LTC3851-1_15 Datasheet, PDF (4/28 Pages) Linear Technology – Synchronous Step-Down Switching Regulator Controller

LTC3851-1
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T_A = 25°C. V_IN = 15V, V_RUN = 5V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
f_HIGH
Highest Frequency
R_MODE/PLLIN MODE/PLLIN Input Resistance
R_FREQ = 36k
710
750
790
kHz
100
kΩ
f_MODE
MODE/PLLIN Minimum Input Frequency V_MODE = External Clock
MODE/PLLIN Maximum Input Frequency V_MODE = External Clock
I_FREQ
Phase Detector Output Current
Sinking Capability
Sourcing Capability
f_MODE > f_OSC
f_MODE < f_OSC
PGOOD Output
250
kHz
750
kHz
–10
μA
10
μA
V_PGL
I_PGOOD
V_PG
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level
I_PGOOD = 2mA
V_PGOOD = 5V
V_FB with Respect to Set Regulated Voltage
V_FB Ramping Negative
V_FB Ramping Positive
0.1
0.3
V
±1
μA
–12
–10
–8
%
8
10
12
%
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 LTC3851E-1 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 LTC3851I-1 is guaranteed
over the –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:
LTC3851MSE-1: T_J = T_A + (P_D • 90°C/W)
LTC3851UD-1: T_J = T_A + (P_D • 68°C/W)
Note 4: The LTC3851-1 is tested in a feedback loop that servos V_ITH to a
specified voltage and measures the resultant V_FB.
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).
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Output Current and
Mode
100
V_IN = 12V
90 V_OUT = 1.5V
80
BURST
70
60
PULSE
SKIP
50
40
CCM
30
20
10
0
10
100
1000 10000 100000
LOAD CURRENT (mA)
38511 G01
Efficiency vs Output Current
and Mode
100
90
BURST
80
70
60
PULSE
50
SKIP
CCM
40
30
20
10
0
10
V_IN = 12V
V_OUT = 3.3V
FIGURE 11 CIRCUIT
100
1000 10000
LOAD CURRENT (mA)
100000
38511 G02
Efficiency vs Output Current and
Mode
100
90
80
BURST
70
60 ^PULSE
SKIP
50
CCM
40
30
20
10
0
10
V_IN = 12V
V_OUT = 5V
100
1000 10000
LOAD CURRENT (mA)
100000
38511 G03
38511fa
4