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LT3514

3514fa

For more information www.linear.com/LT3514

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Triple Step-Down Switching

Regulator with 100%

Duty Cycle Operation

The LT

3514 consists of three buck regulators (2A, 1A,

1A output current). The device has a wide operating input

range of 3.2V to 36V. An on-chip boost regulator allows

each channel to operate up to 100% duty cycle. The LT3514

is designed to minimize external component count and

results in a simple and small application circuit.

The LT3514 operates robustly in fault conditions. Cycle-

by-cycle peak current limit and catch diode current limit

sensing protect the IC during overload conditions. Ther

mal shutdown protects the power switches at elevated

temperatures. Soft-start helps control the peak inductor

current during startup.

The LT3514 also features output voltage tracking and

sequencing, programmable frequency, programmable

undervoltage lockout, and a power good pin to indicate

when all outputs are in regulation.

The LT3514 has one fewer channel (CH2) than the LT3504,

and has one channel (CH3) that outputs 2A instead of 1A.

The LT3514 in QFN is pin compatible with the LT3504. The

LT3504 provides four 1A outputs.

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

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

owners.

Triple Buck Regulator

LT3514 Start-Up and Shutdown

Waveform. V

(Top Trace) Is Ramped

from OV Up to 8V and Then Back Down

to 0V. The Other Three Traces Are the

Output Voltages of All Three Channels

Wide Input Voltage Range: 3.2V to 36V

(40V Transient)

Three Outputs: 2A, 1A, 1A

100% Duty Cycle Operation

Resistor-Programmed Constant Frequency

Short-Circuit Robust

Wide SYNC Range: 350kHz to 2.2MHz

Anti-Phase Switching Reduces Ripple

Feedback Voltage: 800mV

Independent Run/Soft-Start Pins

Shutdown with UVLO

Internal Compensation

Thermal Shutdown

Tiny 28-Lead (4mm × 5mm) Thermally Enhanced

QFN Package

24-Lead Exposed Pad TSSOP

Automotive Battery Regulation

Industrial Control Supplies

Wall Transformer Regulation

Distributed Supply Regulation

3514 TA01a

8.2µH

1µF

×2

10µH

5.4V TO 20V

TRANSIENT TO 40V

47nF

18.2k

1MHz

GND

LT3514

SKY

SW5

EN/UVLO

RUN/SS1

RUN/SS3

RUN/SS4

RT/SYNC

SW1

DA1

FB1

1.8V/1A

100pF

12.7k

10.2k

22µF

SW3

DA3

FB3

3.3V/2A

47pF

31.6k

10.2k

47µF

SW4

DA4

FB4

5V/1A

22pF

53.6k

10.2k

22µF

3.3µH

4.7µH

100ms/DIV

3514 TA01b

5V CHANNEL BEGINS

100% DC OPERATION

UVLO = ~2.9V

PARTS SHUTS

OFF

3.3V CHANNEL BEGINS

100% DC OPERATION

1V/DIV

CH4 1V/DIV

CH3 1V/DIV

CH1 1V/DIV

Summary of content (26 pages)

