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LTC3417A

3417afc

Typical applicaTion

FeaTures

applicaTions

DescripTion

Dual Synchronous

1.5A/1A 4MHz Step-Down

DC/DC Regulator

The LTC

3417A is a dual constant frequency, synchronous

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

applications, it operates from a 2.25V to 5.5V input volt-

age 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 efﬁciency without

the need for external Schottky diodes.

A user selectable mode input allows the user to trade

off ripple voltage for light load efﬁciency. Burst Mode

operation provides high efﬁciency 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 V

and thus a lower RMS derating 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

125µA. In shutdown, the device draws <1µA.

OUT2 Efﬁciency

(Burst Mode Operation)

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 R

DS(ON)

Internal Switches

Short-Circuit Protected

: 2.25V to 5.5V

Current Mode Operation for Excellent Line and Load

Transient Response

125µA Quiescent Current in Sleep Mode

Ultralow Shutdown Current: I

< 1µA

Low Dropout Operation: 100% Duty Cycle

Power Good Output

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

GPS/Navigation

Digital Cameras

PC Cards

Wireless and DSL Modems

General Purpose Point of Load DC/DC

L, LT, LTC, LTM and Burst Mode are registered trademarks and Hot Swap and ThinSOT are

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

GND

10µF

1.5µH

2.2µH

22pF

511k

22pF

866k

412k

22µF

5.9k 2.87k

2200pF

6800pF

3417 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

3417 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

Summary of content (22 pages)

