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LT3493

3493fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

1.2A, 750kHz Step-Down

Switching Regulator in

2mm × 3mm DFN

Automotive Battery Regulation

Industrial Control Supplies

Wall Transformer Regulation

Distributed Supply Regulation

Battery-Powered Equipment

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

3.3V Step-Down Converter

Efﬁ ciency

Wide Input Range: 3.6V to 36V Operating,

40V Maximum

1.2A Output Current

Fixed Frequency Operation: 750kHz

Output Adjustable Down to 780mV

Short-Circuit Robust

Uses Tiny Capacitors and Inductors

Soft-Start

Internally Compensated

Low Shutdown Current: <2μA

Low V

CESAT

Switch: 330mV at 1A

Thermally Enhanced, Low Proﬁ le DFN Package

The LT

3493 is a current mode PWM step-down DC/DC

converter with an internal 1.75A power switch. The wide

operating input range of 3.6V to 36V (40V maximum)

makes the LT3493 ideal for regulating power from a wide

variety of sources, including unregulated wall transform-

ers, 24V industrial supplies and automotive batteries.

Its high operating frequency allows the use of tiny, low

cost inductors and ceramic capacitors, resulting in low,

predictable output ripple.

Cycle-by-cycle current limit provides protection against

shorted outputs and soft-start eliminates input current

surge during start-up. The low current (<2μA) shutdown

mode provides output disconnect, enabling easy power

management in battery-powered systems.

4.2V TO 36V

ON OFF

0.1μF

10μH

32.4k

10μF

3493 TA01a

22pF

1μF

10k

OUT

3.3V

1.2A, V

> 12V

0.95A, V

> 5V

BOOST

GND FB

SHDN

LT3493

LOAD CURRENT (A)

EFFICIENCY (%)

3493 TA01b

0.4

0.8

1.2

0.20

0.6

1.0

= 12V

OUT

= 3.3V

L = 10μH

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Summary of content (20 pages)

