LTC3857-1_15 Datasheet, PDF (4/38 Pages) Linear Technology – Low IQ, Dual, 2-Phase Synchronous Step-Down Controller

LTC3857-1
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 C_LOAD = 3300pF Each Driver
Synchronous Switch-On Delay Time
30
ns
BG/TG t_1D Bottom Gate Off to Top Gate On Delay C_LOAD = 3300pF Each Driver
Top Switch-On Delay Time
30
ns
t_ON(MIN)
Minimum On-Time
(Note 7)
95
ns
INTV_CC Linear Regulator
V_INTVCCVIN Internal V_CC Voltage
V_LDOVIN
INTV_CC Load Regulation
V_INTVCCEXT Internal V_CC Voltage
V_LDOEXT
INTV_CC Load Regulation
V_EXTVCC
EXTV_CC Switchover Voltage
6V < V_IN < 38V, V_EXTVCC = 0V
I_CC = 0mA to 50mA, V_EXTVCC = 0V
6V < V_EXTVCC < 13V
I_CC = 0mA to 50mA, V_EXTVCC = 8.5V
EXTV_CC Ramping Positive
4.85 5.1 5.35
V
0.7
1.1
%
4.85 5.1 5.35
V
0.6
1.1
%
4.5
4.7
4.9
V
V_LDOHYS
EXTV_CC Hysteresis
Oscillator and Phase-Locked Loop
250
mV
f_25kΩ
Programmable Frequency
f_65kΩ
Programmable Frequency
f_105kΩ
Programmable Frequency
f_LOW
Low Fixed Frequency
f_HIGH
High Fixed Frequency
f_SYNC
Synchronizable Frequency
PGOOD1 Output
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
105
kHz
375 440 505
kHz
835
kHz
320 350 380
kHz
485 535 585
kHz
l 75
850
kHz
V_PGL
I_PGOOD
PGOOD1 Voltage Low
PGOOD1 Leakage Current
I_PGOOD = 2mA
V_PGOOD = 5V
0.2
0.4
V
±1
μA
V_PG
PGOOD1 Trip Level
V_FB1 with Respect to Set Regulated Voltage
V_FB1 Ramping Negative
Hysteresis
–13 –10
–7
%
2.5
%
V_FB1 with Respect to Set Regulated Voltage
V_FB1 Ramping Positive
Hysteresis
7
10
13
%
2.5
%
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).
38571fc
4