EXPOSED PAD (PIN 39) IS SGND, MUST BE SOLDERED TO PCB
UJ PACKAGE
40-LEAD (6mm 6mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 33°C/W
EXPOSED PAD (PIN 41) IS SGND, MUST BE SOLDERED TO PCB
SW1
3855f
LTC3855
orDer inForMaTion
LEAD FREE FINISH
LTC3855EFE#PBF
LTC3855IFE#PBF
LTC3855EUJ#PBF
LTC3855IUJ#PBF
TAPE AND REEL
LTC3855EFE#TRPBF
LTC3855IFE#TRPBF
LTC3855EUJ#TRPBF
LTC3855IUJ#TRPBF
PART MARKING*
LTC3855FE
LTC3855FE
LTC3855UJ
LTC3855UJ
PACKAGE DESCRIPTION
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
40-Lead (6mm
×
6mm) Plastic QFN
40-Lead (6mm
×
6mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 85°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
FB1,2
I
FB1,2
V
REFLNREG
V
LOADREG
g
m1,2
I
Q
DF
MAX
UVLO
UVLO
HYS
V
OVL1,2
I
SENSE1,2
I
TEMP1,2
I
TK/SS1,2
V
RUN1,2
V
RUN1,2HYS
PARAMETER
Input Voltage Range
Output Voltage Range
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 (E-Grade), otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN1,2
= 5V unless otherwise noted.
CONDITIONS
MIN
4.5
0.6
I
TH1,2
Voltage = 1.2V (Note 4)
I
TH1,2
Voltage = 1.2V (Note 4), T
A
= 125°C
(Note 4)
V
IN
= 4.5V to 38V (Note 4)
(Note 4)
Measured in Servo Loop; ∆I
TH
Voltage = 1.2V to 0.7V
l
Measured in Servo Loop; ∆I
TH
Voltage = 1.2V to 1.6V
l
I
TH1,2
= 1.2V; Sink/Source 5µA; (Note 4)
(Note 5)
V
IN
= 15V
V
RUN1,2
= 0V
In Dropout, f
OSC
= 500kHz
V
INTVCC
Ramping Down
Measured at V
FB1,2
(Each Channel); V
SENSE1,2
= 3.3V
V
ITEMP1,2
= 0.2V
V
TK/SS1,2
= 0V
V
RUN1
, V
RUN2
Rising
V
FB1,2
= 0.5V, V
SENSE1,2
= 3.3V, I
LIM
= 0V
V
FB1,2
= 0.5V, V
SENSE1,2
= 3.3V, I
LIM
= Float
V
FB1,2
= 0.5V, V
SENSE1,2
= 3.3V, I
LIM
= INTV
CC
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
l
l
l
TYP
MAX
38
12.5
UNITS
V
V
V
V
nA
%/V
%
%
mmho
mA
µA
%
V
V
V
µA
µA
µA
V
mV
mV
mV
mV
ns
ns
ns
ns
3855f
0.5955
0.594
0.600
0.600
–15
0.002
0.01
–0.01
2
3.5
30
0.6045
0.606
–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
50
3.4
0.68
±2
11
1.4
1.35
35
55
82
94
3.0
0.64
9
1
1.1
25
45
68
95
3.2
0.6
0.66
±1
10
1.2
1.22
80
30
50
75
25
25
25
25
l
l
l
l
l
V
SENSE(MAX)
Maximum Current Sense Threshold
TG1, 2 t
r
TG1, 2 t
f
BG1, 2 t
r
BG1, 2 t
f
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
l
l
l
LTC3855
elecTrical characTerisTics
SYMBOL
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
I
FREQ
CLKOUT
PARAMETER
The
l
denotes the specifications which apply over the full operating
junction temperature range (E-Grade), otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN1,2
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
30
30
90
4.8
l
MAX
UNITS
ns
ns
ns
Top Gate Off to Bottom Gate On Delay C
LOAD
= 3300pF Each Driver
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay C
LOAD
= 3300pF Each Driver
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
Frequency Setting Current
Phase (Relative to Controller 1)
PHASMD = GND
PHASMD = Float
PHASMD = INTV
CC
4
V
FREQ
= 1.2V
V
FREQ
= 0V
V
FREQ
≥ 2.4V
450
210
700
9
(Note 7)
6V < V
IN
< 38V
I
CC
= 0mA to 20mA
EXTV
CC
Ramping Positive
I
CC
= 20mA, V
EXTVCC
= 5V
4.5
INTV
CC
Linear Regulator
5
0.5
4.7
50
200
500
250
770
250
10
60
90
120
5
0
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
FB
with Respect to Set Output Voltage
V
FB
Ramping Negative
V
FB
Ramping Positive
l
5.2
2
100
V
%
V
mV
mV
Oscillator and Phase-Locked Loop
550
290
850
11
kHz
kHz
kHz
kΩ
µA
Deg
Deg
Deg
V
0.2
0.3
±2
–10
10
0.998
1
80
2
100
2
I
DIFFOUT
= 300µA
(Note 8)
(Note 8)
3
3
2
V
INTVCC
– 1.4 V
INTVCC
– 1.1
1.002
V
V
µA
%
%
V/V
kΩ
mV
dB
mA
V
MHz
V/µs
R
MODE/PLLIN
MODE/PLLIN Input Resistance
CLK
HIGH
CLK
LOW
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
PGOOD Output
0.1
Differential Amplifier
A
DA
R
IN
V
OS
PSRR
OA
I
CL
V
OUT(MAX)
GBW
Slew Rate
Gain
Input Resistance
Input Offset Voltage
Power Supply Rejection Ratio
Maximum Output Current
Maximum Output Voltage
Gain Bandwidth Product
Differential Amplifier Slew Rate
Measured at DIFFP Input
V
DIFFP
= V
DIFFOUT
= 1.5V, I
DIFFOUT
= 100µA
5V < V
IN
< 38V
3855f
LTC3855
elecTrical characTerisTics
SYMBOL
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
PARAMETER
TG Pull-Up R
DS(ON)
TG Pull-Down R
DS(ON)
BG Pull-Up R
DS(ON)
BG Pull-Down R
DS(ON)
On Chip Driver
TG High
TG Low
BG High
BG Low
2.6
1.5
2.4
1.1
Ω
Ω
Ω
Ω
The
l
denotes the specifications which apply over the full operating
junction temperature range (E-Grade), otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
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 LTC3855E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3855I 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 formulas:
LTC3855UJ: T
J
= T
A
+ (P
D
• 33°C/W)
LTC3855FE: T
J
= T
A
+ (P
D
• 25°C/W)
Note 4:
The LTC3855 is tested in a feedback loop that servos V
ITH1,2
to a
specified voltage and measures the resultant V
FB1,2
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
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 is specified for an inductor
peak-to-peak ripple current ≥40% of I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
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