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LT3055

3055f

For more information www.linear.com/LT3055

TYPICAL APPLICATION

FEATURES DESCRIPTION

500mA, Linear Regulator

with Precision Current Limit

and Diagnostics

The LT

3055 is a micropower, low noise, low dropout volt-

age (LDO) linear regulator. The device supplies 500mA of

output current with a dropout voltage of 350mV. A 10nF

bypass capacitor reduces output noise to 25μV

RMS

in a

10Hz to 100kHz bandwidth and soft starts the reference.

The LT3055’s ±45V input voltage rating combined with its

precision current limit and diagnostic functions make the

IC an ideal choice for robust, high reliability applications.

A single resistor programs the LT3055’s current limit, ac-

curate to ±10% over a wide input voltage and temperature

range. Another resistor programs the LT3055’s minimum

output current monitor, useful for detecting open-circuit

conditions. The current monitor function sources a current

equal to 1/500th of output current. Logic fault pins assert

low if the LT3055 is in current limit (FAULT2), operating

below its minimum output current (FAULT1) or is in thermal

limit (both FAULT1 and FAULT2). PWRGD indicates output

regulation. The TEMP pin indicates average die temperature.

The LT3055 optimizes stability and transient response

with low ESR ceramic capacitors, requiring a minimum of

3.3μF. Internal protection circuitry includes current limit-

ing, thermal limiting, reverse battery protection, reverse

current protection and reverse output protection.

The LT3055 is available as an adjustable device with an

output voltage range from 0.6V to 40V.

5V Supply with 497mA Precision Current Limit, 10mA I

MIN

Precision Current Limit, R

IMAX

= 604Ω

APPLICATIONS

Output Current: 500mA

Dropout Voltage: 350mV

Input Voltage Range: 2V to 45V

Programmable Precision Current Limit: ±10%

Output Current Monitor: 1/500th of I

OUT

Programmable Minimum I

OUT

Monitor

Temperature Monitor: 10mV/°C

FAULT Indicator: Current Limit, Thermal Limit or

Minimum I

OUT

Low Noise: 25μV

RMS

(10Hz to 100kHz)

Adjustable Output (V

REF

= V

OUT(MIN)

= 0.6V)

Output Tolerance: ±2% Over Load, Line and Temperature

Stable with Low ESR, Ceramic Output Capacitors

(3.3μF Minimum)

Shutdown Current: <1μA

Reverse Battery and Thermal Limit Protection

16-Lead 4mm × 3mm DFN and MSOP Packages

Protected Antenna Supplies

Automotive Telematics

Industrial Applications (Trucks, Forklifts, etc.)

High Reliability Applications

Noise-Sensitive RF or DSP Supplies

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

OUT

LT3055

GND

ADJ

MAX

MIN

PWRGD

SHDN

442k

200k200k200k

60.4k

(ADC

FULL-SCALE = 1V)

604Ω

(THRESHOLD = 497mA)

10nF

10µF10µF

22nF

120k

(THRESHOLD = 10mA)

0.1µF

12V

MON

0.1µF

10nF

3055 TA01a

µP

ADC

TEMP

REF/BYP

µP

ADC

FAULT1

FAULT2

TEMPERATURE (°C)

–75

CURRENT LIMIT FAULT THRESHOLD (mA)

510

530

550

125

3055 TA01b

490

470

500

520

540

480

460

450

–25

–50 150

100

175

OUT(NOMINAL)

= 5V

= 7V

= 5.6V

Summary of content (24 pages)

