Datasheet

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LTC3633A-2/LTC3633A-3

3633a23f

3.6V to 20V Input Voltage Range

3A Output Current per Channel

Up to 95% Efﬁ ciency

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

Power Good Status Outputs

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

TSSOP Packages

TYPICAL APPLICATION

DESCRIPTION

Dual Channel 3A, 20V

Monolithic Synchronous

Step-Down Regulator

The LTC

3633A-2 is a high efﬁ ciency, dual-channel mono-

lithic 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 to

relax the requirements for input and output capacitance. The

operating supply voltage range is from 3.6V to 20V, making

it suitable for lithium-ion battery stacks as well as point of

load power supply applications from a 12V or 5V supply.

The operating frequency is programmable from 500kHz to

4MHz with an external resistor and may be synchronized

to an external clock signal. The high frequency capabil-

ity allows the use of small surface mount inductors and

capacitors. The unique constant frequency/controlled on-

time architecture is ideal for high step-down ratio applica-

tions that operate at high frequency while demanding fast

transient response. An internal phase locked 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 LTC3633A-2 can select between forced continuous

mode and high efﬁ ciency Burst Mode operation. The

LTC3633A-2 and LTC3633A-3 differ in their output volt-

age sense range (refer to Table 1 in the Operation section

for a description of the entire LTC3633A product family).

FEATURES

APPLICATIONS

Distributed Power Systems

Battery Powered Instruments

Point of Load Power Supplies

Efﬁ ciency vs Load Current

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.

0.001

EFFICIENCY (%)

0.1

3633a23 TA01b

100

0.01 1

OUT

= 5V

OUT

= 3.3V

LOAD CURRENT (A)

Burst Mode

OPERATION

= 12V

RUN1

RUN2

TRACKSS2

PGOOD2

LTC3633A-2

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

6V TO 20V

47µF

MODE/SYNC

ITH1

ITH2

INTV

2.2µF

3633a23 TA01a

Summary of content (28 pages)

