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LT3990/LT3990-3.3/LT3990-5

3990fa

TYPICAL APPLICATION

DESCRIPTION

62V, 350mA Step-Down

Regulator with 2.5µA

Quiescent Current and

Integrated Diodes

The LT

3990 is an adjustable frequency monolithic buck

switching regulator that accepts a wide input voltage

range up to 62V, and consumes only 2.5µA of quiescent

current. A high efﬁciency switch is included on the die

along with the catch diode, boost diode, and the neces-

sary oscillator, control and logic circuitry. Low ripple Burst

Mode operation maintains high efﬁciency at low output

currents while keeping the output ripple below 5mV in a

typical application. Current mode topology is used for fast

transient response and good loop stability. A catch diode

current limit provides protection against shorted outputs

and overvoltage conditions. An accurate programmable

undervoltage lockout feature is available, producing a low

shutdown current of 0.7µA. A power good ﬂag signals when

OUT

reaches 90% of the programmed output voltage. The

LT3990 is available in small, thermally enhanced 16-pin

MSOP and 3mm × 3mm DFN packages.

5V Step-Down Converter

FEATURES

APPLICATIONS

Low Ripple Burst Mode

Operation

2.5µA I

at 12V

to 3.3V

OUT

Output Ripple < 5mV

P-P

Wide Input Voltage Range: 4.2V to 62V Operating

Adjustable Switching Frequency: 200kHz to 2.2MHz

Integrated Boost and Catch Diodes

350mA Output Current

Fixed Output Voltages: 3.3V, 5V

2µA I

at 12V

Accurate Programmable Undervoltage Lockout

FMEA Fault Tolerant (MSOP Package)

Output Stays at or Below Regulation Voltage During

Adjacent Pin Short or When a Pin is Left Floating

Low Shutdown Current: I

= 0.7µA

Internal Sense Limits Catch Diode Current

Power Good Flag

Small, Thermally Enhanced 16-Pin MSOP

and (3mm × 3mm) DFN Packages

Automotive Battery Regulation

Power for Portable Products

Industrial Supplies

Power Loss

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

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

LOAD CURRENT (mA)

0.001

0.01

POWER LOSS (mW)

100

1000

0.01 0.1 1 10 100

3990 TA01b

0.1

= 12V

BOOST

LT3990-5

SWEN/UVLO

0.22µF

22µF

2.2µF

6.5V TO 62V

OUT

350mA

374k

f = 400kHz

33µH

OUT

GND

OFF ON

3990 TA01a

Summary of content (22 pages)

