Dual Buck Plus Single Boost Synchronous Controllers
Outputs Remain in Regulation Through Cold Crank
Down to 2.5V
Low Operating I
Q
: 55μA (One Channel On)
Wide Bias Input Voltage Range: 4.5V to 38V
Buck Output Voltage Range: 0.8V ≤ V
OUT
≤ 24V
Boost Output Voltage Up to 60V
R
SENSE
or DCR Current Sensing
100% Duty Cycle for Boost Synchronous MOSFET
Even in Burst Mode
®
Operation
Phase-Lockable Frequency (75kHz to 850kHz)
Programmable Fixed Frequency (50kHz to 900kHz)
Selectable Continuous, Pulse-Skipping or Low Ripple
Burst Mode Operation at Light Loads
Very Low Buck Dropout Operation: 99% Duty Cycle
Adjustable Output Voltage Soft-Start or Tracking
Low Shutdown I
Q
: 14μA
Small 38-Pin 5mm × 7mm QFN and TSSOP Packages
LTC3859A
Low I
Q
, Triple Output,
Buck/Buck/Boost Synchronous Controller
with Improved Burst Mode Operation
DESCRIPTION
The
LTC
®
3859A
is a high performance triple output (buck/
buck/boost) synchronous DC/DC switching regulator
controller that drives all N-channel power MOSFET stages.
Constant frequency current mode architecture allows
a phase-lockable switching frequency of up to 850kHz.
The LTC3859A operates from a wide 4.5V to 38V input
supply range. When biased from the output of the boost
converter or another auxiliary supply, the LTC3859A can
operate from an input supply as low as 2.5V after start-up.
The 55μA no-load quiescent current extends operating
runtime in battery powered systems. OPTI-LOOP com-
pensation allows the transient response to be optimized
over a wide range of output capacitance and ESR values.
The LTC3859A features a precision 0.8V reference for the
bucks, 1.2V reference for the boost and a power good
output indicator. The PLLIN/MODE pin selects among
Burst Mode operation, pulse-skipping mode, or continu-
ous inductor current mode at light loads.
Compared to the LTC3859, the LTC3859A's boost controller
has improved performance in Burst Mode operation when
the input voltage is higher than the regulated output voltage.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6580258.
APPLICATIONS
n
n
n
n
Automotive Always-On and Start-Stop Systems
Battery Operated Digital Devices
Distributed DC Power Systems
Multioutput Buck-Boost Applications
TYPICAL APPLICATION
V
OUT3
REGULATED AT 10V WHEN V
IN
< 10V
FOLLOWS V
IN
WHEN V
IN
> 10V
220µF
499k
68.1k
V
IN
2.5V TO 38V
(START-UP ABOVE 5V)
2mΩ
220µF
1.2µH
TG3
SW3
BG3
SENSE3
–
SENSE3
+
INTV
CC
4.7µF
BOOST1, 2, 3
SW1, 2, 3
0.1µF
I
TH1, 2, 3
LTC3859A
1µF
V
FB3
V
BIAS
TG1
4.9µH
SW1
BG1
SENSE1
+
SENSE1
–
V
FB1
RUN1, 2, 3
EXTV
CC
TG2
SW2
BG2
68.1k
V
OUT1
6.5µH
8mΩ
V
OUT2
8.5V
3A
6mΩ
V
OUT1
5V
5A
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
55 FIGURE 12 CIRCUIT
I
LOAD
= 2A
50
0
5
10 15 20 25 30
INPUT VOLTAGE (V)
V
OUT1
= 5V
V
OUT2
= 8.5V
Efficiency vs Input Voltage
357k
220µF
35
40
3859A TA01b
0.1µF
SENSE2+
SENSE2–
TRACK/SS1, 2
V
FB2
SS3
PGND SGND
3859 TA01a
68.1k
649k
68µF
Rev. B
Document Feedback
For more information
www.analog.com
1
LTC3859A
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 3)
Bias Input Supply Voltage (V
BIAS
) .............. –0.3V to 40V
Buck Top Side Driver Voltages
