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LT3693

3693f

36V, 3.5A, 2.4MHz

Step-Down Switching Regulator

The LT

3693 is an adjustable frequency (200kHz to

2.4MHz) monolithic buck switching regulator that accepts

input voltages up to 36V. A high efﬁ ciency 95m switch

is included on the die along with a boost Schottky diode

and the necessary oscillator, control, and logic circuitry.

Current mode topology is used for fast transient response

and good loop stability. Shutdown reduces input supply

current to less than 1μA while a resistor and capacitor on

the RUN/SS pin provide a controlled output voltage ramp

(soft-start). A power good ﬂ ag signals when V

OUT

reaches

91% of the programmed output voltage. The LT3693 is

available in 10-Pin MSOP and 3mm × 3mm DFN packages

with exposed pads for low thermal resistance.

■

Automotive Battery Regulation

■

Power for Portable Products

■

Distributed Supply Regulation

■

Industrial Supplies

■

Wall Transformer Regulation

■

Wide Input Range: 3.6V to 36V

■

3.5A Maximum Output Current

■

Adjustable Switching Frequency: 200kHz to 2.4MHz

■

Low Shutdown Current: I

< 1μA

■

Integrated Boost Diode

■

Synchronizable Between 250kHz to 2MHz

■

Power Good Flag

■

Saturating Switch Design: 95m On-Resistance

■

0.790V Feedback Reference Voltage

■

Output Voltage: 0.79V to 30V

■

Thermal Protection

■

Soft-Start Capability

■

Small 10-Pin Thermally Enhanced MSOP and

(3mm × 3mm) DFN Packages

5V Step-Down Converter

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

6.3V TO 36V

OUT

3.5A

0.47

680pF

100k

15k

63.4k

4.7

536k

GND

OFF ON

LT3693

3693 TA01a

RUN/SS BOOST

SYNC

Efﬁ ciency

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

All other trademarks are the property of their respective owners.

OUTPUT CURRENT (A)

0 0.5

EFFICIENCY (%)

100

2.5

3693 G01

1.5

3.5

= 12V

= 34V

OUT

= 5V

L = 4.7μH

f = 600kHz

= 24V

Downloaded from Arrow.com.

Summary of content (24 pages)

