Datasheet

ManualsBrandsLinear Technology ManualsDC / DC Adjustable Switching RegulatorsSwitching Regulator IC Step-Down TSSOP- 41.6V

LT8616

8616fa

For more information www.linear.com/LT8616

TYPICAL APPLICATION

FEATURES DESCRIPTION

Dual 42V Synchronous

Monolithic Step-Down Regulator

with 6.5µA Quiescent Curr

ent

The LT

8616 is a high efficiency, high speed, dual synchro-

nous monolithic

step-down switching regulator that con-

sumes only 6.5µ

A of quiescent current with both channels

enabled. Both channels contain all switches and necessary

circuitry to minimize the need for external components.

Low ripple Burst Mode operation enables high efficiency

down to very low output currents while minimizing output

ripple. 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

able pins have accurate 1V thresholds and can be used to

program undervoltage lockout. Capacitors on the TR/SS

pins programs the output voltage ramp rate during start-

up while the PG pins signal when each output is within

10% of the programmed output voltage. The LT8616 is

available in a TSSOP package for high reliability.

APPLICATIONS

Wide Input Voltage Range: 3.4V to 42V

2.5A and 1.5A Buck Regulators with Separate Inputs

Fast Minimum Switch On-Time: 35ns

Ultralow Quiescent Current Burst Mode

Operation:

6.5µA I

Regulating 12V

to 5V

OUT

and 3.3V

OUT

Output Ripple < 15mV

180° Out of Phase Switching

Adjustable: 200kHz to 3MHz

Synchronizable: 250kHz to 3MHz

Accurate 1V Enable Pin Thresholds

Internal Compensation

Output Soft-Start and Tracking

TSSOP Package: Output Stays at or Below Regulation

Voltage During Adjacent Pin Short or When a Pin Is

Left Floating

Thermally Enhanced 28-Lead TSSOP and

3mm × 6mm QFN Packages

Automotive and Industrial Supplies

General Purpose Step-Down

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.

BOOST1V

IN1

EN/UV1

INTV

PG1

PG2

SYNC/MODE

TR/SS1

TR/SS2

SW1

LT8616

GND

FB1

BIAS

BOOST2

SW2

8616 TA01a

FB2

0.1µF

OUT1

5V, 1.5A

10pF

2 x 47µF

4.7µF

12V

OUT2

3.3V, 2.5A

10nF

10µH

4.7µH

316k

187k

56.2k

IN2

EN/UV2

4.7µF

5.6pF 47µF

1µF

5V, 3.3V, 700kHz Step-Down Converter Efficiency

LOAD (mA)

0.01

EFFICIENCY (%)

100

1 10 100 10000.1

8616 TA01b

CH2, 3.3V

OUT

CH1, 5V

OUT

IN1

= V

IN2

= 12V

= 700kHz

Downloaded from Arrow.com.

Summary of content (26 pages)

