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LT3085

3085fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Adjustable 500mA Single

Resistor Low Dropout

Regulator

The LT

3085 is a 500mA low dropout linear regulator that

can be paralleled to increase output current or spread

heat on surface mounted boards. Designed as a precision

current source and voltage follower, this new regulator

ﬁ nds use in many applications requiring high current,

adjustability to zero, and no heat sink. The device also

brings out the collector of the pass transistor to allow

low dropout operation—down to 275mV—when used

with a second supply.

A key feature of the LT3085 is the capability to supply a

wide output voltage range. By using a reference current

through a single resistor, the output voltage is programmed

to any level between zero and 36V. The LT3085 is stable

with 2.2μF of capacitance on the output, and the IC uses

small ceramic capacitors that do not require additional

ESR as is common with other regulators.

Internal protection circuitry includes current limiting

and thermal limiting. The LT3085 is offered in the 8-lead

MSOP and a low proﬁ le (0.75mm) 6-lead 2mm × 3mm

DFN package (both with an Exposed Pad for better thermal

characteristics).

Variable Output Voltage 500mA Supply

Outputs May be Paralleled for Higher Current and

Heat Spreading

Output Current: 500mA

Single Resistor Programs Output Voltage

1% Initial Accuracy of SET Pin Current

Output Adjustable to 0V

Current Limit Constant with Temperature

Low Output Noise: 40μV

RMS

(10Hz to 100kHz)

Wide Input Voltage Range: 1.2V to 36V

Low Dropout Voltage: 275mV

< 1mV Load Regulation

< 0.001%/ V Line Regulation

Minimum Load Current: 0.5mA

Stable with Minimum 2.2μF Ceramic Capacitor

Current Limit with Foldback and Overtemperature

Protected

8-Lead MSOP, and 6-Lead 2mm × 3mm DFN Packages

High Current All Surface Mount Supply

High Efﬁ ciency Linear Regulator

Post Regulator for Switching Supplies

Low Parts Count Variable Voltage Supply

Low Output Voltage Power Supplies

–

LT3085

1.2V TO 36V

CONTROL

OUT

3085 TA01a

SET

1μF

2.2μF

SET

OUT

= R

SET

• 10μA

OUT

SET PIN CURRENT DISTRIBUTION (μA)

10.20

3085 TA01b

9.90

10.00

10.10

9.80

N = 1676

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

and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

Summary of content (28 pages)

