LTC1844ES5-SD#TR [Linear]
LTC1844 - 150mA, Micropower, Low Noise, VLDO Linear Regulator; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C;
| 型号： | LTC1844ES5-SD#TR |
| 厂家： | 
Linear |
| 描述： | LTC1844 - 150mA, Micropower, Low Noise, VLDO Linear Regulator; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C 光电二极管 输出元件 调节器 |
| 文件： | 总12页 (文件大小：183K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1844 Series
150mA, Micropower,
Low Noise, VLDO
Linear Regulator
U
FEATURES
DESCRIPTIO
The LTC 1844 Series are low noise VLDOTM (very low
®
■
Very Low Dropout:
90mV at 150mA
dropout)linearregulatorsdesignedforlowpower/portable
applications. These regulators can operate from input
voltages as low as 1.6V. Typical output noise is only
30µVRMS and typical dropout for the LTC1844-3.3 is just
90mVatthemaximumloadcurrentof150mA, reducingto
30mV at 50mA.
30mV at 50mA (LTC1844-3.3)
■
Wide Input Voltage Range: 1.6V to 6.5V
■
Low 35µA Supply Current, Even in Dropout
■
Low Noise: 60µVRMS (10Hz to 100kHz)
■
±1.75% Voltage Accuracy Over Temperature,
Voltage and Current Ranges
The internal P-channel MOSFET pass transistor requires
no base current, allowing the device to draw only 35µA
during normal operation, independent of the dropout
voltage and load current. The quiescent current falls to a
negligible 10nA during shutdown.
■
Fast Transient Response
■
10nA Supply Current in Shutdown
■
Fixed Output Voltages: 1.5V, 1.8V, 2.5V, 2.8V, 3.3V
■
Adjustable Output Voltage: 1.25V to 6V
Output Current Limit
■
■
Other features include high output voltage accuracy,
excellent transient response, stability with ultralow ESR
ceramic capacitors as small as 1µF, reverse-battery and
reverse-current protection, short-circuit and thermal
overload protection and output current limiting.
Reverse-Battery and Reverse-Current Protection
■
No Protection Diodes Needed
■
Stable with 1µF Output Capacitor
■
Stable with Ceramic Capacitors
■
Short-Circuit and Thermal Overload Protection
■
Low Profile (1mm) SOT-23 Package
The LTC1844 regulators are available in a low profile
(1mm) SOT-23 (ThinSOTTM) package.
U
APPLICATIO S
, LTC and LT are registered trademarks of Linear Technology Corporation.
VLDO and ThinSOT are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
■
Portable Instruments and Battery-Powered Systems
■
Bluetooth/802.11 Cards
■
Cellular Phones
PDAs and Notebook Computers
■
U
TYPICAL APPLICATIO
LTC1844-3.3 Dropout Voltage vs Load Current
120
Fixed Voltage Low Noise, VLDO Linear Regulator
100
80
60
40
20
0
V
V
OUT
3.3V
IN
IN
OUT
3.3V TO 6.5V
1µF
1µF
LTC1844-3.3
OFF ON
SHDN
GND
BYP
0.1µF
1844 TA01
0
50
75
(mA)
100
125
150
25
I
OUT
1844 TA02
1844fa
1
LTC1844 Series
W W
U W
ABSOLUTE AXI U RATI GS (Note 1)
Supply Voltage (IN) ....................................... –7V to 7V
Input Voltage
