Datasheet

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LTC3633

3633fc

For more information www.linear.com/LTC3633

Typical applicaTion

FeaTures DescripTion

Dual Channel 3A, 15V

Monolithic Synchronous

Step-Down Regulator

The LT C

3633 is a high efficiency, dual-channel monolithic

synchronous buck regulator using a controlled on-time,

current mode architecture, with phase lockable switching

frequency. The two channels can run 180° out of phase,

which relaxes the requirements for input and output ca

pacitance. The operating supply voltage range is from 3.6V

to 15V

, making it suitable for dual cell lithium-ion batteries

as well as point of load power supply applications from

a 12V or 5V supply.

e operating frequency is programmable and synchroniz

able from 500kHz to 4MHz with an external resistor. The

high frequency capability allows the use of small sur

face

mount inductors and capacitors. The unique constant

frequency/controlled on-time architecture is ideal for high

step-down ratio applications that operate at high frequency

while demanding fast transient response. An internal phase

lock loop servos the on-time of the internal one-shot timer

to match the frequency of the internal clock or an applied

external clock.

The LTC3633 can select between forced continuous mode

and high efficiency Burst Mode operation.

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

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

owners. Protected by U.S. Patents including 5481178, 5847554, 6580258, 6304066, 6476589,

6774611.

applicaTions

3.6V to 15V Input Voltage Range

3A Output Current per Channel

Up to 95% Efficiency

Low Duty Cycle Operation: 5% at 2.25MHz

Selectable 0°/180° Phase Shift Between Channels

Adjustable Switching Frequency: 500kHz to 4MHz

External Frequency Synchronization

Current Mode Operation for Excellent Line and

Load Transient Response

0.6V Reference Allows Low Output Voltages

User Selectable Burst Mode

Operation or Forced

Continuous Operation

Output Voltage Tracking and Soft-Start Capability

Short-Circuit Protected

Overvoltage Input and Overtemperature Protection

Low Power 2.5V Linear Regulator Output

Power Good Status Outputs

Available in (4mm × 5mm) QFN-28 and 28-Lead

TSSOP Packages

Distributed Power Systems

Battery Powered Instruments

Point of Load Power Supplies

Efficiency vs Load Current

EFFICIENCY (%)

POWER LOSS (W)

100

10000

3633 TA01b

100

0.001

0.1

0.01

100

10 1000

OUT

= 5V

OUT

= 3.3V

LOAD CURRENT (mA)

Burst Mode

OPERATION

= 12V

RUN1

RUN2

TRACKSS2

PGOOD2

LTC3633

BOOST2

0.1µF

1.5µH

73.2k

10k

SW2

ON2

IN2

PGNDSGND

IN1

FB2

PHMODE

TRACKSS1

PGOOD1

BOOST1

SW1

ON1

FB1

22µF

OUT2

5V AT 3A

0.1µF

1µH

45.3k

10k

22µF

OUT1

3.3V AT 3A

12V

47µF

MODE/SYNC

V2P5

ITH1

ITH2

INTV

2.2µF

3633 TA01a

Summary of content (28 pages)

