two internal 2A, 50V switches and an additional 500mA
switch to facilitate step-down and inverting conversion.
Each 2A channel can be independently configured as a
buck, boost, SEPIC, flyback or inverting converter. Ca-
pable of generating positive and negative outputs from a
single input rail, the LT8471 is ideal for many local power
supply designs.
The LT8471 has an adjustable oscillator, set by a resistor
placed from the RT pin to ground. Additionally, the LT8471
can be synchronized to an external clock. The free running
or synchronized switching frequency range of the part can
be set between 100kHz and 2MHz.
Additional features such as frequency foldback, soft-start,
and power good are integrated. The LT8471 is available in
20-lead TSSOP and 28-Lead (4mm
×
5mm) QFN packages.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
n
n
n
n
n
n
n
Dual 2A and One 500mA, 50V Internal Power
Switch Channels
2A Primary Channels Can Be Buck, Boost, SEPIC,
ZETA, Flyback or Inverting DC/DC Converter
500mA Skyhook Channel Efficiently Generates
Boosted Input Voltage
Wide Input Voltage Range of 2.6V to 50V
UVLO and OVLO Programmable on OV/UV Pin
Soft-Start Programmable for Each Channel
Fixed Frequency PWM (Set by RT Pin or
Synchronized to External Clock)
Anti-Phase Switching Reduces Input Ripple
20-Lead TSSOP and 28-Lead QFN Packages
applicaTions
n
n
Dual Rail Power for Signal Chain.
Buck/Buck, Buck/Boost, Boost/Boost, Boost/Invert,
Invert/Invert, Buck/Invert
Typical applicaTion
6V to 32V to ±5V, Dual DC/DC Converter
1µF
1µF
6V TO 32V
2.2µF
2.2µF
15µH
C3
475k
100k
100k
OV/UV
PG1
PG2
C2
SS1
2.2µF
0.1µF
0.1µF
187k
8471 TA01a
Efficiency and Power Loss
Load from V
OUT1
to V
OUT2
V
OUT1
5V
1.5A
EFFICIENCY (%)
47µF
×2
59k
90
80
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
LOAD CURRENT (A)
0.8
V
CC
=
1
6V
18V
32V
POWER LOSS
2
EFFICIENCY
3
POWER LOSS (W)
4
V
IN1
V
IN2
SHOUT
C1
FB1
E1
10µH
316k
LT8471
GND
59k
FB2
316k
E2
10µH
47µF
×2
V
OUT2
–5V
0.65A
0
1.0
8471 F10b
SS2
SYNC RT
8471fd
For more information
www.linear.com/8471
1
LT8471
absoluTe MaxiMuM raTings
(Note 1)
V
IN1
, V
IN2
Voltages ..................................... –0.3V to 50V
C1, C2 Voltages .......................................... –0.4V to 50V
E1, E2 Voltages ........................................... –60V to 50V
V
C1
to V
E1
and V
C2
to V
E2
Voltages ............ –0.4V to 60V
V
IN1
to V
E1
and V
IN2
to V
E2
Voltages
Low Side Configurations (Note 6) .......... –0.4V to 40V
High Side Configurations (Note 6) ......... –0.4V to 60V
V
IN1
to V
C1
and V
IN2
to V
C2
Voltages
High Side Configurations (Note 6) ......... –0.4V to 40V
C3 Voltage ................................................. –0.4V to 50V
RT Voltage ................................................... –0.3V to 5V
SYNC Voltage............................................ –0.3V to 5.5V
SS1, SS2 ................................................... –0.3V to 2.5V
FB1, FB2 Voltages ..................................... –2.5V to 2.5V
PG1, PG2 Voltages ..................................... –0.3V to 50V
OV/UV Voltage ............................................. –0.3V to 5V
SHOUT Voltage ......................................... –0.3V to 50V