Output Short-Circuit Duration......................... Indefinite
Operating Junction Temperature Range
SHDN, BYP, ADJ .................................... –0.3V to 7V
Output Voltage
(Notes 2, 10) .....................................–40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
OUT ........................................................ –0.3V to 7V
OUT to IN .................................................. –7V to 7V
U W
U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
TOP VIEW
TOP VIEW
IN 1
GND 2
BYP 3
5 OUT
4 ADJ
IN 1
GND 2
5 OUT
4 ADJ
IN 1
GND 2
5 OUT
4 BYP
SHDN 3
SHDN 3
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 250°C/ W, θJC = 90°C/ W
SEE THE APPLICATIONS INFORMATION SECTION
TJMAX = 125°C, θJA = 250°C/ W, θJC = 90°C/ W
TJMAX = 125°C, θJA = 250°C/ W, θJC = 90°C/ W
SEE THE APPLICATIONS INFORMATION SECTION
SEE THE APPLICATIONS INFORMATION SECTION
S5 PART
MARKING
S5 PART
MARKING
S5 PART
MARKING
ORDER PART
NUMBER
ORDER PART
NUMBER
ORDER PART
NUMBER
LTF1
LTF2
LTF3
LTQK
LTF4
LTE8
LTE9
LTC1844ES5-1.5
LTC1844ES5-1.8
LTC1844ES5-2.5
LTC1844ES5-2.8
LTC1844ES5-3.3
LTC1844ES5-SD
LTC1844ES5-BYP
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating
+ 0.5V, unless otherwise noted. (Note 2)
temperature range, otherwise specifications are at T = 25°C. V = V
OUT
A
IN
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
Input Voltage
●
1.6
6.5
V
IN
I
Quiescent Current
SHDN = V
35
55
80
µA
µA
IN
IN
●
●
I
V
Shutdown Supply Current
IN
SHDN = 0V
0.01
1
µA
INSHDN
V
Regulated Output Voltage
(Notes 3, 4, 5)
LTC1844-3.3
LTC1844-3.3
V
V
= 3.8V to 6.5V, I
= 3.8V to 6.5V, I
= 0mA to 150mA
= 0mA to 150mA
–1.50
–1.75
1.50
1.75
%V
%V
OUT%
IN
IN
OUT
OUT
OUT
OUT
●
●
●
●
LTC1844-2.8
LTC1844-2.8
V
V
= 3.3V to 6.5V, I
= 3.3V to 6.5V, I
= 0mA to 150mA
= 0mA to 150mA
–1.50
–1.75
1.50
1.75
%V
%V
IN
IN
OUT
OUT
OUT
OUT
LTC1844-2.5
LTC1844-2.5
V
V
= 3.0V to 6.5V, I
= 3.0V to 6.5V, I
= 0mA to 150mA
= 0mA to 150mA
–1.50
–1.75
1.50
1.75
%V
%V
IN
IN
OUT
OUT
OUT
OUT
LTC1844-1.8
LTC1844-1.8
V
V
= 2.3V to 6.5V, I
= 2.3V to 6.5V, I
= 0mA to 150mA
= 0mA to 150mA
–1.50
–1.75
1.50
1.75
%V
%V
IN
IN
OUT
OUT
OUT
OUT
1844fa
2
LTC1844 Series
ELECTRICAL CHARACTERISTICS
The
temperature range, otherwise specifications are at T = 25°C. V = V
OUT
●
denotes specifications which apply over the full operating
+ 0.5V, unless otherwise noted. (Note 2)
A
IN
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LTC1844-1.5
LTC1844-1.5
LTC1844-1.5
V
V
V
= 2.0V to 6.5V, I
= 2.2V to 6.5V, I
= 2.0V to 6.5V, I
= 0mA to 150mA
= 0mA to 150mA
= 0mA to 100mA
–1.50
–2.00
–2.50
1.50
2.00
2.00
%V
%V
%V
IN
IN
IN
OUT
OUT
OUT
OUT
OUT
OUT
●
●
LTC1844-BYP
LTC1844-BYP
LTC1844-BYP
V
V
V
= 1.75V to 6.5V, I
= 0mA to 150mA
–1.50
–1.75
–3.50
1.50
1.75
1.75
%V
%V
%V
IN
IN
IN
OUT
OUT
OUT
OUT
= 2.2V to 6.5V, I