PAGE 1
LT3514 Triple Step-Down Switching Regulator with 100% Duty Cycle Operation DESCRIPTION FEATURES n n n n n n n n n n n n n n Wide Input Voltage Range: 3.2V to 36V (40V Transient) Three Outputs: 2A, 1A, 1A 100% Duty Cycle Operation Resistor-Programmed Constant Frequency Short-Circuit Robust Wide SYNC Range: 350kHz to 2.
PAGE 2
LT3514 ABSOLUTE MAXIMUM RATINGS (Note 1) EN/UVLO....................................................................40V EN/UVLO Pin Above VIN...............................................5V VIN.............................................................................40V SKY............................................................................46V SW5...........................................................................47V RUN/SS................................................................
PAGE 3
LT3514 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted. SYMBOL CONDITIONS EN/UVLO Threshold Voltage Rising l MIN TYP MAX 1.2 1.44 1.6 EN/UVLO Threshold Voltage Hysteresis EN/UVLO Threshold Current Hysteresis VEN/UVLO = Measured Rising Threshold – 50mV (Note 3) Internal VIN Undervoltage Lockout 2.4 UNITS V 110 mV 1.3 µA 2.9 3.2 V 0.
PAGE 4
LT3514 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted. SYMBOL CONDITIONS PG Voltage Output Low PG Pin Leakage TYP MAX UNITS IPG = 250µA 180 300 mV VPG = 2V 0.01 1 µA Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
PAGE 5
LT3514 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency, Channel 4, f = 1MHz 100 Efficiency, Channel 3, f = 1MHz 80 VOUT = 5V 90 60 50 40 30 70 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 LOAD CURRENT (A) 50 40 30 20 VIN = 6V VIN = 12V VIN = 24V VIN = 36V 20 VIN = 6V VIN = 12V VIN = 24V VIN = 36V 10 0 1 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 LOAD CURRENT (A) 0 3514 G04 50 40 30 60 50 40 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 LOAD CURRENT (A) –3.5 –2.0 –5.0 2 2 3514 G10 0 0.1 0.2 0.3 0.4 0.
PAGE 6
LT3514 TYPICAL PERFORMANCE CHARACTERISTICS Input Voltage Undervoltage Lockout 10 40 3.4 9 35 8 7 3.0 IVIN (µA) UVLO (V) INPUT QUIESCENT CURRENT (mA) 3.6 2.8 2.6 6 5 4 3 2.4 2 2.2 1 2.0 –50 –25 25 50 0 75 TEMPERATURE (°C) 100 0 125 0 30 25 20 15 10 0 1.20 800 –0.2 1.15 700 –0.4 FREQUENCY (MHz) IRUN/SS (µA) –0.8 –1.0 –1.2 –1.4 200 –1.6 100 –1.
PAGE 7
LT3514 TYPICAL PERFORMANCE CHARACTERISTICS 3.6 56 3.4 54 3.2 52 3.0 2.0 1.9 1A 50 2A 2.8 48 2.6 46 2.4 44 2.2 42 2.0 40 –50 –25 60 40 DUTY CYCLE (%) 80 100 0 25 50 75 100 125 150 TEMPERATURE (°C) Switch Beta, Channels 1 and 4 1.6 1.5 1.4 1.3 1.2 1.0 0 20 40 60 DUTY CYCLE (%) 80 100 3514 G24 Minimum On-Time 120 65 110 0.5A ON-TIME (ns) 100 55 50 1.7 3514 G23 70 60 1.8 1.
PAGE 8
LT3514 TYPICAL PERFORMANCE CHARACTERISTICS Operating Waveforms, Discontinuous Mode Operating Waveforms, Continuous Mode SW1 10V/DIV SW1 10V/DIV SW3 10V/DIV SW3 10V/DIV SW4 10V/DIV SW4 10V/DIV 500ns/DIV 3514 G29 IOUT1,3,4 = 40mA VOUT1,3,4 = 5V PIN FUNCTIONS TA = 25°C, unless otherwise noted. 500ns/DIV 3514 G30 IOUT1,3,4 = 0.5A VOUT1,3,4 = 5V (QFN/TSSOP) NC (Pins 1, 2, 14, 22/Pins 2, 10): No Connection. These pins have no connection to internal circuitry. They can be grounded or left floating.
PAGE 9
LT3514 PIN FUNCTIONS (QFN/TSSOP) RT/SYNC (Pin 17/Pin 17): Set the switching frequency of the LT3514 by tying an external resistor from this pin to ground. Select the value of the programming resistor (RT) according to Table 1 in the Applications Information section. The RT/SYNC pin is also used to synchronize the internal oscillator of the LT3514 to an external signal. The synchronization (sync) signal is directly logical compatible and can be driven by any signal with pulse width greater than 50ns.
PAGE 10
LT3514 BLOCK DIAGRAM PRECISION UVLO ON 1.44V VIN REF EN/UVLO SW5 BOOST ERROR AMP S SKY VIN 4.5V Q5 R NQ 5V VIN 1µA BOOST SWITCH AND DRIVE SKYBAD SKY 0.7V Σ 0.4V LOCK D5 BOOST REGULATOR 1SHOT STARTUP/SHUTDOWN THERMAL SHUTDOWN SLOPE CLK1 CLK2 TO CH3, CH4 SKY OSC 1SHOT SLOPE 0 SYNC DETECT 1 VIN FREQUENCY TO CURRENT 0.7V 2.2V 1µA S Σ 0.8V Q1 R NQ SW1 0.1V +– OUT1 SWITCH AND DRIVE SKYBAD DA1 SKYBAD FB1 ONE OF THREE BUCK REGULATORS SHOWN 0.
PAGE 11
LT3514 OPERATION A comparator starts the reference when the EN/UVLO pin rises above the 1.44V rising threshold. Other comparators prevent switching when the input voltage is below 2.9V or the die temperature is above 175°C. When the EN/UVLO is above 1.44V, the input voltage is above 3.2V, and the temperature is below 175°C, the boost regulator begins switching and charges the SKY capacitor to 4.85V above VIN. When the SKY voltage is less than 4.
PAGE 12
LT3514 APPLICATIONS INFORMATION The three step-down converters in the LT3514 are referred to as channels 1, 3, and 4, while the boost converter is referred to as channel 5. There is no channel 2. This naming convention is intended to maintain consistency and limited pin compatibility with the LT3504, a four channel step-down converter. Essentially, two 1A converters (channels 2 and 3) of the LT3504 were combined to make the 2A converter (channel 3) of the LT3514.
PAGE 13
LT3514 APPLICATIONS INFORMATION peak inductor current. Provided that the inductor does not saturate and that the switch current remains below 2A (SW1, SW4) or below 4A (SW3), operation above VIN(PS) is safe and will not damage the part. For a more detailed discussion on minimum on-time and pulse-skipping, refer to the Applications Information section of the LT3505 data sheet.