Operating Junction Temperature Range
LT8471E (Notes 2, 5) ......................... –40°C to 125°C
LT8471I (Notes 2, 5) .......................... –40°C to 125°C
LT8471H (Notes 2, 5) ......................... –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package ....................................................... 300°C
pin conFiguraTion
TOP VIEW
NC
NC
NC
GND
1
2
3
4
5
6
7
8
9
21
GND
NC
22 E2
21 V
IN2
20 PG2
29
GND
19 FB2
18 SS2
17 SHOUT
16 C3
15 NC
9 10 11 12 13 14
GND
GND
GND
GND
GND
C1
C2
TOP VIEW
C1
E1
V
IN1
PG1
FB1
OV/UV
RT
SS1
SYNC
20 C2
19 E2
18 V
IN2
17 PG2
16 FB2
15 SS2
14
SHOUT
13 C3
12 GND
11 GND
E1 1
V
IN1
2
PG1 3
FB1 4
OV/UV 5
RT 6
SS1 7
SYNC 8
28 27 26 25 24 23
GND 10
FE PACKAGE
20-LEAD PLASTIC TSSOP
θ
JA
= 38°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
θ
JA
= 44°C/W,
θ
JC
= 8°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
2
8471fd
For more information
www.linear.com/8471
LT8471
orDer inForMaTion
LEAD FREE FINISH
LT8471EFE#PBF
LT8471IFE#PBF
LT8471HFE#PBF
LT8471EUFD#PBF
LT8471IUFD#PBF
TAPE AND REEL
LT8471EFE#TRPBF
LT8471IFE#TRPBF
LT8471HFE#TRPBF
LT8471EUFD#TRPBF
LT8471IUFD#TRPBF
PART MARKING*
LT8471FE
LT8471FE
LT8471FE
8471
8471
PACKAGE DESCRIPTION
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
28-LEAD (4mm
×
5mm) Plastic QFN
28-LEAD (4mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
= V
IN2
= 5V, unless otherwise noted (Note 2).
PARAMETER
Input Voltage (V
IN1
, V
IN2
)
Quiescent Current (V
IN1
, Skyhook Disabled)
Quiescent Current (V
IN1
, Skyhook Enabled)
Quiescent Current (V
IN2
)
Quiescent Current in Shutdown (V
IN1
+ V
IN2
)
Positive Feedback Voltage (FB1, FB2)
Negative Feedback Voltage
(FB1, FB2)
Feedback Pin Bias Current (FB1, FB2)
Error Amp Transconductances
Error Amp Voltage Gains
Reference Line Regulation
Switching Frequency, f
OSC
Switching Frequency in Foldback
Switching Frequency Range
SYNC High Level for Sync
SYNC Low Level for Sync
SYNC Clock Pulse Duty Cycle
Recommended Minimum SYNC Ratio f
SYNC
/f
OSC
Switching Phase Between Primary Channels
Skyhook Boost Voltage
Minimum Switch Off-Time
Minimum Switch On-Time
R
T
= 46.4k
R
T
= 732k
V
SHOUT
– V
C2
, Skyhook Enabled
Primary Channels (Note 7)
Skyhook Channel (Note 7)
Primary Channels(Note 7)
Skyhook Channel (Note 7)
170
170
3.0
4.25
170
100
220
30
V
SYNC
= 0V to 2V
(LT8471E,I)
(LT8471H)
V
FB
= Positive Feedback Voltage, Current Out of Pin
V
FB
= Negative Feedback Voltage
Primary Channels, ∆I = 2μA
Primary Channels
2.6V ≤ V
IN1
≤ 50V
R
T
= 46.4k
R
T
= 732k
All Channels. Compared to Normal f
OSC
Synchronizing
l
l
l
l
l
elecTrical characTerisTics
CONDITIONS
l
MIN
2.6
TYP
2.2
2.4
29
0.01
MAX
50
3.3
4
42
1
805
–770
–767
200
100
UNITS
V
mA
mA
µA
μA
mV
mV
mV
nA
nA
μmhos
V/V
V
OV/UV
= 1.3V, Not Switching
V
OV/UV
= 1.3V, C3 = 5V, Not Switching
V
OV/UV
= 1.3V, Not Switching
V
OV/UV
= 0V
l
l
l
773
–806
–806
–100
789
–788
–788
30
0
70
95
0.008
0.05
2.05
135
2000
0.4
%/V
MHz
kHz
Ratio
kHz
V
V
%
Ratio
Deg
Deg
V
ns
ns
ns
ns
1.55
100
100
1.3
35
1.8
117
1/8
65
¾
200
200
5.4
8471fd
For more information
www.linear.com/8471
3
LT8471
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
= V
IN2
= 5V, unless otherwise noted (Note 2).