PAGE 1
LT3493 1.2A, 750kHz Step-Down Switching Regulator in 2mm × 3mm DFN FEATURES DESCRIPTION n The LT®3493 is a current mode PWM step-down DC/DC converter with an internal 1.75A power switch. The wide operating input range of 3.6V to 36V (40V maximum) makes the LT3493 ideal for regulating power from a wide variety of sources, including unregulated wall transformers, 24V industrial supplies and automotive batteries.
PAGE 2
LT3493 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Input Voltage (VIN) ....................................................40V BOOST Pin Voltage ..................................................50V BOOST Pin Above SW Pin.........................................25V SHDN Pin ..................................................................40V FB Voltage ...................................................................6V Operating Temperature Range (Note 2) LT3493E ..............................
PAGE 3
LT3493 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 12V, VBOOST = 17V, unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN TYP MAX Switch Current Limit (Note 3) 1.4 1.75 2.2 Switch VCESAT ISW = 1A ISW = 1A BOOST Pin Current ISW = 1A SHDN Input Voltage High mV 2 μA 1.85 2.2 V 30 50 mA 2.3 V SHDN Input Voltage Low SHDN Bias Current VSHDN = 2.
PAGE 4
LT3493 TYPICAL PERFORMANCE CHARACTERISTICS Maximum Load Current, VOUT = 5V, L = 8.2μH Maximum Load Current, VOUT = 5V, L = 33μH 1.60 1.60 1.50 1.50 1.40 1.30 1.20 MINIMUM 1.10 1.00 OUTPUT CURRENT (A) TYPICAL OUTPUT CURRENT (A) 1.40 1.30 MINIMUM 1.20 1.10 0.90 8 12 16 24 20 VIN (V) 8 12 16 20 VIN (V) 24 1.50 TYPICAL VCE(SW) (mV) MINIMUM 1.10 1.00 500 3.90 3.70 TA = 25°C 350 300 TA = –40°C 250 0.90 25 200 3.40 100 3.20 50 3.10 0 3.00 –50 –25 0.2 0.4 0.6 0.8 1.0 1.2 1.
PAGE 5
LT3493 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted. Typical Minimum Input Voltage (VOUT = 5V) SHDN Pin Current 50 Typical Minimum Input Voltage (VOUT = 3.3V) 5.5 7.5 45 5.3 TO START 40 5.1 7.0 4.9 25 20 6.5 VIN (V) 30 VIN (V) ISHDN (μA) 35 TO RUN 15 4.1 TO RUN 3.9 5.5 3.7 5 0 4.5 4.3 6.0 10 TO START 4.7 0 2 4 6 8 10 12 14 16 18 20 VSHDN (V) 3.5 5.
PAGE 6
LT3493 PIN FUNCTIONS FB (Pin 1): The LT3493 regulates its feedback pin to 780mV. Connect the feedback resistor divider tap to this pin. Set the output voltage according to VOUT = 0.78V • (1 + R1/R2). A good value for R2 is 10k. GND (Pin 2): Tie the GND pin to a local ground plane below the LT3493 and the circuit components. Return the feedback divider to this pin. BOOST (Pin 3): The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch.
PAGE 7
LT3493 OPERATION (Refer to Block Diagram) The LT3493 is a constant frequency, current mode stepdown regulator. A 750kHz oscillator enables an RS ﬂip-ﬂop, turning on the internal 1.75A power switch Q1. 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. An error ampliﬁer measures the output voltage through an external resistor divider tied to the FB pin and servos the VC node.
PAGE 8
LT3493 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 0.78V R2 should be 20k or less to avoid bias current errors. Reference designators refer to the Block Diagram. An optional phase lead capacitor of 22pF between VOUT and FB reduces light-load output ripple.
PAGE 9
LT3493 APPLICATIONS INFORMATION Now the required on-time has decreased below the minimum on time of 120ns. Instead of the switch pulse width becoming narrower to accommodate the lower duty cycle requirement, the switch pulse width remains ﬁxed at 120ns. In Figure 2 the inductor current ramps up to a value exceeding the load current and the output ripple increases to ~200mV. The part then remains off until the output voltage dips below 100% of the programmed value before it begins switching again.
PAGE 10
LT3493 APPLICATIONS INFORMATION Table 1. Inductor Values VENDOR URL PART SERIES INDUCTANCE RANGE (μH) SIZE (MM) Sumida www.sumida.com CDRH4D28 CDRH5D28 CDRH8D28 1.2 to 4.7 2.5 to 10 2.5 to 33 4.5 × 4.5 5.5 × 5.5 8.3 × 8.3 Toko www.toko.com A916CY D585LC 2 to 12 1.1 to 39 6.3 × 6.2 8.1 × 8.0 Würth Elektronik www.we-online.com WE-TPC(M) WE-PD2(M) WE-PD(S) 1 to 10 2.2 to 22 1 to 27 4.8 × 4.8 5.2 × 5.8 7.3 × 7.
PAGE 11
