Linear Technology Analog Devices LT8708, Datasheet

Page: 2 / 64

LT8708
2
Rev 0
For more information www.analog.com
TABLE OF CONTENTS
Features ..................................................... 1
Applications ................................................ 1
Typical Application ........................................ 1
Description.................................................. 1
Absolute Maximum Ratings .............................. 3
Order Information .......................................... 3
Pin Configuration .......................................... 3
Electrical Characteristics ................................. 4
Typical Performance Characteristics ................... 9
Typical Performance Characteristics ..................11
Pin Functions ..............................................13
Block Diagram .............................................15
Operation...................................................16
Typographical Conventions ..................................... 16
Start-Up .................................................................. 16
Start-Up: SHDN Pin ............................................ 16
Start-Up: SWEN Pin ............................................ 16
Start-Up: Soft-Start of Switching Regulator ....... 17
Control Overview .................................................... 17
Power Switch Control ............................................ 18
Switch Control: Buck Region (V
IN
>> V
OUT
) ....... 19
Switch Control: Buck-Boost (V
IN
≅
V
OUT
) ......... 19
Switch Control: Boost Region (V
IN
<< V
OUT
) ......20
Switch Control: Soft-Start ..................................20
Uni and Bidirectional Conduction ............................20
Bidirectional Conduction: CCM ..........................21
Unidirectional Conduction: DCM .........................21
Unidirectional Conduction: HCM .........................22
Unidirectional Conduction: Burst Mode ..............22
Error Amplifiers ......................................................22
V
OUT
Regulation and Sensing .................................23
V
OUT
: Regulation .................................................23
V
OUT
: Above Regulation ......................................23
V
OUT
: Below Regulation and Undervoltage .........23
V
IN
Regulation and Sensing .................................... 24
V
IN
: Regulation ................................................... 24
V
IN
: Above Regulation and Overvoltage .............. 24
V
IN
: Below Regulation ......................................... 24
Current Monitoring and Limiting ............................. 24
Monitoring and Limiting: IMON Pins .................. 24
Monitoring: ICP and ICN Pins .............................25
INTV
CC
/EXTV
CC
/GATEV
CC
/LDO33 Power ...............25
CLKOUT and Temperature Sensing .........................25
Applications Information ................................26
Verify the Power Flow Conditions ...........................26
Operating Frequency Selection ...............................26
Internal Oscillator ...................................................27
SYNC Pin and Clock Synchronization .....................27
CLKOUT Pin and Clock Synchronization .................27
Inductor Current Sensing and Slope Compensation .... 27
R
SENSE
Selection and Maximum Current ................28
R
SENSE
Selection: Max R
SENSE
in the
Boost Region ......................................................28
R
SENSE
Selection: Max R
SENSE
in the
Buck Region .......................................................30
R
SENSE
Selection: Final R
SENSE
Value .................31
R
SENSE
Filtering ......................................................32
Inductor (L) Selection ............................................32
L Selection: Load Current in Buck and
Boost Regions ....................................................32
L Selection: Subharmonic Oscillations ...............33
L Selection: Maximum Current Rating ................33
Power MOSFET Selection .......................................34
C
IN
and C
OUT
Selection ...........................................37
Schottky Diode (D1, D2, D3, D4) Selection .............38
Topside MOSFET Driver Supply (C
B1
, D
B1
, C
B2
, D
B2
) ... 39
Top Driver: Boost Cap Charge Control Block ......39
Top Driver: Boost Diodes D
B1
and D
B2 ...................
39
VINHIMON, VOUTLOMON and RVSOFF ..................39
I
IN
and I
OUT
Current Monitoring and Limiting .........42
Loop Compensation ................................................44
INTV
CC
Regulators and EXTV
CC
Connection ...........45
LDO33 Regulator ....................................................45
Voltage Lockouts ....................................................46
Junction Temperature Measurement ......................46
Thermal Shutdown .................................................47
Efficiency Considerations ......................................47
Circuit Board Layout Checklist ...............................47
Hot Plugging Considerations .................................49
Design Example ......................................................49
Typical Applications ......................................55
Package Description .....................................63
Typical Application .......................................64
Related Parts ..............................................64