FEATURES
n
n
n
n
n
n
n
n
n
n
n
n
n
LT3800
High-Voltage Synchronous
Current Mode Step-Down
Controller
DESCRIPTION
The LT
®
3800 is a 200kHz fixed frequency high voltage
synchronous current mode step-down switching regulator
controller. The IC drives standard gate N-channel power
MOSFETs and can operate with input voltages from 4V to
60V. An onboard regulator provides IC power directly from
V
IN
and provides for output-derived power to minimize
V
IN
quiescent current. MOSFET drivers employ an internal
dynamic bootstrap feature, maximizing gate-source “ON”
voltages during normal operation for improved operating
efficiencies. The LT3800 incorporates Burst Mode
®
opera-
tion, which reduces no load quiescent current to under
100μA. Light load efficiencies are also improved through
a reverse inductor current inhibit, allowing the controller
to support discontinuous operation. Both Burst Mode
operation and the reverse-current inhibit features can be
disabled if desired. The LT3800 incorporates a program-
mable soft-start that directly controls the voltage slew rate
of the converter output for reduced startup surge currents
and overshoot errors. The LT3800 is available in a 16-lead
thermally enhanced TSSOP package.
L,
LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and No R
SENSE
and ThinSOT are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
5481178, 6611131, 6304066, 6498466, 6580258.
Wide 4V to 60V Input Voltage Range
Output Voltages up to 36V
Adaptive Nonoverlap Circuitry Prevents Switch
Shoot-Through
Reverse Inductor Current Inhibit for Discontinuous
Operation Improves Efficiency with Light Loads
Output Slew Rate Controlled Soft-Start with
Auto-Reset
100μA No Load Quiescent Current
Low 10μA Current Shutdown
1% Regulation Accuracy
200kHz Operating Frequency
Standard Gate N-Channel Power MOSFETs
Current Limit Unaffected by Duty Cycle
Reverse Overcurrent Protection
16-Lead Thermally Enhanced TSSOP Package
APPLICATIONS
n
n
n
n
12V and 42V Automotive and Heavy Equipment
48V Telecom Power Supplies
Avionics and Industrial Control Systems
Distributed Power Converters
TYPICAL APPLICATION
12V 75W DC/DC Converter with Reverse Current Inhibit and Input UVLO
V
IN
20V TO 55V
Efficiency and Power Loss
+
56μF
×2
1M
82.5k
1.5nF
SHDN
200k
C
SS
20k
1%
174k
1%
BURST_EN
V
FB
V
C
100pF
82.5k
680pF
V
CC
1μF
BG
PGND
70
0.1
0.015Ω
1
I
LOAD
(A)
3800 TA01b
V
IN
BOOST
1μF
TG
LT3800
SW
BAS19
1μF
×3
Si7850DP
EFFICIENCY (%)
100
V
IN
= 24V
95
90
85
80
LOSS (48V)
B160
75
V
IN
= 36V
V
IN
= 60V
V
IN
= 48V
6
5
POWER LOSS (W)
4
3
2
1
0
1N4148
Si7370DP
15μH
SENSE
–
SENSE
+
SGND
10
+
10μF
V
OUT
12V AT 75W
270μF
3800 TA01a
3800fc
1
LT3800
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
Supply Voltages
Input Supply Pin (V
IN
)............................... –0.3V to 65V
Boosted Supply Pin (BOOST).................... –0.3V to 80V
Boosted Supply Voltage (BOOST – SW) ... –0.3V to 24V
Boosted Supply Reference Pin (SW)............ –2V to 65V
Local Supply Pin (V
CC
).............................. –0.3V to 24V
Input Voltages
SENSE
+
, SENSE
–
...................................... –0.3V to 40V
SENSE
+
– SENSE
–
......................................... –1V to 1V
BURST_EN Pin.......................................... –0.3V to 24V
Other Inputs (SHDN, C
SS
, V
FB
, V
C
) .......... –0.3V to 5.0V
Input Currents
SHDN,
C
SS
............................................... –1mA to 1mA
Maximum Temperatures
Operating Junction Temperature Range (Note 2)
LT3800E (Note 3) .............................. –40°C to 125°C
LT3800I ............................................. –40°C to 125°C
Storage Temperature Range.................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................. 300°C
TOP VIEW
V
IN
NC
SHDN
C
SS
BURST_EN
V
FB
V
C
SENSE
–
1
2
3
4
5
6
7
8
17
16 BOOST
15 TG
14 SW
13 NC
12 V
CC
11 BG
10 PGND
9
SENSE
+
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 17) IS SGND
MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3800EFE#PBF
LT3800IFE#PBF
TAPE AND REEL
LT3800EFE#TRPBF
LT3800IFE#TRPBF
PART MARKING
3800EFE
3800IFE
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
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,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = 0V, CTG = CBG = 3300pF unless otherwise noted.
