Datasheet

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LTC3412

3412fa

The LTC

3412 is a high efficiency monolithic synchro-

nous, step-down DC/DC converter utilizing a constant

frequency, current mode architecture. It operates from an

input voltage range of 2.625V to 5.5V and provides an

adjustable regulated output voltage from 0.8V to 5V while

delivering up to 2.5A of output current. The internal

synchronous power switch with 85mΩ on-resistance

increases efficiency and eliminates the need for an exter-

nal Schottky diode. Switching frequency is set by an

external resistor or can be sychronized to an external

clock. 100% duty cycle provides low dropout operation

extending battery life in portable systems. OPTI-LOOP

compensation allows the transient response to be opti-

mized over a wide range of loads and output capacitors.

The LTC3412 can be configured for either Burst Mode

operation or forced continuous operation. Forced con-

tinuous operation reduces noise and RF interference while

Burst Mode operation provides high efficiency by reduc-

ing gate charge losses at light loads. In Burst Mode

operation, external control of the burst clamp level allows

the output voltage ripple to be adjusted according to the

requirements of the application. To further maximize

battery life, the P-channel MOSFET is turned on continu-

ously in dropout (100% duty cycle).

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Portable Instruments

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Battery-Powered Equipment

■

Notebook Computers

■

Distributed Power Systems

■

Cellular Telephones

■

Digital Cameras

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High Efficiency: Up to 95%

■

2.5A Output Current

■

Low Quiescent Current: 62µA

■

Low R

DS(ON)

Internal Switches: 85mΩ

■

Programmable Frequency: 300kHz to 4MHz

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No Schottky Diode Required

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±2% Output Voltage Accuracy

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0.8V Reference Allows Low Output Voltage

■

Selectable Forced Continuous/Burst Mode Operation

with Adjustable Burst Clamp

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Synchronizable Switching Frequency

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Low Dropout Operation: 100% Duty Cycle

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Power Good Output Voltage Monitor

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Overtemperature Protection

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Available in 16-Lead Thermally Enhanced TSSOP

and QFN Packages

2.5A, 4MHz, Monolithic

Synchronous Step-Down Regulator

Figure 1. 2.5V, 2.5A Step-Down Regulator

Efficiency vs Load Current

PGOOD

LTC3412

PGND

SGND

RUN/SS

309k

2.7V TO 5.5V

1000pF

SYNC/MODE

1µH

4.7M

470pF

75k

100pF

100µF

OUT

2.5V

2.5A

15k

110k

392k

22µF

3412 F01

LOAD CURRENT (A)

0.001

EFFICIENCY (%)

100

3412 G01

= 3.3V

OUT

= 2.5V

Burst Mode OPERATION

FORCED CONTINUOUS

0.1 10.01

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

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

Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Summary of content (20 pages)