PARAMETER
Switch Current Limit (Primary Channels)
Switch Current Limit (Skyhook)
Primary Switches V
CESAT
Skyhook Switch V
CESAT
C1, C2 Leakage Current
C3 Leakage Current
E1, E2 Leakage Current
CONDITIONS
Minimum Duty Cycle (Note 3)
Maximum Duty Cycle (Notes 3, 4)
(Note 3)
I
C1
or I
C2
= 1.5A
I
C3
= 250mA
V
C1
= V
C2
= 12V, V
E1
= V
E2
= 0V, V
OV/UV
= 0V,
Current into Pin
V
C3
= 12V, V
OV/UV
= 0V
V
OV/UV
= 0V, Current Out of Pin
V
C1
= V
C2
= 20V, V
E1
= V
E2
= 5V
V
C1
= V
C2
= 5V, V
E1
= V
E2
= –10V
V
REVERSE
= 12V
V
REVERSE
= 50V
I
DIODE
= 100mA
V
SS1
, V
SS2
= 50mV, Current Flows Out of
SS1, SS2 Pins
Current into OV/UV Pin. V
OV/UV
Internally Clamped
to 1.37V, Current Rising
V
OV/UV
=1V
Active Mode, OV/UV Rising
Active Mode, OV/UV Falling
Shutdown Mode
FB Rising
FB Falling
FB Falling
FB Rising
V
FB
= 0.6V, I
PG
= 250μA
V
PG1
, V
PG2
= 12V, PG Driver Off
l
l
l
l
l
l
l
l
l
l
l
l
elecTrical characTerisTics
MIN
2.1
1.35
400
TYP
2.55
1.8
500
300
250
0.01
0.01
0.01
0.01
0.01
0.02
650
MAX
3.2
2.5
600
UNITS
A
A
mA
mV
mV
1
1
1
1
1
2
μA
μA
µA
µA
µA
µA
mV
Schottky Reverse Leakage
Schottky Forward Voltage
Start-Up Characteristics
Soft-Start Charge Current
OV/UV Current for OVLO
OV/UV Pin Bias Current
OV/UV Minimum Input Voltage High
OV/UV Input Voltage Low
FB Pin Threshold for Power Good
(Positive Output Voltage)
FB Pin Threshold for Power Good
(Negative Output Voltage)
PG1, PG2 Voltage Output Low
PG1, PG2 Leakage
5.5
76
8.5
80
0.01
11.5
84
0.5
1.265
1.22
0.3
765
752
–706
–699
0.6
1
µA
µA
µA
V
V
V
mV
mV
mV
mV
V
µA
1.165
1.13
715
708
–766
–755
1.215
1.18
740
730
–736
–727
0.32
0.01
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LT8471E is guaranteed to meet performance specifications from
0°C to 125°C junction temperature. Specifications over the –40°C to 125°C
operating junction temperature range are assured by design, characterization
and correlation with statistical process controls. The LT8471I is guaranteed
over the full –40°C to 125°C. The LT8471H is guaranteed over the full –40°C
to 150°C operating junction temperature range. Operating lifetime is derated
at junction temperatures greater than 125°C.
Note 3:
Current limit guaranteed by design and/or correlation to static test.
Note 4:
Current Limit measured at equivalent switching frequency of 1MHz.
Note 5:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 150°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 6:
Low side and high side configurations are discussed in the Switch
Configurations and the Skyhook Regulator section.
Note 7:
Minimum switch on-time, off-time is guaranteed by design.
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Programming Basics
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