,
SYMBOL
V
IN
PARAMETER
Operating Voltage Range (Note 4)
Minimum Start Voltage
UVLO Threshold (Falling)
UVLO Hysteresis
V
IN
Supply Current
V
IN
Burst Mode Current
V
IN
Shutdown Current
Operating Voltage
Operating Voltage Range (Note 5)
UVLO Threshold (Rising)
UVLO Hysteresis
V
CC
> 9V
V
BURST_EN
= 0V, V
FB
= 1.35V
V
SHDN
= 0V
V
BOOST
– V
SW
V
BOOST
– V
SW
V
BOOST
– V
SW
CONDITIONS
●
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
4
7.5
3.65
TYP
MAX
60
UNITS
V
V
V
mV
μA
μA
μA
V
V
V
V
3800fc
3.80
670
20
20
8
3.95
I
VIN
15
75
20
V
BOOST
●
●
5
0.4
2
LT3800
ELECTRICAL CHARACTERISTICS
SYMBOL
I
BOOST
PARAMETER
BOOST Supply Current (Note 6)
BOOST Burst Mode Current
BOOST Shutdown Current
Operating Voltage (Note 5)
Output Voltage
UVLO Threshold (Rising)
UVLO Hysteresis
V
CC
Supply Current (Note 6)
V
CC
Burst Mode Current
V
CC
Shutdown Current
Short-Circuit Current
Enable Threshold (Rising)
Threshold Hysteresis
Common Mode Range
Current Limit Sense Voltage
Reverse Protect Sense Voltage
Reverse Current Offset
Input Current
(I
SENSE+
+ I
SENSE–
)
Operating Frequency
●
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,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = 0V, CTG = CBG = 3300pF unless otherwise noted.
,
CONDITIONS
V
BURST_EN
= 0V
V
SHDN
= 0V
●
●
MIN
TYP
1.4
0.1
0.1
8.0
6.25
500
3
80
20
–120
1.35
120
150
–150
10
0.8
–20
–0.3
MAX
UNITS
mA
μA
μA
V
CC
20
8.3
V
V
V
mV
mA
μA
μA
mA
V
mV
mV
mV
mV
mA
μA
mA
I
VCC
●
3.6
V
BURST_EN
= 0V
V
SHDN
= 0V
●
●
●
●
–40
1.30
0
140
V
SHDN
V
SENSE
1.40
36
175
V
SENSE+
– V
SENSE–
V
SENSE+
– V
SENSE–
, V
BURST_EN
= V
CC
V
BURST_EN
= 0V or V
BURST_EN
= V
FB
V
SENSE(CM)
= 0V
V
SENSE(CM)
= 2.75V
V
SENSE(CM)
> 4V
I
SENSE
f
O
V
FB
I
FB
V
FB(SS)
I
CSS
g
m
A
V
V
C
I
VC
V
TG,BG
t
TG,BG
t
TG(OFF)
t
TG(ON)
t
NOL
190
175
1.224
1.215
200
1.231
25
210
220
1.238
1.245
kHz
kHz
V
V
nA
V
mV
μA
Error Amp Reference Voltage
Feedback Input Current
Soft-Start Disable Voltage
Soft-Start Disable Hysteresis
Soft-Start Capacitor Control Current
Error Amp Transconductance
Error Amp DC Voltage Gain
Error Amp Output Range
Error Amp Sink/Source Current
Gate Drive Output On Voltage (Note 7)
Gate Drive Output Off Voltage
Gate Drive Rise/Fall Time
Minimum Off Time
Minimum On Time
Gate Drive Nonoverlap Time
Measured at V
FB
Pin
●
V
FB
Rising
1.185
300
2
●
275
350
62
1.2
±30
9.8
0.1
400
μmhos
dB
V
μA
V
V
ns
ns
Zero Current to Current Limit
10% to 90% or 90% to 10%
●
50
450
300
200
150
500
ns
ns
ns
TG Fall to BG Rise
BG Fall to TG Rise
3800fc
3
LT3800
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:
This IC 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 LT3800E 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
LT3800I 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 V
CC
is externally driven above 6.5V.