(BOOST1, BOOST2) ............................. –0.3V to 46V
Boost Top Side Driver Voltages
(BOOST3) ............................................ –0.3V to 76V
Buck Switch Voltage (SW1, SW2) ................ –5V to 40V
Boost Switch Voltage (SW3) ........................ –5V to 70V
INTV
CC
, (BOOST1–SW1),
(BOOST2–SW2), (BOOST3–SW3), .......... –0.3V to 6V
RUN1, RUN2, RUN3 .................................... –0.3V to 8V
Maximum Current Sourced Into Pin
from Source >8V ..............................................100µA
SENSE1
+
, SENSE2
+
, SENSE1
–
SENSE2
–
Voltages ..................................... –0.3V to 28V
SENSE3
+
, SENSE3
–
Voltages ..................... –0.3V to 40V
FREQ Voltages ......................................–0.3V to INTV
CC
EXTV
CC
...................................................... –0.3V to 14V
I
TH1
, I
TH2
, I
TH3
, V
FB1
, V
FB2
, V
FB3
Voltages.... –0.3V to 6V
PLLIN/MODE, PGOOD1, OV3 Voltages ........ –0.3V to 6V
TRACK/SS1, TRACK/SS2, SS3 Voltages ..... –0.3V to 6V
Operating Junction Temperature Range (Note 2)
LTC3859AE, LTC3859AI..................... –40°C to 125°C
LTC3859AH........................................ –40°C to 150°C
LTC3859AMP..................................... –55°C to 150°C
Storage Temperature Range .............. –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
SENSE1
–
SENSE1
+
I
TH1
V
FB1
SENSE1
+
SENSE1
–
FREQ
PLLIN/MODE
SS3
SENSE3
+
SENSE3
–
1
2
3
4
5
6
7
8
9
39
PGND
38 TRACK/SS1
37 PGOOD1
36 TG1
35 SW1
34 BOOST1
33 BG1
32 SW3
31 TG3
30 BOOST3
29 BG3
28 V
BIAS
27 EXTV
CC
26 INTV
CC
25 BG2
24 BOOST2
23 SW2
22 TG2
21 OV3
20 TRACK/SS2
FREQ 1
PLLIN/MODE 2
SS3 3
SENSE3
+
TOP VIEW
TRACK/SS1
PGOOD1
V
FB1
I
TH1
38 37 36 35 34 33 32
31 SW1
30 BOOST1
29 BG1
28 SW3
27 TG3
39
PGND
26 BOOST3
25 BG3
24 V
BIAS
23 EXTV
CC
22 INTV
CC
21 BG2
20 BOOST2
13 14 15 16 17 18 19
OV3
TG2
TRACK/SS2
SENSE2
+
SW2
V
FB2
I
TH2
4
5
SENSE3
–
V
FB3
10
I
TH3
11
SGND 12
RUN1 13
RUN2 14
RUN3 15
SENSE2
–
SENSE2
+
V
FB3
6
I
TH3
7
SGND 8
RUN1 9
RUN2 10
RUN3 11
SENSE2 12
–
16
17
V
FB2
18
I
TH2
19
FE PACKAGE
38-LEAD PLASTIC TSSOP
T
JMAX
= 150°C,
q
JA
= 25°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
UHF PACKAGE
38-LEAD (5mm
×
7mm) PLASTIC QFN
T
JMAX
= 150°C,
q
JA
= 34.7°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
TG1
Rev. B
2
For more information
www.analog.com
LTC3859A
ORDER INFORMATION
LEAD FREE FINISH
LTC3859AEFE#PBF
LTC3859AIFE#PBF
LTC3859AHFE#PBF
LTC3859AMPFE#PBF
LTC3859AEUHF#PBF
LTC3859AIUHF#PBF
LTC3859AHUHF#PBF
LTC3859AMPUHF#PBF
TAPE AND REEL
LTC3859AEFE#TRPBF
LTC3859AIFE#TRPBF
LTC3859AHFE#TRPBF
LTC3859AMPFE#TRPBF
LTC3859AEUHF#TRPBF
LTC3859AIUHF#TRPBF
LTC3859AHUHF#TRPBF
PART MARKING*
LTC3859AFE
LTC3859AFE
LTC3859AFE
LTC3859AFE
3859A
3859A
3859A
PACKAGE DESCRIPTION
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
38-Lead (5mm × 7mm) Plastic QFN
38-Lead (5mm × 7mm) Plastic QFN
38-Lead (5mm × 7mm) Plastic QFN
38-Lead (5mm × 7mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–55°C to 150°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–55°C to 150°C
LTC3859AMPUHF#TRPBF 3859A
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications.
Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
BIAS
= 12V, V
RUN1,2,3
= 5V, EXTV
CC
= 0V unless otherwise
noted. (Note 2)
SYMBOL
V
BIAS
V
FB1,2
PARAMETER
Bias Input Supply Operating Voltage
Range
Buck Regulated Feedback Voltage
(Note 4); I
TH1,2
Voltage = 1.2V
–40°C to 85°C, All Grades
LTC3859AE, LTC3859AI
LTC3859AH, LTC3859AMP
(Note 4); I
TH3
Voltage = 1.2V
–40°C to 85°C, All Grades
LTC3859AE, LTC3859AI
LTC3859AH, LTC3859AMP
(Note 4)
(Note 4); V
BIAS
= 4.5V to 38V
(Note 4)
Measured in Servo Loop;
DI
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop;
DI
TH
Voltage = 1.2V to 2V
g
m1,2,3
Transconductance Amplifier g
m
(Note 4); I
TH1,2,3
= 1.2V;
Sink/Source 5µA
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
4.5
TYP
MAX
38
UNITS
V
l
l
0.792
0.788
0.786
1.188
1.182
1.179
0.800
0.800
0.800
1.200
1.200
1.200
–10
0.002
0.01
–0.01
2
0.808
0.812
0.812
1.212
1.218
1.218
±50
0.02
0.1
–0.1
V
V
V
V
V
V
nA
%/V
%
%
mmho
V
FB3
Boost Regulated Feedback Voltage
l
l
I
FB1,2,3
V
REFLNREG
V
LOADREG
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Rev. B
For more information
www.analog.com
3
LTC3859A
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
PARAMETER
Input DC Supply Current
Pulse-Skipping or
Forced Continuous Mode
(One Channel On)
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
BIAS
= 12V, V
RUN1,2,3
= 5V, EXTV
CC
= 0V unless otherwise
noted. (Note 2)
CONDITIONS
(Note 5)
RUN1 = 5V and RUN2,3 = 0V or
RUN2 = 5V and RUN1,3 = 0V or
RUN3 = 5V and RUN1,2 = 0V
V
FB1, 2
ON = 0.83V (No Load)
V
FB3
= 1.25V
RUN1,2,3 = 5V,
V
FB1,2
= 0.83V (No Load)
V
FB3
= 1.25V
RUN1 = 5V and RUN2,3 = 0V or
RUN2 = 5V and RUN1,3 = 0V
V
FB,ON
= 0.83V (No Load)
RUN3 = 5V and RUN1,2 = 0V
V
FB3
= 1.25V
RUN1 = 5V and RUN2 = 0V or
RUN2 = 5V and RUN1 = 0V
RUN3 = 5V
V
FB1,2
= 0.83V (No Load)
V
FB3
= 1.25V
RUN1,2,3 = 5V,
V
FB1,2
= 0.83V (No Load)
V
FB3
= 1.25V
RUN1,2,3 = 0V
INTV
CC
Ramping Up
INTV
CC
Ramping Down
V
OVL1,2
I
SENSE1,2
+
I
SENSE3
+
I
SENSE1,2
–
I
SENSE3
–
DF
MAX,TG
DF
MAX,BG
I
TRACK/SS1,2
I
SS3
V
RUN1
ON
V
RUN2,3
ON
V
RUN1,2,3
Hyst
Buck Feedback Overvoltage Protection
SENSE
+
Pin Current
SENSE
+
Pin Current
SENSE
–
Pin Current
SENSE
–
Pin Current
Maximum Duty Factor for TG
Maximum Duty Factor for BG
Soft-Start Charge Current
Soft-Start Charge Current
RUN1 Pin Threshold