PAGE 1
LT3055 500mA, Linear Regulator with Precision Current Limit and Diagnostics DESCRIPTION FEATURES n n n n n n n n n n n n n n Output Current: 500mA Dropout Voltage: 350mV Input Voltage Range: 2V to 45V Programmable Precision Current Limit: ±10% Output Current Monitor: 1/500th of IOUT Programmable Minimum IOUT Monitor Temperature Monitor: 10mV/°C FAULT Indicator: Current Limit, Thermal Limit or Minimum IOUT Low Noise: 25μVRMS (10Hz to 100kHz) Adjustable Output (VREF = VOUT(MIN) = 0.
PAGE 2
LT3055 ABSOLUTE MAXIMUM RATINGS (Note 1) IN Pin Voltage..........................................................±50V OUT Pin Voltage............................................ +40V, –50V Input-to-Output Differential Voltage...............+50V, –40V ADJ Pin Voltage.......................................................±50V SHDN Pin Voltage....................................................±50V FAULT1, FAULT2, PWRGD Pin Voltage.............–0.3V, 50V IMON Pin Voltage......................................
PAGE 3
LT3055 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 2) PARAMETER CONDITIONS Minimum Input Voltage (Note 3, 11) ILOAD = 500mA ADJ Pin Voltage (Note 3, 4) VIN = 2.2V, ILOAD = 1mA 2.2V < VIN < 45V, 1mA < ILOAD < 500mA Line Regulation (Note 3) ∆VIN = 2.2V to 45V, ILOAD = 1mA Load Regulation (Note 3) VIN = 2.
PAGE 4
LT3055 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 2) PARAMETER CONDITIONS Current Monitor Ratio (Notes 6,10), Ratio = IOUT/IMON ILOAD = 10mA, 250mA, 500mA TEMP Voltage (Note 16) TJ = 25°C TJ = 125°C l TEMP Error (Note 16) l Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
PAGE 5
LT3055 TYPICAL PERFORMANCE CHARACTERISTICS Guaranteed Dropout Voltage 600 550 TJ = 150°C 450 TJ = 125°C 350 300 TJ = 25°C 250 200 150 100 50 0 0 50 100 150 200 250 300 350 400 450 500 OUTPUT CURRENT (mA) 550 500 TJ = 150°C TJ = 25°C 0 200 150 3055 G03 Output Voltage = 3.3V 3.366 IL = 1mA 4.98 4.96 4.94 4.92 4.90 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 3055 G07 IL = 1mA 3.355 3.344 3.333 OUTPUT VOLTAGE (V) 608 606 604 602 600 598 596 594 3.322 3.311 3.300 3.289 3.278 3.
PAGE 6
LT3055 TYPICAL PERFORMANCE CHARACTERISTICS GND Pin Current, VOUT = 5V GND Pin Current vs ILOAD 20 RL = 10Ω, IL = 500mA 11 GND PIN CURRENT (mA) GND PIN CURRENT (mA) 9 8 7 6 5 RL = 20Ω, IL = 250mA 4 3 16 14 12 10 8 6 2 RL = 50Ω, IL = 100mA 4 1 RL = 500Ω, IL = 10mA 2 0 0 1 2 3 4 5 6 7 VIN (V) 8 VIN = 5.
PAGE 7
LT3055 TYPICAL PERFORMANCE CHARACTERISTICS Input Ripple Rejection 90 VOUT = VADJ = 1.2V VIN = 0V RIPPLE REJECTION (dB) OUTPUT CURRENT (µA) 80 70 60 50 40 30 IADJ 20 CREF/BYP = 0pF CREF/BYP = 100pF CREF/BYP = 10nF 80 60 50 40 30 ILOAD = 500mA COUT = 10µF VOUT = 3.3V VIN = 4.3V + 50mVRMS RIPPLE 20 10 IOUT 10 70 0 0 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 10 1M 80 2.0 60 50 40 ILOAD = 500mA CREF/BYP = 10nF VOUT = 3.3V VIN = 4.3V + 50mVRMS RIPPLE f = 120Hz 1.8 1.
PAGE 8
LT3055 TYPICAL PERFORMANCE CHARACTERISTICS CREF/BYP = 0pF 80 70 CREF/BYP = 100pF 60 50 40 CREF/BYP = 1nF 30 20 CREF/BYP = 10nF 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 160 150 f = 10Hz TO 100kHz VOUT = 5V 140 COUT = 10µF 130 120 VOUT = 3.3V 110 100 90 80 VOUT = 2.5V 70 60 50 40 VOUT = 1.2V 30 20 VOUT = 0.6V 10 0 0.01 0.
PAGE 9
