Datasheet

LTC3850/LTC3850-1
5
38501fc
Efficiency vs Output Current
and Mode
Efficiency and Power Loss
vs Input Voltage
ELECTRICAL CHARACTERISTICS
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 LTC3850E/LTC3850E-1 are 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 LTC3850I/LTC3850I-1 are
guaranteed to meet performance specifications over the –40°C to 85°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:
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 15V, V
RUN1,2
= 5V, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Oscillator and Phase-Locked Loop
f
NOM
Nominal Frequency V
FREQ
= 1.2V 450 500 550 kHz
f
LOW
Lowest Frequency V
FREQ
= 0V 210 250 290 kHz
f
HIGH
Highest Frequency V
FREQ
≥ 2.4V 700 780 860 kHz
R
MODE/PLLIN
MODE/PLLIN Input Resistance 250 kΩ
I
FREQ
Phase Detector Output Current
Sinking Capability
Sourcing Capability
f
MODE
< f
OSC
f
MODE
> f
OSC
–13
13
µA
µA
PGOOD Output
V
PGL
PGOOD Voltage Low I
PGOOD
= 2mA 0.1 0.3 V
I
PGOOD
PGOOD Leakage Current V
PGOOD
= 5V ±2 µA
V
PG
PGOOD Trip Level V
FB
with Respect to Set Regulated Voltage
V
FB
Ramping Negative
V
FB
Ramping Positive
–5
5
–7.5
7.5
–10
10
%
%
LTC3850GN: T
J
= T
A
+ (P
D
• 95°C/W)
LTC3850UF: T
J
= T
A
+ (P
D
• 37°C/W)
LTC3850UFD: T
J
= T
A
+ (P
D
• 43°C/W)
Note 4: The LTC3850 is tested in a feedback loop that servos V
ITH1,2
to a
specified voltage and measures the resultant V
FB1,2
.
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).
Note 8: V
SENSE(MAX)
defaults to 50mV typical for the LTC3850-1.
Efficiency vs Output Current
and Mode
LOAD CURRENT (mA)
CIRCUIT OF FIGURE 14
10
40
EFFICIENCY (%)
50
60
70
80
100 1000 10000
30
20
10
0
90
100
38501 G01
BURST
DCM
CCM
V
IN
= 12V
V
OUT
= 1.8V
LOAD CURRENT (mA)
10
40
EFFICIENCY (%)
50
60
70
80
100 1000 10000
30
20
10
0
90
100
38501 G02
BURST
DCM
CCM
CIRCUIT OF FIGURE 14
V
IN
= 12V
V
OUT
= 3.3V
INPUT VOLTAGE (V)
5
80
EFFICIENCY (%)
POWER LOSS (mW)
90
100
95
10
15
85
0
1000
2000
500
1500
20 25
38501 G03
POWER LOSS
EFFICIENCY
CIRCUIT OF FIGURE 14
V
OUT
= 3.3V
I
OUT
= 2A
TYPICAL PERFORMANCE CHARACTERISTICS