LT3844
3
3844fc
For more information www.linear.com/LT3844
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 20V, V
CC
= BOOST = BURST_EN = 10V, SHDN = 2V, R
SET
= 49.9k,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = SYNC = 0V, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
V
CC
Operating Voltage Range (Note 5)
V
CC
Output Voltage
V
CC
UVLO Threshold (Rising)
V
CC
UVLO Threshold Hysteresis
Over Full Line and Load Range
l
l
8
6.25
500
20
8.3
V
V
V
mV
V
CC
Supply Current (Note 6)
V
CC
Burst Mode Current
V
CC
Shutdown Current
V
CC
Current Limit
V
BURST_EN
= 0V
V
SHDN
= 0V
l
l
–40
1.7
95
20
–120
2.1 mA
µA
µA
mA
Error Amp Reference Voltage Measured at V
FB
Pin
l
1.224
1.215
1.231 1.238
1.245
V
V
V
FB
Pin Input Current V
FB
= 1.231V 25 nA
SHDN Enable Threshold (Rising)
SHDN Threshold Hysteresis
l
1.3 1.35
120
1.4 V
mV
Sense Pins Common Mode Range
Current Limit Sense Voltage
V
SENSE
+
– V
SENSE
–
l
l
0
90
100
36
115
V
mV
Input Current
(I
SENSE
+
+ I
SENSE
–
)
V
SENSE(CM)
= 0V
V
SENSE(CM)
= 2V
V
SENSE(CM)
> 4V
350
–25
–170
µA
µA
µA
Operating Frequency
l
290
270
300 310
330
kHz
kHz
Minimum Programmable Frequency
Maximum Programmable Frequency
l
l
500
100 kHz
kHz
External Sync Frequency Range
l
100 600 kHz
SYNC Input Resistance 40 kΩ
SYNC Voltage Threshold
l
1.4 2 V
Soft-Start Capacitor Control Current 2 µA
Error Amp Transconductance
l
270 340 410 µS
Error Amp DC Voltage Gain 62 dB
Error Amp Sink/Source Current ±30 µA
TG Drive On Voltage (Note 7)
TG Drive Off Voltage
C
LOAD
= 2200pF
C
LOAD
= 2200pF
9.8
0.1
V
V
TG Drive Rise/Fall Time 10% to 90% or 90% to 10%, C
LOAD
= 2200pF 40 ns
Minimum TG Off Time
l
350 500 ns
Minimum TG On Time
l
250 350 ns
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 LT3844 includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 3: The LT3844E is guaranteed to meet performance specifications from
0°C to 125°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 LT3844I is guaranteed
over the full –40°C to 125°C operating junction temperature range.
Note 4: V
IN
voltages below the start-up threshold (7.5V) are only
supported when the V
CC
is externally driven above 6.5V.
Note 5: Operating range is dictated by MOSFET absolute maximum VGS.
Note 6: Supply current specification does not include switch drive
currents. Actual supply currents will be higher.
Note 7: DC measurement of gate drive output “ON” voltage is typically
8.6V. Internal dynamic bootstrap operation yields typical gate “ON”
voltages of 9.8V during standard switching operation. Standard operation
gate “ON” voltage is not tested but guaranteed by design.
Note 8: The –1V
absolute maximum on the SW pin is a transient condition.
It is guaranteed by design and not subject to test.
