT3008’s maximum rated junction temperature of
125°C limits its power-handling capability. Two components
comprise the power dissipated by the device:
1. Output current multiplied by the input/output voltage
differential: IOUT • (VIN – VOUT)
2. GND pin current multiplied by the input voltage:
IGND • VIN
GND pin current is found by examining the GND Pin Current curves in the Typical Performance Characteristics
section. Power dissipation is equal to the sum of the two
components listed prior.
The LT3008 regulator has internal thermal limiting designed
to protect the device during overload conditions. For continuous normal conditions, do not exceed the maximum
junction temperature rating of 125°C. Carefully consider
all sources of thermal resistance from junction to ambient including other heat sources mounted in proximity to
the LT3008. For surface mount devices, heat sinking is
accomplished by using the heat spreading capabilities of
the PC board and its copper traces. Copper board stiffeners and plated through-holes can also be used to spread
the heat generated by power devices.
3008f
10
LT3008
APPLICATIONS INFORMATION
The following tables list thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 two-layer boards with
one ounce copper.
PCB layers, copper weight, board layout and thermal vias
affect the resultant thermal resistance. Although Tables
2 and 3 provide thermal resistance numbers for 2-layer
boards with 1 ounce copper, modern multi-layer PCBs
provide better performance than found in these tables.
For example, a 4-layer, 1 ounce copper PCB board with
3 thermal vias from the DFN exposed backside or the
3 fused TSOT-23 GND pins to inner layer GND planes
achieves 45°C/W thermal resistance. Demo circuit DC
1388A’s board layout achieves this 45°C/W performance.
This is approximately a 30% improvement over the lowest
numbers shown in Tables 2 and 3.
Table 2: Measured Thermal Resistance for DC Package
COPPER AREA
TOPSIDE*
BACKSIDE
BOARD
AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2500mm2
2500mm2
2500mm2
65°C/W
1000mm2
2500mm2
2500mm2
70°C/W
225mm2
2500mm2
2500mm2
75°C/W
100mm2
2500mm2
2500mm2
80°C/W
50mm2
2500mm2
2500mm2
85°C/W
*Device is mounted on the topside.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage range of 12V ±5%, an output current range of 0mA
to 20mA and a maximum ambient temperature of 85°C,
what will the maximum junction temperature be for an
application using the DC package?
The power dissipated by the device is equal to:
IOUT(MAX) (VIN(MAX) – VOUT) + IGND (VIN(MAX))
where,
IOUT(MAX) = 20mA
VIN(MAX) = 12.6V
IGND at (IOUT = 20mA, VIN = 12.6V) = 0.3mA
So,
P = 20mA(12.6V – 3.3V) + 0.3mA(12.6V) = 189.8mW
The thermal resistance ranges from 65°C/W to 85°C/W
depending on the copper area. So the junction temperature
rise above ambient approximately equals:
0.1898W(75°C/W) = 14.2°C
The maximum junction temperature equals the maximum
junction temperature rise above ambient plus the maximum
ambient temperature or:
TJ(MAX) = 85°C + 14.2°C = 99.2°C
Table 3: Measured Thermal Resistance for TSOT-23 Package
COPPER AREA
TOPSIDE*
BACKSIDE
BOARD
AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2500mm2
2500mm2
2500mm2
65°C/W
1000mm2
2500mm2
2500mm2
67°C/W
225mm2
2500mm2
2500mm2
70°C/W
100mm2
2500mm2
2500mm2
75°C/W
50mm2
2500mm2
2500mm2
85°C/W
*Device is mounted on the topside.
3008f
11
LT3008
APPLICATIONS INFORMATION
Protection Features
The LT3008 incorporates several protection features that
make it ideal for use in battery-powered circuits. In addition
to the normal protection features associated with monolithic
regulators, such as current limiting and thermal limiting, the
device also protects against reverse-input voltages, reverseoutput voltages and reverse output-to-input voltages.