PAGE 1
LTC3417A 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 RDS(ON) Internal Switches Short-Circuit Protected VIN: 2.25V to 5.
PAGE 2
LTC3417A 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/VIN2 + 0.3V) VIN1 – VIN2, VIN2 – VIN1 ........................................... 0.3V PGOOD Voltage............................................ – 0.3V to 6V Operating Ambient Temperature Range (Note 2) ...................................................
PAGE 3
LTC3417A 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 IS Input DC Supply Current (Note 4) Active Mode TYP MAX UNITS VFB1 = VFB2 = 0.75V, VSYNC/MODE = VIN, VRUN1 = VRUN2 = VIN 400 600 µA VFB1 = 0.75V, VSYNC/MODE = VIN, VRUN1 = VIN 260 400 µA Half Active Mode (VRUN1 = 0V, 1A Only) VFB2 = 0.
PAGE 4
LTC3417A Typical Performance Characteristics OUT1 Pulse Skipping Mode Operation OUT1 Burst Mode Operation OUT1 Forced Continuous Mode Operation VOUT 20mV/DIV VOUT 20mV/DIV VOUT 20mV/DIV IL 250mA/DIV IL 250mA/DIV IL 250mA/DIV 2µs/DIV VIN = 3.6V VOUT = 1.8V ILOAD = 100mA REFER TO FIGURE 4 2µs/DIV VIN = 3.6V VOUT = 1.8V ILOAD = 100mA REFER TO FIGURE 4 3417 G01 2µs/DIV VIN = 3.6V VOUT = 1.
PAGE 5
LTC3417A Typical Performance Characteristics OUT2 Efficiency vs VIN (Pulse Skipping Mode) Load Step OUT1 Load Step OUT2 100 ILOAD = 250mA EFFICIENCY (%) 95 ILOAD = 800mA 90 85 VOUT1 100mV/DIV VOUT2 100mV/DIV IOUT1 500mA/DIV IOUT2 500mA/DIV 80 75 70 VIN = 3.6V 100µs/DIV VOUT = 1.8V ILOAD = 0.25A to 1.4A REFER TO FIGURE 4 VOUT = 2.5V REFER TO FIGURE 4 2 2.5 3 3.5 4 4.5 5 5.5 3417 G12 VIN = 3.6V 100µs/DIV VOUT = 2.5V ILOAD = 0.25A to 0.
PAGE 6
LTC3417A Pin Functions (DFN/TSSOP) RUN1 (Pin 1/Pin 2): Enable for 1.5A Regulator. When at Logic 1, 1.5A regulator is running. When at 0V, 1.5A regulator is off. When both RUN1 and RUN2 are at 0V, the part is in shutdown. VIN1 (Pin 2/Pin 3): Supply Pin for P-Channel Switch of 1.5A Regulator. ITH1 (Pin 3/Pin 4): Error Amplifier Compensation Point for 1.5A Regulator. The current comparator threshold increases with this control voltage. Nominal voltage range for this pin is 0V to 1.5V.
PAGE 7
LTC3417A functional Diagram 1.5A REGULATOR ITH1 + VFB1 – – + + – VB 0.752V SLOPE COMPENSATION + ANTI-SHOOTTHROUGH – SW1 + + LOGIC 0.848V VIN1 ITH LIMIT – – – + PGND1 RUN1 PGOOD VOLTAGE REFERENCE VIN2 RUN2 PHASE SYNC/MODE OSCILLATOR FREQ PGND2 + – – LOGIC + – 0.848V + – SLOPE COMPENSATION – + VB – + 1A REGULATOR ITH2 + VFB2 + – 0.
PAGE 8
LTC3417A Operation The LTC3417A 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 applications information A general LTC3417A 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. Operating Frequency 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 applications information Inductor Core Selection RMS current must be used. Some capacitors have a de-rating spec for maximum RMS current. If the capacitor being used has this requirement, it is necessary to calculate the maximum RMS current. The RMS current calculation is different if the part is used in “in phase” or “out of phase”. Different core materials and shapes will change the size/ current relationship of an inductor.
PAGE 11
LTC3417A 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: ∆IL1 2 ∆I – L2 2 I1 = ILIM1 – I2 = ILIM2 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 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 applications information VRUN 2V/DIV VRUN 2V/DIV VOUT 1V/DIV VOUT 1V/DIV IL 1A/DIV IL 0.5A/DIV VIN = 3.6V VOUT = 1.8V RL = 0.9Ω 200µs/DIV VIN = 3.6V VOUT = 2.5V RL = 2Ω 200µs/DIV Figure 2. Digital Soft-Start OUT1 Figure 3. Digital Soft-Start OUT2 ITH over 1024 clock cycles, as can be seen in Figures 2 and 3. As the voltage on ITH ramps through its operating range, the internal peak current limit is also ramped at a proportional linear rate.
PAGE 14
LTC3417A applications information determined. The output capacitors need to be selected because of various types and values determine the loop feedback factor gain and phase. An output current pulse of 20% to 100% of full load current having a rise time of 1µs to 10µs will produce output voltage and ITH pin waveforms that will give a sense of overall loop stability without breaking the feedback loop. Switching regulators take several cycles to respond to a step in load current.
PAGE 15
LTC3417A applications information low to high to low again, a packet of charge moves from VIN to ground. The resulting charge over the switching period is a current out of VIN that is typically much larger than the DC bias current. The gate charge losses are proportional to VIN and thus their effects will be more pronounced at higher supply voltages. 3) I2R losses are calculated from the DC resistances of the internal switches, RSW, and the external inductor, RL.
PAGE 16
LTC3417A applications information Remembering that the above junction temperature is obtained from an RDS(ON) at 25°C, we might recalculate the junction temperature based on a higher RDS(ON) since it increases with temperature. However, we can safely assume that the actual junction temperature will not exceed the absolute maximum junction temperature of 125°C. Design Example As a design example, consider using the LTC3417A in a portable application with a Li-Ion battery. The battery provides a VIN from 2.
PAGE 17
LTC3417A applications information VIN 2.25V TO 5.5V CIN 10µF VOUT1 1.8V 1.5A L2 2.2µH SYNC/MODE PGOOD SW1 C1 22pF R7 100k VIN1 VIN2 L1 1.5µH VIN SW2 RUN1 RUN2 C2 22pF VIN LTC3417A R1 511k VFB1 R2 412k PHASE R3 866k VFB2 FREQ VOUT2 2.5V 1A R4 412k VIN ITH2 EXPOSED GNDA PAD GNDD COUT2 22µF ITH1 R5 5.9k R6 2.
PAGE 18
LTC3417A applications information Board Layout Considerations must be connected between the (+) plate of COUT2 and a ground line terminated near GNDA. The feedback signals VFB1 and VFB2 should be routed away from noise components and traces, such as the SW lines, and its trace should be minimized. When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3417A. These items are also illustrated graphically in the layout diagram of Figure 5.
PAGE 19
LTC3417A Package Description DHC Package 16-Lead Plastic DFN (5mm × 3mm) (Reference LTC DWG # 05-08-1706) 0.65 ±0.05 3.50 ±0.05 1.65 ±0.05 2.20 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 4.40 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 5.00 ±0.10 (2 SIDES) R = 0.20 TYP 3.00 ±0.10 (2 SIDES) 9 R = 0.115 TYP 0.40 ± 0.10 16 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) PIN 1 NOTCH 8 0.200 REF 1 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.00 – 0.05 (DHC16) DFN 1103 4.40 ±0.
PAGE 20
LTC3417A Package Description FE Package 20-Lead Plastic TSSOP (4.4mm) FELTC Package (Reference DWG # 05-08-1663 Rev I) 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG #Pad 05-08-1663 Rev I) Exposed Variation CA Exposed Pad Variation CA 6.40 – 6.60* (.252 – .260) 4.95 (.195) 4.95 (.195) 20 1918 17 16 15 14 13 12 11 6.60 ±0.10 4.50 ±0.10 2.74 (.108) 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 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .
PAGE 21
LTC3417A Revision History (Revision history begins at Rev C) REV DATE DESCRIPTION C 3/11 Changed 100µA to 125µA in the last paragraph of the Description section. PAGE NUMBER 1 3417afc 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PAGE 22
LTC3417A related parts PART NUMBER DESCRIPTION COMMENTS LTC3404 600mA (IOUT), 1.4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 10µA, ISD < 1µA, MS8 Package LTC3405/LTC3405A 300mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converters 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 20µA, ISD < 1µA, ThinSOT™ Package LTC3406/LTC3406B 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converters 96% Efficiency, VIN: 2.5V to 5.