PAGE 1
LT3990/LT3990-3.3/LT3990-5 62V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes FEATURES DESCRIPTION Low Ripple Burst Mode® Operation 2.5µA IQ at 12VIN to 3.3VOUT Output Ripple < 5mVP-P n Wide Input Voltage Range: 4.2V to 62V Operating n Adjustable Switching Frequency: 200kHz to 2.2MHz n Integrated Boost and Catch Diodes n 350mA Output Current n Fixed Output Voltages: 3.
PAGE 2
LT3990/LT3990-3.3/LT3990-5 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, EN/UVLO Voltage................................................62V BOOST Pin Voltage....................................................75V BOOST Pin Above SW Pin..........................................30V FB/VOUT, RT Voltage.....................................................6V PG, BD Voltage..........................................................30V Operating Junction Temperature Range (Note 2) LT3990E/LT3990E-X.......................
PAGE 3
LT3990/LT3990-3.3/LT3990-5 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VBD = 3.3V unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN Minimum Input Voltage Quiescent Current from VIN l VEN/UVLO Low VEN/UVLO High VEN/UVLO High TYP MAX 4 4.2 V 0.7 1.9 1.2 2.8 4 µA µA µA l LT3990 Feedback Voltage l 1.195 1.185 1.21 1.21 1.225 1.235 V V l 3.26 3.234 3.3 3.
PAGE 4
LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. Efficiency, VOUT = 3.3V Efficiency, VOUT = 5V 90 VIN = 24V VIN = 12V 80 70 VIN = 12V 60 EFFICIENCY (%) 70 VIN = 36V 50 VIN = 48V 40 30 10 0.01 0.1 1 10 LOAD CURRENT (mA) 60 VIN = 48V 50 1.215 VIN = 36V 40 FRONT PAGE APPLICATION VOUT = 3.3V R1 = 1M R2 = 576k 20 VIN = 24V FEEDBACK VOLTAGE (V) 80 EFFICIENCY (%) LT3990 Feedback Voltage 1.220 90 FRONT PAGE APPLICATION 20 0.01 0.
PAGE 5
LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. Maximum Load Current H-GRADE 400 LIMITED BY MAXIMUM JUNCTION TEMPERATURE θJA = 45°C/W 300 200 100 FRONT PAGE APPLICATION VIN = 12V VOUT = 5V 0 –50 –25 0 Switch Current Limit 800 0.20 LIMITED BY CURRENT LIMIT LOAD REGULATION (%) LOAD CURRENT (A) 500 Load Regulation 0.25 25 50 75 100 125 150 TEMPERATURE (°C) SWITCH CURRENT LIMIT (mA) 600 0.15 0.10 0.05 0 –0.05 –0.10 –0.
PAGE 6
LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. 6.5 FRONT PAGE APPLICATION VOUT = 3.3V TO START 4.0 TO RUN 3.5 3.0 2.5 5.5 TO RUN 5.0 4.5 0 50 100 150 200 250 LOAD CURRENT (mA) 300 4.0 350 12 0.6 0.4 –50°C 25°C 125°C 150°C 200 100 300 CATCH DIODE CURRENT (mA) 0.4 400 –50°C 25°C 125°C 150°C 0.
PAGE 7
LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
PAGE 8
LT3990/LT3990-3.3/LT3990-5 BLOCK DIAGRAM VIN VIN C1 INTERNAL 1.21V REF 1.19V EN/UVLO – + + SHDN – BD DBOOST SLOPE COMP BOOST SWITCH LATCH R RT RT PG OSCILLATOR 200kHz TO 2.2MHz + + 1.09V ERROR AMP – VC Burst Mode DETECT – R2 FB GND R2 LT3990 ONLY Q C3 S SW DCATCH L1 VOUT C2 R1 LT3990-X ONLY* VOUT R1 *LT3990-3.3: R1 = 12.65M, R2 = 7.35M LT3990-5: R1 = 15.15M, R2 = 4.
PAGE 9
LT3990/LT3990-3.3/LT3990-5 OPERATION The LT3990 is a constant frequency, current mode stepdown regulator. An oscillator, with frequency set by RT, sets an RS flip-flop, turning on the internal power switch. An amplifier and comparator monitor the current flowing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC (see Block Diagram).
PAGE 10
LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the 1% resistors according to: V  R1= R2  OUT – 1  1.21  Reference designators refer to the Block Diagram. Note that choosing larger resistors will decrease the quiescent current of the application circuit.
PAGE 11
LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION If a lower dropout voltage is desired, a lower switching frequency should be used. The highest allowed VIN during normal operation (VIN(OP‑MAX)) is limited by minimum duty cycle and can be calculated by the following equation: VIN(OP-MAX) = VOUT + VD –V +V fSW • tON(MIN) D SW where tON(MIN) is the minimum switch on-time.
PAGE 12
LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3990 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1µF capacitor is capable of this task, but only if it is placed close to the LT3990 (see the PCB Layout section).
PAGE 13
LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LT3990. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3990 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3990’s rating.
PAGE 14
LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION VOUT 5.0 FRONT PAGE APPLICATION VOUT = 3.3V BD VIN 4.5 BOOST C3 LT3990 INPUT VOLTAGE (V) VIN SW GND (4a) For VOUT ≥ 2.2V VIN 3.5 2.5 BOOST C3 LT3990 SW TO RUN 3.0 BD VIN TO START 4.0 6.5 VOUT GND 0 50 Figure 4. Two Circuits for Generating the Boost Voltage the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly.
PAGE 15
LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION VIN VIN R3 1.19V EN/UVLO LT3990 + – D4 BD VIN VIN BOOST LT3990 SHDN R4 EN/UVLO SW GND FB VOUT + 3990 F06 BACKUP Figure 6. Undervoltage Lockoout Shorted and Reversed Input Protection If the inductor is chosen so that it won’t saturate excessively, a LT3990 buck regulator will tolerate a shorted output. There is another situation to consider in systems where the output will be held high when the input to the LT3990 is absent.
PAGE 16
LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION Hot Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3990 circuits. However, these capacitors can cause problems if the LT3990 is plugged into a live supply.
PAGE 17
LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATIONS 3.3V Step-Down Converter VIN 4.2V TO 62V VIN BOOST C1 2.2µF EN/UVLO PG VIN 6.5V TO 62V C3 0.22µF VIN L1 33µH LT3990 OFF ON 5V Step-Down Converter BD R1 1M 22pF RT FB GND 374k C2 22µF R2 576k f = 400kHz OFF ON 374k LT3990-3.3 RT 2.2µF 33µH 0.22µF VOUT 22µF OFF ON RT BOOST OFF ON C1 2.2µF EN/UVLO PG 511k f = 300kHz GND BD VOUT 22µF 3990 TA11 VIN 4.2V TO 30V VIN R1 1M R2 931k 3990 TA04 C2 47µF BOOST LT3990 VOUT 2.
PAGE 18
LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATIONS 12V Step-Down Converter VIN 15V TO 62V VIN BOOST EN/ULVO PG VIN 8.5V TO 16V TRANSIENTS TO 62V C3 0.1µF L1 33µH LT3990 OFF ON 5V, 2MHz Step-Down Converter VOUT 12V 350mA SW BD R1 1M 22pF C1 2.2µF RT 127k GND FB f = 1MHz VIN BOOST LT3990 OFF ON C2 22µF R2 113k C3 0.1µF EN/UVLO PG L1 10µH BD 22pF C1 1µF RT 51.
PAGE 19
LT3990/LT3990-3.3/LT3990-5 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.
PAGE 20
LT3990/LT3990-3.3/LT3990-5 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.
PAGE 21
LT3990/LT3990-3.
PAGE 22
LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATION 1.21V Step-Down Converter VIN 4.2V TO 30V VIN BOOST LT3990 OFF ON C1 2.2µF 374k C3 0.22µF L1 15µH EN/UVLO SW BD FB PG RT GND f = 400kHz VOUT 1.2V 350mA C2 47µF 3990 TA09 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT3970/LT3970-3.3/ 40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC LT3970-5 Converter with IQ = 2.5µA VIN: 4.2V to 40V, VOUT(MIN) = 1.21V, IQ = 2.5µA, ISD < 1µA, 3mm × 2mm DFN-10, MSOP-10 LT3971 38V, 1.2A, 2.