Datasheet

ManualsBrandsLinear Technology ManualsDC / DC Adjustable Switching RegulatorsSwitching Regulator IC Step-Down MSOP- 41.5V

LT8609/LT8609A/LT8609B

Rev. H

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TYPICAL APPLICATION

FEATURES DESCRIPTION

42V, 3A Synchronous Step-Down

Regulator with 2.5µA Quiescent Current

The LT

8609/LT8609A/LT8609B is a compact, high effi-

ciency, high speed synchronous monolithic step-down

switching regulator that consumes only 1.7µA of non-

switching quiescent current. The LT8609/LT8609A/

LT8609B can deliver 3A of continuous current. Burst Mode

operation enables high efficiency down to very low output

currents while keeping the output ripple below 10mV

P-P

A SYNC pin allows synchronization to an external clock, or

spread spectrum modulation for low EMI operation. Internal

compensation with peak current mode topology allows the

use of small inductors and results in fast transient response

and good loop stability. The EN/UV pin has an accurate 1V

threshold and can be used to program V

UVLO or to shut

down the part. Acapacitor on the TR/SS pin programs the

output voltage ramp rate during start-up while the PG flag

signals when V

OUT

is within ±8.5% of the programmed

output voltage as well as fault conditions. The LT8609A has

slower switch edges for lower EMI emissions. The LT8609B

operates in pulse-skipping mode only.

APPLICATIONS

Wide Input Voltage Range: 3.0V to 42V

Ultralow Quiescent Current Burst Mode

Operation:

<2.5µA I

Regulating 12V

to 3.3V

OUT

Output Ripple <10mV

P-P

High Efﬁciency 2MHz Synchronous Operation:

>93% Efficiency at 1A, 5V

OUT

from 12V

3A Maximum Continuous Output

Fast Minimum Switch-On Time: 45ns

Adjustable and Synchronizable: 200kHz to 2.2MHz

Spread Spectrum Frequency Modulation for Low EMI

Allows Use of Small Inductors

Low Dropout

Peak Current Mode Operation

Accurate 1V Enable Pin Threshold

Internal Compensation

Output Soft-Start and Tracking

Small 10-Lead or 16-Lead MSOP Package

GSM Transceivers

General Purpose Step-Down

Low EMI Step-Down

All registered trademarks and trademarks are the property of their respective owners.

BST

EN/UV

ON OFF

0.1µF

22µF

10pF

4.7µF

6V TO 40V

1µF

OUT

187k

8609 TA01a

2.2µH

SYNC

INTV

TR/SS

LT8609

GND

18.2k

5V, 2MHz Step-Down

12V

to 5V

OUT

Efficiency

L = 2.2µH

= 2MHz

OUT

(A)

0.00

0.50

1.00

1.50

2.00

2.50

100

EFFICIENCY (%)

8609 TA01b

PULSE-SKIPPING MODE,

BurstMode OPERATION SWITCH EDGE SPEED

LT8609 Both Fast

LT8609A Both Medium

LT8609B Pulse-Skipping Fast

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Summary of content (26 pages)

