Datasheet

LTC3855
5
3855f
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)
elecTrical characTerisTics
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.
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).
Note 8: Guaranteed by design.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
On Chip Driver
TG R
UP
TG Pull-Up R
DS(ON)
TG High 2.6 Ω
TG R
DOWN
TG Pull-Down R
DS(ON)
TG Low 1.5 Ω
BG R
UP
BG Pull-Up R
DS(ON)
BG High 2.4 Ω
BG R
DOWN
BG Pull-Down R
DS(ON)
BG Low 1.1 Ω
Typical perForMance characTerisTics
Efficiency vs Output Current
and Mode
Efficiency vs Output Current
and Mode
LOAD CURRENT (A)
0.01
EFFICIENCY (%)
100
10
90
70
50
30
80
60
40
20
0
10
3855 G23
10010.1
V
IN
= 12V
V
OUT
= 1.8V
Burst Mode
OPERATION
DCM
CCM
CIRCUIT OF FIGURE 19
LOAD CURRENT (A)
0.01
EFFICIENCY (%)
100
10
90
70
50
30
80
60
40
20
0
10
3855 G24
10010.1
V
IN
= 12V
V
OUT
= 1.2V
Burst Mode
OPERATION
DCM
CCM
CIRCUIT OF FIGURE 19
Full Load Efficiency and Power
Loss vs Input Voltage
INPUT VOLTAGE (V)
5
75
EFFICIENCY (%)
80
85
90
2
POWER LOSS (W)
3
4
5
10 2015
3855 G24
1.8V
1.8V
1.2V
1.2V
EFFICIENCY
POWER LOSS
CIRCUIT OF FIGURE 19