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

LTC3857
Electrical Characteristics The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T_A = 25°C. V_IN = 12V, V_RUN1,2 = 5V, EXTV_CC = 0V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX UNITS
t_ON(MIN)
Minimum On-Time
(Note 7)
95
ns
INTV_CC Linear Regulator
V_INTVCCVIN
V_LDOVIN
V_INTVCCEXT
V_LDOEXT
Internal V_CC Voltage
INTV_CC Load Regulation
Internal V_CC Voltage
INTV_CC Load Regulation
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
4.85
5.1
5.35
V
0.7
1.1
%
4.85
5.1
5.35
V
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
Oscillator and Phase-Locked Loop
250
mV
f_25kΩ
f_65kΩ
f_105kΩ
Programmable Frequency
Programmable Frequency
Programmable Frequency
R_FREQ = 25k, PLLIN/MODE = DC Voltage
R_FREQ = 65k, PLLIN/MODE = DC Voltage
R_FREQ = 105k, PLLIN/MODE = DC Voltage
105
kHz
375
440
505
kHz
835
kHz
f_LOW
Low Fixed Frequency
V_FREQ = 0V, PLLIN/MODE = DC Voltage
320
350
380
kHz
f_HIGH
High Fixed Frequency
f_SYNC
Synchronizable Frequency
PGOOD1 and PGOOD2 Outputs
V_FREQ = INTV_CC, PLLIN/MODE = DC Voltage
PLLIN/MODE = External Clock
485
535
585
kHz
l 75
850
kHz
V_PGL
I_PGOOD
PGOOD Voltage Low
PGOOD Leakage Current
I_PGOOD = 2mA
V_PGOOD = 5V
0.2
0.4
V
±1
µA
V_PG
PGOOD Trip Level
V_FB with Respect to Set Regulated Voltage
V_FB Ramping Negative
Hysteresis
–13
–10
–7
%
2.5
%
V_FB with Respect to Set Regulated Voltage
V_FB 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 4: The LTC3857 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 2: The LTC3857E 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 is guaranteed
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:
T_J = T_A + (P_D • 34°C/W)
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).
3857fa