PAGE 1
LT8609/LT8609A/LT8609B 42V, 3A Synchronous Step-Down Regulator with 2.5µA Quiescent Current FEATURES n n n n n n n n n n n n n n DESCRIPTION Wide Input Voltage Range: 3.0V to 42V Ultralow Quiescent Current Burst Mode® Operation: n <2.5µA I Regulating 12V to 3.3V Q IN OUT n Output Ripple <10mV P-P High Efficiency 2MHz Synchronous Operation: n >93% Efficiency at 1A, 5V OUT from 12VIN 3A Maximum Continuous Output Fast Minimum Switch-On Time: 45ns Adjustable and Synchronizable: 200kHz to 2.
PAGE 2
LT8609/LT8609A/LT8609B ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, EN/UV, PG..........................................................42V FB, TR/SS . .................................................................4V SYNC Voltage .............................................................6V Operating Junction Temperature Range (Note 2) LT8609E/LT8609AE/LT8609BE ......... –40°C to 125°C LT8609I/LT8609AI/LT8609BI ............ –40°C to 125°C LT8609H/LT8609AH ..........................
PAGE 3
LT8609/LT8609A/LT8609B ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS MIN TYP MAX 2.7 V l 3.0 3.2 l 1 1.
PAGE 4
LT8609/LT8609A/LT8609B ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS PG Lower Threshold Offset from VFB LT8609/LT8609A: VFB Falling LT8609B: VFB Falling MIN TYP MAX UNITS l 5.0 8.5 13.0 % l 4.0 8.5 14.0 PG Hysteresis PG Leakage 0.5 VPG = 42V l PG Pull-Down Resistance VPG = 0.
PAGE 5
LT8609/LT8609A/LT8609B TYPICAL PERFORMANCE CHARACTERISTICS Efficiency (3.3V Output, Burst Mode Operation) 100 100 L = 8.2µH fSW = 700kHz 95 85 70 85 75 70 65 50 100 EFFICIENCY (%) 90 80 60 50 40 30 20 VIN = 12V VIN = 24V 0 0.5 1 1.5 IOUT (A) 2 0 0.001 0.01 3 0.1 1 10 IOUT (mA) 8609 G01 Efficiency (5V Output, Burst Mode Operation) 100 L = 8.2µH 90 fSW = 700kHz 80 75 70 65 60 VIN = 12V VIN = 24V 10 2.5 100 1k 50 10k 100 L = 2.
PAGE 6
LT8609/LT8609A/LT8609B TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation Line Line Regulation Regulation 0.500 0.20 0.400 0.300 0.200 CHANGE IN VOUT (%) CHANGE IN VOUT (%) ILOAD = 1A 0.15 0.100 0.000 –0.100 –0.200 –0.300 0.10 0.05 0.00 –0.05 –0.10 –0.15 –0.400 –0.500 0.0 0.5 1.0 1.5 2.0 OUTPUT CURRENT (A) 2.5 –0.20 4.0 3.0 11.6 8609 G10 3.3 4.5 3.1 4.0 2.9 3.5 2.7 INPUT CURRENT (µA) IIN (µA) No-Load Supply Current vs Temperature No Load Supply Current Vs Temperature 5.0 3.
PAGE 7
LT8609/LT8609A/LT8609B TYPICAL PERFORMANCE CHARACTERISTICS Switch Drop vs Temperature 350 Switch Drop vs Switch Current 800 SWITCH CURRENT = 1A 700 250 SWITCH DROP (mV) SWITCH DROP (mV) 300 200 150 100 50 600 500 400 300 200 100 TOP SW BOT SW 0 –50 –30 –10 10 30 50 70 90 110 130 150 TEMPERATURE (°C) 0 TOP SW 0 0.5 1 1.
PAGE 8
LT8609/LT8609A/LT8609B TYPICAL PERFORMANCE CHARACTERISTICS Minimum Load to Full Frequency (SYNC Float to 1.9V) Burst Frequency vs Load Current L = 2.2µH VOUT = 3.3V VIN = 12V SYNC = 0V 80 1500 1000 500 Frequency Foldback 2500 VOUT = 5V fSW = 700kHz SYNC = FLOAT 90 LOAD CURRENT (mA) 2000 FREQUENCY (kHz) 100 VIN = 12V VOUT = 3.3V RT = 18.
PAGE 9
LT8609/LT8609A/LT8609B TYPICAL PERFORMANCE CHARACTERISTICS Switching Waveforms Switching Waveforms Switching Waveforms 1A/DIV 200mA/DIV 1A/DIV 5V/DIV 5V/DIV 10V/DIV 8609 G33 500ns/DIV 12VIN TO 5VOUT AT 1A 8609 G34 10µs/DIV 12VIN TO 5VOUT AT 10mA SYNC = 0 Transient Response 500mA/DIV 100mV/DIV 100mV/DIV 8609 G36 50µs/DIV 8609 G37 20µs/DIV 50mA TO 1A TRANSIENT 12VIN TO 5VOUT COUT = 47µF 0.5A TO 1.
PAGE 10