Note 5:
Operating range dictated by MOSFET absolute maximum gate-
source voltage ratings.
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Threshold (Rising)
vs Temperature
1.37
SHUTDOWN THRESHOLD, FALLING (V)
SHUTDOWN THRESHOLD, RISING (V)
1.240
Shutdown Threshold (Falling)
vs Temperature
8.1
V
CC
vs Temperature
1.36
1.235
8.0
1.230
V
CC
(V)
I
CC
= 0mA
1.35
I
CC
= 20mA
7.9
1.34
1.225
1.33
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1.220
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
7.8
–50
–25
0
50
75
25
TEMPERATURE (°C)
100
125
3800 G01
3800 G02
3800 G03
V
CC
vs I
CC(LOAD)
8.05
8
T
A
= 25°C
7
8.00
V
CC
(V)
6
V
CC
vs V
IN
I
CC
= 20mA
T
A
= 25°C
I
CC
CURRENT LIMIT (mA)
4
5
6
7
8
V
IN
(V)
3800 G04
3800 G05
I
CC
Current Limit vs Temperature
200
175
150
125
100
75
50
–50
V
CC
(V)
7.95
5
7.90
4
7.85
3
0
5
10
15 20 25
I
CC(LOAD)
(mA)
30
35
40
9
10
11
12
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3800 G06
3800fc
4
LT3800
TYPICAL PERFORMANCE CHARACTERISTICS
V
CC
UVLO Threshold (Rising)
vs Temperature
6.30
V
CC
UVLO THRESHOLD, RISING (V)
25
I
CC
vs V
CC
(SHDN = 0V)
ERROR AMP TRANSCONDUCTANCE (μmho)
T
A
= 25°C
380
Error Amp Transconductance
vs Temperature
20
6.25
I
CC
(μA)
15
360
10
6.20
5
340
6.15
–50
0
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0
2
4
6
8
10 12 14 16 18 20
V
CC
(V)
3800 G12
320
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3800 G07
3800 G08
I
(SENSE+ + SENSE–)
vs V
SENSE(CM)
800
600
I
(SENSE+ + SENSE
–
)
(μA)
400
200
0
–200
–400
T
A
= 25°C
OPERATING FREQUENCY (kHz)
220
Operating Frequency
vs Temperature
1.232
Error Amp Reference
vs Temperature
210
ERROR AMP REFERENCE (V)
1.231
1.230
200
1.229
190
1.228
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
SENSE(CM)
(V)
3800 G09
180
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1.227
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3800 G10
3800 G11
PIN FUNCTIONS
V
IN
(Pin 1):
Converter Input Supply.
NC (Pin 2):
No Connection.
SHDN
(Pin 3):
Precision Shutdown Pin. Enable threshold
is 1.35V (rising) with 120mV of input hysteresis. When
in shutdown mode, all internal IC functions are disabled.
The precision threshold allows use of the
SHDN
pin to
incorporate UVLO functions. If the
SHDN
pin is pulled
below 0.7V, the IC enters a low current shutdown mode
with I
VIN
< 10μA. In low-current shutdown, the IC will
sink 20μA from the V
CC
pin until that local supply has
collapsed. Typical pin input bias current is <10nA and the
pin is internally clamped to 6V.
C
SS
(Pin 4):
Soft-Start AC Coupling Capacitor Input.
Connect capacitor (C
SS
) in series with a 200k resistor
from pin to converter output (V
OUT
). Controls converter
start-up output voltage slew rate (∆V
OUT
/∆t). Slew rate
corresponds to 2μA average current through the soft-start
coupling capacitor. The capacitor value for a desired output
startup slew rate follows the relation:
C
SS
= 2μA/(∆V
OUT
/∆t)
Shorting this pin to SGND disables the soft-start function
BURST_EN (Pin 5):
Burst Mode Operation Enable Pin.
This pin also controls reverse-inhibit mode of operation.
When the pin voltage is below 0.5V, Burst Mode operation
3800fc
5
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