= 0mA to 150mA
●
●
OUT
= 1.75V to 6.5V, I
= 0mA to 100mA
OUT
LTC1844-SD
LTC1844-SD
LTC1844-SD
V
V
V
= 1.75V to 6.5V, I
= 0mA to 150mA
–1.50
–1.75
–3.50
1.50
1.75
1.75
%V
%V
%V
IN
IN
IN
OUT
OUT
OUT
OUT
= 2.2V to 6.5V, I
= 0mA to 150mA
●
●
OUT
= 1.75V to 6.5V, I
= 0mA to 100mA
OUT
V
ADJ Pin Voltage (Notes 3, 5)
Line Regulation (Notes 3, 5)
LTC1844-BYP
LTC1844-BYP
LTC1844-BYP
V
V
V
= 1.75V to 6.5V, I
= 0mA to 150mA
1.233
1.230
1.208
1.25
1.25
1.271
1.274
1.274
V
V
V
ADJ
IN
IN
IN
OUT
= 2.2V to 6.5V, I
= 0mA to 150mA
●
●
OUT
= 1.75V to 6.5V, I
= 0mA to 100mA
OUT
LTC1844-SD
LTC1844-SD
LTC1844-SD
V
V
V
= 1.75V to 6.5V, I
= 0mA to 150mA
1.233
1.230
1.208
1.271
1.274
1.274
V
V
V
IN
IN
IN
OUT
= 2.2V to 6.5V, I
= 0mA to 150mA
●
●
OUT
= 1.75V to 6.5V, I
= 0mA to 100mA
OUT
∆V
LTC1844-3.3
LTC1844-2.8
LTC1844-2.5
LTC1844-1.8
V
V
V
= 3.4V to 6.5V, I = 1mA
●
●
●
●
4
4
4
20
20
20
mV
mV
mV
LNR
IN
IN
IN
L
= 2.9V to 6.5V, I = 1mA
L
= 2.6V to 6.5V, I = 1mA
L
V
V
V
= 2.2V to 6.5V, I = 1mA
4
4
4
20
20
30
mV
mV
mV
IN
IN
IN
L
= 1.9V to 6.5V, I = 1mA
L
= 1.9V to 6.5V, I = 1mA
●
●
L
LTC1844-1.5
LTC1844-BYP
LTC1844-SD
V
V
V
= 2.2V to 6.5V, I = 1mA
4
4
4
20
20
80
mV
mV
mV
IN
IN
IN
L
= 1.6V to 6.5V, I = 1mA
L
= 1.6V to 6.5V, I = 1mA
●
●
L
V
V
V
= 2.2V to 6.5V, I = 1mA
4
4
4
20
20
80
mV
mV
mV
IN
IN
IN
L
= 1.6V to 6.5V, I = 1mA
L
= 1.6V to 6.5V, I = 1mA
●
●
L
V
V
V
= 2.2V to 6.5V, I = 1mA
4
4
4
20
20
80
mV
mV
mV
IN
IN
IN
L
= 1.6V to 6.5V, I = 1mA
L
= 1.6V to 6.5V, I = 1mA
●
●
●
●
●
L
∆V
Load Regulation (Notes 3, 5)
LTC1844-3.3
LTC1844-2.8
LTC1844-2.5
LTC1844-1.8
LTC1844-1.5
V
V
V
V
= 3.8V, I
= 3.3V, I
= 3.0V, I
= 2.3V, I
= 0mA to 150mA
= 0mA to 150mA
= 0mA to 150mA
= 0mA to 150mA
9
9
9
9
20
20
20
20
mV
mV
mV
mV
LDR
IN
IN
IN
IN
OUT
OUT
OUT
OUT
V
V
= 2.2V, I
= 2.0V, I
= 0mA to 150mA
= 0mA to 100mA
●
●
9
9
20
40
mV
mV
IN
IN
OUT
OUT
LTC1844-BYP
LTC1844-SD
LTC1844-3.3
LTC1844-2.8
LTC1844-2.5
LTC1844-1.8
V
V
= 2.2V, I
= 0mA to 150mA
OUT
●
●
9
9
20
50
mV
mV
IN
IN
OUT
= 1.75V, I
= 0mA to 100mA
V
V
= 2.2V, I
= 0mA to 150mA
●
●
9
9
20
50
mV
mV
IN
IN
OUT
= 1.75V, I
= 0mA to 100mA
OUT
∆V
Dropout Voltage (Notes 6, 7)
I
I
= 50mA
= 150mA
●
●
30
90
55
150
mV
mV
DO
OUT
OUT
I
I
= 50mA
= 150mA
●
●
35
105
60
165
mV
mV
OUT
OUT
I
I
= 50mA
= 150mA
●
●
45
135
75
200
mV
mV
OUT
OUT
I
I
= 50mA
= 150mA
●
●
85
230
120
300
mV
mV
OUT
OUT
1844fa
3
LTC1844 Series
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating
+ 0.5V, unless otherwise noted. (Note 2)
temperature range, otherwise specifications are at T = 25°C. V = V
A
IN
OUT
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LTC1844-1.5
LTC1844-BYP
LTC1844-SD
I
I
= 50mA
●
●
115
350
160
450
mV
mV
OUT
OUT
= 150mA
I
I
= 50mA
= 150mA
●
●
45
135
75
200
mV
mV
OUT
OUT
I
I
= 50mA
= 150mA
●
●
45
135
75
200
mV
mV
OUT
OUT
I
Output Current Limit
Output Voltage Noise
●
160
350
