Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - linear/switching voltage regulator Automotive TSSOP 38 EP

LT3507A

3507af

FEATURES

APPLICATIONS

DESCRIPTION

Triple Monolithic Step-Down

Regulator with LDO

The LT

3507A is a triple, current mode, DC/DC converter

with internal power switches and a low dropout regulator.

The switching converters are step-down converters capable

of generating one 2.7A output and two 1.8A outputs. All

three converters are synchronized to a single oscillator.

The 2.7A output runs with opposite phase to the other two

converters, reducing input ripple current. Each regulator

has independent shutdown and soft-start circuits, and

generates a power good signal when its output is in regu-

lation, easing power supply sequencing and interfacing

with microcontrollers and DSPs.

The switching frequency is set with a single resistor yielding

a range of 250kHz to 2.5MHz. The high switching frequency

allows the use of small inductors and capacitors resulting

in a very small triple output supply. The constant switching

frequency, combined with low impedance ceramic capaci-

tors, results in low, predictable output ripple. Frequency

foldback and thermal shutdown provide protection against

fault conditions. The LT3507A provides higher output cur-

rent than available with the LT3507.

Wide Input Range: 4V to 36V

One 2.7A and Two 1.8A Output Switching

Regulators with Internal Power Switches

Low Dropout Linear Regulator with External

Transistor

Antiphase Switching Reduces Ripple

Independent Run, Tracking/Soft-Start, and Power

Good Indicators Ease Supply Sequencing

Uses Small Inductors and Ceramic Capacitors

Adjustable, 250kHz to 2.5MHz Switching Frequency,

Synchronizable Over the Full Range

User Programmable Overvoltage and Undervoltage

Lockouts

Thermally Enhanced, 38-Lead TSSOP and

5mm × 7mm QFN Packages

Automotive

Industrial Supplies

Distributed Power Regulation

DSP Power

TYPICAL APPLICATION

IN1

BOOST1

BOOST3

SW3

FB3

BIAS

DRIVE

FB4

SW1

FB1

BOOST2

0.22µF

10.2k

53.6k

6V TO 36V

OUT3

1.8A

IN2

IN3

SW2

FB2

GND

LT3507A

22µF

25.5k

3507A TA01a

107k 11.5k

OUT2

3.3V

1.5A

OUT4

2.5V

0.3A

RT/SYNC

680pF

15µH

2.2µF

33µF

= 450kHz

0.22µF

15k

18.7k

OUT1

1.8V

2.7A

100µF

680pF

25.5k

4.7µH

24.3k

680pF

25.5k

11k

34.8k

10µH

22µF

OUT2

Start-Up Waveforms—Coincident Tracking

5V, 3.3V, 2.5V and 1.8V Step-Down Regulator

1V/DIV

OUT1

OUT2

OUT3

OUT4

1ms/DIV

3507 TA01b

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

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

Summary of content (28 pages)