PAGE 1
LT3085 Adjustable 500mA Single Resistor Low Dropout Regulator DESCRIPTION FEATURES n n n n n n n n n n n n n n n Outputs May be Paralleled for Higher Current and Heat Spreading Output Current: 500mA Single Resistor Programs Output Voltage 1% Initial Accuracy of SET Pin Current Output Adjustable to 0V Current Limit Constant with Temperature Low Output Noise: 40μVRMS (10Hz to 100kHz) Wide Input Voltage Range: 1.2V to 36V Low Dropout Voltage: 275mV < 1mV Load Regulation < 0.
PAGE 2
LT3085 ABSOLUTE MAXIMUM RATINGS (Note 1) All Voltages Relative to VOUT VCONTROL Pin Voltage ..................................... 40V, –0.3V IN Pin Voltage ................................................ 40V, –0.3V SET Pin Current (Note 7) .................................... ±15mA SET Pin Voltage (Relative to OUT) ..........................±10V Output Short-Circuit Duration .......................... Indeﬁnite Operating Junction Temperature Range (Notes 2, 10) E, I Grade ...............................
PAGE 3
LT3085 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 MIN TYP MAX UNITS 10 10 10.1 10.2 μA μA 1.5 3 mV mV –1 nA mV SET Pin Current ISET VIN = 1V, VCONTROL = 2V, ILOAD = 1mA, TJ = 25°C VIN ≥ 1V, VCONTROL ≥ 2V, 1mA ≤ ILOAD ≤ 500mA (Note 9) l 9.9 9.
PAGE 4
LT3085 TYPICAL PERFORMANCE CHARACTERISTICS Set Pin Current Set Pin Current Distribution Offset Voltage (VOUT – VSET) 10.20 2.0 N = 1676 1.5 10.10 OFFSET VOLTAGE (mV) SET PIN CURRENT (μA) 10.15 10.05 10.00 9.95 9.90 9.85 1.0 0.5 0 –0.5 –1.0 –1.5 9.80 –50 –25 0 9.80 25 50 75 100 125 150 TEMPERATURE (°C) –2.0 –50 –25 10.00 10.20 9.90 10.
PAGE 5
LT3085 TYPICAL PERFORMANCE CHARACTERISTICS Dropout Voltage (Minimum IN Voltage) 1.6 1.6 1.4 MINIMUM CONTROL VOLTAGE (VCONTROL – VOUT) (V) 350 ILOAD = 500mA 300 250 200 150 ILOAD = 100mA 100 1.2 1.0 TJ = 125°C 0.8 TJ = 25°C 0.6 0.4 0.
PAGE 6
LT3085 TYPICAL PERFORMANCE CHARACTERISTICS VCONTROL Pin Current 8 7 CONTROL PIN CURRENT (mA) CONTROL PIN CURRENT (mA) 18 800 VIN = VCONTROL = 2V VIN = VOUT = 1V 16 14 ILOAD = 500mA 12 10 DEVICE IN CURRENT LIMIT 8 6 4 TJ = –50°C 6 TJ = 25°C 5 4 TJ = 125°C 3 2 VOUT VIN = 20V RTEST 500 400 VIN = 10V 300 VIN = 5V 200 100 ILOAD = 1mA 0 0 30 12 18 24 6 INPUT-TO-OUTPUT DIFFERENTIAL (V) 0 0 36 0.1 0.2 0.3 LOAD CURRENT (A) 0.
PAGE 7
LT3085 TYPICAL PERFORMANCE CHARACTERISTICS Error Ampliﬁer Gain and Phase Ripple Rejection - SET Pin Current 150 144 135 15 72 120 12 0 ILOAD = 500mA 9 –72 ILOAD = 100mA 6 –144 ILOAD = 500mA 3 –216 0 –288 –3 ILOAD = 100mA –6 –9 PHASE (deg) GAIN (dB) 18 10 100 10k 1k FREQUENCY (Hz) 100k 90 75 CSET = 0 60 45 30 –432 15 –504 1M CSET = 0.
PAGE 8
LT3085 BLOCK DIAGRAM IN VCONTROL 10μA + – 3085 BD SET OUT APPLICATIONS INFORMATION The LT3085 regulator is easy to use and has all the protection features expected in high performance regulators. Included are short-circuit protection and safe operating area protection, as well as thermal shutdown. The LT3085 is especially well suited to applications needing multiple rails.
PAGE 9
LT3085 APPLICATIONS INFORMATION The LT3085 can be operated in two modes. Three terminal mode has the control pin connected to the power input pin which gives a limitation of 1.35V dropout. Alternatively, the “control” pin can be tied to a higher voltage and the power IN pin to a lower voltage giving 275mV dropout on the IN pin and minimizing the power dissipation. This allows for a 500mA supply regulating from 2.5VIN to 1.8VOUT or 1.8VIN to 1.2VOUT with low dissipation.
PAGE 10
LT3085 APPLICATIONS INFORMATION Input Capacitance and Stability The LT3085 is designed to be stable with a minimum capacitance of 1μF at each input pin. Ceramic capacitors with low ESR are available for use to bypass these pins, but in cases where long wires connect the LT3085 inputs to a power supply (and also from ground of the LT3085 circuitry back to power supply ground), this causes instabilities.
