Datasheet

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LTC3122

3122fa

For more information www.linear.com/LTC3122

Typical applicaTion

FeaTures DescripTion

15V, 2.5A Synchronous

Step-Up DC/DC Converter

with Output Disconnect

The LTC

3122 is a synchronous step-up DC/DC converter

with true output disconnect and inrush current limiting. The

2.5A current limit along with the ability to program output

voltages up to 15V makes the LTC3122 well suited for a

variety of demanding applications. Once started, opera-

tion will continue with inputs down to 500mV, extending

runtime in many applications.

The LTC3122 features output disconnect in shutdown,

dramatically reducing input power drain and enabling

OUT

to completely discharge. Adjustable PWM switching

from 100kHz to 3MHz optimizes applications for highest

efficiency or smallest solution footprint. The oscillator

can also be synchronized to an external clock for noise

sensitive applications. Selectable Burst Mode operation

reduces quiescent current to 25µA, ensuring high efficiency

across the entire load range. An internal soft-start limits

inrush current during start-up.

Other features include a <1µA shutdown current and ro-

bust protection under short-circuit, thermal overload, and

output overvoltage conditions. The LTC3122 is offered in

both a low profile 12-lead (3mm × 4mm × 0.75 mm) DFN

package and a 12-lead thermally enhanced MSOP package.

5V to 12V Synchronous Boost Converter with Output Disconnect

applicaTions

Range: 1.8V to 5.5V, 500mV After Start-Up

Output Voltage Range: 2.2V to 15V

800mA Output Current for V

= 5V and V

OUT

= 12V

Output Disconnects from Input When Shut Down

Synchronous Rectification: Up to 95% Efficiency

Inrush Current Limit

Up to 3MHz Adjustable Switching Frequency

Synchronizable to External Clock

Selectable Burst Mode

Operation: 25µA I

Output Overvoltage Protection

Soft-Start

<1µA I

in Shutdown

12-Lead, 3mm × 4mm × 0.75mm Thermally

Enhanced DFN and MSOP Packages

RF Power

Piezo Actuators

Small DC Motors

12V Analog Rail From Battery, 5V, or Backup Capacitor

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

and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

Efficiency Curve

3122 TA01a

PWM/SYNC

OUT

CAP

LTC3122

SGND PGND 210k

390pF

3.3µH

113k

1.02M

10pF

4.7µF

100nF

22µF

OUT

12V

800mA

57.6k

4.7µF

ONOFF

PWMBURST

LOAD CURRENT (mA)

0.01

EFFICIENCY (%)

POWER LOSS (W)

100

0.1

0.01

100.1

3122 TA01b

10001 100

PWM

Burst Mode

OPERATION

PWM POWER LOSS

Summary of content (26 pages)