PAGE 1
LT3693 36V, 3.5A, 2.4MHz Step-Down Switching Regulator U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT®3693 is an adjustable frequency (200kHz to 2.4MHz) monolithic buck switching regulator that accepts input voltages up to 36V. A high efﬁciency 95m switch is included on the die along with a boost Schottky diode and the necessary oscillator, control, and logic circuitry. Current mode topology is used for fast transient response and good loop stability.
PAGE 2
LT3693 U W W W ABSOLUTE AXI U RATI GS (Note 1) VIN, RUN/SS Voltage .................................................36V BOOST Pin Voltage ...................................................56V BOOST Pin Above SW Pin.........................................30V FB, RT, VC Voltage .......................................................5V PG, BD Voltage .........................................................30V SYNC Voltage ............................................................
PAGE 3
LT3693 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBOOST = 15V, VBD = 3.3V unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN VBD = 0, Not Switching Minimum Bias Voltage (BD Pin) Feedback Voltage ● FB Pin Bias Current (Note 3) VFB = 0.8V, VC = 0.4V FB Voltage Line Regulation 4V < VIN < 36V 780 775 ● TYP MAX 1 10 μA 2.
PAGE 4
LT3693 U W TYPICAL PERFOR A CE CHARACTERISTICS Efﬁciency Efﬁciency Efﬁciency 100 100 VIN = 12V VIN = 24V 70 60 50 0 0.5 VIN = 34V 80 VIN = 24V 70 60 VOUT = 5V L = 4.7μH f = 600kHz 2 1.5 1 2.5 OUTPUT CURRENT (A) 3 3.5 EFFICIENCY (%) VIN = 34V 80 EFFICIENCY (%) 90 2.5 80 2.0 70 1.5 VIN = 12V VOUT = 5V L = 4.7μH f = 600kHz 60 VOUT = 3.3V L = 3.3μH f = 600kHz 1.0 50 50 0 0.5 2 1.5 1 2.5 OUTPUT CURRENT (A) 0.5 0 3.5 3 3693 G01 0.5 2 1.5 1 2.
PAGE 5
LT3693 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted. Switching Frequency Feedback Voltage Frequency Foldback 1200 1.20 840 RT = 34.0k RT = 34.0k SWITCHING FREQUENCY (kHz) 1.10 820 FREQUENCY (MHz) FEEDBACK VOLTAGE (mV) 1.15 800 1.05 1.00 0.95 0.90 780 1000 0.85 760 –50 –25 0 0.
PAGE 6
LT3693 U W TYPICAL PERFOR A CE CHARACTERISTICS VC Voltages 6.5 2.50 6.0 2.00 Power Good Threshold 95 THRESHOLD VOLTAGE (%) Minimum Input Voltage CURRENT LIMIT CLAMP VC VOLTAGE (V) INPUT VOLTAGE (V) TA = 25°C unless otherwise noted. 5.5 5.0 VOUT = 5V TA = 25 oC L = 4.7MH f = 600kHz 4.5 1.00 SWITCHING THRESHOLD 0.50 4.0 1 1.
PAGE 7
LT3693 U U U PI FU CTIO S BD (Pin 1): This pin connects to the anode of the boost Schottky diode. BD also supplies current to the internal regulator. BOOST (Pin 2): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. SW (Pin 3): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor.
PAGE 8
LT3693 OPERATION The LT3693 is a constant frequency, current mode stepdown regulator. An oscillator, with frequency set by RT, enables 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. An error ampliﬁer measures the output voltage through an external resistor divider tied to the FB pin and servos the VC pin.
PAGE 9
LT3693 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⎟ ⎝ 0.79 V ⎠ Reference designators refer to the Block Diagram. Setting the Switching Frequency The LT3693 uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.4MHz by using a resistor tied from the RT pin to ground.
PAGE 10
LT3693 APPLICATIONS INFORMATION operating input voltage. Conversely, a lower switching frequency will be necessary to achieve safe operation at high input voltages. If the output is in regulation and no short-circuit, startup, or overload events are expected, then input voltage transients of up to 36V are acceptable regardless of the switching frequency. In this mode, the LT3693 may enter pulse skipping operation where some switching pulses are skipped to maintain output regulation.
PAGE 11
LT3693 APPLICATIONS INFORMATION Of course, such a simple design guide will not always result in the optimum inductor for your application. A larger value inductor provides a slightly higher maximum load current and will reduce the output voltage ripple. If your load is lower than 3.5A, then you can decrease the value of the inductor and operate with higher ripple current. This allows you to use a physically smaller inductor, or one with a lower DCR resulting in higher efﬁciency.
PAGE 12
LT3693 APPLICATIONS INFORMATION Table 2. Capacitor Vendors VENDOR PHONE URL PART SERIES Panasonic (714) 373-7366 www.panasonic.com Ceramic, COMMANDS Polymer, EEF Series Tantalum Kemet (864) 963-6300 www.kemet.com Ceramic, Tantalum Sanyo (408) 749-9714 www.sanyovideo.com T494, T495 Ceramic, Polymer, POSCAP Tantalum Murata (408) 436-1300 AVX www.murata.com Ceramic www.avxcorp.com Ceramic, Tantalum Taiyo Yuden (864) 963-6300 www.taiyo-yuden.
