LTC3851
4
3851fb
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25°C. V
IN
= 15V, V
RUN
= 5V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Oscillator and Phase-Locked Loop
f
NOM
Nominal Frequency R
FREQ
= 60k 480 500 530 kHz
f
LOW
Lowest Frequency R
FREQ
= 160k 220 250 280 kHz
f
HIGH
Highest Frequency R
FREQ
= 36k 710 750 790 kHz
R
MODE/PLLIN
MODE/PLLIN Input Resistance 100 k
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
–10
10
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 LTC3851E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3851I is guaranteed to meet
specifi cations over the –40°C to 125°C operating temperature range.
Note 3: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC3851GN: T
J
= T
A
+ (P
D
• 110°C/W)
LTC3851UD: T
J
= T
A
+ (P
D
• 68°C/W)
LTC3851MSE: T
J
= T
A
+ (P
D
• 40°C/W)
Note 4: The LTC3851 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
Effi ciency vs Output Current
and Mode
Effi ciency vs Output Current
and Mode
Effi ciency vs Output Current
and Mode
LOAD CURRENT (mA)
10
40
EFFICIENCY(%)
50
60
70
80
100 1000 10000 100000
3851 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
3851 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
3851 G03
30
20
10
0
90
100
V
IN
= 12V
V
OUT
= 5V
BURST
CCM
PULSE
SKIP
