Datasheet

ManualsBrandsLinear Technology ManualsDC / DC Adjustable Switching RegulatorsSwitching Regulator IC Step-Down MSOP- 64.8V

LT8620

8620fa

For more information www.linear.com/LT8620

LOAD CURRENT (A)

EFFICIENCY (%)

100

1.75

8620 TA01b

0.5 0.750.25

1.0

1.25 1.5

2.0

= 12V

= 24V

= 700kHz

TYPICAL APPLICATION

FEATURES DESCRIPTION

65V, 2A Synchronous

Step-Down Regulator

with 2.5µA Quiescent

Current

The LT

8620 is a compact, high efficiency, high speed

synchronous monolithic step-down switching regulator

that accepts a wide input voltage range up to 65V, and

consumes only 2.5µA of quiescent current. Top and bottom

power switches are included with all necessary circuitry

to minimize the need for external components. Low ripple

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. 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

undervoltage lockout or to shut down

the LT8620 reducing the input supply current to 1µA. A

capacitor on the TR/SS pin programs the output voltage

ramp rate during start-up. The PG flag signals when V

OUT

is within ±9% of the programmed output voltage as well as

fault conditions. The LT8620 is available in small 16-Lead

MSOP and 3mm × 5mm QFN packages with

exposed pads

for low thermal resistance.

5V 2A Step-Down Converter

Efficiency at 5V

OUT

APPLICATIONS

Wide Input Voltage Range: 3.4V to 65V

Ultralow Quiescent Current Burst Mode

Operation:

2.5μA I

Regulating 12V

to 3.3V

OUT

Output Ripple < 10mV

P-P

High Efﬁciency Synchronous Operation:

94% Efﬁciency at 1A, 12V

to 5V

OUT

92% Efﬁciency at 1A, 12V

3.3V

OUT

Fast 30ns Minimum Switch-On Time

Low Dropout Under All Conditions: 250mV at 1A

Safely Tolerates Inductor Saturation in Overload

Low EMI

Adjustable and Synchronizable: 200kHz to 2.2MHz

Accurate 1V Enable Pin Threshold

Internal Compensation

Output Soft-Start and Tracking

Small Thermally Enhanced 16-Lead MSOP and

24-Lead 3mm × 5mm QFN Packages

Automotive and Industrial Supplies

General Purpose Step-Down

GSM Power Supplies

L, LT , LT C , LT M , 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.

BSTV

EN/UV

SYNC

INTV

TR/SS

LT8620

GND

BIAS

8620 TA01a

0.1µF

OUT

4.7µF

5.5V TO 65V

1µF

10nF

10pF

4.7µH

243k

= 700kHz

60.4k

47µF

Downloaded from Arrow.com.

Summary of content (26 pages)