PAGE 13
LT3693 APPLICATIONS INFORMATION LT3693 CURRENT MODE POWER STAGE gm = 5.3mho SW ERROR AMPLIFIER OUTPUT R1 CPL FB gm = 525Mmho + The LT3693 uses current mode control to regulate the output. This simpliﬁes loop compensation. In particular, the LT3693 does not require the ESR of the output capacitor for stability, so you are free to use ceramic capacitors to achieve low output ripple and small circuit size. Frequency compensation is provided by the components tied to the VC pin, as shown in Figure 2.
PAGE 14
LT3693 APPLICATIONS INFORMATION VOUT BD BOOST VIN VIN LT3693 GND 4.7MF C3 SW (4a) For VOUT > 2.8V VOUT D2 BD is marginally adequate to support the boosted drive stage while using the internal boost diode. For reliable BOOST pin operation with 2.5V outputs use a good external Schottky diode (such as the ON Semi MBR0540), and a 1μF boost capacitor (see Figure 4b). For lower output voltages the boost diode can be tied to the input (Figure 4c), or to another supply greater than 2.8V.
PAGE 15
LT3693 APPLICATIONS INFORMATION The minimum operating voltage of an LT3693 application is limited by the minimum input voltage (3.6V) and by the maximum duty cycle as outlined in a previous section. For proper startup, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3693 is turned on with its RUN/SS pin when the output is already in regulation, then the boost capacitor may not be fully charged.
PAGE 16
LT3693 APPLICATIONS INFORMATION Shorted and Reversed Input Protection PCB Layout If the inductor is chosen so that it won’t saturate excessively, an LT3693 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 LT3693 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode OR-ed with the LT3693’s output.
PAGE 17
LT3693 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 LT3693 circuits. However, these capacitors can cause problems if the LT3693 is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion).
PAGE 18
LT3693 APPLICATIONS INFORMATION High Temperature Considerations The PCB must provide heat sinking to keep the LT3693 cool. The Exposed Pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread the heat dissipated by the LT3693. Place additional vias can reduce thermal resistance further.
PAGE 19
LT3693 TYPICAL APPLICATIONS 3.3V Step-Down Converter VOUT 3.3V 3.5A VIN 4.6V TO 36V VIN BD RUN/SS ON OFF BOOST L 3.3MH 0.47MF VC 4.7MF SW LT3693 D RT 19k PG SYNC 63.4k 316k FB GND 680pF 47MF 100k f = 600kHz 3693 TA03 D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 2.5V Step-Down Converter VOUT 2.5V 3.5A VIN 4V TO 36V BD VIN RUN/SS ON OFF D2 BOOST L 3.3mH 1mF VC 4.7mF LT3693 SW D1 RT 15.4k PG 215k SYNC 63.
PAGE 20
LT3693 TYPICAL APPLICATIONS 5V, 2MHz Step-Down Converter VOUT 5V 2.5A VIN 8.6V TO 22V TRANSIENT TO 36V BD VIN RUN/SS ON OFF BOOST 0.47mF VC 4.7mF SW LT3693 D RT 15k L 2.2mH PG 536k SYNC 12.7k FB GND 680pF 22mF 100k f = 2MHz 3693 TA05 D: ON SEMI MBRA340 L: NEC MPLC0730L2R2 12V Step-Down Converter VOUT 12V 3.5A VIN 15V TO 36V BD VIN RUN/SS ON OFF BOOST 0.47mF VC 10mF LT3693 SW D RT 17.4k L 8.2mH PG 715k SYNC 63.
PAGE 21
LT3693 TYPICAL APPLICATIONS 1.8V Step-Down Converter VOUT 1.8V 3.5A VIN 3.6V TO 27V VIN BD RUN/SS ON OFF BOOST 0.47MF VC 4.7MF LT3693 SW D RT 16.9k L 3.3MH PG SYNC 78.7k 680pF f = 500kHz 127k GND FB 47MF 100k 3693 TA08 D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 3693f 21 Downloaded from Arrow.com.
PAGE 22
LT3693 PACKAGE DESCRIPTION DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 ±0.05 3.50 ±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 = 0.115 TYP 6 0.38 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD) DFN 1103 5 0.200 REF 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1.
PAGE 23
LT3693 PACKAGE DESCRIPTION MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev B) BOTTOM VIEW OF EXPOSED PAD OPTION 2.794 ± 0.102 (.110 ± .004) 5.23 (.206) MIN 0.889 ± 0.127 (.035 ± .005) 1 2.06 ± 0.102 (.081 ± .004) 1.83 ± 0.102 (.072 ± .004) 2.083 ± 0.102 3.20 – 3.45 (.082 ± .004) (.126 – .136) 10 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.
PAGE 24
LT3693 U TYPICAL APPLICATIO 1.2V Step-Down Converter VOUT 1.2V 3.5A VIN 3.6V TO 27V VIN BD RUN/SS ON OFF BOOST L 3.3mH 0.47mF VC 4.7mF LT3693 SW D RT 17k PG 52.3k SYNC 78.7k GND FB 470pF 100mF 100k f = 500kHz 3693 TA09 D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 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.