PAGE 1
LTC3633 Dual Channel 3A, 15V Monolithic Synchronous Step-Down Regulator Description Features n n n n n n n n n n n n n n n n 3.6V to 15V Input Voltage Range 3A Output Current per Channel Up to 95% Efficiency Low Duty Cycle Operation: 5% at 2.25MHz Selectable 0°/180° Phase Shift Between Channels Adjustable Switching Frequency: 500kHz to 4MHz External Frequency Synchronization Current Mode Operation for Excellent Line and Load Transient Response 0.
PAGE 2
LTC3633 Absolute Maximum Ratings (Note 1) VIN1, VIN2.................................................... –0.3V to 16V VIN1, VIN2 Transient....................................................18V PGOOD1, PGOOD2, VON1, VON2................... –0.3V to 16V BOOST1, BOOST2.....................................–0.3V to 19.6V BOOST1-SW1, BOOST2-SW2..................... –0.3V to 3.6V V2P5, INTVCC, TRACKSS1, TRACKSS2....... –0.3V to 3.6V ITH1, ITH2, RT, MODE/SYNC.........–0.3V to INTVCC + 0.3V VFB1, VFB2, PHMODE....
PAGE 3
LTC3633 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TJ = 25°C (Note 2). VIN1 = VIN2 = 12V, unless otherwise noted. SYMBOL PARAMETER VIN Supply Range IQ Input DC Supply Current (VIN1 + VIN2) Both Channels Active (Note 4) Sleep Current Shutdown VFB Feedback Reference Voltage CONDITIONS MIN l TYP 3.6 MODE = 0V MODE = INTVCC, VFB1, VFB2 > 0.6 RUN1 = RUN2 = 0V MAX 15 1.3 500 13 l 0.
PAGE 4
LTC3633 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 LTC3633 is tested under pulsed load conditions such that TJ ≈ TA. The LTC3633E is guaranteed to meet performance specifications from 0°C to 85°C junction temperature.
PAGE 5
LTC3633 Typical Performance Characteristics otherwise noted. Efficiency vs Load Current Forced Continuous Mode Operation Efficiency vs Load Current Burst Mode Operation 100 90 Efficiency vs Load Current 100 VOUT = 1.8V 80 70 70 50 40 30 20 0 10 1 1000 100 LOAD CURRENT (mA) 60 50 40 30 20 VIN = 4V VIN = 8V VIN = 12V 10 EFFICIENCY (%) 80 70 60 0 10 1 1000 100 LOAD CURRENT (mA) 100 VOUT = 5V VOUT = 3.
PAGE 6
LTC3633 Typical Performance Characteristics TJ = 25°C, VIN = 12V, fSW = 1MHz, L = 1µH unless otherwise noted. Internal MOSFET RDS(ON) vs Temperature 800 160 TOP SWITCH 600 100 500 80 BOTTOM SWITCH 20 100 –25 0 50 75 25 TEMPERATURE (°C) 100 14 300 200 0 –50 16 400 40 0 125 4 TA = 90°C TA = 25°C TA = –40°C 4 6 8 10 VIN (V) 2 12 0 16 0 25 50 75 TEMPERATURE (°C) 100 125 12 14 16 1.6 3.6 1.4 1.2 1.0 3.4 1000 10 VIN (V) 1.8 3.5 2000 8 2.
PAGE 7
LTC3633 Typical Performance Characteristics otherwise noted. Load Step (Internal Compensation) VOUT AC-COUPLED 100mV/DIV IL 2A/DIV RUN 2V/DIV RUN 2V/DIV VOUT 1V/DIV VOUT 1V/DIV IL 2A/DIV IL 1A/DIV CSS = 4.7nF ILOAD = 150mA 3633 G20 400µs/DIV 3633 G21 Start-Up into Prebiased Output (Forced Continuous Mode) RUN 2V/DIV RUN 2V/DIV VOUT 1.8V 1V/DIV VOUT 1.8V 1V/DIV IL 1A/DIV IL 2A/DIV 200µs/DIV 400µs/DIV CSS = 4.
PAGE 8
LTC3633 Pin Functions (QFN/TSSOP) PGOOD1 (Pin 1/Pin 4): Channel 1 Open-Drain Power Good Output Pin. PGOOD1 is pulled to ground when the voltage on the VFB1 pin is not within ±8% (typical) of the internal 0.6V reference. PGOOD1 becomes high impedance once the VFB1 pin returns to within ±5% (typical) of the internal reference. PHMODE (Pin 2/Pin 5): Phase Select Input. Tie this pin to ground to force both channels to switch in phase. Tie this pin to INTVCC to force both channels to switch 180° out of phase.
PAGE 9
LTC3633 Pin Functions (QFN/TSSOP) V2P5 (Pin 18/Pin 21): 2.5V Regulator Output. Outputs a regulated 2.5V supply voltage capable of supplying 10mA. Bypass this pin with a minimum of 1µF low ESR ceramic capacitor. Tie this pin to INTVCC when this output is not being used in the application. INTVCC (Pin 19/Pin 22): Internal 3.3V Regulator Output. The internal power drivers and control circuits are powered from this voltage.
PAGE 10