LT3055 TYPICAL PERFORMANCE CHARACTERISTICS SHDN Transient Response CREF/BYP = 0 TJ = 25°C, unless otherwise noted. SHDN Transient Response CREF/BYP = 10nF Precision Current Limit, RIMAX = 1.5k OUT 5V/DIV IL=500mA OUT 5V/DIV IL = 500mA REF/BYP 500mV/DIV REF/BYP 500mV/DIV SHDN 2V/DIV SHDN 2V/DIV 2ms/DIV 2ms/DIV 3055 G37 3055 G38 CURRENT LIMIT FAULT THRESHOLD (mA) 220 VOUT(NOMINAL) = 5V 216 212 208 204 VIN = 10V 200 VIN = 5.
PAGE 10
LT3055 TYPICAL PERFORMANCE CHARACTERISTICS TJ = 25°C, unless otherwise noted. TEMP Output Voltage vs Temperature 11.0 1.75 10.8 1.50 10.6 1.25 TEMP PIN VOLTAGE (V) MINIMUM OUTPUT CURRENT THRESHOLD (mA) Minimum Output Current Threshold RIMIN = 120k 10.4 10.2 IMIN RISING THRESHOLD 10.0 9.8 IMIN FALLING THRESHOLD 9.6 1.00 0.75 0.50 0.25 0 9.4 –0.25 9.2 –0.50 9.0 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) –0.
PAGE 11
LT3055 PIN FUNCTIONS IN (Pins 1, 2): Input. These pins supply power to the device. The LT3055 requires a local IN bypass capacitor if it is located more than six inches from the main input filter capacitor. In general, battery output impedance rises with frequency, so adding a bypass capacitor in batterypowered circuits is advisable. A bypass capacitor in the range of 1µF to 10µF is sufficient. See Input Capacitance and Stability in the Applications Information section for more information.
PAGE 12
LT3055 PIN FUNCTIONS REF/BYP (Pin 11): Bypass/Soft-Start. Connecting a capacitor from this pin to GND bypasses the LT3055’s reference noise and soft starts the reference. A 10nF bypass capacitor typically reduces output voltage noise to 25μVRMS in a 10Hz to 100kHz bandwidth. Soft-start time is directly proportional to BYP/SS capacitor value. If the LT3055 is placed in shutdown, BYP/SS is actively pulled low by an internal device to reset soft-start.
PAGE 13
LT3055 BLOCK DIAGRAM IN R1 ADJ 30k R4 Q3 ERROR AMPLIFIER D2 CURRENT LIMIT AMPLIFIER QPOWER 1 OUT 100k R3 + – IDEAL DIODE D3 SHDN QIMAX 1/500 THERMAL/ CURRENT LIMITS – + Q2 QIMON 1/500 QIMIN 1/2000 D1 IMAX IMON IMIN COMPARATOR + – 100k R2 + – 600mV REFERENCE IMIN FAULT1 IMIN QFAULT1 U1 THERMAL LIMIT FAULT2 CURRENT LIMITS QFAULT2 U2 THERMAL LIMIT – + + – REF/BYP PWRGD QPWRGD 540mV REFERENCE GND 3055 F02 Figure 2 3055f For more information www.linear.
PAGE 14
LT3055 OPERATION IMON Pin Operation (Current Monitor) The IMON pin is the collector of a PNP which mirrors the LT3055 output PNP at a ratio of 1:500 (see Block Diagram). There is additional circuitry which compensates for early voltage variation by regulating the collector of the IMON mirror PNP at the output voltage. This circuitry is active for VIMON ≤ (VOUT – 500mV).
PAGE 15
LT3055 OPERATION The IMAX pin requires a 22nF decoupling capacitor. If the external programmable current limit is not needed, the IMAX pin must be connected to GND. The IMAX threshold is affected by power dissipation in the LT3055; it increases at a rate of approximately 0.5 percent per watt. FAULT Pins Operation The FAULT1 and FAULT2 pins are open-drain high voltage NMOS digital outputs. The FAULT1 pin asserts during a low current fault (open circuit).
PAGE 16
