Peak Output Current ................................100mA
Operating Junction Temperature Range
(Notes 2, 3) ............................................ –40°C to 125°C
Storage Temperature Range................... –65°C to 125°C
Reflow Peak Body Temperature (UH Package) ...... 260°C
Lead Temperature (Soldering, 10 sec.)
FE Package............................................................ 300°C
pin conFiguraTion
TOP VIEW
FREQ
RUN
SENSE1
+
SENSE1
–
NC
TK/SS
V
FB
I
TH
SGND
1
2
3
4
5
6
7
8
9
39
SGND
38 PLLIN
37 CLKOUT
36 SW1
SENSE1
–
SENSE1
+
35 TG1
34 NC
33 BOOST1
32 PGND1
31 BG1
30 V
IN
29 INTV
CC
28 EXTV
CC
27 BG2
26 PGND2
25 NC
24 BOOST2
23 TG2
22 SW2
21 PGOOD
20 MODE
TK/SS 1
V
FB
2
I
TH
3
AVP 4
ITEMP 5
PHASMD 6
SENSE2
+
TOP VIEW
CLKOUT
PLLIN
FREQ
SW1
PGOOD
RUN
32 31 30 29 28 27 26 25
24 BOOST1
23 BG1
22 V
IN
33
SGND/PGND
21 INTV
CC
20 EXTV
CC
19 BG2
18 BOOST2
17 TG2
9 10 11 12 13 14 15 16
DIFFP
ISET
ILIM
DIFFN
DIFFOUT
MODE
SW2
AVP 10
ITEMP 11
PHASMD 12
SENSE2
+
13
SENSE2– 14
DIFFP 15
DIFFN 16
DIFFOUT 17
ISET 18
ILIM 19
7
SENSE2
–
8
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 33) IS SGND/PGND, MUST BE SOLDERED TO PCB
FE PACKAGE
38-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 25°C/W
EXPOSED PAD (PIN 39) IS SGND/PGND, MUST BE SOLDERED TO PCB
TG1
3856fa
2
For more information
www.linear.com/LTC3856
LTC3856
orDer inForMaTion
LEAD FREE FINISH
LTC3856EFE#PBF
LTC3856IFE#PBF
LTC3856EUH#PBF
LTC3856IUH#PBF
TAPE AND REEL
LTC3856EFE#TRPBF
LTC3856IFE#TRPBF
LTC3856EUH#TRPBF
LTC3856IUH#TRPBF
PART MARKING*
LTC3856FE
LTC3856FE
3856
3856
PACKAGE DESCRIPTION
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
32-Lead (5mm
×
5mm) Plastic QFN
32-Lead (5mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°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 non-standard 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/
elecTrical characTerisTics
SYMBOL
V
IN
V
OUT
V
FB
I
FB
V
REFLNREG
V
LOADREG
g
m
I
Q
DF
MAX
UVLO
UVLO Hyst
V
OVL
I
SENSE+
I
TEMP
I
TK/SS
V
RUN
V
RUNHYS
V
SENSE(MAX)
PARAMETER
Input Voltage
Output Voltage
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Main Control Loops
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 15V, V
RUN
= 5V, unless otherwise noted.
CONDITIONS
MIN
4.5
0.6
I
TH
Voltage = 1.2V, E-Grade (Note 4)
I
TH
Voltage = 1.2V, I-Grade (Note 4)
(Note 4)
V
IN
= 4.5V to 38V (Note 4)
(Note 4)
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 1.6V
I
TH
= 1.2V, Sink/Source 5µA (Note 4)
(Note 5)
V
IN
= 15V
V
RUN
= 0V
In Dropout; f
OSC
= 500kHz
V
INTVCC
Ramping Down
Measured at V
FB
Each Channel, V
SENSE1,2
= 3.3V
V
ITEMP
= 0.3V
V
TK/SS
= 0V
V
RUN
Rising
V
FB
= 0.5V, V
SENSE1,2
= 3.3V
I
LIM
= 0V
I
LIM
= Float
I
LIM
= INTV
CC
V
FB
= 0.5V, V
SENSE1,2
= 3.3V
I
LIM
= 0V
I
LIM
= Float
I
LIM
= INTV
CC
l
l
l
l
l
TYP
MAX
38
5.0
UNITS
V
V
V
V
nA
%/V
%
%
mmho
mA
µA
%
V
V
V
µA
µA
µA
V
mV
0.5955
0.593
0.600 0.6045
0.600 0.607
–15
0.002
0.01
–0.01
2.0
4.0
40
–50
0.02
0.1
–0.1
Transconductance Amplifier g
m
Input DC Supply Current
Normal Mode
Shutdown
Maximum Duty Factor
Undervoltage Lockout
UVLO Hysteresis
Feedback Overvoltage Lockout
SENSE
+
Pins Bias Current
DCR Tempco Compensation Current
Soft-Start Charge Current
RUN Pin On Threshold
RUN Pin On Hysteresis
Maximum Current Sense Threshold
(E-Grade)
70
3.4
0.68
±2
11
1.5
1.35
93
3.0
0.64
9
1.0
1.1
94
3.2
0.6
0.66
±1
10
1.25
1.22
80
l
l
l
l
l
l
l
l
l
l
l
25
45
68
23
43
66
30
50
75
30
50
75
35
55
82
37
57
84
mV
mV
mV
mV
mV
mV
V
SENSE(MAX)
Maximum Current Sense Threshold
(I-Grade)
3856fa
For more information
www.linear.com/LTC3856
3
LTC3856
elecTrical characTerisTics
SYMBOL
TG1,2 t
r
TG1,2 t
f
BG1,2 t
r
BG1,2 t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
V
EXTVCC
V
LDO
EXT
V
LDOHYS
f
NOM
f
LOW
f
HIGH
R
MODE
I
FREQ
CLKOUT
PARAMETER
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
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Voltage Drop
EXTV
CC
Hysteresis
Nominal Frequency
Lowest Frequency
Highest Frequency
MODE Input Resistance
Frequency Setting Output Current
Phase (Relative to Controller 1)
PHASMD = GND; Non Stage Shedding Mode
PHASMD = FLOAT; Non Stage Shedding Mode
PHASMD = INTV
CC
; Non Stage Shedding Mode
Stage Shedding Mode
4
9
V
FREQ
= 1.2V
V
FREQ
= 0V
V
FREQ
≥ 2.4V
450
210
700
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 15V, V
RUN
= 5V, unless otherwise noted.