PAGE 1
FEATURES n n n n n n n n n Wide Input Range: 4V to 36V One 2.7A and Two 1.8A Output Switching Regulators with Internal Power Switches Low Dropout Linear Regulator with External Transistor Antiphase Switching Reduces Ripple Independent Run, Tracking/Soft-Start, and Power Good Indicators Ease Supply Sequencing Uses Small Inductors and Ceramic Capacitors Adjustable, 250kHz to 2.
PAGE 2
LT3507A ABSOLUTE MAXIMUM RATINGS (Note 1) VIN Pins....................................................... –0.3V to 36V BOOST Pins...............................................................55V BOOST Above SW......................................................25V PGOOD Pins...............................................................36V BIAS Pin.....................................................................16V TRK/SS, VC, FB, RT/SYNC Pins....................................
PAGE 3
LT3507A ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN1, VIN2, VIN3 = 12V, VBOOST1, VBOOST2, VBOOST3 = 17V, unless otherwise noted. (Notes 2, 7) PARAMETER CONDITIONS Minimum Operating Voltage Internal UVLO on VIN1 Input Quiescent Current Bias Quiescent Current TYP MAX 3.8 4 Not Switching, VBIAS = 3.3V 2 3.5 mA Not Switching, VBIAS = 3.3V 5 7.
PAGE 4
LT3507A ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN1, VIN2, VIN3 = 12V, VBOOST1, VBOOST2, VBOOST3 = 17V, unless otherwise noted (Notes 2, 7) PARAMETER CONDITIONS MIN TYP MAX UNITS Converter 3 VC3 to Switch Current Gain 4.3 4 ISW3 = 1.5A (Note 6) 350 500 mV ISW3 = 1.5A 40 60 mA Duty Cycle = 15% Switch 3 VCESAT BOOST3 Operating Current l 2.7 A/V 3.
PAGE 5
LT3507A TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V 70 VIN = 36V 60 50 40 Efficiency vs Load Current, Channels 2 and 3, VOUT = 3.3V VIN = 6V 0.5 80 VIN = 12V 0.4 VIN = 36V 70 0 0.3 804 80 803 70 802 60 CHANNELS 2, 3 50 CHANNEL 1 40 797 10 796 1.0 1.5 ISW (A) 2.0 0 1.8 2.5 3507A G04 0.5 1 1.5 ISW (A) 2 2.5 3 3507A G03 Frequency vs RT 2.5 2.0 1.5 1.0 0.5 795 –50 –30 –10 30 50 70 90 110 130 150 TEMPERATURE (°C) 3.0 0 3507A G02 799 20 0.5 1.5 800 798 0 0.
PAGE 6
LT3507A TYPICAL PERFORMANCE CHARACTERISTICS RUN Threshold vs Temperature VIN1-VINSW Voltage Drop vs IVINSW 0.40 1.2 TA = 25°C 0.35 1.0 5 0.30 0.6 0.4 CHANNEL 1 4 0.25 ILIM (A) 0.8 VIN–VINSW (V) RUN THRESHOLD (V) Current Limit vs Duty Cycle 6 0.20 3 CHANNELS 2 AND 3 0.15 2 0.10 0.2 1 0.05 0.00 0.0 –50 –30 –10 30 50 70 90 110 130 150 TEMPERATURE (°C) 0 0.2 3507A G10 0.4 0.6 IVINSW (mA) 0.8 0 1.
PAGE 7
LT3507A PIN FUNCTIONS BIAS: The BIAS pin supplies the current to the LT3507A’s internal regulator. This pin should be tied to the lowest available voltage source above 3V (either VIN, VOUT or any other available supply). The LDO pass transistor’s base current is supplied from the BIAS pin if it is at least 0.8V above the LDO DRIVE output. BOOST1, BOOST2, BOOST3: The BOOST pins are used to provide drive voltages, higher than the input voltage, to the internal bipolar NPN power switches.
PAGE 8
LT3507A BLOCK DIAGRAM VINSW VIN1 + BIAS OVLO – RUN1 INT REG AND REF RUN2 MASTER OSC CLK1 CLK2 CLK3 1.2V + RUN3 RT/SYNC – UVLO VIN4 DRIVE SHDN THERMAL SHUTDOWN + + – 0.8V – C1 + + SLOPE C3 SLAVE OSC VOUTX D1 0.4V RC – CC 1.8V +CLAMP GND R2 0.8V + ILIMIT + 1.25µA C1 R1 FB – ERROR – AMP + VC PGOOD L1 SW + CF D2 BOOST R S Q – – VINX CIN + 0.9V CLK FB4 VIN UNDERVOLTAGE DETECTION CHANNEL SHUTDOWN VOUT4 1.
PAGE 9
LT3507A OPERATION The LT3507A contains three independent, constant frequency, current mode, switching regulators with internal power switches plus a low dropout linear regulator. The three regulators share common circuitry including input source, voltage reference and oscillator, but are otherwise independent. Operation can be best understood by referring to the Block Diagram (Figure 1). If the RUN pins are tied to ground, the LT3507A is shut down and draws <1µA from the input source tied to VIN1.
PAGE 10