PAGE 1
LTC3412 2.5A, 4MHz, Monolithic Synchronous Step-Down Regulator U FEATURES DESCRIPTIO ■ The LTC®3412 is a high efficiency monolithic synchronous, step-down DC/DC converter utilizing a constant frequency, current mode architecture. It operates from an input voltage range of 2.625V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering up to 2.5A of output current.
PAGE 2
LTC3412 W W U W ABSOLUTE AXI U RATI GS (Note 1) Input Supply Voltage ...................................– 0.3V to 6V ITH, RUN, VFB Voltages ............................... – 0.3V to VIN SYNC/MODE Voltages ................................ – 0.3V to VIN SW Voltage ................................... – 0.3V to (VIN + 0.3V) Peak SW Sink and Source Current ......................... 6.5A Operating Ambient Temperature Range (Note 2) .......................................
PAGE 3
LTC3412 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V unless otherwise specified.
PAGE 4
LTC3412 U W TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Input Voltage Load Regulation Efficiency vs Frequency 98 0.02 97 96 LOAD = 2.5A 90 VOUT = 2.5V 1MHz Burst Mode OPERATION 86 2.55 3.05 3.55 4.05 4.55 INPUT VOLTAGE (V) –0.04 95 1µH 0.47µH 94 2.2µH 93 92 –0.06 –0.08 –0.10 –0.12 VIN = 3.3V VOUT = 2.5V LOAD = 1A Burst Mode OPERATION 91 300 5.05 %∆VOUT/VOUT 92 88 –0.02 LOAD = 1A EFFICIENCY (%) EFFICIENCY (%) 96 94 VIN = 3.3V VOUT = 2.5V 0.00 LOAD = 100mA –0.14 –0.
PAGE 5
LTC3412 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch On-Resistance vs Temperature VIN = 3.3V ON-RESISTANCE (mΩ) 2.0 PFET ON-RESISTANCE 90 80 70 60 NFET ON-RESISTANCE 50 3500 1.5 1.0 SYNCHRONOUS SWITCH 30 3000 2500 2000 1500 1000 0.5 40 500 MAIN SWITCH 20 –40 –20 0 0 20 40 60 80 TEMPERATURE (°C) 2.5 100 120 3 3.5 4 4.5 INPUT VOLTAGE (V) 5 0 5.
PAGE 6
LTC3412 U U U PI FU CTIO S (FE/UH Package) SVIN (Pin 1/Pin 11): Signal Input Supply. Decouple this pin to SGND with a capacitor. Normally SVIN is equal to PVIN. SVIN can be greater than PVIN but keep the voltage difference between SVIN and PVIN less than 0.5V. PGOOD (Pin 2/Pin 12): Power Good Output. Open-drain logic output that is pulled to ground when the output voltage is not within ±7.5% of regulation point. ITH (Pin 3/Pin 13): Error Amplifier Compensation Point.
PAGE 7
LTC3412 W FU CTIO AL BLOCK DIAGRA U SVIN SGND ITH 1 8 3 PVIN 9 SLOPE COMPENSATION RECOVERY U VOLTAGE REFERENCE 0.8V 16 PMOS CURRENT COMPARATOR + BCLAMP + – – VFB 4 ERROR AMPLIFIER SYNC/MODE 0.74V + – + – + – P-CH BURST COMPARATOR 10 SLOPE COMPENSATION OSCILLATOR 11 SW 14 15 + RUN/SS 7 RUN 0.
PAGE 8
LTC3412 U OPERATIO Overvoltage and undervoltage comparators will pull the PGOOD output low if the output voltage comes out of regulation by ±7.5%. In an overvoltage condition, the top power MOSFET is turned off and the bottom power MOSFET is switched on until either the overvoltage condition clears or the bottom MOSFET’s current limit is reached. peak inductor current will be determined by the voltage on the ITH pin until the ITH voltage drops below 200mV.
PAGE 9
LTC3412 U OPERATIO internally by adding a compensating ramp to the inductor current signal at duty cycles in excess of 40%. Normally, the maximum inductor peak current is reduced when slope compensation is added. In the LTC3412, however, slope compensation recovery is implemented to keep the maximum inductor peak current constant throughout the range of duty cycles. This keeps the maximum output current relatively constant regardless of duty cycle.
PAGE 10
LTC3412 U W U U APPLICATIO S I FOR ATIO Inductor Core Selection Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite, mollypermalloy, or Kool Mµ® cores. Actual core loss is independent of core size for a fixed inductor value but it is very dependent on the inductance selected. As the inductance increases, core losses decrease.
PAGE 11
LTC3412 U W U U APPLICATIO S I FOR ATIO the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part.
PAGE 12