PAGE 1
LTC3633A-2/LTC3633A-3 Dual Channel 3A, 20V Monolithic Synchronous Step-Down Regulator DESCRIPTION FEATURES n n n n n n n n n n n n n n n 3.6V to 20V 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
LTC3633A-2/LTC3633A-3 ABSOLUTE MAXIMUM RATINGS (Note 1) PVIN1, PVIN2, SVIN ...................................... –0.3V to 20V PGOOD1, PGOOD2, VON1, VON2 ................. –0.3V to 18V BOOST1, BOOST2 ...................................... –0.3V to 23V BOOST1-SW1, BOOST2-SW2 ................... –0.3V to 3.6V INTVCC, TRACKSS1, TRACKSS2 ................ –0.3V to 3.6V ITH1, ITH2, RT, MODE/SYNC ........ –0.3V to INTVCC + 0.3V VFB1, VFB2, PHMODE. .................. –0.3V to INTVCC + 0.3V RUN1 .................
PAGE 3
LTC3633A-2/LTC3633A-3 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). PVIN1 = PVIN2 = SVIN = 12V unless otherwise noted. SYMBOL PARAMETER SVIN Supply Range PVIN1 Supply Range PVIN2 Supply Range Output Voltage Range (Note 4) IQ CONDITIONS 3.6V < SVIN < 20V MIN TYP MAX UNITS l 3.6 20 V l l 1.5 1.5 20 20 V V 0.6 1.
PAGE 4
LTC3633A-2/LTC3633A-3 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). PVIN1 = PVIN2 = SVIN = 12V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN VPHMODE PHMODE Threshold Voltage PHMODE VIH PHMODE VIL 1 MODE VIH MODE VIL 1 SYNC Threshold Voltage SYNC VIH 0.
PAGE 5
LTC3633A-2/LTC3633A-3 TYPICAL PERFORMANCE CHARACTERISTICS L = 1μH unless otherwise noted. Efﬁciency vs Load Current Forced Continuous Mode Operation Efﬁciency vs Load Current Burst Mode Operation 100 100 VOUT = 1.8V 90 Efﬁciency vs Load Current 100 VOUT = 1.8V 80 70 70 50 40 30 EFFICIENCY (%) 80 70 60 60 50 40 VIN = 4V VIN = 8V VIN = 12V VIN = 20V 10 0 0.001 0.01 1 0.1 LOAD CURRENT (A) VIN = 4V VIN = 8V VIN = 12V VIN = 20V 20 10 0 0.001 10 0.01 1 0.
PAGE 6
LTC3633A-2/LTC3633A-3 TYPICAL PERFORMANCE CHARACTERISTICS TJ = 25°C, PVIN1 = PVIN2 = SVIN = 12V, fSW = 1MHz, L = 1μH unless otherwise noted.
PAGE 7
LTC3633A-2/LTC3633A-3 TYPICAL PERFORMANCE CHARACTERISTICS L = 1μH unless otherwise noted. Load Step (Internal Compensation) VOUT AC-COUPLED 100mV/DIV IL 2A/DIV 20μs/DIV VOUT = 1.8V ILOAD = 100mA to 3A ITH = INTVCC Start-Up (Burst Mode Operation) RUN 2V/DIV VOUT 1V/DIV VOUT 1V/DIV IL 2A/DIV IL 1A/DIV 3633a23 G19 400μs/DIV 3633a23 G20 400μs/DIV 3633a23 G21 VOUT = 1.8V CSS = 4.7nF ILOAD = 150mA VOUT = 1.8V CSS = 4.
PAGE 8
LTC3633A-2/LTC3633A-3 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.
PAGE 9
LTC3633A-2/LTC3633A-3 PIN FUNCTIONS (QFN/TSSOP) BOOST2 (Pin 17/Pin 20): Boosted Floating Driver Supply for Channel 2. The (+) terminal of the bootstrap capacitor connects to this pin while the (–) terminal connects to the SW pin. The normal operation voltage swing of this pin ranges from a diode voltage drop below INTVCC up to PVIN+INTVCC. INTVCC (Pin 18/Pin 21): Internal 3.3V Regulator Output. The internal power drivers and control circuits are powered from this voltage.
PAGE 10
LTC3633A-2/LTC3633A-3 BLOCK DIAGRAM CIN RUN VON PVIN 1.22V 140k + AV = 1 – RUN PVIN 0.6V (LTC3633A-2) 1.5V (LTC3633A-3) ION ION CONTROLLER OSC1 INTVCC 6V (LTC3633A-2) 12V (LTC3633A-3) V tON = VON IION RUN R S Q ON BOOST SWITCH LOGIC AND ANTISHOOT THROUGH TG M1 + M2 IREV – – L1 COUT BG ICMP CBOOST SW PGND + COMP SELECT 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.
PAGE 11
LTC3633A-2/LTC3633A-3 OPERATION The LTC3633A-2 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. The LTC3633A-2 has a VON sense range of 0.6V to 6V, while the LTC3633A-3 has a VON sense range of 1.5V to 12V.
