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LTC3417A-2

3417a2fa

Dual Synchronous

1.5A/1A 4MHz

Step-Down DC/DC Regulator

The LTC

3417A-2 is a dual constant frequency, synchro-

nous step-down DC/DC converter. Intended for medium

power applications, it operates from a 2.25V to 5.5V input

voltage range and has a constant programmable switching

frequency, allowing the use of tiny, low cost capacitors

and inductors 2mm or less in height. Each output voltage

is adjustable from 0.8V to 5V. Internal synchronous, low

DS(ON)

power switches provide high efﬁ ciency without

the need for external Schottky diodes.

A user selectable mode input allows the user to trade

off ripple voltage for light load efﬁ ciency. Burst Mode

operation provides high efﬁ ciency at light loads, while

Pulse Skip mode provides low ripple noise at light loads.

A phase mode pin allows the second channel to operate

in-phase or 180° out-of-phase with respect to channel 1.

Out-of-phase operation produces lower RMS current on

and thus lower stress on the input capacitor.

To further maximize battery life, the P-channel MOSFETs

are turned on continuously in dropout (100% duty cycle)

and both channels draw a total quiescent current of only

100µA. In shutdown, the device draws <1µA.

OUT2

Efﬁ ciency

(Burst Mode Operation)

FEATURES

High Efﬁ ciency: Up to 95%

1.5A/1A Guaranteed Minimum Output Current

Synchronizable to External Clock

No Schottky Diodes Required

Programmable Frequency Operation: 1.5MHz or

Adjustable From 0.6MHz to 4MHz

Low Ripple (<35mV

P-P

) BurstMode

Operation

: 125μA in Sleep

Low R

DS(ON)

Internal Switches

Short-Circuit Protected

: 2.25V to 5.5V

Current Mode Operation for Excellent Line and Load

Transient Response

Ultralow Shutdown Current: I

< 1µA

Low Dropout Operation: 100% Duty Cycle

Power Good Ouput

Phase Pin Selects 2nd Channel Phase Relationship

with Respect to 1st Channel

Internal Soft-Start with Individual Run Pin Control

Available in Small Thermally Enhanced

(5mm × 3mm) DFN and 20-Lead TSSOP Packages

APPLICATIONS

GPS/Navigation Systems

Automotive Instrumentation

PC Cards

Industrial Power Supplies

General Purpose Point of Load DC/DC

DESCRIPTION

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

All other trademarks are the property of their respective owners. Protected by U.S. Patents

including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131, 6144194.

FREQ

SW1

RUN1

FB1

TH1

SW2

RUN2

FB2

TH2

LTC3417A-2

GND

10µF

1.5µH

2.2µH

22pF

511k

22pF

866k

412k

22µF

5.9k 2.87k

2200pF

6800pF

3417A-2 TA01

47µF

OUT1

1.8V

1.5A

OUT2

2.5V

2.5V TO 5.5V

LOAD CURRENT (A)

0.001

EFFICIENCY (%)

100

0.01 0.1 1

3417A-2 TA01a

POWER LOSS (W)

0.001

0.01

0.1

0.0001

EFFICIENCY

REFER TO FIGURE 4

POWER LOSS

= 3.6V

OUT

= 2.5V

FREQ = 1MHz

TYPICAL APPLICATION

Summary of content (20 pages)