PAGE 11
LT3085 APPLICATIONS INFORMATION in a small package, but they tend to have 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 result in more stable characteristics and are more suitable for use as the output capacitor.
PAGE 12
LT3085 APPLICATIONS INFORMATION The worst-case offset between the SET pin and the output of only ±1.5mV allows very small ballast resistors to be used. As shown in Figure 4, the two devices have a small 10mΩ and 20mΩ ballast resistors, which at full output current gives better than 80% equalized sharing of the current. The external resistance of 20mΩ (6.6mΩ for the two devices in parallel) only adds about 10mV of output regulation drop at an output of 1.5A.
PAGE 13
LT3085 APPLICATIONS INFORMATION between the devices is within 2°C, showing excellent tracking between the devices. The board temperature has reached approximately 40°C within about 0.75 inches of each device. While 90°C is an acceptable operating temperature for these devices, this is in 25°C ambient. For higher ambients, the temperature must be controlled to prevent device temperature from exceeding 125°C.
PAGE 14
LT3085 APPLICATIONS INFORMATION The problem occurs with a heavy output load when the input voltage is high and the output voltage is low. Common situations are immediately after the removal of a short circuit. The load line for such a load may intersect the output current curve at two points. If this happens, there are two stable operating points for the regulator. With this double intersection, the input power supply may need to be cycled down to zero and brought up again to make the output recover.
PAGE 15
LT3085 APPLICATIONS INFORMATION If the LT3085 is conﬁgured as a three-terminal (single supply) regulator with IN and VCONTROL shorted together, the internal diode of the IN pin will protect the VCONTROL pin. Like any other regulator, exceeding the maximum inputto-output differential causes internal transistors to break down and then none of the internal protection circuitry is functional.
PAGE 16
LT3085 APPLICATIONS INFORMATION The power in the output transistor equals: POUTPUT = (VIN – VOUT)(IOUT) The total power equals: PTOTAL = PDRIVE + POUTPUT The current delivered to the SET pin is negligible and can be ignored. VCONTROL(MAX CONTINUOUS) = 3.630V (3.3V + 10%) Reducing Power Dissipation In some applications it may be necessary to reduce the power dissipation in the LT3085 package without sacriﬁcing output current capability. Two techniques are available.
PAGE 17
LT3085 APPLICATIONS INFORMATION Without series resistor RS, power dissipation in the LT3085 equals: 0.5A PTOTAL = ( 5V – 3.3V ) • + ( 5V – 3.3V ) • 0.5A 60 = 0.86W If the voltage differential (VDIFF) across the NPN pass transistor is chosen as 0.5V, then RS equals: RS = 5V – 3.3V − 0.5V = 2.4Ω 0.5A Power dissipation in the LT3085 now equals: PTOTAL = ( 5V – 3.3V ) • 0.5A + ( 0.5V ) • 0.5A = 0.26W 60 The LT3085’s power dissipation is now only 30% compared to no series resistor. RS dissipates 0.
PAGE 18
LT3085 TYPICAL APPLICATIONS Higher Output Current MJ4502 VIN 6V 50Ω LT3085 IN VCONTROL + + – 100μF 1μF VOUT 3.3V 5A OUT + SET 4.7μF 100μF 332k 3085 TA02 Current Source LT3085 IN VIN 10V VCONTROL + – 1μF OUT 2Ω 0.5W SET IOUT 0A TO 0.5A 4.7μF 100k 3085 TA03 Power Oscillator VIN LT3085 IN VCONTROL + – VOUT 400Hz 4VACP-P OUT SET 10μF 6.3V, 150mA LIGHT BULB #47 47nF 2.21k 4.7μF 8.45k 20Ω 499k 8.
PAGE 19
LT3085 TYPICAL APPLICATIONS Adding Shutdown VIN LT3085 IN VIN Low Dropout Voltage LED Driver C1 LT3085 VCONTROL + – 3085 TA04 SET ON OFF IN OUT Q2* VN2222LL R1 100mA D1 + – OUT VOUT Q1 VN2222LL VCONTROL SET R1 24.9k SHUTDOWN R2 2.49Ω 3085 TA05 *Q2 INSURES ZERO OUTPUT IN THE ABSENCE OF ANY OUTPUT LOAD. Using a Lower Value SET Resistor IN VIN 12V LT3085 VCONTROL C1 1μF + – OUT SET R1 49.9k 1% 1mA VOUT 0.5V TO 10V R2 499Ω 1% VOUT = 0.5V + 1mA • RSET COUT 4.
