LTC3857-1
4
38571fc
ELECTRICAL CHARACTERISTICS
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
= 12V, V
RUN1,2
= 5V, EXTV
CC
= 0V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
TG/BG t
1D
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
C
LOAD
= 3300pF Each Driver 30 ns
BG/TG t
1D
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
C
LOAD
= 3300pF Each Driver 30 ns
t
ON(MIN)
Minimum On-Time (Note 7) 95 ns
INTV
CC
Linear Regulator
V
INTVCCVIN
Internal V
CC
Voltage 6V < V
IN
< 38V, V
EXTVCC
= 0V 4.85 5.1 5.35 V
V
LDOVIN
INTV
CC
Load Regulation I
CC
= 0mA to 50mA, V
EXTVCC
= 0V 0.7 1.1 %
V
INTVCCEXT
Internal V
CC
Voltage 6V < V
EXTVCC
< 13V 4.85 5.1 5.35 V
V
LDOEXT
INTV
CC
Load Regulation I
CC
= 0mA to 50mA, V
EXTVCC
= 8.5V 0.6 1.1 %
V
EXTVCC
EXTV
CC
Switchover Voltage EXTV
CC
Ramping Positive 4.5 4.7 4.9 V
V
LDOHYS
EXTV
CC
Hysteresis 250 mV
Oscillator and Phase-Locked Loop
f
25k
Programmable Frequency R
FREQ
= 25k, PLLIN/MODE = DC Voltage 105 kHz
f
65k
Programmable Frequency R
FREQ
= 65k, PLLIN/MODE = DC Voltage 375 440 505 kHz
f
105k
Programmable Frequency R
FREQ
= 105k, PLLIN/MODE = DC Voltage 835 kHz
f
LOW
Low Fixed Frequency V
FREQ
= 0V, PLLIN/MODE = DC Voltage 320 350 380 kHz
f
HIGH
High Fixed Frequency V
FREQ
= INTV
CC
, PLLIN/MODE = DC Voltage 485 535 585 kHz
f
SYNC
Synchronizable Frequency PLLIN/MODE = External Clock
l
75 850 kHz
PGOOD1 Output
V
PGL
PGOOD1 Voltage Low I
PGOOD
= 2mA 0.2 0.4 V
I
PGOOD
PGOOD1 Leakage Current V
PGOOD
= 5V ±1 µA
V
PG
PGOOD1 Trip Level V
FB1
with Respect to Set Regulated Voltage
V
FB1
Ramping Negative
Hysteresis
–13 –10
2.5
–7 %
%
V
FB1
with Respect to Set Regulated Voltage
V
FB1
Ramping Positive
Hysteresis
710
2.5
13 %
%
t
PG
Delay for Reporting a Fault 25 µs
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Ratings for extended periods may affect device reliability and
lifetime.
Note 2: The LTC3857-1 is tested under pulsed conditions such that
T
J
≈
T
A
. The LTC3857E-1 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3857I-1 is guaranteed
over the full –40°C to 125°C operating junction temperature range. Note
that the maximum ambient temperature is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
resistance and other environmental factors.
Note 3: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
• 90°C/W)
Note 4: The LTC3857-1 is tested in a feedback loop that servos V
ITH1,2
to
a specified voltage and measures the resultant V
FB1,2
. The specification at
85°C is not tested in production. This specification is assured by design,
characterization and correlation to production testing at 125°C.
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).