LT3507A APPLICATIONS INFORMATION STEP-DOWN CONSIDERATIONS DCMAX = FB Resistor Network The output voltage is programmed with a resistor divider (refer to the Block Diagram) between the output and the FB pin. Choose the resistors according to:  V  R1= R2  OUT – 1  800mV  The parallel combination of R1 and R2 should be 10k or less to avoid bias current errors.
PAGE 11
LT3507A APPLICATIONS INFORMATION fMAX2 is the frequency at which the maximum duty cycle is exceeded. If there is sufficient charge on the BOOST capacitor, the regulator will skip OFF periods to increase the overall duty cycle at frequencies about fMAX2. It will continue to regulate but with increased inductor current and greatly increased output ripple.
PAGE 12
LT3507A APPLICATIONS INFORMATION To maintain output regulation, this peak current must be less than the LT3507A’s switch current limit, ILIM. For SW1, ILIM is typically 5.1A at low duty cycles and decreases linearly to 3.7A at DC = 0.8. For SW2 and SW3, ILIM is typically 3.3A for at low duty cycles and decreases linearly to 2.4A at DC = 0.8.
PAGE 13
LT3507A APPLICATIONS INFORMATION Electrolytic capacitors are also an option. The ESRs of most aluminum electrolytic capacitors are too large to deliver low output ripple. Tantalum, as well as newer, lower-ESR organic electrolytic capacitors intended for power supply use are suitable. Chose a capacitor with a low enough ESR for the required output ripple.
PAGE 14
LT3507A APPLICATIONS INFORMATION D2 D2 C3 BOOST VIN VIN C3 BOOST LT3507A LT3507A VIN VOUT SW VIN VOUT SW GND GND VBOOST – VSW ≅ VIN MAX VBOOST ≅ 2VIN VBOOST – VSW ≅ VOUT MAX VBOOST ≅ VIN + VOUT (3a) (3b) D2 VINB > 3V BOOST C3 LT3507A VIN VIN VOUT SW GND VBOOST – VSW ≅ VINB MAX VBOOST ≅ VINB + VIN MINIMUM VALUE FOR VINB = 3V 3507A F03 (3c) Figure 3. Generating the Boost Voltage the output is already in regulation, the boost capacitor may not be fully charged.
PAGE 15
LT3507A APPLICATIONS INFORMATION if the system can tolerate a few mA of load in this state. With all three RUN pins grounded, the LT3507A enters shutdown mode and the SW pin current drops to <50µA. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LT3507A can pull large currents from the output through the SW pin and the VIN pin.
PAGE 16
LT3507A APPLICATIONS INFORMATION Frequency Compensation Loop compensation determines the stability and transient performance. Designing the compensation network is a bit complicated and the best values depend on the application and the type of output capacitor. A practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance.
PAGE 17
LT3507A APPLICATIONS INFORMATION LT3507A RUN1 RUN1 RUN2 RUN3 LT3507A RUN1 TRK/SS1 RUN2 RUN2 TRK/SS2 RUN3 RUN3 TRK/SS3 RUN LT3507A C RUN RUN1 2C VINSW 4C PG1 RUN2 (7a) (7b) PG2 RUN3 LT3507A RUN RUN1 TRK/SS1 RUN2 PG1 RUN3 TRK/SS2 PG2 (7c) VIN LT3507A RUN2 PG1 TRK/SS3 3507A F07 (7d) (7e) Doesn’t Work! Figure 7. Output Sequencing OUTPUT SEQUENCING The LT3507A outputs can be sequenced in several ways. The circuits in Figure 7 show some examples of these.
PAGE 18
LT3507A APPLICATIONS INFORMATION VOUT1 OUTPUT VOLTAGE OUTPUT VOLTAGE VOUT1 VOUT2 VOUT2 3507A F08 TIME TIME (8a) Coincident Tracking (8b) Ratiometric Tracking Figure 8. Two Different Modes of Output Voltage Tracking VOUT1 TO TRK/SS2 PIN VOUT2 R5 R6 R1 R2 TO VFB1 PIN TO VFB2 PIN Tracking Setup R3 SELECTING VALUES FOR R5 AND R6 R4 R5 = R6 = COINCIDENT RATIOMETRIC R3 R1 R4 R1 VOUT1/1V – 1 R3 VOUT2   R1 VOUT1  R2 = 0.8 – 1, R4 = 0.8 – 1 Figure 9.
PAGE 19
LT3507A APPLICATIONS INFORMATION voltage is substantially higher than 0.8V at steady state and effectively turns off D1. D2 and D3 will therefore conduct the same current and offer tight matching between VFB2 and the internal precision 0.8V reference. In the ratiometric mode with R6 = R2, TRK/SS2 equals 0.8V at steady state. D1 will divert part of the bias current and make VFB2 slightly lower than 0.8V.
PAGE 20
