LT8645S/LT8646S

1

Rev. B

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TYPICAL APPLICATION

FEATURES

DESCRIPTION

65V, 8A Synchronous

Step-Down Silent Switcher 2

with 2.5µA Quiescent Current

TheLT®8645S/LT8646Ssynchronousstep-downregulator

features second generation Silent Switcher architecture

designed to minimize EMI emissions while delivering high

efficiency at high switching frequencies. This includes the

integration of bypass capacitors to optimize all the fast

currentloopsinsideandmakeiteasytoachieveadvertised

EMI performance by eliminating layout sensitivity.

The fast, clean, low-overshoot switching edges enable

high efficiency operation even at high switching frequen-

cies, leading to a small overall solution size. Peak current

mode control with a 40ns minimum on-time allows high

step-down ratios even at high switching frequencies. The

LT8646S has external compensation to enable current

sharing and fast transient response at high switching

frequencies.

Burst Mode® operation enables ultralow standby current

consumption, pulse-skipping mode allows full switching

frequency at lower output loads, or spread spectrum

operation can further reduce EMI emissions.

INTERNAL CAPS

VC COMP

150°C GRADE

LT8645S

Yes

Internal

No

LT8646S

Yes

External

No

LT8645S-2*

No

Internal

Yes

*See LT8645S-2 Data Sheet

5V 8A Step-Down Converter

APPLICATIONS

n

Silent Switcher®2 Architecture

n

Ultralow EMI Emissions on Any PCB

n

Eliminates PCB Layout Sensitivity

n

Internal Bypass Capacitors Reduce Radiated EMI

n

Optional Spread Spectrum Modulation

n

High Efficiency at High Frequency

n

Up to 95% Efficiency at 1MHz, 12VIN to 5VOUT

n

Up to 94% Efficiency at 2MHz, 12VIN to 5VOUT

n

Wide Input Voltage Range: 3.4V to 65V

n

Ultralow Quiescent Current Burst Mode Operation

n

2.5μA IQ Regulating 12VIN to 3.3VOUT (LT8645S)

n

Output Ripple < 10mVP-P

n

External Compensation: Fast Transient Response

and Current Sharing (LT8646S)

n

Fast Minimum Switch On-Time: 40ns

n

Low Dropout Under All Conditions: 60mV at 1A

n

Adjustable and Synchronizable: 200kHz to 2.2MHz

n

Peak Current Mode Operation

n

Output Soft-Start and Tracking

n

Small 32-Lead 6mm × 4mm LQFN Package

n

AEC-Q100 Qualified for Automotive Applications

n

Automotive and Industrial Supplies

n

General Purpose Step-Down

n

GSM Power Supplies

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

by U.S. patents, including 8823345.

12VIN to 5VOUT Efficiency

LT8645S

8645S TA01a

SW

BIAS

FB

VIN

5.5V TO 65V

GND

RT

VIN

EN/UV

VOUT

5V

8A

100µF

2.2pF

4.7µF

41.2k

1M

243k

2.2µH

fSW = 1MHz

EFFICIENCY

POWER LOSS

1MHz, L = 2.2µH

2MHz, L = 1µH

LOAD CURRENT (A)

1

2

3

4

5

6

7

8

60

65

70

75

80

85

90

95

100

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

8645S TA01b