LT8609/LT8609A/LT8609B PIN FUNCTIONS BST: This pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. Place a 0.1µF boost capacitor as close as possible to the IC. Do not place a resistor in series with this pin. SW: The SW pin is the output of the internal power switches. Connect this pin to the inductor and boost capacitor. This node should be kept small on the PCB for good performance. INTVCC: Internal 3.5V Regulator Bypass Pin.
PAGE 11
LT8609/LT8609A/LT8609B BLOCK DIAGRAM VIN VIN CIN R3 OPT – + INTERNAL 0.782V REF EN/UV 1V + – SHDN SLOPE COMP R4 OPT PG ±8.5% ERROR AMP + + – RPG CFF R2 CSS RT FB VC TR/SS SHDN TSD INTVCC UVLO VIN UVLO 2µA INTVCC CVCC OSCILLATOR 200kHz TO 2.2MHz VOUT R1 3.5V REG BST BURST DETECT SWITCH LOGIC AND ANTISHOOT THROUGH SHDN TSD VIN UVLO CBST M1 L SW VOUT COUT M2 GND RT SYNC 8609 BD Rev. H For more information www.analog.com Downloaded from Arrow.com.
PAGE 12
LT8609/LT8609A/LT8609B OPERATION The LT8609/LT8609A/LT8609B is a monolithic constant frequency current mode step-down DC/DC converter. An oscillator with frequency set using a resistor on the RT pin turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. The peak inductor current at which the top switch turns off is controlled by the voltage on the internal VC node.
PAGE 13
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION Achieving Ultralow Quiescent Current To enhance efficiency at light loads, the LT8609/LT8609A enters into low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimizing output voltage ripple.
PAGE 14
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION FB Resistor Network Operating Frequency Selection and Trade-Offs The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the resistor values according to: Selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. The advantage of high frequency operation is that smaller inductor and capacitor values may be used.
PAGE 15
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION Note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. Inductor Selection and Maximum Output Current The LT8609/LT8609A/LT8609B is designed to minimize solution size by allowing the inductor to be chosen based on the output load requirements of the application.
PAGE 16
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION and should not be used. A 4.7μF to 10μF ceramic capacitor is adequate to bypass the LT8609/LT8609A/LT8609B and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used. If the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor.
PAGE 17
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION feature is not used, or tied to a logic level if shutdown control is required. Adding a resistor divider from VIN to EN programs the LT8609/LT8609A/LT8609B to regulate the output only when VIN is above a desired voltage (see Block Diagram). Typically, this threshold, VIN(EN), is used in situations where the input supply is current limited, or has a relatively high source resistance.
PAGE 18
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION amplitude should have valleys that are below 0.9V and peaks above 2.7V (up to 5V). The LT8609/LT8609A will not enter Burst Mode operation at low output loads while synchronized to an external clock, but instead will pulse skip to maintain regulation. The LT8609/LT8609A may be synchronized over a 200kHz to 2.2MHz range. The RT resistor should be chosen to set the LT8609/LT8609A switching frequency equal to or below the lowest synchronization input.