mA
LIM
e
f = 10Hz to 100kHz, C = 0.1µF, C
= 10µF, I = 150mA
60
65
µV
µV
n
BP
OUT
OUT
L
RMS
RMS
f = 10Hz to 100kHz, C = 0.1µF, C
= 1µF, I = 150mA
BP
L
V
SHDN Input Threshold
Shutdown Exit Delay
●
●
0.35
0.65
70
0.9
V
SHDN
t
C
C
= 0.01µF, C
= 0.01µF, C
= 1µF, No load
= 1µF, No load
100
200
µs
µs
DELAY
BP
BP
OUT
OUT
T
Thermal Shutdown Limit
Thermal Shutdown Hysteresis
ADJ Pin Bias Current
155
10
°C
°C
nA
µA
SHDN
∆T
SHDN
I
I
(Notes 3, 8)
LTC1844-3.3, LTC1844-2.8, LTC1844-2.5, LTC1844-1.8,
LTC1844-1.5, V = –5V, V = 0V
●
●
30
100
500
ADJ
Input Reverse Leakage Current
200
IRL
IN
OUT
LTC1844-BYP, LTC1844-SD, V = –5V, V
= 0V
●
●
1000
0.01
1500
µA
IN
OUT
I
Output Reverse Leakage Current
(Note 9)
V
V
= 0V, V
= 0V, V
= V
= V
0.1
1.2
µA
µA
ORL
IN
IN
OUT
OUT
OUT(NOMINAL)
OUT(NOMINAL)
V
V
Start-Up Overshoot
R = 1k, SHDN Rise Time ≤ 1µs
2
%V
OUT
OSH
RP
L
Output Ripple Rejection
(V – V ) = 1V (Avg), V
= 0.5V ,
P-P
50
dB
IN
OUT
RIPPLE
f
= 120Hz, I
= 100mA
RIPPLE
LOAD
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1844 is tested and specified under pulse load conditions
Note 6: To ensure adequate input supply voltage, the LTC1844 adjustable
versions are tested and specified for these conditions with an external
resistor divider (two 100k resistors) for an output voltage of 2.50V. The
external resistor divider will add a 5µA load on the output.
such that T ≈ T . The LTC1844E is guaranteed to meet performance
J
A
specifications from 0°C to 70°C. Specifications over the –40°C to 125°C
operating junction temperature range are assured by design,
characterization and correlation with statistical process controls.
Note 7: Dropout voltage is (V – V ) when V falls to 100mV below
IN
OUT
OUT
its nominal value measured at V = V
LTC1844-3.3 is tested by measuring the V
+ 0.5V. For example, the
IN
OUT
at V = 3.8V, then V is
IN IN
OUT
lowered until V
falls 100mV below the measured value. The difference
Note 3: The LTC1844 adjustable versions are tested and specified for
these conditions with the ADJ pin connected to the OUT pin for a
OUT
(V – V ) is then measured and defined as ∆V .
IN
OUT
DO
V
of 1.25V.
Note 8: ADJ pin bias current flows into the ADJ pin.
OUT(NOMINAL)
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 maximum input voltage, the output current range must be
limited. When operating at maximum output current, the input voltage
range must be limited.
Note 9: Output reverse leakage current is tested with the IN pin grounded
and the OUT pin forced to the rated output voltage.
Note 10: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 5: The LTC1844’s high precision degrades slightly at high
temperatures (T > 70°C) with input voltages below 2.2V. The lower output
J
voltage versions have been split into higher and lower accuracy input
voltage ranges to reflect this.