LTC3412 U W U U APPLICATIO S I FOR ATIO The LTC3412 contains an internal soft-start clamp that gradually raises the clamp on ITH after the RUN/SS pin is pulled above 2V. The full current range becomes available on ITH after 1024 switching cycles. If a longer soft-start period is desired, the clamp on ITH can be set externally with a resistor and capacitor on the RUN/SS pin as shown in Figure 1.
PAGE 13
LTC3412 U W U U APPLICATIO S I FOR ATIO The junction temperature, TJ, is given by: TJ = TA + TR where TA is the ambient temperature. First, calculate the timing resistor: ROSC = 3.23 • 1011 − 10k = 313k 1• 106 As an example, consider the LTC3412 in dropout at an input voltage of 3.3V, a load current of 2.5A and an ambient temperature of 70°C. From the typical performance graph of switch resistance, the RDS(ON) of the Pchannel switch at 70°C is approximately 97mΩ.
PAGE 14
LTC3412 U W U U APPLICATIO S I FOR ATIO If we set the sum of R2 and R3 to 185k, then the following equations can be solved: R2 + R3 = 185k R2 0.8V 1+ = R3 0.32V The last two equations shown result in the following values for R2 and R3: R2 = 110k , R3 = 75k. The value of R1 can now be determined by solving the equation shown below: R1 2.5V = 185k 0.8V R1 = 393k 1+ A value of 392k will be selected for R1. Figure 4 shows the complete schematic for this design example.
PAGE 15
LTC3412 U U W U APPLICATIO S I FOR ATIO VIN 2.7V TO 4.2V CFB 22pF X5R R1 392k 1 RPG 100k PGOOD CITH 680pF X7R RITH 7.15k 2 3 CC 100pF RSS 4.7M R2 110k ROSC 309k PVIN PGOOD SW ITH SW LTC3412 4 R3 75k SVIN 5 PGND CSS 470pF X7R 8 CIN1†† 220µF 15 14 L1* 1µH 13 VFB PGND SW RUN SW SGND PVIN COUT2† 10µF 11 + 10 COUT1** 100µF ×2 9 CIN2 22µF X5R 6.3V *TOKO D62CB A920CY-1ROM **SANYO POSCAP 4TPB100M †TAIYO YUDEN LMK325BJ106MN ††SANYO POSCAP 2R5TPC220M VOUT 2.5V 2.
PAGE 16
LTC3412 U TYPICAL APPLICATIO S 2.5V, 2.5A Regulator Using All Ceramic Capacitors VIN 2.7V TO 5.5V CIN3** 100µF C1 22pF X5R R1 392k 1 RPG 100k PGOOD CITH 1000pF X7R RITH 15k 2 3 CC 100pF RSS 4.7M PVIN PGOOD SW ITH SW LTC3412 4 R3 75k SVIN R2 110k 5 ROSC 309k 6 7 CSS 470pF X7R 8 PGND 16 CIN1 22µF X5R 6.3V 15 14 L1* 1µH 13 VFB PGND VOUT 2.5V 2.5A 12 RT SW 11 COUT** 100µF SYNC/MODE RUN SW SGND PVIN 10 9 CIN2 22µF X5R 6.
PAGE 17
LTC3412 U TYPICAL APPLICATIO S 2.5V, 2.5A Low Output Noise Regulator at 2MHz CIN3 0.1µF X5R RIN 5Ω R1 392k 1 RPG 100k CITH 1000pF X7R RITH 22.1k 2 3 C1 56pF R2 182k 5 ROSC 137k 6 7 CSS 470pF X7R 8 RSS 4.7M SVIN PVIN PGOOD SW ITH SW LTC3412 4 PGND CIN1** 100µF 16 15 14 L1 0.47µH* 13 VFB PGND VOUT 2.5V 2.5A 12 RT SW 11 COUT** 100µF ×2 SYNC/MODE RUN SW SGND PVIN 10 9 CIN2 100µF** 3412 TA06 GND *VISHAY DALE IHLP-2525CZ-01 0.
PAGE 18
LTC3412 U TYPICAL APPLICATIO S 3.3V, 2.5A Step-Down Regulator at 1MHz, Forced Continuous Mode Operation VIN 5V CIN3** 100µF C1 22pF X5R R1 634k 1 RPG 100k PGOOD 2 CITH 1000pF X7R RITH 15k 3 CC 100pF PVIN PGOOD CIN1 22µF X5R 6.3V 15 SW ITH 14 SW LTC3412 4 L1* 1µH 13 PGND VFB R2 200k 5 ROSC 309k 6 7 CSS 470pF X7R 8 RSS 4.7M SVIN 16 VOUT 3.3V 2.5A 12 PGND RT 11 SW COUT** 100µF SYNC/MODE RUN SW SGND PVIN 10 9 CIN2 22µF X5R 6.3V GND 3412 TA01 *PULSE P1166.
PAGE 19
LTC3412 U PACKAGE DESCRIPTIO FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation BA 4.90 – 5.10* (.193 – .201) 2.74 (.108) 2.74 (.108) 16 1514 13 12 1110 6.60 ±0.10 9 2.74 (.108) 4.50 ±0.10 SEE NOTE 4 2.74 6.40 (.108) BSC 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 1.10 (.0433) MAX 4.30 – 4.50* (.169 – .177) 0° – 8° 0.65 (.0256) BSC 0.45 – 0.75 (.018 – .030) 0.09 – 0.20 (.0036 – .0079) NOTE: 1.
PAGE 20
LTC3412 U TYPICAL APPLICATIO 2.5V, 2.5A Step-Down Regulator Synchronized to 1.25MHz CIN3** 100µF C1 22pF X5R VIN 2.7V TO 5.5V R1 392k 1 RPG 100k PGOOD CITH 1000pF X7R RITH 15k 2 3 SVIN PVIN PGOOD SW ITH SW LTC3412 CC 100pF 4 PGND CIN1 22µF X5R 6.3V 15 14 L1* 1µH 13 VFB R2 182k 5 16 PGND VOUT 2.5V 2.5A 12 RT ROSC 309k 1.25MHz 6 SYNC/MODE EXT CLOCK 7 RUN CSS 470pF X7R 8 SGND RSS 4.7M SW SW PVIN 11 COUT1** 100µF 10 9 CIN2 22µF X5R 6.