PAGE 14
LT3514 APPLICATIONS INFORMATION BOOST Regulator and SKY Pin Considerations The on-chip boost regulator generates the SKY voltage to be 4.85V above VIN. The SKY voltage is the source of drive current for the buck regulators which is used to fully saturate the power switch. The boost regulator requires two external components: an inductor and a capacitor. A good first choice for an inductor is given by: 20.
PAGE 15
LT3514 APPLICATIONS INFORMATION is required to regulate the output, with little overshoot. Figure 4 shows the start-up waveforms with and without a soft-start capacitor (CSS) on the RUN/SS pin. IL 0.5A/DIV VOUT 2V/DIV 3514 F04a 100µs/DIV Undervoltage Lockout The LT3514 prevents switching when the input voltage decreases below 3.2V. Alternatively, the EN/UVLO pin can be used to program an undervoltage lockout at input voltages exceeding 3.
PAGE 16
LT3514 APPLICATIONS INFORMATION For a falling threshold of 10V, the minimum hysteresis is 0.827V. For a falling threshold of 30V, the minimum hysteresis is 2.48V. R2 can be calculated once R1 is known: R2 = R1• 1.33 VIN, FALLING − 1.33 The circuit shown in Figure 5 will start when the input voltage rises above 11V and will shutdown when the input voltage falls below 10V.
PAGE 17
LT3514 APPLICATIONS INFORMATION group of two VIN pins. The ceramic bypass capacitors should be located as close to the VIN pins as possible. See the sample layout shown in the PCB Layout section. All four VIN pins should be tied together on the board and bypassing with a low performance electrolytic capacitor is recommended especially if the input power source has high impedance, or there is significant inductance due to long wires or cables.
PAGE 18
LT3514 APPLICATIONS INFORMATION Figure 6 shows the transient response of the LT3514 with several output capacitor choices. The output is 3.3V. The load current is stepped from 500mA to 1A and back to 500mA and the oscilloscope traces show the output voltage. The upper photo shows the recommended value. The second photo shows the improved response (less voltage drop) resulting from a larger output capacitor and a larger phase lead capacitor.
PAGE 19
LT3514 APPLICATIONS INFORMATION tied to VIN), then the LT3514’s internal circuitry will pull its quiescent current through its SW pin. This is fine if your system can tolerate a few mA in this state. If you ground the EN/UVLO pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LT3514 can pull large currents from the output through the SW pin and the VIN pin.
PAGE 20
LT3514 APPLICATIONS INFORMATION PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 8 shows the recommended component placement with trace, ground plane, and via locations for the QFN package. Note that large, switched currents flow in the LT3514’s VIN, SW and DA pins, the catch diodes (D1, D3, D4) and the input capacitors (C5, C6).
PAGE 21
LT3514 APPLICATIONS INFORMATION pins (Pins 10, 27) are provided near the VIN pins so that the VIN pins can be bypassed to these ground pins. The SW nodes should be kept as small as possible and kept far away from the RT/SYNC and FB nodes. Keep the RT/ SYNC node and FB nodes small so that the ground pin and ground traces will shield them from the SW nodes. If the user plans on using a SYNC signal to set the oscillator frequency then the RT/SYNC node should be kept away from the FB nodes.
PAGE 22
LT3514 APPLICATIONS INFORMATION Bear in mind that significant power dissipation occurs in Q1 during an overvoltage event. The MOSFET junction temperature must be kept below its absolute maximum rating. For the overvoltage transient shown in Figure 10, MOSFET Q1 conducts 0.55A (full load on all buck channels) while withstanding the voltage difference between VSUPPLY (180V peak) and VIN (33V). This results in a peak power of 81W.
PAGE 23
LT3514 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 24-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1771 Rev B) Exposed Pad Variation AA 7.70 – 7.90* (.303 – .311) 3.25 (.128) 3.25 (.128) 24 23 22 21 20 19 18 17 16 15 14 13 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 6.40 2.74 (.252) (.108) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 9 10 11 12 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.
PAGE 24
LT3514 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UFD Package UFDQFN Package 28-Lead Plastic (4mm × 5mm) 28-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1712 Rev B) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 ±0.05 4.50 ±0.05 3.10 ±0.05 2.50 REF 2.65 ±0.05 3.65 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 3.50 REF 4.10 ±0.05 5.50 ±0.
PAGE 25
LT3514 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 01/14 Added H-grade option 2 Clarified Switching Frequency parameters 3 Clarified resistor value for R2 11 3514fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representaFor more information www.linear.
PAGE 26
LT3514 TYPICAL APPLICATION Complete Triple Buck Regulator with 180V Surge Protection VSUPPLY 3.2V TO 30V SURGE PROTECTION TO 180V R1 10Ω Q1 R2 100k D2 6.8V R3 1k C1 0.1µF D3 D1 36V VSKY CSKY 2.2µF L5 10µH VIN + 22µF 2.2µF ×2 PG Q1: FQB34N20L D1: BZT52C36-7-F D2: BZT52C6V8-7-F D3: BAT54-7-F L1: CDRH5D28-4R2 L3: CDRH8D28-4R7 L4: CDRH5D28-8R2 L5: CBC2016100M 4.2µH SW1 SKY SW5 LT3514 0.1µF 18.2k 2.5V/1A 21.5k 22µF 10.2k 4.