PAGE 1
LTC3122 15V, 2.5A Synchronous Step-Up DC/DC Converter with Output Disconnect Description Features n n n n n n n n n n n n VIN Range: 1.8V to 5.5V, 500mV After Start-Up Output Voltage Range: 2.
PAGE 2
LTC3122 Absolute Maximum Ratings (Note 1) VIN Voltage ................................................... –0.3V to 6V VOUT Voltage ............................................. –0.3V to 18V SW Voltage (Note 2)................................... –0.3V to 18V SW Voltage (Pulsed < 100ns) (Note 2)........ –0.3V to 19V VC, RT Voltage ........................................... –0.3V to VCC CAP Voltage VOUT < 5.7V.............................–0.3V to (VOUT + 0.3V) 5.7V ≤ VOUT ≤ 11.7V......
PAGE 3
LTC3122 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 3). VIN = 3.6V, VOUT = 12V, RT = 57.6k unless otherwise noted. PARAMETER CONDITIONS Minimum Start-Up Voltage VOUT = 0V l MIN. Input Voltage Range After VOUT ≥ 2.2V TYP MAX 1.7 1.8 UNITS V l 0.5 5.5 V Output Voltage Adjust Range l 2.2 15 V Feedback Voltage l 1.178 1.202 1.225 V Feedback Input Current VFB = 1.
PAGE 4
LTC3122 Typical Performance Characteristics Configured as front page application unless otherwise specified. Efficiency vs Load Current, VOUT = 7.5V Efficiency vs Load Current, VOUT = 5V 100 100 90 90 80 80 EFFICIENCY (%) EFFICIENCY (%) 70 60 50 PWM 40 30 20 0 0.01 0.1 70 60 50 PWM 40 30 0 0.01 0.1 30 0 0.01 ILOAD = 200mA OUTPUT CURRENT 500mA/DIV 80mA 80mA INPUT CURRENT 1A/DIV 3122 G05 2ms/DIV 1.0 80 CHANGE IN RDS(ON) FROM 25°C (%) –0.1 –0.2 –0.3 –0.4 –0.
PAGE 5
LTC3122 Typical Performance Characteristics Peak Current Limit Change vs Temperature 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.5 1.5 3.5 2.5 VIN (V) 4.5 70 1 60 0 –1 –2 70 110 30 TEMPERATURE (°C) 0 150 Burst Mode No Load Input Current vs VIN 10000 200 150 100 2.5 3.5 VIN , FALLING (V) 4.5 100 10 0.5 5.5 1.5 3122 G13 SD Pin Threshold 2.5 3.5 VIN , FALLING (V) FREQUENCY (MHz) 400mV 1s/DIV 3122 G16 15 0 4 0.
PAGE 6
LTC3122 Typical Performance Characteristics Efficiency vs Frequency 0 100 90 VCC vs VIN 60 50 40 30 20 fOSC = 200kHz fOSC = 1MHz fOSC = 3MHz 10 10 100 OUTPUT CURRENT (mA) 4.0 –2 –3 VCC (V) VCAP, REFERRED TO VOUT (V) 70 EFFICIENCY (%) 4.5 –1 80 0 CAP Pin Voltage vs VOUT –4 –5 3.5 3.0 –6 1000 –7 0 2 4 8 6 10 VOUT (V) 3122 G19 12 14 2.
PAGE 7
LTC3122 Pin Functions SW (Pin 1): Switch Pin. Connect an inductor from this pin to VIN. Keep PCB trace lengths as short and wide as possible to reduce EMI and voltage overshoot. When VOUT ≥ VIN + 2V, an internal anti-ringing resistor is connected between SW and VIN after the inductor current has dropped to near zero, to minimize EMI. The anti-ringing resistor is also activated in shutdown and during the sleep periods of Burst Mode operation. VCC (Pin 5): VCC Regulator Output.
PAGE 8
LTC3122 Block Diagram 1 BULK CONTROL SIGNALS SW VIN ANTI-RING L1 VIN 1.8V TO 5.5V 3 COUT TSD VREF_UP OSC SD OVLO SD SHUTDOWN PWM LOGIC AND DRIVERS + – CURRENT SENSE SD PWM/SYNC PWM BURST SYNC CONTROL + – IZERO COMP OVLO –+ – – + VC 5 LDO 6 FB CPL 8 1.202V VC R2 OSC REFERENCE UVLO SOFT-START VC CLAMP RC CC VREF_UP 1.202V RT THERMAL SD 7 CF SD TSD OVLO CVCC 4.
PAGE 9
LTC3122 Operation The LTC3122 is an adjustable frequency, 100kHz to 3MHz synchronous boost converter housed in either a 12-lead 4mm × 3mm DFN or a thermally enhanced MSOP package. The LTC3122 offers the unique ability to start-up and regulate the output from inputs as low as 1.8V and continue to operate from inputs as low as 0.5V. Output voltages can be programmed between 2.2V and 15V. The device also features fixed frequency, current mode PWM control for exceptional line and load regulation.
