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LTC3413

3413fc

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

3A, 2MHz Monolithic

Synchronous Regulator for

DDR/QDR Memory Termination

The LTC

3413 is a high efﬁ ciency monolithic synchro-

nous step-down DC/DC converter utilizing a constant

frequency, current mode architecture. It operates from

an input voltage range of 2.25V to 5.5V and provides a

regulated output voltage equal to (0.5)V

REF

while sourcing

or sinking up to 3A of output current. An internal voltage

divider reduces component count and eliminates the need

for external resistors by dividing the reference voltage in

half. The internal synchronous power switch with 85mΩ

on-resistance increases efﬁ ciency and eliminates the need

for an external Schottky diode. Switching frequencies up

to 2MHz are set by an external resistor.

Forced-continuous operation in the LTC3413 reduces

noise and RF interference. Fault protection is provided

by an overcurrent comparator that limits output current

during both sourcing and sinking operations. Adjustable

compensation allows the transient response to be optimized

over a wide range of loads and output capacitors.

Figure 1a. High Efﬁ ciency Bus Termination Supply

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

All other trademarks are the property of their respective owners.

Protected by U.S. Patents including 5481178.

High Efﬁ ciency: Up to 90%

±3A Output Current

Symmetrical Source and Sink Output Current Limit

Low R

DS(ON)

Internal Switch: 85mΩ

No Schottky Diode Required

2.25V to 5.5V Input Voltage Range

OUT

= V

REF

±1% Output Voltage Accuracy

Programmable Switching Frequency: Up to 2MHz

Power Good Output Voltage Monitor

Overtemperature Protected

Available in 16-Lead TSSOP Exposed Pad Package

Bus Termination: DDR and QDR

™

Memory,

SSTL, HSTL, ...

Notebook Computers

Distributed Power Systems

PGOOD

SWV

REF

22μF

4.7M

309k

L1: VISHAY DALE IHLP-2525CZ-01 0.47

OUT

: TDK C4532X5R0J107M

2.5V

OUT

100μF

3413 F01a

OUT

1.25V

±3A

0.47μH

LTC3413

PGNDRUN/SS

SGND

330pF

2200pF

5.11k

Figure 1b. Efﬁ ciency vs Load Current

LOAD CURRENT (A)

0.01

EFFICIENCY (%)

0.1 1 10

3413 F01b

100

= 2.5V

f = 1MHz

Summary of content (16 pages)

