LTC3851A_15 Datasheet, PDF (4/30 Pages) Linear Technology – Synchronous Step-Down Switching Regulator Controller

LTC3851A
Electrical Characteristics The l denotes the specifications which apply over the specified operating
temperature range, otherwise specifications are at T_A = 25°C (Note 2). V_IN = 15V, V_RUN = 5V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
INTV_CC Linear Regulator
V_INTVCC
Internal V_CC Voltage
V_LDO INT INTV_CC Load Regulation
Oscillator and Phase-Locked Loop
6V < V_IN < 38V
I_CC = 0mA to 50mA
4.8
5
5.2
V
0.5 2
%
f_NOM
Nominal Frequency
R_FREQ = 60k
460 500 540 kHz
f_LOW
Lowest Frequency
f_HIGH
Highest Frequency
R_MODE/PLLIN MODE/PLLIN Input Resistance
f_MODE
MODE/PLLIN Minimum Input Frequency
MODE/PLLIN Maximum Input Frequency
I_FREQ
Phase Detector Output Current
Sinking Capability
Sourcing Capability
R_FREQ = 160k
R_FREQ = 36k
V_MODE = External Clock
V_MODE = External Clock
f_MODE > f_OSC
f_MODE < f_OSC
205 235 265 kHz
690 750 810 kHz
100
kΩ
250
kHz
750
kHz
–90
µA
75
µA
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 LTC3851A is tested under pulsed load conditions such that
T_A ≈ T_J. The LTC3851AE is guaranteed to meet performance specifications
from 0°C to 85°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3851AI is guaranteed to meet specifications over the –40°C to 125°C
operating junction temperature range, the LTC3851AH is guaranteed
over the –40°C to 150°C operating junction temperature range and the
LTC3851AMP is tested and guaranteed over the –55°C to 150°C operating
junction temperature range. High junction temperatures degrade operating
lifetimes; operating lifetime is derated for junction temperatures greater
than 125°C. Note that the maximum ambient temperature consistent with
these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance 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 formulas:
LTC3851AGN: T_J = T_A + (P_D • 110°C/W)
LTC3851AUD: T_J = T_A + (P_D • 68°C/W)
LTC3851AMSE: T_J = T_A + (P_D • 40°C/W)
Note 4: The LTC3851A 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. Rise and fall times are assured by
design, characterization and correlation with statistical process controls.
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; not tested in production.
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)
3851A 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
3851A G02
4
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 100000
LOAD CURRENT (mA)
3851A G03
3851afa