LT3507A APPLICATIONS INFORMATION FB Resistor Network The output voltage of the LDO regulator is programmed with a resistor divider (Refer to Block Diagram) between the emitter of the external NPN pass resistor and the feedback pin, FB4. Choose the resistors according to  V  R1= R2  OUT4 − 1  800mV  The parallel combination of R1 and R2 should be 10k or less to avoid bias current errors.
PAGE 21
LT3507A APPLICATIONS INFORMATION IIN IOUT VIN IOUT – IIN IIN SW GND VIN (12a Switch On) IOUT IC1 (12b Switch Off) VSW VIN C1 L1 SW GND IOUT GND IIN IIN SW D1 (12c High Frequency Switching Loop) C2 3507A F12 Figure 12. Subtracting the Current When the Switch Is On (12a) from the Current When the Switch Is Off (12b) Reveals the Path of the High Frequency Switching Current (12c) Figure 13.
PAGE 22
LT3507A APPLICATIONS INFORMATION The maximum allowed power dissipation by the LT3507A can be determined by: PDISS(MAX) = TJ(MAX) – TA θJA where RSWi is the equivalent switch resistance (0.18Ω for channel 1 and 0.22Ω for channels 2 and 3) and f is the operating frequency. The boost loss in channel i is: I  VOUTi ( VBOOSTi )  OUTi + 0.02A   50  PBSTi = VINi where TJMAX is the maximum die temperature of 125°C (150°C for H-grade).
PAGE 23
LT3507A APPLICATIONS INFORMATION The LDO pass transistor power is: PNPN = IOUTLDO(VC – VOUTLDO) where VC is the collector voltage on the NPN pass transistor. Example: An LT3507A design requirements are: VIN = 8V, f= 500kHz PDIODE1 = 0.45V ( 8V – 2.5V – 0.45) 1.6A = 0.46W 8V PIND1 = (1.6A ) 0.05Ω = 0.13W 2 V1 = 2.5V at I1 = 1.6A V2 = 3.3V at I2 = 0.8A (used for boost, bias and V4) V3 = 1.2V at I3 = 1A V4 = 3V at I4 = 0.2A (from 3.3V output) TA = 50°C, TJMAX = 125°C θJA = 34°C/W Schottky VF = 0.
PAGE 24
LT3507A TYPICAL APPLICATIONS 3.3V, 5V and 12V from a 24V Input with Ratiometric Tracking VIN 21V TO 27V 10µF 50V BAT54 L1 3.3µH VOUT1 3.3V 2A 0.1µF 34.8k 22µF D1 11k 16.2k 41.2k 1000pF 4.53k 4.32k UVLO SW1 OVLO UVLO = 16V VOUT1 FB1 100k VC1 PGOOD1 PGOOD2 PGOOD3 TRK/SS1 BOOST3 470nF D2 22µF 10.2k FB3 SW2 53.6k PGOOD1 PGOOD2 PGOOD3 VOUT1 L3 10µH SW3 BOOST2 0.1µF 100k 0.1µF TRK/SS3 LT3507A L2 6.8µH 100k BAT54 TRK/SS2 18.2k OVLO = 29V VIN3 VINSW BOOST1 1.
PAGE 25
LT3507A TYPICAL APPLICATIONS 15V, 1.8V and 1.2V 2-Stage Step Down VIN 21V TO 36V 10µF 49.9k 3.4k UVLO = 19V 22µF VIN1 VOUT1 15V 0.4A L1 10µH 0.1µF 169k D1 9.53k 68.1k 220pF VIN2 VIN3 VINSW BOOST1 UVLO SW1 OVLO FB1 VC1 TRK/SS2 TRK/SS3 PGOOD1 TRK/SS1 PGOOD2 PGOOD3 BIAS BOOST 2 0.01µF VOUT2 100k PGOOD VBST 0.1µF LT3507A Q1 VBST 3V 2.2µF SW2 DRIVE 11.5k FB2 FB4 31.6k L2 3.3µH 1000pF 33µF D2 VC2 TRK/SS4 270pF 13.3k 15k VBST BOOST3 SHDN D1: DIODES, INC.
PAGE 26
LT3507A PACKAGE DESCRIPTION UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701 Rev C) 0.70 ± 0.05 5.50 ± 0.05 5.15 ± 0.05 4.10 ± 0.05 3.00 REF 3.15 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 5.5 REF 6.10 ± 0.05 7.50 ± 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 ± 0.10 0.75 ± 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 3.00 REF 37 0.00 – 0.05 38 0.40 ±0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 5.15 ± 0.10 5.50 REF 7.
PAGE 27
LT3507A PACKAGE DESCRIPTION FE Package 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev C) Exposed Pad Variation AA 4.75 REF 38 9.60 – 9.80* (.378 – .386) 4.75 REF (.187) 20 6.60 ±0.10 4.50 REF 2.74 REF SEE NOTE 4 6.40 2.74 REF (.252) (.108) BSC 0.315 ±0.05 1.05 ±0.10 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.50 – 0.75 (.020 – .030) 0.09 – 0.20 (.0035 – .0079) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3.
PAGE 28
LT3507A TYPICAL APPLICATION 12V to 5V, 3.3V, 1.8V and 1.6V with 1.5mm Maximum Height VIN 8V TO 16V 10µF VIN1 VOUT1 1.8V 2A L1 2µH 0.1µF 22.6k 33µF D1 18.2k 13.3k 1000pF VIN2 L2 4.5µH BOOST1 UVLO SW1 OVLO D2 10µF 2000pF 7.32k 13.3k LT3507A 100k 100k PGOOD1 PGOOD2 PGOOD3 VOUT2 0.1µF SW3 FB3 FB2 VC2 L3 4.5µH VOUT3 5V 1.4A 61.9k 1200pF 10µF D3 VC3 11.3k 1.5nF 11.8k TRK/SS3 BIAS TRK/SS2 D1: DIODES, INC. DFLS220L D2, D3: DIODES, INC.