CONDITIONS
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
(Note 7)
6V < V
IN
≤ 38V
I
CC
= 0mA to 20mA
EXTV
CC
Ramping Positive
I
CC
= 20mA, V
EXTVCC
= 5V
l
MIN
TYP
25
25
25
25
30
30
90
MAX
UNITS
ns
ns
ns
ns
ns
ns
ns
INTV
CC
Linear Regulator
4.8
4.5
5.0
0.5
4.7
50
200
500
250
770
250
10
60
90
120
180
5
0
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
FB
with Respect to Set Output Voltage
V
FB
Ramping Negative
V
FB
Ramping Positive
–10
10
0.1
0.2
0.2
±2
11
550
290
850
100
5.2
2.0
V
%
V
mV
mV
kHz
kHz
kHz
kΩ
µA
Deg
Deg
Deg
Deg
V
V
V
µA
%
%
Oscillator and Phase-Locked Loop
CLKHIGH
CLKLOW
PGOOD Output
V
PGL
I
PGOOD
V
PG
Clock High Output Voltage
Clock Low Output Voltage
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
3856fa
4
For more information
www.linear.com/LTC3856
LTC3856
elecTrical characTerisTics
SYMBOL
A
DA
R
IN
V
OS
PSRR
I
CL
V
OUT(MAX)
PARAMETER
Gain
Input Resistance
Input Offset Voltage
Power Supply Rejection Ratio
Maximum Output Current
Maximum Output Voltage
I
DIFFOUT
= 300µA
Differential Amplifier
E-Grade
I-Grade
Measured at DIFFP Input
V
DIFFP
= V
DIFFOUT
= 1.5V, I
DIFFOUT
= 100µA
4.5V < V
IN
< 38V
2
100
3
V
INTVCC
V
INTVCC
–1.4
–1.1
2.6
1.5
2.4
1.1
3
2
6.5
7.5
8.5
l
l
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 15V, V
RUN
= 5V, unless otherwise noted.
CONDITIONS
MIN
0.998
0.997
TYP
1
1
80
2
MAX
1.002
1.003
UNITS
V/V
V/V
kΩ
mV
dB
mA
V
On-Chip Driver
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
GBW
SR
I
ISET
TG Pull-Up R
DS(ON)
TG Pull-Down R
DS(ON)
BG Pull-Up R
DS(ON)
BG Pull-Down R
DS(ON)
Gain-Bandwidth Product
Slew Rate
Programmable Stage Shedding
Mode Current
Maximum V
OUT
with AVP
Sink Current of AVP Pin
Source Current of AVP Pin
SENSE
+
= 1.2V
SENSE
+
= 1.2V
SENSE
+
= 1.2V
TG High
TG Low
BG High
BG Low
(Note 8)
(Note 8)
Ω
Ω
Ω
Ω
MHz
V/µs
µA
Stage Shedding Mode
AVP (Active Voltage Positioning)
V
AVP
I
SINK
I
SOURCE
2.5
250
2
120
V
µA
mA
mV
V
AVP
-V
O(MAX)
Maximum Voltage Drop V
AVP
to V
O
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 LTC3856 is tested under pulse load conditions such that
T
J
≈
T
A
. The LTC3856E is guaranteed to meet performance specifications
from 0°C to 85°C operating 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 LTC3856I is guaranteed to meet performance specifications over the
full –40°C to 125°C operating junction temperature range.
Note 3:
T
J
is calculated from the ambient temperature, T
A
, and power
dissipation, P
D
, according to the following formula:
LTC3856UH: T
J
= T
A
+ (P
D
• 34°C/W)
LTC3856FE: T
J
= T
A
+ (P
D
• 25°C/W)
Note 4:
The LTC3856 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
FB
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See the Applications Information
section.
Note 6:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 7:
The minimum on-time condition corresponds to the on inductor
peak-to-peak ripple current ≥40% of I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
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PCB Design
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