1844fa
4
LTC1844 Series
U W
TYPICAL PERFOR A CE CHARACTERISTICS
V
vs Temperature
V
vs Temperature
V vs Temperature
OUT
OUT
OUT
1.520
2.520
1.820
V
= 1.5V
V
= 2.5V
V
= 1.8V
OUT
OUT
OUT
1.515
1.510
2.515
2.510
1.815
1.810
1.505
1.500
1.495
1.490
1.485
2.505
2.500
2.495
2.490
2.485
1.805
1.800
1.795
1.790
1.785
1.480
2.480
1.780
–25
0
50
75 100 125
–25
0
50
75 100 125
–50
25
–50
25
–25
0
50
75 100 125
–50
25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1844 G01
1844 G03
1844 G02
V
vs Temperature
V
vs Temperature
V
vs Temperature
OUT
OUT
OUT
2.820
3.320
1.270
V
= 2.8V
V
= 3.3V
V = ADJ
OUT
OUT
OUT
2.815
2.810
3.315
3.310
1.265
1.260
2.805
2.800
2.795
2.790
2.785
3.305
3.300
3.295
3.290
3.285
1.255
1.250
1.245
1.240
1.235
2.780
3.280
1.230
–25
0
50
75 100 125
–25
0
50
75 100 125
–25
0
50
75 100 125
–50
25
–50
25
–50
25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1844 G04
1844 G05
1844 G05
Quiescent Current vs Temperature
Current Limit vs Temperature
SHDN Threshold vs Temperature
70
60
500
450
400
350
800
I
= 1mA
V
= 2.8V
LOAD
OUT
750
700
50
40
30
20
10
650
600
550
500
450
300
250
200
0
400
50
TEMPERATURE (°C)
100 125
50
TEMPERATURE (°C)
100 125
–25
0
50
75 100 125
–50 –25
0
25
75
–50 –25
0
25
75
–50
25
TEMPERATURE (°C)
1844 G07
1844 G08
1844 G09
1844fa
5
LTC1844 Series
TYPICAL PERFOR A CE CHARACTERISTICS
U W
RMS Output Noise vs Load
Current (10Hz to 100kHz)
Input Ripple Rejection
vs Frequency
Input Ripple Rejection
vs Temperature
300
100
90
60
50
40
30
C
C
I
= 10µF
OUT
BYP
L
= 1000pF
= 100µA
250
200
C
= 0µF
BYP
80
70
60
50
150
100
40
30
20
10
0
20
10
0
C
= 0.1µF
BYP
50
0
0.01
0.1
1
10
100
1000
10
100
1k
10k
100k
1M
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
LOAD CURRENT (mA)
FREQUENCY (Hz)
1844 G10
1844 G11
1844 G12
U
U
U
PI FU CTIO S
IN(Pin1):PowerforLTC1844andLoad.Powerissupplied
to the device through the IN pin. The IN pin should be
locally bypassed to ground if the LTC1844 is more than a
few inches away from another source of bulk capacitance.
In general, the output impedance of a battery rises with
frequency, so it is usually advisable to include an input
bypass capacitor in battery-powered circuits. A capacitor
in the range of 0.1µF to 1µF is usually sufficient. The
LTC1844 is designed to withstand reverse voltages on the
IN pin with respect to both ground and the output pin. In
the case of a reversed input, which can happen if a battery
is plugged in backwards, the LTC1844 will act as if there
is a large resistor in series with its input and only a small
amount of current will flow.
ADJ (Pin 4, Adjustable Devices): Output Adjust. For the
adjustable versions of the LTC1844, this is the input to the
erroramplifier. Ithasatypicalbiascurrentof30nAflowing
into the pin. The ADJ pin reference voltage is 1.25V
referencedtoground. Theoutputvoltagerangeis1.25Vto
6V and is typically set by connecting ADJ to a resistor
divider from OUT to GND. See Figure 2.
BYP (Pin 4, Fixed/Pin 3, BYP Devices): Noise Bypass.
The BYP pin is used to augment the internal noise filter to
improve low noise performance. A small low leakage
bypasscapacitorfromthispintogroundwillfiltertheinput
of the error amplifier to lower the output voltage noise.
Any value may be used; larger values will result in lower
output noise, but will increase initial power-up time.
Shutdown exit delay time after a brief shutdown (<10ms)
will not be affected. If not used, this pin must be left
unconnected.
GND (Pin 2): Ground and Heat Sink. Solder to a ground
plane or large pad to maximize heat dissipation.
SHDN (Pin 3, Fixed and SD Devices): Shutdown, Active
Low. This pin is used to put the LTC1844 into shutdown.
The SHDN pin current is typically less than 10nA. The
SHDN pin cannot be left floating and must be tied to the
input pin if not used. If reverse-battery protection is
desired,theSHDNpinmustbetiedtotheinputpinthrough
a large value resistor (10kto1M).
OUT (Pin 5): Voltage Regulated Output. The OUT pin
suppliespowertotheload. Aminimumoutputcapacitorof
1µFisrequiredtoensurestability.Largeroutputcapacitors
may be required for applications with large transient loads
to limit peak voltage transients. See the Applications
Information section for more information on output
capacitance.
1844fa
6
LTC1844 Series
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APPLICATIO S I FOR ATIO
U
The LTC1844 family are a series of 150mA ultralow
dropout regulators with micropower quiescent current
and shutdown. The devices are capable of supplying
150mA at a dropout voltage of 90mV (LTC1844-3.3, see
Electrical Characteristics for dropout voltage of other
versions). Output voltage noise is as low as 30µVRMS over
a 10Hz to 100kHz bandwidth with the addition of a 0.1µF
bypass capacitor. The low operating quiescent current
(35µA) drops to 10nA in shutdown.