PAGE 1
LT8620 65V, 2A Synchronous Step-Down Regulator with 2.5µA Quiescent Current DESCRIPTION FEATURES Wide Input Voltage Range: 3.4V to 65V nn Ultralow Quiescent Current Burst Mode® Operation: nn 2.5μA I Regulating 12V to 3.3V Q IN OUT nn Output Ripple < 10mV P-P nn High Efficiency Synchronous Operation: nn 94% Efficiency at 1A, 12V to 5V IN OUT nn 92% Efficiency at 1A, 12V to 3.
PAGE 2
LT8620 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, EN/UV.................................................................65V PG..............................................................................42V BIAS...........................................................................25V BST Pin Above SW Pin................................................4V FB, TR/SS, RT, INTVCC ................................................4V SYNC Voltage ..............................................................
PAGE 3
LT8620 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
PAGE 4
LT8620 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency at 5VOUT Efficiency at 3.3VOUT 95 95 90 90 90 80 85 85 70 75 70 fSW = 700kHz L = IHLP2525CZ-01, 4.7µH 65 VIN = 12V VIN = 24V VIN = 36V VIN = 48V 60 55 50 0 80 75 70 fSW = 700kHz L = IHLP2525CZ-01, 4.7µH 65 VIN = 12V VIN = 24V VIN = 36V VIN = 48V 60 55 50 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 LOAD CURRENT (A) fSW = 700kHz L = IHLP2525CZ-01, 4.7µH 0 0.01 10 100 1.0 LOAD CURRENT (mA) 0.1 86 82 80 0.25 1000 1.
PAGE 5
LT8620 TYPICAL PERFORMANCE CHARACTERISTICS No Load Supply Current VOUT = 3.3V IN REGULATION 4.5 4.0 3.5 CURRENT LIMIT (A) INPUT CURRENT (µA) Top FET Current Limit Top FET Current Limit vs Duty Cycle 3.0 2.5 2.0 1.5 4.0 5.0 3.5 4.5 CURRENT LIMIT (A) 5.0 TA = 25°C, unless otherwise noted. 3.0 DUTY CYCLE = 5% 3.5 2.5 1.0 4.0 0.5 0 0 50 20 40 30 INPUT VOLTAGE (V) 10 2.0 60 0.2 0 0.4 0.6 DUTY CYCLE 0.8 3.0 –55 1.
PAGE 6
LT8620 TYPICAL PERFORMANCE CHARACTERISTICS Minimum Load to Full Frequency (SYNC DC High) Burst Frequency 100 VIN = 12V VOUT = 5V 700 Frequency Foldback 800 VOUT = 5V fSW = 700kHz 400 300 200 SWITCHING FREQUENCY (kHz) 500 60 40 20 100 50 150 LOAD CURRENT (mA) 0 0 200 5 15 25 35 45 INPUT VOLTAGE (V) 55 Soft-Start Tracking 200 0.6 0.4 0.2 0.2 1.0 0.4 0.6 0.8 TR/SS VOLTAGE (V) 1.2 2.1 2.0 1.9 1.8 –55 1.4 8620 G22 –7.5 225 –8.0 200 RT PIN RESISTOR (kΩ) 250 FB RISING –9.
PAGE 7
LT8620 TYPICAL PERFORMANCE CHARACTERISTICS Bias Pin Current 10 VBIAS = 5V VOUT = 5V ILOAD = 1A fSW = 700kHz 4.0 3.5 3.0 2.5 5 15 25 35 45 INPUT VOLTAGE (V) Switching Waveforms, Full Frequency Continuous Operation Bias Pin Current BIAS PIN CURRENT (mA) BIAS PIN CURRENT (mA) 4.5 TA = 25°C, unless otherwise noted. 55 65 VBIAS = 5V VOUT = 5V VIN = 12V ILOAD = 1A 8 IL 1A/DIV 6 VSW 5V/DIV 4 500ns/DIV 12VIN TO 5VOUT AT 1A 2 0 0 2.5 0.5 1 1.
PAGE 8
LT8620 PIN FUNCTIONS SYNC: External Clock Synchronization Input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a clock source for synchronization to an external frequency. Apply a DC voltage of 3V or higher or tie to INTVCC for pulse-skipping mode. When in pulse-skipping mode, the IQ will increase to several hundred µA. Do not float this pin. TR/SS: Output Tracking and Soft-Start Pin. This pin allows user control of output voltage ramp rate during start-up.
PAGE 9
LT8620 BLOCK DIAGRAM VIN VIN CIN R3 OPT EN/UV + – 1V R4 OPT PG SHDN ±9% R1 R2 CSS OPT RT FB TR/SS 3.4V REG SLOPE COMP VC BURST DETECT SHDN THERMAL SHDN INTVCC UVLO VIN UVLO 2µA BIAS INTVCC CVCC OSCILLATOR 200kHz TO 2.2MHz ERROR AMP + + – VOUT C1 – + INTERNAL 0.97V REF BST SWITCH LOGIC AND ANTISHOOT THROUGH CBST SW L VOUT COUT SHDN THERMAL SHDN VIN UVLO RT SYNC GND 8620 BD 8620fa For more information www.linear.com/LT8620 Downloaded from Arrow.com.
PAGE 10
LT8620 OPERATION The LT8620 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 11
LT8620 APPLICATIONS INFORMATION Achieving Ultralow Quiescent Current To enhance efficiency at light loads, the LT8620 operates in 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. In Burst Mode operation the LT8620 delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor.
PAGE 12
LT8620 APPLICATIONS INFORMATION For some applications it is desirable for the LT8620 to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. In this mode much of the internal circuitry is awake at all times, increasing quiescent current to several hundred µA. Second is that full switching frequency is reached at lower output load than in Burst Mode operation (see Figure 1b).
PAGE 13
LT8620 APPLICATIONS INFORMATION Operating Frequency Selection and Trade-Offs 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. The disadvantages are lower efficiency and a smaller input voltage range.
PAGE 14