PAGE 10
LTC3122 Operation Internal Current Limit The current limit comparator shuts off the N-channel MOSFET switch once its threshold is reached. Peak switch current is limited to 3.5A, independent of input or output voltage, except when VOUT is below 1.5V, resulting in the current limit being approximately half of the nominal peak. Lossless current sensing converts the peak current signal of the N-channel MOSFET switch into a voltage that is summed with the internal slope compensation.
PAGE 11
LTC3122 Applications Information An overvoltage condition occurs when VOUT exceeds approximately 16.2V. Switching is disabled and the internal soft-start ramp is reset. Once VOUT drops below approximately 15.6V, a soft-start cycle is initiated and switching is enabled.
PAGE 12
LTC3122 Applications Information Pcb Layout Guidelines The high switching frequency of the LTC3122 demands careful attention to board layout. A careless layout will result in reduced performance. Maximizing the copper area for ground will help to minimize die temperature rise. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. See Figure 3 for an example of a two-layer board layout. rent capability by reducing the inductor ripple current.
PAGE 13
LTC3122 Applications Information Output and Input Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. Y5V types should not be used.
PAGE 14
LTC3122 Applications Information a resistor across the top resistor of the feedback divider (from VOUT to FB). This adds a phase-lead zero and pole to the transfer function of the converter as calculated in the Compensating the Feedback Loop section. possible. If the junction temperature rises above ~170°C, the part will go into thermal shutdown, and all switching will stop until the temperature drops approximately 7°C.
PAGE 15
LTC3122 Applications Information GEA = g ma • RO ≈ 950V/V (Not Adjustable; g ma = 95µS, RO ≈ 10MΩ) GMP = g mp = GPOWER = ΔIL ΔVC ≈ 3.4S (Not Adjustable) ΔVOUT η • VIN = ΔIL 2 •IOUT Combining the two equations above yields: GDC = GMP • GPOWER ≈ 1.7 • η • VIN IOUT V/V Converter efficiency η will vary with IOUT and switching frequency ƒOSC as shown in the typical performance characteristics curves.
PAGE 16
LTC3122 Applications Information The compensation will force the converter gain GBOOST to unity at ƒC by using the following expression for CC: 10 3 • g ma • R2 • G ƒC ( a 1 − 1) a 2 CC = pF 2π • ƒ C • (R1+ R2 ) a 1 (gma in µS, ƒ C in kHz, G ƒC in V/V) Once CC is calculated, RC and CF are determined by: RC = 6 10 • a1 kΩ (ƒC in kHz, C C in pF) 2π • ƒC • CC C CF = C a1 − 1 The values of the phase lead components are given by the expressions: RPL ⎛ R1• R2 ⎞ R1− a2 • ⎜ ⎟ ⎝ R1+R2 ⎠ = kΩ and a2 − 1 CPL =
PAGE 17
LTC3122 Applications Information VIN 5V L1 3.3µH SW VIN CIN 4.7µF SD OFF ON LTC3122 PWM/SYNC BURST PWM C1 100nF FB VCC VC SGND R1 1.02M CAP RT RT 57.6k VOUT 12V 800mA VOUT COUT 22µF R2 113k RC 210k PGND CF 10pF CC 390pF CVCC 4.7µF 3122 F05a Transient Response with 400mA to 800mA Load Step Switching Waveforms with 800mA Load VOUT 100mV/DIV AC-COUPLED VOUT 500mV/DIV AC-COUPLED SW 10V/DIV INDUCTOR CURRENT 1A/DIV OUTPUT CURRENT 500mA/DIV 3122 F05b 100µs/DIV 3122 F05c Figure 5.
PAGE 18