Current limit protection and thermal overload protection
protect the device against current overload conditions at
the output of the device. For normal operation, do not
exceed a junction temperature of 125°C.
The IN pin withstands reverse voltages of 50V. The device
limits current ﬂow to less than 20μA (typically less than
1μA) and no negative voltage appears at OUT. The device
protects both itself and the load against batteries that are
plugged in backwards.
The SHDN pin cannot be driven below GND unless tied to
the IN pin. If the SHDN pin is driven below GND while IN
is powered, the output will turn on. SHDN pin logic cannot
be referenced to a negative rail.
The LT3008 incurs no damage if OUT is pulled below
ground. If IN is left open circuit or grounded, OUT can be
pulled below ground by 50V. No current ﬂows from the
pass transistor connected to OUT. However, current ﬂows
in (but is limited by) the resistor divider that sets output
voltage. Current ﬂows from the bottom resistor in the
divider and from the ADJ pin’s internal clamp through the
top resistor in the divider to the external circuitry pulling
OUT below ground. If IN is powered by a voltage source,
OUT sources current equal to its current limit capability
and the LT3008 protects itself by thermal limiting if necessary. In this case, grounding the SHDN pin turns off the
LT3008 and stops OUT from sourcing current.
The LT3008 incurs no damage if the ADJ pin is pulled
above or below ground by 50V. If IN is left open circuit or
grounded, ADJ acts like a 100k resistor in series with a
diode when pulled above or below ground.
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled
to ground, pulled to some intermediate voltage or is left
open circuit. Current ﬂow back into the output follows the
curve shown in Figure 5.
If the LT3008 IN pin is forced below the OUT pin or the
OUT pin is pulled above the IN pin, input current typically
drops to less than 1μA. This occurs if the LT3008 input is
connected to a discharged (low voltage) battery and either
a backup battery or a second regulator circuit holds up
the output. The state of the SHDN pin has no effect in the
reverse current if OUT is pulled above IN.
100
REVERSE CURRENT (μA)
90
80
70
ADJ CURRENT
60
50
40
30
20
OUT CURRENT
10
0
0
1
2 3 4 5 6 7 8 9
OUTPUT AND ADJ VOLTAGE (V)
10
3008 F05
Figure 5. Reverse Output Current
3008f
12
LT3008
TYPICAL APPLICATIONS
Keep-Alive Power Supply
NO PROTECTION
DIODES NEEDED!
VIN
12V
IN
1μF
3.3V
OUT
2.8M
1%
LT3008
SHDN
ADJ
619k
1%
GND
2.2μF
LOAD:
SYSTEM MONITOR,
VOLATILE MEMORY, ETC.
3009 TA02
Last-Gasp Circuit
LINE POWER
VLINE
12V TO 15V
SENSE
DCHARGE
LINE
INTERRUPT
DETECT
RLIMIT
IN
SUPERCAP
1μF
OUT
4.32M
1%
LT3008
SHDN
GND
5V
PWR
2.2μF
FAULT
GND
TO
MONITORING
CENTER
3008 TA03
ADJ
590k
1%
3008f
13
LT3008
PACKAGE DESCRIPTION
DC Package
6-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1703)
R = 0.115
TYP
0.56 p 0.05
(2 SIDES)
0.675 p 0.05
2.50 p 0.05
0.61 p 0.05
1.15 p 0.05 (2 SIDES)
PIN 1 BAR
PACKAGE
TOP MARK
OUTLINE
(SEE NOTE 6)
0.38 p 0.05
4
2.00 p 0.10
(4 SIDES)
PIN 1
CHAMFER OF
EXPOSED PAD
3
0.25 p 0.05
0.50 BSC
1.42 p 0.05
(2 SIDES)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
6
0.75 p 0.05
1
(DC6) DFN 1103
0.25 p 0.05
0.50 BSC
1.37 p 0.05
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3008f
14
LT3008
PACKAGE DESCRIPTION
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1639 Rev Ø)
0.52
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3008f
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.