PAGE 12
LTC3633A-2/LTC3633A-3 OPERATION When running the LTC3633A-2 channels out of phase, the large current pulses are interleaved, effectively reducing the amount of time the pulses overlap. Thus, the total RMS input current is decreased, which both relaxes the capacitance requirements for the input bypass capacitors and reduces the voltage noise on the supply line. One potential disadvantage to this conﬁguration occurs when one channel is operating at 50% duty cycle.
PAGE 13
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION A reasonable starting point is to choose a ripple current that is about 40% of IOUT(MAX). Note that the largest ripple current occurs at the highest PVIN. Exceeding 60% of IOUT(MAX) is not recommended. To guarantee that ripple current does not exceed a speciﬁed maximum, the inductance should be chosen according to: ⎛ V ⎞⎛ ⎞ V OUT ⎟⎟ ⎜⎜1– OUT ⎟⎟ L = ⎜⎜ ⎝ f • ΔIL(MAX) ⎠ ⎝ VIN(MAX) ⎠ Once the value for L is known, the type of inductor must be selected.
PAGE 14
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION Several capacitors may also be paralleled to meet size or height requirements in the design. For low input voltage applications, sufﬁcient bulk input capacitance is needed to minimize transient effects during output load changes. Even though the LTC3633A-2 design includes an overvoltage protection circuit, care must always be taken to ensure input voltage transients do not pose an overvoltage hazard to the part.
PAGE 15
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION SUPPLY1 PVIN1 LTC3633A-2 SVIN SUPPLY2 PVIN2 3633a23 F02 Figure 2. Diode-OR Circuit Furthermore, as long as SVIN is powered, the LTC3633A-2/ LTC3633A-3 operates as a step-down regulator with PVIN voltages as low as 1.5V (subject to minimum off-time constraints). However, at PVIN voltages less than 3V, internal on-time calculation errors increase, and controlled on-time operation is not guaranteed.
PAGE 16
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION Conversely, the minimum on-time is the smallest duration of time in which the top power MOSFET can be in its “on” state. This time is typically 20ns. In continuous mode operation, the minimum on-time limit imposes a minimum duty cycle of: capacitor CF can be added to improve the high frequency response, as previously shown in Figure 3. Capacitor CF provides phase lead by creating a high frequency zero with R2 which improves the phase margin.
PAGE 17
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION steady-state value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem. When observing the response of VOUT to a load step, the initial output voltage step may not be within the bandwidth of the feedback loop, so the standard second order overshoot/DC ratio cannot be used to determine phase margin.
PAGE 18
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION VOUT1 OUTPUT VOLTAGE OUTPUT VOLTAGE VOUT1 VOUT2 TIME VOUT2 TIME 3633a23 F05a (5a) Coincident Tracking 3633a23 F05b (5b) Ratiometric Tracking Figure 5. Two Different Modes of Output Voltage Tracking VOUT1 VOUT2 R3 R1 TO TRACKSS2 PIN TO VFB1 PIN R4 R2 VOUT1 R3 VOUT2 R1 TO TRACKSS2 PIN TO VFB2 PIN R4 R2 R3 TO VFB1 PIN TO VFB2 PIN R4 3633a23 F06a 3633a23 F06b (6a) Coincident Tracking Setup (6b) Ratiometric Tracking Setup Figure 6.
PAGE 19
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION Efﬁciency Considerations The percent 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. 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