LTC3122 Applications Information VIN 5V L1 3.3µH SW VIN CIN 4.7µF SD OFF ON BURST PWM VOUT 12V 800mA VOUT C1 100nF LTC3122 CAP PWM/SYNC RPL 604k 1.02M CPL 10pF VCC RT 57.6k COUT 22µF FB RT SGND PGND VC RC 127k CF 33pF CC 220pF CVCC 4.7µF R2 113k 3122 F06 Figure 7. Boost Converter with Phase Lead The circuit in Figure 7 shows the same application as that in Figure 5 with Type III compensation. This is accomplished by adding CPL and RPL and adjusting CC, CF, and RC accordingly.
PAGE 19
LTC3122 Typical Applications Single Li-Cell to 6V, 5W, 3MHz Synchronous Boost Converter for RF Transmitter VIN 2.5V TO 4.2V L1 1µH SW VIN CIN 4.7µF OFF ON SD LTC3122 C1 100nF RT FB VCC VC SGND R1 487k CAP PWM/SYNC RT 17.4k VOUT 6V 833mA VOUT COUT 47µF RC 137k PGND CC 150pF CVCC 4.7µF VIN = 3.6V VOUT 500mV/DIV AC-COUPLED 833mA R2 121k OUTPUT CURRENT 500mA/DIV CF 12pF 80mA 80mA 3122 TA02b 100µs/DIV CIN, CVCC: 4.7µF, 6.3V, X7R, 1206 C1: 100nF, 6.
PAGE 20
LTC3122 Typical Applications 3.3V to 12V, 300kHz Synchronous Boost Converter with Output Disconnect, 500mA 100 SW VIN CIN 4.7µF BURST PWM LTC3122 SD C1 100nF RT FB VCC VC SGND R1 1.02M CAP PWM/SYNC RT 196k VOUT 12V 500mA VOUT COUT 68µF RC 154k PGND CVCC 4.7µF CC 1.2nF R2 113k CF 56pF 10 Burst Mode OPERATION 80 70 1 60 PWM 50 40 0.1 30 20 PWM POWER LOSS 10 0 0.01 CIN, CVCC: 4.7µF, 6.3V, X7R, 1206 C1: 100nF, 6.
PAGE 21
LTC3122 Typical Applications 5V to Dual Output Synchronous Boost Converter, ±15V SW VIN OFF ON LTC3122 SD CIN 4.7µF C1 100nF CAP RT FB VCC VC RT 57.6k SGND VOUT1 15V VOUT PWM/SYNC PGND RC 365k CVCC 4.7µF CC 150pF U1 R1 1.3M COUT1 22µF R2 113k VOUT2 –15V CF 10pF COUT2 47µF Z1 CIN, CVCC: 4.7µF, 6.3V, X7R, 1206 COUT2: 47µF, 16V, X7R, 1206 C1: 100nF, 6.
PAGE 22
LTC3122 Typical Applications Single Li-Cell 3-LED Driver, 2.5V/4.2V to 350mA VIN 2.5V TO 4.2V L1 3.3µH SW VIN SD OFF ON CIN 4.7µF LTC3122 PWM/SYNC VOUT FB VCC VC SGND PGND CVCC 4.7µF D2 VCC CAP RT RT 57.6k D1 C1 100nF + – LT1006 RC 2k CC 3.9nF COUT1 22µF D3 RS 0.1Ω R1 1.02M R2 30.9k CIN, CVCC: 4.7µF, 6.3V, X7R, 1206 C1: 100nF, 6.3V, X7R, 1206 COUT: 22µF, 16V, X7R, 1812 L1: TDK SPM6530T-3R3M D1, D2, D3: CREE XPGWHT-L1-0000-00G51 3122 TA07a 100 1 1 POWER LOSS 0.
PAGE 23
LTC3122 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695 Rev D) 0.70 ±0.05 3.60 ±0.05 2.20 ±0.05 3.30 ±0.05 1.70 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 ± 0.10 12 R = 0.05 TYP PIN 1 TOP MARK (NOTE 6) 0.
PAGE 24
LTC3122 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 12-Lead Plastic MSOP , Exposed Die Pad MSE Package (Reference LTC DWG # 05-08-1666 12-Lead Plastic MSOP, Exposed Rev DieF)Pad (Reference LTC DWG # 05-08-1666 Rev F) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 5.23 (.206) MIN 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.035 ±.005) 6 1 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 3.20 – 3.45 (.065 ±.004) (.
PAGE 25
LTC3122 Revision History REV DATE DESCRIPTION A 05/13 Clarified temperature ranges. PAGE NUMBER 2 Added LTC3122HMSE#PBF to the Order Information. 2 Added H-grade to Note 3, clarified N/P channel switch leakage current. 3 Clarified Load Transient Response graph. 4 Clarified Burst Mode Operation No Load graph. 5 Clarified multiple graphs. 6 Clarified SW (Pin 1) description. 7 Clarified the Block Diagram. 8 Clarified Boost Anti-Ringing Control description.
PAGE 26
LTC3122 Typical Application Dual Supercapacitor Backup Power Supply, 0.5V to 5V L1 3.3µH VIN 0.5V TO 5V CIN 4.7µF OFF ON VIN SW SD LTC3122 SC2 50F RT 57.6k C1 100nF RT FB VCC VC SGND R1 383k CAP PWM/SYNC SC1 50F VOUT 5V VOUT PGND CVCC 4.7µF SD 2V/DIV COUT 100µF RC 43.2k CC 1nF R2 121k VOUT 5V/DIV OUTPUT CURRENT 50mA/DIV CF 68pF CIN, CVCC: 4.7µF, 6.3V, X7R, 1206 C1: 100nF, 6.3V, X7R, 1206 COUT: 100µF, 6.