Adjustable Operation
The adjustable version of the LTC1844 has an output
voltage range of 1.25V to 6V. The output voltage is set by
theratiooftwoexternalresistorsasshowninFigure2.The
device servos the output to maintain the ADJ pin voltage
at 1.25V (referenced to ground). The current in R1 is then
equalto1.25V/R1andthecurrentinR2isthecurrentinR1
plus the ADJ pin bias current. The ADJ pin bias current,
30nA at 25°C, flows through R2 into the ADJ pin. The
output voltage can be calculated using the formula in
Figure 2. The value of R1 should be no greater than 1MΩ
to minimize errors in the output voltage caused by the ADJ
pinbiascurrent.Notethatinshutdowntheoutputisturned
off and the divider current will be zero once COUT is
discharged.
In addition to the low quiescent current, the LTC1844
regulators incorporate several protection features which
make them ideal for use in battery-powered systems. The
devices are protected against both reverse input voltages
and reverse voltages from output to input (reverse current
protection). The devices also include current limit and
thermal overload protection, and will survive an output
short circuit indefinitely. The fast transient response over-
comes the traditional tradeoff between dropout voltage,
quiescent current and load transient response inherent in
most regulators by using a proprietary new architecture
(see Figure 1).
Adjustable devices are tested and specified with the ADJ
pin tied to the OUT pin for an output voltage of 1.25V.
Specifications for output voltages greater than 1.25V will
be proportional to the ratio of the desired output voltage to
1.25V: VOUT/1.25V. For example, load regulation for an
V
C
C
= 3V
IN
IN
0.04
0.02
0
= 1µF
IN
OUT
LTC1844
V
OUT
= 1µF
OUT
+
C
FF
V
IN
R2
R1
ADJ
–0.02
–0.04
GND
1844 F02
R2
R1
⎛
⎝
⎞
⎟
⎠
50
0
VOUT = 1.25V 1+
+ I
R2
(
ADJ)(
)
⎜
VADJ = 1.25V
IADJ = 30nA AT 25°C
OUTPUT RANGE = 1.25V TO 6V
CFF RECOMMENDED— SEE TEXT
0
10 20 30 40 50 60 70 80 90 100
TIME (µs)
1844 F01
Figure 2. Adjustable Operation
Figure 1. LTC1844-2.5 Transient Response 1mA to 50mA to 1mA
1844fa
7
LTC1844 Series
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APPLICATIO S I FOR ATIO
delay can be much shorter (≈70µs) than initial power-up
time if the shutdown duration is brief (<10ms). The
maximum shutdown duration required to allow fast shut-
down exit is determined by the capacitor leakage current,
thus a low leakage bypass capacitor is recommended.
output current change of 1mA to 100mA is –4mV typical
at VOUT = 1.25V. At VOUT = 5V, load regulation is:
(5V/1.25V)(–4mV) = –16mV
BecausetheADJpinisrelativelyhighimpedance(depend-
ing on the resistor divider used), stray capacitance at this
pin can introduce significant phase shift in the error
amplifier loop. The PCB layout should be designed to
absolutely minimize the capacitance seen at the ADJ pin.
To ensure stability over all operating conditions when
utilizing large divider resistors, a small feedforward ca-
pacitor (≈1000pF) in parallel with the upper divider resis-
tor (CFF in Figure 2) is recommended. As an added bonus,
this capacitor will improve transient response.
Output Capacitance and Transient Response
The LTC1844 regulators are designed to be stable with a
wide range of output capacitors. The ESR of the output
capacitor affects stability, most notably with small capaci-
tors. A minimum output capacitor of 1µF with an ESR of
0.3Ω or less is recommended to ensure stability. The
LTC1844 is a micropower device and output transient
response will be a function of output capacitance. Larger
values of output capacitance decrease the peak deviations
and provide improved transient response for larger load
current changes. Note that bypass capacitors used to
decoupleindividualcomponentspoweredbytheLTC1844
will increase the effective output capacitor value. The
shaded region of Figure 3 defines the region over which
the LTC1844 regulators are stable. The maximum ESR
allowed is 0.3Ω. High ESR tantalum and electrolytic ca-
pacitors may be used, but a low ESR ceramic capacitor
mustbeinparallelattheoutput. ThereisnominimumESR
requirement.
Bypass Capacitance and Low Noise Performance
A bypass capacitor can optionally be connected from the
BYP pin to ground to lower output voltage noise. A good
quality low leakage capacitor is recommended. This ca-
pacitor will bypass the input of the error amplifier, provid-
ing a low frequency noise pole. The noise pole provided by
thisbypasscapacitorwilllowertheoutputvoltagenoiseto
as low as 30µVRMS with the addition of a 0.1µF capacitor.