LTC3633 Block Diagram CIN RUN VON VIN 1.22V 140k + AV = 1 – RUN INTVCC VIN 0.72V ION ION CONTROLLER OSC1 6V V tON = VON IION RUN R S Q ON BOOST SWITCH LOGIC AND ANTISHOOT THROUGH TG M1 COUT BG ICMP + COMP SELECT M2 IREV – – CBOOST L1 SW PGND + SENSE– SENSE+ R2 ITH FB RC IDEAL DIODES CC1 R1 0.6V REF – EA – + 0.648V INTERNAL SOFT-START 0V PGOOD + INTVCC 1.4µA – TRACK – UV TRACKSS SS + 0.552V + FC BURST MODE SELECT CSS 0.48V AT START-UP 0.
PAGE 11
LTC3633 Operation The LTC3633 is a dual-channel, current mode monolithic step down regulator capable of providing 3A of output current from each channel. Its unique controlled on-time architecture allows extremely low step-down ratios while maintaining a constant switching frequency. Each channel is enabled by raising the voltage on the RUN pin above 1.22V nominally.
PAGE 12
LTC3633 Applications Information A general LTC3633 application circuit is shown on the first page of this data sheet. External component selection is largely driven by the load requirement and switching frequency. Component selection typically begins with the selection of the inductor L and resistor RT. Once the inductor is chosen, the input capacitor, CIN, and the output capacitor, COUT, can be selected. Next, the feedback resistors are selected to set the desired output voltage.
PAGE 13
LTC3633 Applications Information Ferrite designs exhibit very low core loss and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. This results in an abrupt increase in inductor ripple current, so it is important to ensure that the core will not saturate.
PAGE 14
LTC3633 Applications Information must instantaneously supply the current to support the load until the feedback loop raises the switch current enough to support the load. The time required for the feedback loop to respond is dependent on the compensation and the output capacitor size. Typically, 3 to 4 cycles are required to respond to a load step, but only in the first cycle does the output drop linearly. The output droop, VDROOP, is usually about 3 times the linear drop of the first cycle.
PAGE 15
LTC3633 Applications Information Output Voltage Programming Each regulator’s output voltage is set by an external resistive divider according to the following equation:  R2  VOUT = 0.6V 1+   R1  The desired output voltage is set by appropriate selection of resistors R1 and R2 as shown in Figure 2. Choosing large values for R1 and R2 will result in improved zeroload efficiency but may lead to undesirable noise coupling or phase margin reduction due to stray capacitances at the VFB node.
PAGE 16
LTC3633 Applications Information Suggested compensation component values are shown in Figure 3. For a 2MHz application, an R-C network of 220pF and 13kΩ provides a good starting point. The bandwidth of the loop increases with decreasing C. If R is increased by the same factor that C is decreased, the zero frequency will be kept the same, thereby keeping the phase the same in the most critical frequency range of the feedback loop.
PAGE 17
LTC3633 Applications Information MODE/SYNC Operation The MODE/SYNC pin is a multipurpose pin allowing both mode selection and operating frequency synchronization. Floating this pin or connecting it to INTVCC enables Burst Mode operation for superior efficiency at low load currents at the expense of slightly higher output voltage ripple. When the MODE/SYNC pin is tied to ground, forced continuous mode operation is selected, creating the lowest fixed output ripple at the expense of light load efficiency.
PAGE 18
LTC3633 Applications Information The ratio of this divider should be the same as that of the slave channel’s feedback divider shown in Figure 5a. In this tracking mode, VOUT1 must be set higher than VOUT2. To implement the ratiometric tracking, the feedback pin of the master channel should connect to the TRACKSS pin of the slave channel (as in Figure 5b). By selecting different resistors, the LTC3633 can achieve different modes of tracking including the two in Figure 4.
