LTC3851A
4
3851afa
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 6V < V
IN
< 38V 4.8 5 5.2 V
V
LDO
INT INTV
CC
Load Regulation I
CC
= 0mA to 50mA 0.5 2 %
Oscillator and Phase-Locked Loop
f
NOM
Nominal Frequency R
FREQ
= 60k 460 500 540 kHz
f
LOW
Lowest Frequency R
FREQ
= 160k 205 235 265 kHz
f
HIGH
Highest Frequency R
FREQ
= 36k 690 750 810 kHz
R
MODE/PLLIN
MODE/PLLIN Input Resistance 100 kΩ
f
MODE
MODE/PLLIN Minimum Input Frequency
MODE/PLLIN Maximum Input Frequency
V
MODE
= External Clock
V
MODE
= External Clock
250
750
kHz
kHz
I
FREQ
Phase Detector Output Current
Sinking Capability
Sourcing Capability
f
MODE
> f
OSC
f
MODE
< f
OSC
–90
75
µA
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
Efficiency vs Output Current
and Mode
Efficiency vs Output Current
and Mode
LOAD CURRENT (mA)
10
40
EFFICIENCY(%)
50
60
70
80
100 1000 10000 100000
3851A G01
30
20
10
0
90
100
V
IN
= 12V
V
OUT
= 1.5V
BURST
CCM
PULSE
SKIP
LOAD CURRENT (mA)
10
40
EFFICIENCY(%)
50
60
70
80
100 1000 10000 100000
3851A G02
30
20
10
0
90
100
V
IN
= 12V
V
OUT
= 3.3V
FIGURE 11 CIRCUIT
BURST
CCM
PULSE
SKIP
LOAD CURRENT (mA)
10
40
EFFICIENCY (%)
50
60
70
80
100 1000 10000 100000
3851A G03
30
20
10
0
90
100
V
IN
= 12V
V
OUT
= 5V
BURST
CCM
PULSE
SKIP