PAGE 1
LTC3417A-2 Dual Synchronous 1.5A/1A 4MHz Step-Down DC/DC Regulator DESCRIPTION FEATURES n n n n n n n n n n n n n n n n High Efﬁciency: Up to 95% 1.5A/1A Guaranteed Minimum Output Current Synchronizable to External Clock No Schottky Diodes Required Programmable Frequency Operation: 1.5MHz or Adjustable From 0.6MHz to 4MHz Low Ripple (<35mVP-P) BurstMode® Operation IQ: 125μA in Sleep Low RDS(ON) Internal Switches Short-Circuit Protected VIN: 2.25V to 5.
PAGE 2
LTC3417A-2 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN1, VIN2 Voltages ...................................... – 0.3V to 6V SYNC/MODE, SW1, SW2, RUN1, RUN2, VFB1, VFB2, PHASE, FREQ, ITH1, ITH2 Voltages......... –0.3V to ((VIN1 or VIN2)+ 0.3V) VIN1 – VIN2, VIN2 – VIN1 .......................................... 0.3V PGOOD Voltage ........................................... –0.3V to 6V Operating Temperature Range (Note 2) LTC3417AE-2 ....................................... –40°C to 85°C LTC3417AI-2 ................
PAGE 3
LTC3417A-2 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 3.6V unless otherwise speciﬁed (Note 2). SYMBOL PARAMETER CONDITIONS MIN VIN1, VIN2 Operating Voltage Range VIN1 = VIN2 2.25 IFB1, IFB2 Feedback Pin Input Current VIN = 6V Pin Under Test = 3V l MAX UNITS 5.5 V ± 0.1 μA VFB1, VFB2 Feedback Voltage (Note 3) 0.8 0.816 ΔVLINEREG Reference Voltage Line Regulation.
PAGE 4
LTC3417A-2 ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3417AE-2 is guaranteed to meet speciﬁed performance from 0°C to 85°C. Speciﬁcations over the –40°C to 85°C operating ambient temperature range are assured by design, characterization and correlation with statistical process controls.
PAGE 5
LTC3417A-2 TYPICAL PERFORMANCE CHARACTERISTICS OUT1 Efﬁciency vs Load Current 100 100 90 90 100 VIN = 3.6V 95 VOUT = 2.5V 85 80 75 Burst Mode OPERATION PULSE SKIP FORCED CONTINUOUS REFER TO FIGURE 4 70 65 0.01 0.1 1 85 80 75 Burst Mode OPERATION PULSE SKIP FORCED CONTINUOUS REFER TO FIGURE 4 70 65 60 0.001 10 0.01 LOAD CURRENT (A) VOUT = 1.8V 95 EFFICIENCY (%) EFFICIENCY (%) EFFICIENCY (%) VIN = 2.5V 95 VOUT = 1.8V 60 0.
PAGE 6
LTC3417A-2 TYPICAL PERFORMANCE CHARACTERISTICS RDS(ON) vs VIN OUT2 Frequency vs VIN 0.20 TA = 27°C FREQUENCY VARIATION (%) P-CHANNEL SWITCH 0.18 0.17 0.16 2 FREQUENCY VARIATION (%) 4 0.19 RDS(ON) (Ω) Frequency vs Temperature 15 6 FREQ = 143k TO GROUND 0 –2 –4 FREQ = VIN –6 0.15 0.14 2 2.5 3 3.5 4 4.5 5 5.5 –10 2 2.5 3 3.5 4 4.5 5 5.
PAGE 7
LTC3417A-2 PIN FUNCTIONS ( DFN/ TSSOP) VIN, the 1.5A regulator and the 1A regulator are in phase. When PHASE is at 0V, the 1.5A regulator and the 1A regulator are switching 180 degrees out-of-phase. Do not ﬂoat this pin. PGND1 ( Pi n 16/ Pi n 19)Ground : for SW1 N-Channel Driver. PGND2, GNDD ( Pi ns 1, 10, 11, 20)TSSOP : Package Only. Ground for SW2 N-channel driver and digital ground for circuit. SW1 ( Pi n 15/ Pi n 18) :Switch Node Connection to the Inductor for the 1.5A Regulator.
PAGE 8
LTC3417A-2 OPERATION The LTC3417A-2 uses a constant frequency, current mode architecture. Both channels share the same clock frequency. The PHASE pin sets whether the channels are running in-phase or out of phase. The operating frequency is determined by connecting the FREQ pin to VIN for 1.5MHz operation or by connecting a resistor from FREQ to ground for a frequency from 0.6MHz to 4MHz. To suit a variety of applications, the SYNC/MODE pin allows the user to trade off noise for efﬁciency.
PAGE 9
LTC3417A-2 APPLICATIONS INFORMATION 160 140 120 100 RT (kΩ) A general LTC3417A-2 application circuit is shown in Figure 4. External component selection is driven by the load requirement, and begins with the selection of the inductors L1 and L2. Once L1 and L2 are chosen, CIN, COUT1 and COUT2 can be selected. 80 Operating Frequency 60 Selection of the operating frequency is a tradeoff between efﬁciency and component size. High frequency operation allows the use of smaller inductor and capacitor values.
PAGE 10
LTC3417A-2 APPLICATIONS INFORMATION The inductor value will also have an effect on Burst Mode operation. The transition from low current operation begins when the peak inductor current falls below a level set by the burst clamp. Lower inductor values result in higher ripple current which causes this to occur at lower load currents. This causes a dip in efﬁciency in the upper range of low current operation. In Burst Mode operation, lower inductor values will cause the burst frequency to increase.
PAGE 11