PAGE 20
LT3085 TYPICAL APPLICATIONS Adding Soft-Start LT3085 IN VIN 4.8V to 28V VCONTROL C1 1μF + – D1 1N4148 OUT SET C2 0.01μF VOUT 3.3V 0.5A COUT 4.7μF R1 332k 3085 TA07 Coincident Tracking LT3085 IN VCONTROL IN LT3085 + – VCONTROL VIN 7V TO 28V IN LT3085 + – VCONTROL C1 1.5μF OUT SET 169k OUT + – OUT SET R1 249k SET R2 80.6k C2 4.7μF C3 4.7μF VOUT2 3.3V 0.5A VOUT3 5V 0.5A 4.7μF 3085 TA08 VOUT1 2.5V 0.
PAGE 21
LT3085 TYPICAL APPLICATIONS Lab Supply LT3085 IN VIN 12V TO 18V LT3085 IN VCONTROL VCONTROL + – + 15μF + – 1Ω OUT 0.25W OUT + SET 50k 0A TO 0.5A + SET 15μF VOUT 0V TO 10V 4.7μF R4 1M 100μF 3085 TA09 High Voltage Regulator 6.1V 10k VIN 50V 1N4148 IN LT3085 BUZ11 VCONTROL + + – 10μF OUT SET RSET 2M + 15μF VOUT 0.5A 4.7μF VOUT = 20V VOUT = 10μA • RSET 3085 TA10 Ramp Generator IN VIN 5V LT3085 VCONTROL + – 1μF OUT VOUT SET VN2222LL 1μF VN2222LL 4.
PAGE 22
LT3085 TYPICAL APPLICATIONS Reference Buffer LT3085 IN VIN VCONTROL + – OUT VOUT* C2 4.7μF INPUT SET OUTPUT LT1019 C1 1μF GND 3085 TA11 *MIN LOAD 0.5mA Ground Clamp LT3085 IN VIN VEXT VCONTROL 20Ω + – OUT 1μF SET VOUT 1N4148 4.7μF 5k 3085 TA13 Boosting Fixed Output Regulators IN LT3085 VCONTROL + – OUT 20mΩ SET 20mΩ 5V 3.3VOUT 2A LT1963-3.
PAGE 23
LT3085 TYPICAL APPLICATIONS Low Voltage, High Current Adjustable High Efﬁciency Regulator* 0.47μH 2.7V TO 5.5V† 100μF ×2 + 2.2MEG 100k PVIN SW SVIN ITH LTC3414 10k + 12.1k RT 470pF 294k PGOOD 100μF ×2 2N3906 LT3085 IN VCONTROL RUN/SS + – VFB 1000pF OUT 78.7k SGND PGND 20mΩ SET SYNC/MODE 124k LT3085 IN VCONTROL + – *DIFFERENTIAL VOLTAGE ON LT3085 IS 0.6V SET BY THE VBE OF THE 2N3906 PNP. OUT †MAXIMUM OUTPUT VOLTAGE IS 1.
PAGE 24
LT3085 TYPICAL APPLICATIONS Adjustable High Efﬁciency Regulator* CMDSH-4E 4.5V TO 25V† VIN 10μF 1μF 100k BOOST LT3493 SHDN 0.1μF 10μH 0.1μF MBRM140 GND LT3085 IN SW 68μF 200k TP0610L VCONTROL + – FB OUT 10k 3085 TA19 SET 0V TO 10V† 0.5A 4.7μF 1MEG *DIFFERENTIAL VOLTAGE ON LT3085 ≈ 1.4V SET BY THE TPO610L P-CHANNEL THRESHOLD.
PAGE 25
LT3085 PACKAGE DESCRIPTION DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715 Rev A) 0.70 p 0.05 3.55 p 0.05 1.65 p 0.05 (2 SIDES) 2.15 p 0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 1.35 p 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP R = 0.05 TYP 2.00 p 0.10 (2 SIDES) 3.00 p 0.10 (2 SIDES) 0.40 p 0.10 4 6 1.65 p 0.10 (2 SIDES) PIN 1 NOTCH R0.20 OR 0.25 s 45° CHAMFER PIN 1 BAR TOP MARK (SEE NOTE 6) 3 0.200 REF 0.75 p 0.05 1 (DCB6) DFN 0405 0.
PAGE 26
LT3085 PACKAGE DESCRIPTION MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev F) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 (.074) 1 0.889 p 0.127 (.035 p .005) 1.88 p 0.102 (.074 p .004) 0.29 REF 1.68 (.066) 0.05 REF 5.23 (.206) MIN DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 1.68 p 0.102 3.20 – 3.45 (.066 p .004) (.126 – .136) 8 0.42 p 0.038 (.0165 p .0015) TYP 3.00 p 0.102 (.118 p .
PAGE 27
LT3085 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 6/10 Updated trademarks 1 Revised Conditions in Electrical Characteristics table 3 Changed ILOAD value on curve G27 in Typical Performance Characteristics section 6 Revised Figure 1 9 Added 200k resistor to drawing 3085 TA19 in Typical Applications section Updated Package Description drawings 24 25, 26 3085fb Information furnished by Linear Technology Corporation is believed to be accurate and re
PAGE 28
LT3085 TYPICAL APPLICATION Paralleling Regulators IN LT3080 VCONTROL + – OUT 10mΩ SET IN VIN 4.8V TO 36V LT3085 VCONTROL + – 1μF OUT 20mΩ VOUT 3.3V 1.5A SET 10μF 165k 3085 TA14 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS 1.5A Low Dropout Regulator Fixed 2.85V, 3.3V, 3.6V, 5V and 12V Output LDOs LT1086 LT1763 500mA, Low Noise LDO 300mV Dropout Voltage, Low Noise = 20μVRMS, VIN: 1.8V to 20V, SO-8 Package LT3021 500mA VLDO Regulator LT3080 1.