LT3493 APPLICATIONS INFORMATION Table 2. Capacitor Vendors VENDOR PHONE URL PART SERIES COMMENTS Panasonic (714) 373-7366 www.panasonic.com Ceramic, Polymer, Tantalum Kemet Sanyo Murata (864) 963-6300 (408) 749-9714 (404) 436-1300 AVX Taiyo Yuden (864) 963-6300 www.kemet.com www.sanyovideo.com Ceramic, Tantalum Ceramic, Polymer, Tantalum www.murata.com Ceramic www.avxcorp.com Ceramic, Tantalum www.taiyo-yuden.com capacitor must be large to achieve low ESR.
PAGE 12
LT3493 APPLICATIONS INFORMATION ILOAD 2A/DIV VOUT IL 0.5A/DIV 32.4k FB 10μF 10k VOUT 0.1V/DIV AC COUPLED 40μs/DIV 3493 F04a 40μs/DIV 3493 F04b 40μs/DIV 3493 F04c ILOAD 2A/DIV VOUT 32.4k IL 0.5A/DIV 3.3nF 10μF s2 FB 10k VOUT 0.1V/DIV AC COUPLED ILOAD 2A/DIV VOUT 32.4k IL 0.5A/DIV + FB 100μF 10k SANYO 4TPB100M VOUT 0.1V/DIV AC COUPLED Figure 4. Transient Load Response of the LT3493 With Different Output Capacitors as the Load Current is Stepped from 250mA to 1A. VIN = 12V, VOUT = 3.
PAGE 13
LT3493 APPLICATIONS INFORMATION 5.5 7.5 5.3 TO START 7.0 5.1 VIN (V) VIN (V) 4.9 6.5 TO START 4.7 4.5 4.3 6.0 TO RUN 4.1 TO RUN 3.9 5.5 3.7 3.5 5.0 1 10 100 1000 1 10 100 1000 IOUT (mA) IOUT (mA) 3493 G16 3493 G15 (6a) Typical Minimum Input Voltage, VOUT = 5V (6b) Typical Minimum Input Voltage, VOUT = 3.3V Figure 6 At light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high.
PAGE 14
LT3493 APPLICATIONS INFORMATION VSW 10V/DIV SHDN RUN IL 0.5A/DIV GND 3493 F07a VOUT 2V/DIV VIN = 12V VOUT = 3.3V L = 10μH COUT = 10μF 20μs/DIV VIN = 12V VOUT = 3.3V L = 10μH COUT = 10μF 20μs/DIV VSW 10V/DIV RUN 15k SHDN 0.1μF IL 0.5A/DIV GND 3493 F07b VOUT 2V/DIV Figure 7. To Soft-Start the LT3493, Add a Resistor and Capacitor to the SHDN Pin. VIN = 12V, VOUT = 3.3V, COUT = 10μF, RLOAD = 5Ω D4 VIN VIN BOOST LT3493 SHDN GND VOUT SW FB BACKUP D4: MBR0540 3493 F08 Figure 8.
PAGE 15
LT3493 APPLICATIONS INFORMATION a 2.2μF ceramic capacitor at the input. The input voltage rings as high as 35V and the input current peaks at 20A. One method of damping the tank circuit is to add another capacitor with a series resistor to the circuit. In Figure 9b an aluminum electrolytic capacitor has been added. This capacitor’s high equivalent series resistance damps the circuit and eliminates the voltage overshoot.
PAGE 16
LT3493 APPLICATIONS INFORMATION model works well as long as the value of the inductor is not too high and the loop crossover frequency is much lower than the switching frequency. With a larger ceramic capacitor (very low ESR), crossover may be lower and a phase lead capacitor (CPL) across the feedback divider may improve the phase margin and transient response. Large electrolytic capacitors may have an ESR large enough to create an additional zero, and the phase lead may not be necessary.
PAGE 17
LT3493 APPLICATIONS INFORMATION High Temperature Considerations Outputs Greater Than 6V The die temperature of the LT3493 must be lower than the maximum rating of 125°C. This is generally not a concern unless the ambient temperature is above 85°C. For higher temperatures, care should be taken in the layout of the circuit to ensure good heat sinking of the LT3493. The maximum load current should be derated as the ambient temperature approaches 125°C.
PAGE 18
LT3493 TYPICAL APPLICATIONS 2.5V Step-Down Converter BAT54 VIN 3.6V TO 28V VIN 0.47μF 6.8μH LT3493 ON OFF VOUT 2.5V 1A, VIN > 5V 1.2A, VIN > 10V BOOST SHDN SW MBRM140 GND 22.1k FB 22μF 10k 1μF 3493 TA04 3.3V Step-Down Converter VIN 4.2V TO 36V 1N4148 VIN 0.1μF 8.2μH LT3493 ON OFF VOUT 3.3V 0.9A, VIN > 4.5V 1.2A, VIN > 12V BOOST SHDN SW MBRM140 GND 32.4k FB 10μF 10k 1μF 3493 TA05 5V Step-Down Converter VIN 6.4V TO 36V 1N4148 VIN 0.
PAGE 19
LT3493 PACKAGE DESCRIPTION DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 (2 SIDES) 2.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 1.35 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 2.00 ±0.10 (2 SIDES) R = 0.05 TYP 3.00 ±0.10 (2 SIDES) 0.40 ± 0.10 4 6 1.65 ± 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 1 (DCB6) DFN 0405 0.25 ± 0.05 0.50 BSC 0.
PAGE 20
LT3493 TYPICAL APPLICATION 12V Step-Down Converter D1 6V 1N4148 1k* 0.25W VIN 14.5V TO 36V VIN BOOST 0.1μF LT3493 SHDN ON OFF 22μH SW MBRM140 GND 71.5k FB VOUT 12V 1A 4.7μF 4.99k 1μF *FOR CONTINUOUS OPERATION ABOVE 30V USE TWO 2k, 0.25Ω RESISTORS IN PARALLEL. D1: CMDZ5235B 3493 TA07 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1766 60V, 1.2A IOUT , 200kHz, High Efﬁciency Step-Down DC/DC Converter VIN: 5.5V to 60V, VOUT(MIN) = 1.2V, IQ = 2.