LT8620 APPLICATIONS INFORMATION As a quick example, an application requiring 1A output should use an inductor with an RMS rating of greater than 1A and an ISAT of greater than 1.3A. During long duration overload or short-circuit conditions, the inductor RMS routing requirement is greater to avoid overheating of the inductor. To keep the efficiency high, the series resistance (DCR) should be less than 0.04Ω, and the core material should be intended for high frequency applications.
PAGE 15
LT8620 APPLICATIONS INFORMATION tank circuit. If the LT8620 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8620’s voltage rating. This situation is easily avoided (see Linear Technology Application Note 88). Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT8620 to produce the DC output.
PAGE 16
LT8620 APPLICATIONS INFORMATION When operating in Burst Mode operation for light load currents, the current through the VIN(EN) resistor network can easily be greater than the supply current consumed by the LT8620. Therefore, the VIN(EN) resistors should be large to minimize their effect on efficiency at low loads. INTVCC Regulator An internal low dropout (LDO) regulator produces the 3.4V supply from VIN that powers the drivers and the internal bias circuitry.
PAGE 17
LT8620 APPLICATIONS INFORMATION subharmonic oscillations at the frequency set by RT, then the slope compensation will be sufficient for all synchronization frequencies. For some applications it is desirable for the LT8620 to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. Second is that full switching frequency is reached at lower output load than in Burst Mode operation.
PAGE 18
LT8620 APPLICATIONS INFORMATION small so that the ground traces will shield them from the SW and BOOST nodes. The exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT8620 to additional ground planes within the circuit board and on the bottom side.
PAGE 19
LT8620 TYPICAL APPLICATIONS 5V 2MHz Step-Down Converter VIN 5.5V TO 65V 4.7µF VIN BST EN/UV LT8620 0.1µF 2.2µH SW SYNC BIAS TR/SS PG 10nF VOUT 5V 47µF 2A 100k 1µF 1M FB INTVCC RT POWER GOOD 10pF GND 18.2k 243k fSW = 2MHz L: XFL4020 8620 TA02 5V Step-Down Converter VIN 5.5V TO 65V 4.7µF VIN BST EN/UV LT8620 0.1µF 4.7µH SW SYNC BIAS TR/SS PG 10nF VOUT 5V 47µF 2A 100k 1µF INTVCC RT 60.
PAGE 20
LT8620 TYPICAL APPLICATIONS 3.3V 2MHz Step-Down Converter VIN 3.8V TO 65V VIN 4.7µF BST EN/UV PG 0.1µF 1.8µH SW LT8620 BIAS SYNC VOUT 3.3V 47µF 2A 10nF TR/SS 1µF INTVCC RT FB 1M 10pF GND 18.2k 412k fSW = 2MHz L: XFL4020 8620 TA04 3.3V Step-Down Converter VIN 3.8V TO 65V 4.7µF VIN BST EN/UV PG SYNC LT8620 0.1µF 4.7µH SW BIAS VOUT 3.3V 47µF 2A 10nF 1µF TR/SS INTVCC RT 60.4k fSW = 700kHz L: IHLP2020CZ-01 20 Downloaded from Arrow.com.
PAGE 21
LT8620 TYPICAL APPLICATIONS 12V Step-Down Converter VIN 12.5V TO 65V VIN 4.7µF BST 0.1µF 10µH EN/UV SW LT8620 SYNC BIAS TR/SS PG 10nF VOUT 12V 47µF 2A 100k 1µF 1M FB INTVCC RT POWER GOOD 10pF GND 41.2k 88.7k fSW = 1MHz L: IHLP2525CZ-01 8620 TA09 1.8V 2MHz Step-Down Converter VIN 3.4V TO 22V (65V TRANSIENT) VIN 4.7µF BST EN/UV PG SYNC 1µH LT8620 SW BIAS 10nF TR/SS 1µF INTVCC RT 18.2k fSW = 2MHz L: XFL4020 0.1µF FB EXTERNAL SOURCE >3.1V OR GND 1µF 100µF VOUT 1.
PAGE 22
LT8620 TYPICAL APPLICATIONS 1.8V Step-Down Converter VIN 3.4V TO 65V VIN 4.7µF BST 0.1µF EN/UV PG 4.7µH SW LT8620 BIAS SYNC 1µF 10nF 1µF TR/SS INTVCC RT PGND GND VOUT 1.8V 120µF 2A EXTERNAL SOURCE >3.1V OR GND 866k FB 10pF 110k 1M fSW = 400kHz L: IHLP2020CZ-01 8620 TA07 Ultralow EMI 5V 2A Step-Down Converter VIN 5.5V TO 65V FB1 BEAD 4.7µH 4.7µF 4.7µF 4.7µF VIN EN/UV PG SYNC 10nF 1µF BST LT8620 SW BIAS TR/SS FB Downloaded from Arrow.com. 47µF GND 18.
PAGE 23
LT8620 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. 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 ±.
PAGE 24
LT8620 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UDD Package 24-Lead Plastic QFN (3mm × 5mm) (Reference LTC DWG # 05-08-1833 Rev Ø) 0.70 ±0.05 3.50 ±0.05 2.10 ±0.05 3.65 ±0.05 1.50 REF 1.65 ±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 3.00 ±0.10 0.75 ±0.05 1.50 REF 23 R = 0.05 TYP PIN 1 NOTCH R = 0.
PAGE 25
LT8620 REVISION HISTORY REV DATE DESCRIPTION A 05/15 Added H- and MP-Grade Versions ABS Max Table, Order Information PAGE NUMBER 2 Clarified Specifications to 150°C and Note 2 3 Clarified Current Limit Graphs 5 Clarified RT Programmed Switching Frequency, Soft-Start Current 6 Clarified TR/SS and BIAS Pin Function Description 8 Clarified Overload Conditions from 3.8A to 3.9A 10 8620fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
PAGE 26
LT8620 TYPICAL APPLICATION Ultralow IQ 2.5V, 3.3V Step-Down with LDO VIN 3.8V TO 65V VIN BST EN/UV 4.7µF PG VOUT1 3.3V 2A SW LT8620 SYNC 0.1µF 1.8µH BIAS 10nF 47µF TR/SS 1µF INTVCC RT FB 1M 10pF GND 18.2k IN 412k fSW = 2MHz L: XFL4020 OUT LT3008-2.5 SHDN SENSE VOUT2 2.5V 20mA 2.2µF 8620 TA10 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT8610 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous Micropower Step-Down DC/DC Converter with IQ = 2.5µA VIN: 3.4V to 42V, VOUT(MIN) = 0.