Initial regulator power-up time is inversely proportional to
the size of the bypass capacitor, slowing to 10ms with a
0.1µF bypass capacitor and 10µF output capacitor. How-
ever, the LTC1844 does not discharge the bypass capaci-
tor when put into shutdown and thus the shutdown exit
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
STABLE REGION
0.33
1
3.3
10
33
100
OUTPUT CAPACITANCE (µF)
1844 F03
Figure 3. Stability
1844fa
8
LTC1844 Series
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APPLICATIONS INFORMATION
temperature and applied voltage. The most common di-
electrics used are Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but exhibit strong voltage and tem-
perature coefficients as shown in Figures 4 and 5. When
used with a 5V regulator, a 10µF Y5V capacitor can exhibit
an effective value as low as 1µF to 2µF over the operating
temperature range. The X5R and X7R dielectrics result in
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.
Additionally,someceramiccapacitorshaveapiezoelectric
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, espe-
cially when a ceramic capacitor is used for noise bypass-
ing. A ceramic capacitor produced Figure 6’s trace in
response to light tapping from a pencil. Similar vibration-
induced behavior can masquerade as increased output
voltage noise.
LTC1844-2.8
COUT = 10µF
CBYP = 0.01µF
20
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
ILOAD = 100mA
0
X5R
–20
VOUT
500µV/DIV
–40
–60
Y5V
–80
100ms/DIV
1844 F06
–100
0
8
12 14
2
4
6
10
16
DC BIAS VOLTAGE (V)
Figure 6. Noise Resulting from Tapping on a Ceramic Capacitor
1844 F04
Figure 4. Ceramic Capacitor DC Bias Characteristics
Dropout Recovery and Output Overshoot
40
20
If the input supply voltage drops too low for the LTC1844
to maintain regulation, the internal feedback loop goes
intodropoutandtheinternalpasstransistorturnsfullyon.
If the input supply then suddenly rises, the output may
briefly overshoot the intended output voltage while the
LTC1844 transitions back from dropout to normal opera-
tion. This behavior occurs when the input supply slew rate
is greater than 1V/ms and the output bypass capacitor is
small. If the input is expected to slew rapidly, an output
bypass capacitor of 10µF or greater should be used to
minimize output overshoot. Note that overshoot typically
does not occur at start-up since the feedback loop does
not spend a significant amount of time in dropout.
X5R
0
–20
–40
Y5V
–60
–80
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–100
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
1844 F05
Figure 5. Ceramic Capacitor Temperature Characteristics
1844fa
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LTC1844 Series
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APPLICATIONS INFORMATION
Thermal Considerations
The power dissipated by the device will be equal to:
IOUT(MAX)(VIN(MAX) – VOUT
where:
OUT(MAX) = 50mA
VIN(MAX) = 6V
So:
The power handling capability of the device will be limited
bythemaximumratedjunctiontemperature(125°C). The
power dissipated by the device will be the output current
multiplied by the input/output voltage differential:
(IOUT)(VIN – VOUT).
)
I
The LTC1844 series regulators have internal thermal lim-
iting designed to protect the device during momentary
overload conditions. For continuous normal conditions,
the maximum junction temperature rating of 125°C must
not be exceeded. It is important to give careful consider-
ation to all sources of thermal resistance from junction to
ambient. Additional heat sources mounted nearby must
also be considered.
P = 50mA(6V – 3.3V) = 0.135W
The power dissipated by the LTC1844’s quiescent current
(240µW) is insignificant. The thermal resistance will be in
the range of 125°C/W to 150°C/W depending on the
copper area. The junction temperature rise above ambient
will be approximately equal to:
0.135W(150°C/W) = 20.3°C
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 gener-
ated by power devices.
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
T = 50°C + 20.3°C = 70.3°C
Table 1 lists thermal resistance for several different board
sizes and copper areas. All measurements were taken in
still air on 3/32" FR-4 board with one ounce copper.
Protection Features
The LTC1844 regulators incorporate several protection
featureswhichmakethemidealforuseinbattery-powered
circuits. In addition to the usual protection features asso-
ciated with monolithic regulators, such as current limiting
and thermal limiting, the devices are protected against
reverseinputvoltagesandreversevoltagesfromoutputto
input.