PAGE 1
LTC3413 3A, 2MHz Monolithic Synchronous Regulator for DDR/QDR Memory Termination FEATURES DESCRIPTION n The LTC®3413 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 2.25V to 5.5V and provides a regulated output voltage equal to (0.5)VREF while sourcing or sinking up to 3A of output current.
PAGE 2
LTC3413 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) SVIN, PVIN Supply Voltages ......................... –0.3V to 6V ITH, RUN/SS, VFB, PGOOD Voltages ............ –0.3V to VIN VREF Voltage................................................ –0.3V to VIN SW Voltage ................................... –0.3V to (VIN + 0.3V) Operating Ambient Temperature Range (Note 2) ................................................... –40°C to 85°C Junction Temperature (Notes 5, 8).......................
PAGE 3
LTC3413 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 3.3V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS fOSC Switching Frequency Switching Frequency Range ROSC = 309k (Note 6) 0.88 0.30 1.00 1.12 2.
PAGE 4
LTC3413 TYPICAL PERFORMANCE CHARACTERISTICS Switch On-Resistance vs Temperature VIN = 3.3V TA = 25°C 100 PFET ON-RESISTANCE 80 NFET ON-RESISTANCE 60 Switch Leakage vs Input Voltage 2.5 40 20 PFET ON-RESISTANCE LEAKAGE CURRENT (nA) ON-RESISTANCE (mΩ) 100 120 ON-RESISTANCE (mΩ) 120 Switch On-Resistance vs Input Voltage 80 60 NFET ON-RESISTANCE 40 0 20 40 60 80 TEMPERATURE (°C) 2.5 3 5 3.5 4 4.5 INPUT VOLTAGE (V) 3413 G04 4000 NFET 2.5 Frequency vs Input Voltage 1050 VIN = 3.
PAGE 5
LTC3413 TYPICAL PERFORMANCE CHARACTERISTICS Load Step Transient Start-Up OUTPUT VOLTAGE 100mV/DIV OUTPUT VOLTAGE 500mV/DIV INDUCTOR CURRENT 1A/DIV INDUCTOR CURRENT 1A/DIV VIN = 2.5V 20μs/DIV VOUT = 1.25V LOAD STEP = 0A TO –3A 3413 G12 VIN = 2.5V VOUT = 1.25V LOAD = 0.4Ω 1ms/DIV 3413 G13 PIN FUNCTIONS SVIN (Pin 1): Signal Input Supply. Decouple this pin to SGND with a capacitor. SVIN must be greater or equal to PVIN, however, the difference between SVIN and PVIN must be less than 0.5V.
PAGE 6
LTC3413 FUNCTIONAL DIAGRAM SVIN VREF ITH PVIN PVIN 1 6 3 9 16 SVIN SGND SLOPE COMPENSATION RECOVERY + 8 VFB PMOS CURRENT COMPARATOR + – 4 ERROR AMPLIFIER 0.9VREF 2 – + – SLOPE COMPENSATION OSCILLATOR 10 SW 11 SW LOGIC + PGOOD 1.
PAGE 7
LTC3413 OPERATION main switch to remain on for more than one cycle until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the internal P-channel MOSFET and the inductor. Low Supply Operation The LTC3413 is designed to operate down to an SVIN input supply voltage of 2.25V. One important consideration at low input supply voltages is that the RDS(ON) of the P-channel and N-channel power switches increases.
PAGE 8
LTC3413 APPLICATIONS INFORMATION Inductor Selection For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current ΔIL increases with higher VIN or VOUT and decreases with higher inductance. ΔIL = ⎛ V ⎞ 1 VOUT ⎜1 – OUT ⎟ ( f)(L) VIN ⎠ ⎝ Having a lower ripple current reduces the core losses in the inductor, the ESR losses in the output capacitors and the output voltage ripple.
PAGE 9
LTC3413 APPLICATIONS INFORMATION and load step transients as well as the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, ΔVOUT, is determined by: ΔVOUT ⎛ 1 ≤ ΔIL ⎜ESR + 8 fC ⎝ OUT ⎞ ⎟⎠ The output ripple is highest at maximum input voltage since ΔIL increases with input voltage.
PAGE 10
LTC3413 APPLICATIONS INFORMATION in Figure 1a. The soft-start duration can be calculated by using the following formula: ⎛ VIN ⎞ t SS = RSS • CSS ln ⎜ (Seconds) ⎝ VIN – 1.8 V ⎟⎠ Efﬁciency Considerations The efﬁciency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efﬁciency and which change would produce the most improvement.
PAGE 11
LTC3413 APPLICATIONS INFORMATION The junction temperature, TJ, is given by: TJ = TA + TR where TA is the ambient temperature. As an example, consider the LTC3413 in dropout at an input voltage of 3.3V, a load current of 3A and an ambient temperature of 70°C. From the Typical Performance graph of switch resistance, the RDS(ON) of the P-channel switch at 70°C is approximately 97mΩ. Therefore, power dissipated by the part is: PD = (ILOAD2)(RDS(ON)) = (3A)2(97mΩ) = 0.
PAGE 12
LTC3413 APPLICATIONS INFORMATION VIN 2.5V 1 RPG 100k PGOOD RITH 5.11k CITH CC 2200pF 100pF X7R 2 3 4 RSS 4.7M CSS 330pF X7R PVIN PGOOD SW ITH SWVFB VFB PGND 16 CIN1** 100μF 15 14 13 L1* 0.47μH VOUT 1.25V ±3A LTC3413 5 ROSC 309k SVIN 6 7 8 RT PGND VREF SW RUN/SS SW SGND PVIN 12 11 COUT** 100μF s2 10 9 GND CIN2** 100μF 3413 F03 *VISHAY DALE IHLP-2525CZ-01 0.47μH **TDK C4532X5R0J107M Figure 3.
PAGE 13
LTC3413 APPLICATIONS INFORMATION (4a) Top Layer (4b) Bottom Layer (4c) PCB Photo Figure 4.
PAGE 14
LTC3413 TYPICAL APPLICATIONS 1.25V, ±3A DDR Memory Termination Supply at 1MHz VIN 3.3V 1 RPG 100k PGOOD RITH 5.11k 2 3 CITH CC 2200pF 100pF X7R 4 6 2.5V RSS 4.7M 7 CSS 330pF X7R PVIN PGOOD SW ITH SWVFB VFB PGND 16 CIN1** 100μF 15 14 13 L1* 0.47μH VOUT 1.25V ±3A LTC3413 5 ROSC 309k SVIN 8 RT PGND VREF SW RUN/SS SW SGND PVIN 12 11 COUT** 100μF s2 10 9 GND CIN2** 100μF 3413 TA01 *VISHAY DALE IHLP-2525CZ-01 0.47μH **TDK C4532X5R0J107M Efﬁciency vs Load Current, VIN = 3.
PAGE 15
LTC3413 PACKAGE DESCRIPTION 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 2.74 6.40 (.108) (.252) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2.
PAGE 16
LTC3413 TYPICAL APPLICATION 3.3V to 0.75V, ±3A HSTL Application VIN 3.3V 1 RPG 100k PGOOD RITH 10k 2 3 CITH CC 2200pF 100pF X7R 4 6 1.5V RSS 4.7M 7 CSS 330pF X7R PVIN PGOOD SW ITH SWVFB VFB PGND 16 CIN1** 100μF 15 14 13 L1* 0.47μH VOUT 0.75V ±3A LTC3413 5 ROSC 309k SVIN 8 RT PGND VREF SW RUN/SS SW SGND PVIN 12 11 COUT1† 22μF + COUT2†† 470μF 10 9 GND CIN2** 100μF 3413 TA02 *VISHAY DALE IHLP-2525CZ-01 0.