RUN2,3 Pin Threshold
RUN Pin Hysteresis
V
FB1,2
= 0.7V, V
SENSE1,2
– = 3.3V
V
FB1,2,3
= 1.1V, V
SENSE3
+ = 12V
l
l
l
MIN
TYP
1.5
MAX
UNITS
mA
Pulse-Skipping or
Forced Continuous Mode
(All Channels On)
Sleep Mode
(One Channel On, Buck)
Sleep Mode
(One Channel On, Boost)
Sleep Mode
(Buck and Boost Channel On)
3
mA
55
80
µA
55
65
80
100
µA
µA
Sleep Mode
(All Three Channels On)
Shutdown
UVLO
Undervoltage Lockout
80
120
µA
14
4.15
3.5
7
3.8
10
30
4.5
4.0
13
±1
µA
V
V
%
µA
µA
Measured at V
FB1,2
Relative to
Regulated V
FB1,2
Bucks (Channels 1 and 2)
Boost (Channel 3)
Bucks (Channels 1 and 2)
V
OUT1,2
< V
INTVCC
– 0.5V
V
OUT1,2
> V
INTVCC
+ 0.5V
Boost (Channel 3)
V
SENSE3
+, V
SENSE3
– = 12V
Bucks (Channels 1,2) in Dropout, FREQ = 0V
Boost (Channel 3) in Overvoltage
Bucks (Channels 1,2) in Overvoltage
Boost (Channel 3)
V
TRACK/SS1,2
= 0V
V
SS3
= 0V
V
RUN1
Rising
V
RUN2,3
Rising
l
l
170
±2
±1
98
99
100
100
96
0.7
0.7
1.19
1.23
43
2.5
1.0
1.0
1.25
1.28
80
50
57
38
1.4
1.4
1.31
1.33
700
µA
µA
µA
%
%
%
%
µA
µA
V
V
mV
mV
V
V
SENSE1,2,3(MAX)
Maximum Current Sense Threshold
V
SENSE3(CM)
SENSE3 Pins Common Mode Range
(BOOST Converter Input Supply Voltage)
Rev. B
4
For more information
www.analog.com
LTC3859A
ELECTRICAL CHARACTERISTICS
SYMBOL
Gate Driver
TG1,2
BG1,2
TG3
BG3
Pull-Up On-Resistance
Pull-Down On-Resistance
Pull-Up On-Resistance
Pull-Down On-Resistance
Pull-Up On-Resistance
Pull-Down On-Resistance
Pull-Up On-Resistance
Pull-Down On-Resistance
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
Buck Minimum On-Time
Boost Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Hysteresis
Programmable Frequency
Programmable Frequency
Programmable Frequency
Low Fixed Frequency
High Fixed Frequency
Synchronizable Frequency
PGOOD1 Voltage Low
PGOOD1 Leakage Current
PGOOD1 Trip Level
R
FREQ
= 25k; PLLIN/MODE = DC Voltage
R
FREQ
= 65k; PLLIN/MODE = DC Voltage
R
FREQ
= 105k; PLLIN/MODE = DC Voltage
V
FREQ
= 0V PLLIN/MODE = DC Voltage
V
FREQ
= INTV
CC
; PLLIN/MODE = DC Voltage
PLLIN/MODE = External Clock
I
PGOOD1
= 2mA
V
PGOOD1
= 5V
V
FB1
with Respect to Set Regulated Voltage
V
FB1
Ramping Negative
Hysteresis
V
FB1
Ramping Positive
Hysteresis
7
–13
–10
2.5
10
2.5
13
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
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