Table 1. Measured Thermal Resistance
COPPER AREA
THERMAL RESISTANCE
TOPSIDE*
2500mm2
1000mm2
225mm2
100mm2
50mm2
BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
125°C/W
125°C/W
130°C/W
135°C/W
150°C/W
Current limit protection and thermal overload protection
areintendedtoprotectthedeviceagainstcurrentoverload
conditions at the output of the device. For normal opera-
tion, the junction temperature should not exceed 125°C.
*Device is mounted on topside.
Calculating Junction Temperature
The input of the device will withstand input voltages of
–7V. Current flow into the device will be limited to less
than 500µA (typically less than 200µA) and only a small
negative voltage will appear at the output (~–300mV with
no load). The LTC1844 will protect both itself and the load
against batteries plugged in backward. The shutdown pin
will require current limiting if used (see Pin Functions).
Example: Given an output voltage of 3.3V, an input voltage
of 4V to 6V, an output current range of 0mA to 50mA and
a maximum ambient temperature of 50°C, what will the
maximum junction temperature be?
1844fa
10
LTC1844 Series
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APPLICATIONS INFORMATION
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up externally while the input is either
pulled to ground, pulled to some intermediate voltage or
left open circuit. The LTC1844 features reverse current
protection to limit current draw from any supplementary
power source at the output. When VIN is pulled to ground
or is left open circuit, IIN and IOUT are less than 0.1µA for
VOUT = 0V to 7V.
trying to pull VOUT up. With VOUT held between VOUT(NOM)
and VIN, IIN will be at the normal quiescent current level
and IOUT will be 1µA to 2µA. As VOUT is pulled above VIN,
I
OUT temporarily increases to 30µA until the reverse cur-
rent protection circuitry activates and reduces IOUT to less
than 10µA.
Alternatively, when VOUT is held constant and VIN varied,
currentflowwillfollowFigure8’scurves. IOUT willbeless
than 10µA at all times except for a brief spike just below
2.7V before the reverse current protection circuitry
activates.
When VIN is held constant and VOUT varied, current flow
will follow the curves shown in Figure 7. With VOUT held
below VOUT(NOM), the LTC1844 will be in current limit
50
100
LTC1844-2.8
LTC1844-2.8
IN CURRENT
90
45
T
= 25°C
T
= 25°C
J
IN
J
LIMIT ABOVE
2.7V
V
= 3.3V
V
= 2.7V
OUT
40
35
30
25
20
15
10
5
80
70
60
50
40
30
20
10
0
CURRENT FLOWS
INTO PINS
CURRENT FLOW
INTO PINS
IN CURRENT
LIMIT BELOW
2.8V
I
IN
I
I
IN
OUT
3
I
OUT
0
0
2
4
5
6
7
1
0
0.5
1.5
2.0
2.5
3.0
1.0
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1844 F07
1844 F08
Figure 8. Reverse Current vs Input Voltage
Figure 7. Reverse Current vs Output Voltage
1844fa
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.
11
LTC1844 Series
U
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.50 – 1.75
(NOTE 4)
2.80 BSC
1.4 MIN
3.85 MAX 2.62 REF
PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.90 BSC
0.09 – 0.20
(NOTE 3)
NOTE:
S5 TSOT-23 0302
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
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LT1761
LT1762
100mA, Low Noise LDO in ThinSOT
300mV Dropout Voltage, Low Noise: 20µV
300mV Dropout Voltage, Low Noise: 20µV
MS8 Package
, V = 1.8V to 20V, ThinSOT
RMS IN
150mA, Low Noise LDO
, V = 1.8V to 20V,
RMS IN
LT1763
500mA, Low Noise LDO
300mV Dropout Voltage, Low Noise: 20µV , V = 1.8V to 20V, SO-8 Package
RMS IN
LT1764A
3A, Fast Transient Response, Low Noise LDO
340mV Dropout Voltage, Low Noise: 40µV
TO-220 and DD Packages
, V = 2.7V to 20V,
RMS IN
LT1962
300mA, Low Noise LDO
270mV Dropout Voltage, Low Noise: 20µV
MS8 Package
, V = 1.8V to 20V,
RMS IN
LT1963A
1.5A Low Noise, Fast Transient Response LDO
200mA, Low Noise, Negative LDO
340mV Dropout Voltage, Low Noise: 40µV
, V = 2.5V to 20V, TO-220, DD,
RMS IN
SOT-223 and SO-8 Packages
LT1964
LT3150
340mV Dropout Voltage, Low Noise 30µV
, V = –1.8V to –20V, ThinSOT
RMS IN
Fast Transient Response, VLDO Regulator
Controller
0.035mV Dropout Voltage via External FET, V : 1.3V to 10V
IN
1844fa
LT/TP 0905 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2003
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