LTC3417A-2 APPLICATIONS INFORMATION When D1 = D2 then the equation simpliﬁes to: IRMS = (I1 +I2 ) D (1– D) or IRMS = (I1 +I2 ) VOUT ( VIN – VOUT ) VIN where the maximum average output currents I1 and I2 equal the respective peak currents minus half the peakto-peak ripple currents: ΔI I1 =ILIM1 – L1 2 ΔIL2 I2 =ILIM2 – 2 These formula have a maximum at VIN = 2VOUT, where IRMS = (I1 + I2)/2. This simple worst case is commonly used to determine the highest IRMS.
PAGE 12
LTC3417A-2 APPLICATIONS INFORMATION is given to ripple current ratings and long term reliability. Ceramic capacitors have the lowest ESR and cost but also have the lowest capacitance density, high voltage and temperature coefﬁcient and exhibit audible piezoelectric effects. In addition, the high Q of ceramic capacitors along with trace inductance can lead to signiﬁcant ringing. Other capacitor types include the Panasonic specialty polymer (SP) capacitors. In most cases, 0.
PAGE 13
LTC3417A-2 APPLICATIONS INFORMATION VRUN 2V/DIV VOUT 1V/DIV IL 1A/DIV VIN = 3.6V VOUT = 1.8V RL = 0.9Ω 200μs/DIV 3417A-2 F02 Figure 2. Digital Soft-Start OUT1 Soft-Start Soft-start reduces surge currents from VIN by gradually increasing the peak inductor current. Power supply sequencing can also be accomplished by controlling the ITH pin. The LTC3417A-2 has an internal digital soft-start for each regulator output, which steps up a clamp on ITH over 1024 clock cycles, as can be seen in Figures 2 and 3.
PAGE 14
LTC3417A-2 APPLICATIONS INFORMATION The ITH external components shown in the Figure 4 circuit will provide an adequate starting point for most applications. The series RC ﬁlter sets the dominant pole-zero loop compensation. The values can be modiﬁed slightly (from 0.5 to 2 times their suggested values) to optimize transient response once the ﬁnal PC layout is done and the particular output capacitor type and value have been determined.
PAGE 15
LTC3417A-2 APPLICATIONS INFORMATION Although all dissipative elements in the circuit produce losses, four main sources account for most of the losses in LTC3417A-2 circuits: 1) LTC3417A-2 IS current, 2) switching losses, 3) I2R losses, 4) other losses. 1) The IS current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and control currents. IS current results in a small (< 0.1%) loss that increases with VIN, even at no load.
PAGE 16
LTC3417A-2 APPLICATIONS INFORMATION The power dissipated by the part is: Using the 1.5MHz frequency setting (FREQ = VIN), we get the following equations for L1 and L2: PD = I12 • RDS(ON)1 + I22 • RDS(ON)2 PD = 1.52 • 0.09 + 12 • 0.163 1.8V 1.8V 1– = 1.3μH 1.5MHz • 525mA 4.2V Use 1.5μH. L1= PD = 366mW The DFN package junction-to-ambient thermal resistance, θJA, is about 43°C/W. Therefore, the junction temperature of the regulator operating in a 70°C ambient temperature is approximately: TJ = 0.
PAGE 17
LTC3417A-2 APPLICATIONS INFORMATION VIN 2.25V TO 5.5V CIN 10μF CIN2 0.1μF CIN1 0.1μF R7 100k VIN1 VIN2 VOUT1 1.8V 1.5A L1 1.5μH SW1 C1 22pF VIN SW2 RUN1 RUN2 C2 22pF VIN LTC3417A-2 R1 511k VFB1 R2 412k PHASE VOUT2 2.5V 1A R3 866k VFB2 FREQ ITH2 EXPOSED GNDA PAD GNDD R4 412k VIN COUT2 22μF ITH1 R5 5.9k R6 2.
PAGE 18
LTC3417A-2 APPLICATIONS INFORMATION Board Layout Considerations When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3417A-2. These items are also illustrated graphically in the layout diagram of Figure 5. Check the following in your layout. 1. Does the capacitor CIN connect to the power VIN1 (Pin 2), VIN2 (Pin 8), and PGND2/GNDD (Pin 17) as close as possible (DFN package)? It may be necessary to split CIN into two capacitors.
PAGE 19
LTC3417A-2 PACKAGE DESCRIPTION DHC Package 16-Lead Plastic DFN (5mm × 3mm) (Reference LTC DWG # 05-08-1706) R = 0.115 TYP 5.00 ± 0.10 (2 SIDES) R = 0.20 TYP 0.65 ± 0.05 3.50 ± 0.05 1.65 ± 0.05 2.20 ± 0.05 (2 SIDES) 9 3.00 ± 0.10 (2 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH PIN 1 TOP MARK (SEE NOTE 6) (DHC16) DFN 1103 8 1 0.25 ± 0.05 0.50 BSC 0.75 ± 0.05 0.200 REF 0.25 ± 0.05 0.50 BSC 0.40 ± 0.10 16 4.40 ± 0.05 (2 SIDES) 4.40 ± 0.10 (2 SIDES) 0.00 – 0.
PAGE 20
LTC3417A-2 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3406A/B 600mA, 1.5MHz, Synchronous Step-Down DC/DC Converter 96% Efﬁciency, VIN(MIN): 2.5V, VIN(MAX): 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD < 1μA, ThinSOT™ Package LTC3407A Dual 600mA/600mA 1.5MHz, Synchronous Step-Down DC/DC Converter 95% Efﬁciency, VIN(MIN): 2.5V, VIN(MAX): 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, MS10E, 3mm × 3mm DFN-10 Package LTC3409 600mA, 1.7/2.