LT3055 APPLICATIONS INFORMATION Adjustable Operation + The adjustable LT3055 has an output voltage range of 0.6V to 40V. The output voltage is set by the ratio of two external resistors, as shown in Figure 4. The device servos the output to maintain the ADJ pin voltage at 0.6V referenced to ground. The current in R1 is then equal to 0.6V/R1, and the current in R2 is the current in R1 minus the ADJ pin bias current. The ADJ pin bias current, 16nA at 25°C, flows from the ADJ pin through R1 to GND.
PAGE 17
LT3055 APPLICATIONS INFORMATION Using a feedforward capacitor (CFF) from VOUT to the ADJ pin has the added benefit of improving transient response for output voltages greater than 0.6V. With no feedforward capacitor, the settling time increases as the output voltage increases above 0.6V. Use the equation in Figure 5 to determine the minimum value of CFF to achieve a transient response that is similar to the 0.
PAGE 18
LT3055 APPLICATIONS INFORMATION 20 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF CHANGE IN VALUE (%) 0 X5R –20 VOUT 1mV/DIV –40 –60 Y5V –80 –100 0 2 4 14 8 6 10 12 DC BIAS VOLTAGE (V) 16 3055 F07 VOUT = 5V COUT = 10µF CREF/BYP = 10nF 10ms/DIV 3055 F09 Figure 9. Noise Resulting from Tapping On a Ceramic Capacitor Figure 7. Ceramic Capacitor DC Bias Characteristics Figure 9 in response to light tapping from a pencil.
PAGE 19
LT3055 APPLICATIONS INFORMATION two parallel conductors. In this case, the farther apart the wires are from each other, the more the self-inductance is reduced; up to a 50% reduction when placed a few inches apart. Splitting the wires connects two equal inductors in parallel, but placing them in close proximity creates mutual inductance adding to the self-inductance.
PAGE 20
LT3055 APPLICATIONS INFORMATION Spreading the devices on the PC board also spreads the heat. Series input resistors can further spread the heat if the input-to-output differential is high. Overload Recovery Like many IC power regulators, the LT3055 has safe operating area protection. The safe area protection decreases current limit as input-to-output voltage increases, and keeps the power transistor inside a safe operating region for all values of input-to-output voltage.
PAGE 21
LT3055 APPLICATIONS INFORMATION Table 4.
PAGE 22
LT3055 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev E) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 5.23 (.206) MIN 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.035 ±.005) 8 1 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 3.20 – 3.45 (.065 ±.004) (.126 – .136) 0.305 ±0.038 (.0120 ±.0015) TYP 16 0.50 (.0197) BSC 4.039 ±0.102 (.159 ±.
PAGE 23
LT3055 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE Package 16-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1732 Rev Ø) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.45 BSC 3.15 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) R = 0.05 TYP 9 R = 0.115 TYP 0.40 ±0.10 16 3.30 ±0.10 3.00 ±0.10 (2 SIDES) 1.
PAGE 24
LT3055 TYPICAL APPLICATION Cable Drop Compensation VIN 5.6V TO 45V LT3055 IN 10µF REF 1x 500x + – + – 600mV RCABLE/2 OUT IMON ADJ 100nF 10µF RCABLE • 500 + 5V, COMPENSATED 10µF FOR DROP ALONG RCABLE/2 RESISTORS – RCABLE/2 440k – RCABLE • 500 2N3904 1k 1k 10nF 60k 3055 TA02FF RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1761 100mA, Low Noise LDO 300mV Dropout Voltage, Low Noise: 20μVRMS, VIN: 1.