Datasheet

LTC3891
5
3891fa
TYPICAL PERFORMANCE CHARACTERISTICS
OUTPUT CURRENT (A)
FIGURE 12 CIRCUIT
0
EFFICIENCY (%)
POWER LOSS (mW)
70
100
10.10.010.0010.0001 10
3891 G01
50
40
30
20 1
10
100
1000
10000
0.1
10
60
80
90
V
IN
= 12V
V
OUT
= 3.3V
BURST EFFICIENCY
FCM LOSS
PULSE-SKIPPING
LOSS
BURST LOSS
FCM EFFICIENCY
PULSE-SKIPPING
EFFICIENCY
OUTPUT CURRENT (A)
0
EFFICIENCY (%)
70
100
10.10.010.0010.0001 10
3891 G02
50
40
30
20
10
60
80
90
V
OUT
= 8.5V
V
OUT
= 3.3V
V
IN
= 12V
Burst Mode OPERATION
FIGURES 12, 14 CIRCUITS
INPUT VOLTAGE (V)
80
EFFICIENCY (%)
94
100
20 30 35 40 45 50 55 60151050 25
3891 G03
90
88
86
84
82
92
96
98
V
OUT
= 3.3V
V
OUT
= 8.5V
I
LOAD
= 2A
FIGURES 12, 14 CIRCUITS
Efficiency and Power Loss vs
Output Current
Efficiency vs Output Current Efficiency vs Input Voltage
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 LTC3891 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC3891E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3891I is guaranteed
over the –40°C to 125°C operating junction temperature range, the
LTC3891H is guaranteed over the –40°C to 150°C operating junction
temperature range and the LTC3891MP 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: The junction temperature (T
J
, in °C) is calculated from the ambient
temperature (T
A
, in °C) and power dissipation (P
D
, in Watts) according to
the formula:
T
J
= T
A
+ (P
D
• θ
JA
), where θ
JA
is 43°C/W for the QFN or 38°C/W for the
TSSOP.
Note 4: The LTC3891 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
FB
. The specification at
85°C is not tested in production and is assured by design, characterization
and correlation to production testing at other temperatures (125°C for
the LTC3891E/LTC3891I, 150°C for the LTC3891H/LTC3891MP). For the
LTC3891MP, the specification at –40°C is not tested in production and is
assured by design, characterization and correlation to production testing
at –55°C.
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).
ELECTRICAL CHARACTERISTICS