PAGE 19
LTC3633 Applications Information what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: % Efficiency = 100% – (L1 + L2 + L3 +…) where L1, L2, etc. are the individual losses as a percentage of input power.
PAGE 20
LTC3633 Applications Information TRISE = PD • θJA As an example, consider the case when one of the regulators is used in an application where VIN = 12V, IOUT = 2A, frequency = 2MHz, VOUT = 1.8V. From the RDS(ON) graphs in the Typical Performance Characteristics section, the top switch on-resistance is nominally 140mΩ and the bottom switch on-resistance is nominally 80mΩ at 70°C ambient. The equivalent power MOSFET resistance RSW is: 1.8V 10.
PAGE 21
LTC3633 Applications Information of power loss in the package with corresponding output load current. Although making this measurement with this method does violate absolute maximum voltage ratings on the PGOOD pin, the applied power is so low that there should be no significant risk of damaging the device. Board Layout Considerations When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3633.
PAGE 22
LTC3633 Applications Information A 47µF ceramic capacitor should be sufficient for channel 1. Solving the same equation for channel 2 (using 5% of VOUT for VDROOP) results in 27µF of capacitance (22µF is the closest standard value). Lastly, the feedback resistors must be chosen. Picking R1 and R3 to be 12.1k, R2 and R4 are calculated to be:  1.8V  R2 = (12.1k) •  – 1 = 24.2k  0.6V  CIN should be sized for a maximum current rating of: 1.8V (13.2V – 1.8V ) IRMS = 3A = 1A 13.2V R4 = (12.
PAGE 23
LTC3633 Applications Information VIA TO BOOST1 VIA TO VON1/R2 (NOT SHOWN) VOUT1 COUT1 L1 GND VIAS TO GROUND PLANE SW1 CBOOST1 CIN VIAS TO GROUND PLANE VIN SGND (TO NONPOWER COMPONENTS) CBOOST2 CIN SW2 GND VIAS TO GROUND PLANE L2 COUT2 VOUT2 3633 F09 VIA TO BOOST2 VIA TO VON2/R4 (NOT SHOWN) Figure 9.
PAGE 24
LTC3633 Typical Applications 1.2V/2.5V 4MHz Buck Regulator VIN 3.6V TO 15V C1 22µF ×2 VIN2 RUN1 RUN2 ITH2 VIN1 C2 2.2µF V2P5 PHMODE ITH1 6.98k 10pF INTVCC 220pF 6.98k LTC3633 10pF 220pF RT R5 80.6k VOUT2 2.5V AT 3A MODE/SYNC 0.1µF R4 31.6k COUT2 22µF BOOST1 BOOST2 L2 0.82µH L1 0.47µH 0.1µF SW2 VON2 VFB2 R3 10k SGND PGND SW1 VON1 VFB1 R1 10k R2 10k VOUT1 1.2V AT 3A COUT1 47µF 3633 TA02 3.3V/1.
PAGE 25
LTC3633 Typical Applications 1.2V/1.8V Buck Regulator with Coincident Tracking and 6V Input UVLO VIN 3.6V TO 15V R7 154k C1 47µF ×2 VIN2 RUN1 VIN1 RUN2 INTVCC C2 2.2µF ITH1 ITH2 R8 40k MODE/SYNC V2P5 LTC3633 PHMODE RT TRACKSS2 R5 162k BOOST2 L2 0.47µH VOUT2 1.2V AT 3A BOOST1 0.1µF SW2 VON2 VFB2 R4 10k COUT2 68µF L1 0.68µH 0.1µF R3 10k SGND PGND SW1 VON1 VFB1 R1 10k VOUT1 1.8V AT 3A R2 15k R6 4.99k COUT1 47µF 3633 TA03 Package Description Please refer to http://www.linear.
PAGE 26
LTC3633 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UFD Package 28-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 ±0.05 4.50 ± 0.05 3.10 ± 0.05 2.50 REF 2.65 ± 0.05 3.65 ± 0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 3.50 REF 4.10 ± 0.05 5.50 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ± 0.10 (2 SIDES) 0.75 ± 0.05 R = 0.
PAGE 27
LTC3633 Revision History REV DATE DESCRIPTION A 11/11 Updated Typical Application and Graph. PAGE NUMBER Updated Absolute Maximum Ratings section. B C 6/12 12/13 1 2 Updated • statement and Note 3 on Electrical Characteristics section. 3, 4 Updated graphs G04, G05, G10 in Typical Performance Characteristics section. 5, 6 Updated Block Diagram. 10 Updated Typical Application.
PAGE 28
LTC3633 Typical Application 3.3V/1.8V Buck Regulator with 2.5V LDO Output VIN 12V C1 47µF ×2 RUN1 RUN2 VIN2 VIN1 INTVCC ITH1 ITH2 C2 2.2µF PHMODE MODE/SYNC LTC3633 RT V2P5 2.5V AT 10mA R5 162k VOUT2 1.8V AT 3A COUT2 47µF 1µF BOOST1 BOOST2 L2 0.68µH 0.1µF R4 20k 0.1µF SW2 VON2 VFB2 R3 10k SGND PGND SW1 VON1 VFB1 R1 10k L1 1µH R2 45.3k VOUT1 3.