PAGE 1
LT8616 Dual 42V Synchronous Monolithic Step-Down Regulator with 6.5µA Quiescent Current FEATURES n n n n n n n n n n n DESCRIPTION Wide Input Voltage Range: 3.4V to 42V 2.5A and 1.5A Buck Regulators with Separate Inputs Fast Minimum Switch On-Time: 35ns Ultralow Quiescent Current Burst Mode® Operation: n 6.5µA I Regulating 12V to 5V Q IN OUT and 3.
PAGE 2
LT8616 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN1, VIN2, EN/UV1, EN/UV2, PG1, PG2......................42V BIAS...........................................................................30V BST1 Above SW1, BST2 Above SW2, FB1, FB2, TR/SS1, TR/SS2......................................................4V SYNC/MODE................................................................6V Operating Junction Temperature Range (Note 2) LT8616E.............................................. –40°C to 125°C LT8616I............
PAGE 3
LT8616 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 UNITS l 1.7 1.7 4.0 8.0 µA µA l 3.0 3.0 5.0 12.0 µA µA l 0.5 1.
PAGE 4
LT8616 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 UNITS 3.0 3.4 V 80 620 110 910 µA µA 35 55 ns Channel 2 Minimum VIN1 Voltage to Use Channel2 l Supply Current in Regulation VIN = 6V, VOUT2 = 3.3V, Load2 = 100µA VIN = 6V, VOUT2 = 3.3V Load2 = 1mA SW2 Minimum On-Time Load = 0.25A, Pulse-Skipping Mode l 20 (Note 3) l 4.
PAGE 5
LT8616 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency at 5VOUT fSW = 700kHz 94 EFFICIENCY (%) 92 90 88 86 CH1, 12VIN CH1, 24VIN CH2, 12VIN CH2, 24VIN 84 82 80 0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5 LOAD (A) 94 92 CH1, 12VIN CH1, 24VIN CH2, 12VIN CH2, 24VIN 100 98 fSW = 700kHz 96 EFFICIENCY (%) EFFICIENCY (%) 94 88 86 CH1, 12VIN CH1, 24VIN CH2, 12VIN CH2, 24VIN 84 82 80 0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5 LOAD (A) 30 VIN1 = VIN2 = 12V VOUT1 = 5V 25 VOUT2 = 3.
PAGE 6
LT8616 TYPICAL PERFORMANCE CHARACTERISTICS 0.1 Line Regulation vs VIN1 0.15 0.06 CHANGE IN VOUT (%) 0.04 0.02 0 –0.02 –0.06 –0.1 25 50 75 100 125 150 TEMPERATURE (°C) Power-Good Thresholds 0 5 10 15 20 25 VIN1 (V) 35 –0.2 40 PG LOW FALLING PG HIGH RISING PG LOW RISING PG HIGH FALLING 2.25 800 2.2 2.15 600 500 400 300 25 50 75 100 125 150 TEMPERATURE (°C) 2 1.85 –50 –25 0 100 200 300 400 500 600 700 800 900 1000 SS/TR VOLTAGE (mV) RT = 14.
PAGE 7
LT8616 TYPICAL PERFORMANCE CHARACTERISTICS Burst Frequency vs Load 80 600 60 500 VIN1 = VIN2 =12V fSW = 700kHz SYNC = 0V 300 200 100 50 50 40 30 20 10 CH1, 5V CH2, 3.3V 0 5.0 0 100 150 200 250 300 350 400 LOAD CURRENT (mA) 0 5 10 15 20 25 VIN (V) 30 35 8616 G19 600 3.0 2.
PAGE 8
LT8616 TYPICAL PERFORMANCE CHARACTERISTICS 3.6 VIN1 UVLO Transient CH1, 5V Transient CH2, 3.3V 3.4 VOUT1 (AC) 200mV/DIV 3.2 VOUT2 (AC) 50mV/DIV VIN1 (V) 3.0 IL1 500mA/DIV 2.8 IL2 1A/DIV 2.6 2.4 20µs/DIV 2.2 2.0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 8616 G25 CCM 8616 G29 20µs/DIV VIN1 = 12V VOUT1 = 5V L1 = 10µH COUT1 = 47µF CFF = 5.6pF VIN2 = 12V VOUT2 = 3.3V L2 = 4.
PAGE 9
LT8616 PIN FUNCTIONS BIAS: The BIAS pin supplies the internal regulator when tied to a voltage higher than 3.1V. For output voltages of 3.3V and above this pin should be tied to the appropriate VOUT. Connect a 1µF bypass capacitor to this pin if it is connected to a supply other than VOUT1 or VOUT2. Ground if unused. BOOST1, BOOST2: The BOOST pins are used to provide drive voltages, higher than the input voltage, to the internal topside power switches. Place 0.
PAGE 10
LT8616 BLOCK DIAGRAM VIN1 R5 1.03V EN/UV1 + – SHDN1 BIAS R7 1.03V EN/UV2 VIN1 INTERNAL REFERENCE AND 3.3V REGULATOR R6 VIN2 + – INTVCC VIN1 INTVCC CIN1 SHDN2 R8 CVCC PG1 SHDN1 TSD VIN1 UVLO INTVCC UVLO BOOST1 0.
PAGE 11
LT8616 OPERATION Foreword The LT8616 is a dual monolithic step down regulator. The two channels differ in maximum current and input range. The following sections describe the operation of channel 1 and common circuits. They will highlight channel 2 differences and interactions only when relevant. To simplify the application, both VIN1 and VIN2 are assumed to be connected to the same input supply. However, note that VIN1 must be greater than 3.4V for either channel to operate.
PAGE 12
LT8616 APPLICATIONS INFORMATION Achieving Ultralow Quiescent Current As the output load decreases, the frequency of single current pulses decreases (see Figure 1a) and the percentage of time that the LT8616 is in sleep mode increases, resulting in much higher light load efficiency than for typical converters. By maximizing the time between pulses, the converter quiescent current approaches 6.5µA for a typical application when there is no output load.
PAGE 13