15
LT3008
TYPICAL APPLICATION
Low Duty Cycle Applications
IN
1μF
OUT
90
2.8M
1%
LT3008
SHDN
100
3.3V
2.2μF
LOW DUTY CYCLE
PULSED LOAD
0 TO 10mA
ADJ
GND
619k
1%
3008 TA04a
80
POWER SAVINGS (%)
VIN
12V
Average Power Savings for Low Duty Cycle Applications
0mA to 10mA Pulsed Load, IN = 12V
70
60
100μA IQ
50
40
30μA IQ
30
20
10
0
0.1
10μA IQ
1
10
DUTY CYCLE (%)
3008 TA04b
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1761
100mA, Low Noise Micropower LDO
VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 20μA, ISD < 1μA, Low Noise < 20μVRMS ,
Stable with 1μF Ceramic Capacitors, ThinSOTTM Package
LT1762
150mA, Low Noise Micropower LDO
VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 25μA, ISD < 1μA, Low Noise < 20μVRMS ,
MS8 Package
LT1763
500mA, Low Noise Micropower LDO
VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 30μA, ISD < 1μA, Low Noise < 20μVRMS ,
S8 Package
LT1764/LT1764A
3A, Low Noise, Fast Transient
Response LDOs
VIN : 2.7V to 20V, VOUT = 1.21V, VDO = 0.34V, IQ = 1mA, ISD < 1μA, Low Noise < 40μVRMS ,
“A” Version Stable with Ceramic Capacitors, DD and TO220-5 Packages
LT1962
300mA, Low Noise Micropower LDO
VIN : 1.8V to 20V, VOUT(MIN) = 1.22V, VDO = 0.27V, IQ = 30μA, ISD < 1μA,
Low Noise: < 20μVRMS , MS8 Package
LT1963/LT1963A
1.5A, Low Noise, Fast Transient
Response LDOs
VIN : 2.1V to 20V, VOUT(MIN) = 1.21V, VDO = 0.34V, IQ = 1mA, ISD < 1μA,
Low Noise: < 40μVRMS , “A” Version Stable with Ceramic Capacitors, DD, TO220-5,
SOT223 and S8 Packages
LT3009
20mA, 3μA IQ Micropower LDO
VIN : 1.6V to 20V, Low IQ: 3μA, VDO = 0.28V, 2mm × 2mm DFN and SC-70-8 Packages
LT3020
100mA, Low Voltage VLDO
VIN : 0.9V to 10V, VOUT(MIN) = 0.20V, VDO = 0.15V, IQ = 120μA, ISD < 1μA, 3mm × 3mm DFN
and MS8 Packages
LT3021
500mA, Low Voltage VLDO
VIN : 0.9V to 10V, VOUT(MIN) = 0.20V, VDO = 0.16V, IQ = 120μA, ISD < 3μA, 5mm × 5mm DFN
and SO8 Packages
LT3080/ LT3080-1
1.1A, Parallelable, Low Noise,
Low Dropout Linear Regulator
300mV Dropout Voltage (2-supply operation), Low Noise: 40μVRMS, VIN: 1.2V to 36V,
VOUT: 0V to 35.7V, current-based reference with 1-resistor VOUT set; directly parallelable
(no op amp required), stable with ceramic caps, TO-220, SOT-223, MSOP and 3 × 3 DFN
Packages; “-1” version has integrated internal ballast resistor
LT3085
500mA, Parallelable, Low Noise,
Low Dropout Linear Regulator
275mV Dropout Voltage (2-supply operation), Low Noise: 40μVRMS, VIN: 1.2V to 36V,
VOUT: 0V to 35.7V, current-based reference with 1-resistor VOUT set; directly parallelable
(no op amp required), stable with ceramic caps, MSOP-8 and 2 × 3 DFN packages
ThinSOT is a trademark of Linear Technology Corporation.
3008f
16 Linear Technology Corporation
LT 1108 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007

Open as PDF

Similar pages