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION 1.8V 10.2V RDS(ON)TOP • +RDS(ON)BOT • = 81.3mΩ 12V 12V From the previous section’s discussion on gate drive, we estimate the total gate drive current through the LDO to be 2MHz • 2.3nC = 4.6mA, and IQ of one channel is 0.65mA (see Electrical Characteristics). Therefore, the total power dissipated by a single regulator is: PD = IOUT2 • RSW + SVIN • (IGATECHG + IQ) PD = (2A)2 • (0.0813Ω) + (12V) • (4.6mA + 0.65mA) = 0.
PAGE 21
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION Board Layout Considerations When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3633A-2. Check the following in your layout: 1) Do the input capacitors connect to the PVIN and PGND pins as close as possible? These capacitors provide the AC current to the internal power MOSFETs and their drivers. 2) The output capacitor, COUT, and inductor L should be closely connected to minimize loss.
PAGE 22
LTC3633A-2/LTC3633A-3 APPLICATIONS INFORMATION VIN 12V CIN 47μF ×2 PVIN2 RUN1 RUN2 L2 1μH C2 2.2μF MODE/SYNC PHMODE TRACKSS1 PGOOD1 BOOST1 0.1μF 0.1μF SW2 VON2 VFB2 R4 R3 54.9k 12.1k COUT2 22μF SVIN INTVCC ITH1 ITH2 LTC3633A-2 RT TRACKSS2 PGOOD2 BOOST2 R5 162k VOUT2 3.3V AT 3A PVIN1 SGND PGND L1 0.68μH VOUT1 1.8V AT 3A SW1 VON1 VFB1 R2 R1 12.1k 24.3k COUT1 47μF 3633a23 F09 Figure 9.
PAGE 23
LTC3633A-2/LTC3633A-3 TYPICAL APPLICATIONS 1.8V/2.5V 4MHz Buck Regulator VIN 12V PVIN2 C1 22μF ×2 PVIN1 SVIN INTVCC RUN1 RUN2 ITH2 ITH1 6.98k 10pF C2 2.2μF PHMODE 6.98k 220pF 10pF LTC3633A-2 220pF RT R5 80.6k VOUT2 2.5V AT 3A MODE/SYNC BOOST2 L2 0.82μH R4 31.6k L1 0.68μH 0.1μF SW2 VON2 VFB2 COUT2 22μF BOOST1 0.1μF R3 10k SW1 VON1 VFB1 SGND PGND R1 12.1k R2 24.3k VOUT1 1.8V AT 3A COUT1 47μF 3633a23 TA02 3.3V/1.
PAGE 24
LTC3633A-2/LTC3633A-3 TYPICAL APPLICATIONS 1.2V/1.8V Buck Regulator with Coincident Tracking and 6V Input UVLO VIN 6V TO 20V PVIN2 R7 154k C1 47μF ×2 RUN1 RUN2 PVIN1 SVIN INTVCC ITH1 ITH2 MODE/SYNC R8 40k C2 2.2μF LTC3633A-2 PHMODE RT TRACKSS2 R5 196k L2 0.47μH VOUT2 1.2V AT 3A BOOST2 0.1μF SW2 VON2 VFB2 R4 10k COUT2 68μF BOOST1 0.1μF R3 10k SGND PGND L1 0.68μH VOUT1 1.8V AT 3A SW1 VON1 VFB1 R1 10k R2 15k R6 4.
PAGE 25
LTC3633A-2/LTC3633A-3 TYPICAL APPLICATIONS 6A 1MHz 2-Phase Buck Regulator VIN 3.6V TO 20V SVIN C1 22μF ×2 PVIN1 PVIN2 RUN1 RUN2 C2 2.2μF BOOST1 0.1μF 1μH LTC3633A-2 BOOST2 COUT 47μF ×2 0.1μF 1μH INTVCC PHMODE SW2 VON1 ITH1 ITH2 6.04k VOUT 1.5V AT 6A SW1 VON2 29.4k VFB1 1nF VFB2 RT 324k 19.
PAGE 26
LTC3633A-2/LTC3633A-3 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 28-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev I) Exposed Pad Variation EB 9.60 – 9.80* (.378 – .386) 4.75 (.187) 4.75 (.187) 28 27 26 2524 23 22 21 20 1918 17 16 15 2.74 (.108) 6.60 t0.10 4.50 t0.10 SEE NOTE 4 0.45 t0.05 EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE 6.40 2.74 (.252) (.108) BSC 1.05 t0.10 0.
PAGE 27
LTC3633A-2/LTC3633A-3 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 28
LTC3633A-2/LTC3633A-3 TYPICAL APPLICATION 2.5V Regulator with Battery Backup Q3 20k Q1 PVIN2 22μF 2 CELL Li-Ion BATTERY 5V TO 20V SVIN 1μF LTC3633A-2 Q4 Q2 20k MAIN SUPPLY 5V TO 20V PGOOD2 PVIN1 22μF BOOST1 20k 0.1μF 2.2μH 274k 100k 309k SW1 RUN1 BOOST2 INTVCC PHMODE MODE/SYNC PGOOD1 ITH1 ITH2 C2 2.2μF 13k COUT 47μF ×2 SGND PGND 324k SW2 VON1 VON2 84.5k VFB2 604Ω VFB1 RT 13k 200pF VOUT 2.5V AT 6A 0.1μF 2.2μH 20k 100k 200pF RUN2 26.