LT8616 APPLICATIONS INFORMATION Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain output voltage accuracy. If low input quiescent current and good light-load efficiency are desired, use large resistor values for the FB resistor divider.
PAGE 14
LT8616 APPLICATIONS INFORMATION The highest switching frequency (fSW(MAX)) for a given application can be calculated as follows: fSW(MAX) = ( VOUT + VSW(BOT) tON(MIN) VIN – VSW(TOP) + VSW(BOT) ) (4) where VIN is the typical input voltage, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~0.53V, ~0.38V, respectively at maximum load for channel 1 and ~0.78V, ~0.
PAGE 15
LT8616 APPLICATIONS INFORMATION The LT8616 limits the peak switch current in order to protect the switches and the system from overload faults. The top switch current limit (ILIM) is 4.2A at 0% duty cycle and decreases linearly to 2.9A at DC = 80% (channel 2 current limit are 5.5A at 0% duty cycle and 3.7A at DC = 80%). The inductor value must then be sufficient to supply the desired maximum output current (IOUT(MAX)), which is a function of the switch current limit (ILIM) and the ripple current.
PAGE 16
LT8616 APPLICATIONS INFORMATION switching current into a tight local loop, minimizing EMI. A 2.2μF capacitor is capable of this task, but only if it is placed close to the LT8616 (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT8616. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit.
PAGE 17
LT8616 APPLICATIONS INFORMATION ⎛ VIN1(EN) ⎞ R5 = R6 ⎜ –1 ⎝ 1.03V ⎟⎠ (10) where the corresponding channel will remain off until VIN is above VIN(EN). Due to the comparator’s hysteresis, switching will not stop until the input falls slightly below VIN(EN). 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 LT8616.
PAGE 18
LT8616 APPLICATIONS INFORMATION Synchronization TR/SS 500mV/DIV VOUT 2V/DIV 2ms/DIV 8616 F05 Figure 5. TR/SS Does Not Discharge VOUT Channel 1 will synchronize its positive switch edge transitions to the positive edge of the SYNC signal, and channel 2 will synchronize to the negative edge of the SYNC signal.
PAGE 19
LT8616 APPLICATIONS INFORMATION Pulse-Skipping Mode Pulse-skipping mode is activated by applying logic high (above 2.4V) or an external clock to the SYNC/MODE pin. While in pulse-skipping mode, the oscillator operates continuously and SW transitions are aligned to the clock. During light loads, switch pulses are skipped to regulate the output and the quiescent current per channel will be several hundred µA. Full switching frequency is reached at lower output load than in Burst Mode operation.
PAGE 20
LT8616 APPLICATIONS INFORMATION High Temperature Considerations For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the LT8616. 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 LT8616. Placing additional vias can reduce thermal resistance further.
PAGE 21
LT8616 APPLICATIONS INFORMATION Table 4.
PAGE 22
LT8616 TYPICAL APPLICATIONS 5V, 2.5V, 2.05MHz Step-Down Converter VIN 5.8V TO 42V 4.7µF 4.7µF VIN1 BOOST1 0.1µF EN/UV1 3.3µH SW1 VIN2 EN/UV2 IHLP-2525CZ-01 10nF 1µF 14.7k 47µF 10V, 1210 BIAS BOOST2 0.1µF TR/SS1 TR/SS2 INTVCC RT 5.6pF 187k LT8616 PG1 PG2 SYNC/MODE 1M 1M FB1 VOUT1 5V, 1.5A 1.5µH SW2 IHLP-2020BZ-01 1M VOUT2 2.5V, 2.5A 10pF FB2 GND 100µF 6.3V, 1210 464k 8616 TA02 3.3V, 0.79V, 1MHz 2-Stage Step-Down Converter, Sequenced Start-Up 0.7A VIN 4.2V TO 42V VIN1 4.7µF 0.
PAGE 23
LT8616 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT8616#packaging for the most recent package drawings. FE Package 28-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev K) 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 6.60 ±0.10 4.50 ±0.10 2.74 (.108) SEE NOTE 4 0.45 ±0.05 EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE 6.40 2.74 (.252) (.108) BSC 1.05 ±0.10 0.
PAGE 24
LT8616 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT8616#packaging for the most recent package drawings. UDE Package 28-Lead Plastic QFN (3mm × 6mm) (Reference LTC DWG # 05-08-1926 Rev Ø) 0.70 ±0.05 3.50 ±0.05 2.10 ±0.05 4.75 ±0.05 1.50 REF 1.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 4.50 REF 5.10 ±0.05 6.50 ±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 27 R = 0.05 TYP PIN 1 NOTCH R = 0.
PAGE 25
LT8616 REVISION HISTORY REV DATE DESCRIPTION A 10/16 Added 3mm × 6mm QFN package option. PAGE NUMBER 1, 2, 24 8616fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. For more information www.linear.com/LT8616 Downloaded from Arrow.com.
PAGE 26
LT8616 TYPICAL APPLICATION 5V, 3.3V, 2.05MHz Step-Down Converter VIN 5.8V TO 42V 0.1µF 2.2µF 0.1µF VIN1 BOOST1 0.1µF EN/UV1 3.3µH SW1 0.1µF 2.2µF 0.1µF VIN2 XAL4030-332ME 1M FB1 EN/UV2 10nF BIAS BOOST2 0.1µF TR/SS1 2.2µH SW2 TR/SS2 1µF 14.7k 22µF 10V, 1210 PG1 PG2 SYNC/MODE 10nF 4.7pF 187k LT8616 1M VOUT1 5V, 1.5A XFL4020-222ME INTVCC RT GND 1M 4.7pF VOUT2 3.3V, 2.