PAGE 19
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION the resulting loop may become too large in which case using a small case/value capacitor placed close to the VIN and GND pins plus a larger capacitor further away is preferred. These components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane under the application circuit on the layer closest to the surface layer.
PAGE 20
LT8609/LT8609A/LT8609B APPLICATIONS INFORMATION Thermal Considerations and Peak Current Output For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the LT8609/LT8609A/LT8609B. The exposed pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread heat dissipated by the LT8609/LT8609A/LT8609B.
PAGE 21
LT8609/LT8609A/LT8609B TYPICAL APPLICATIONS 3.3V Step-Down VIN 4.3V TO 42V C2 4.7µF C1 0.1µF VIN EN/UV BST SYNC SW L1 2.2µH R4 100k LT8609 INTVCC C3 1µF C6 10nF R1 18.2k PG C5 10pF TR/SS RT FB GND fSW = 2MHz R3 309k R2 1M L1 = COILCRAFT XFL4020-222ME VOUT 3.3V 3A POWER GOOD C4 22µF 1206 8609 TA02 5V Step-Down VIN 6V TO 42V C2 4.7µF C1 0.1µF VIN EN/UV BST SYNC SW L1 2.2µH R4 100k LT8609 INTVCC C3 1µF C6 10nF R1 18.
PAGE 22
LT8609/LT8609A/LT8609B TYPICAL APPLICATIONS 1.8V 2MHz Step-Down Converter VIN 2.8V TO 20V (42V TRANSIENT) C2 4.7µF L1 2.2µH SW R4 100k LT8609 INTVCC C3 1µF PG C5 10pF TR/SS C6 10nF M1 NFET BST EN/UV SYNC PSKIP C1 0.1µF VIN RT R1 18.2k GND fSW = 2MHz FB R3 768k R2 1M L1 = COILCRAFT XFL4020-222ME VOUT 1.8V 3A POWER GOOD C4 47µF 1210 8609 TA05 Ultralow EMI 5V 2A Step-Down Converter VIN 6V TO 40V FB1 BEAD L3 4.7µH C8 4.7µF C7 4.7µF C9 33μF VIN C2 4.7µF BST C1 0.
PAGE 23
LT8609/LT8609A/LT8609B PACKAGE DESCRIPTION MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 ±0.102 (.074 ±.004) 5.10 (.201) MIN 1 0.889 ±0.127 (.035 ±.005) 1.68 ±0.102 (.066 ±.004) 0.05 REF 10 0.305 ± 0.038 (.0120 ±.0015) TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 ±0.102 (.118 ±.004) (NOTE 3) DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE.
PAGE 24
LT8609/LT8609A/LT8609B PACKAGE DESCRIPTION MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev F) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 5.10 (.201) MIN 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.035 ±.005) 8 1 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 3.20 – 3.45 (.065 ±.004) (.126 – .136) 0.305 ±0.038 (.0120 ±.0015) TYP 16 0.50 (.0197) BSC 4.039 ±0.102 (.159 ±.004) (NOTE 3) RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.35 REF 0.
PAGE 25
LT8609/LT8609A/LT8609B REVISION HISTORY REV DATE DESCRIPTION A 01/16 Added the LT8609A Version to Header All Added the LT8609A Version to Description 1 Clarified Description 1 Clarified Electrical Specifications 3 Clarified Load Regulation, Line Regulation, No-Load Supply Current vs Temperature, Minimum On-Time vs Temperature Graphs, Frequency Foldback and Soft-Start vs Temperature Graphs B C 06/16 10/16 10 Replaced Figure 1 with Table 1 in text 12 Clarified CIN Capacitor in Text and PCB
PAGE 26
LT8609/LT8609A/LT8609B TYPICAL APPLICATION Tracking 3.3V and 1.8V 2MHz Converters VIN 4.3V TO 20V (42V TRANSIENT) C2 4.7µF C1 0.1µF VIN BST EN/UV R1 18.2k R4 100k LT8609 INTVCC C6 10nF VOUT 3.3V, 3A SW SYNC C3 1µF L1 2.2µH PG C5 10pF TR/SS RT FB GND R2 1M R3 309k POWER GOOD C4 47µF 1210 fSW = 2MHz C8 4.7µF R9 10k BST EN/UV SYNC R8 100k LT8609 PG C11 10pF TR/SS R10 31.6k R5 18.2k L2 2.2µH SW INTVCC C12 1µF C7 0.1µF VIN RT GND FB R7 768k fSW = 2MHz R6 1M VOUT 1.