EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
θ
JA
= 43°C/W,
θ
JC
= 5.5°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3999EMSE#PBF
LT3999IMSE#PBF
LT3999HMSE#PBF
LT3999MPMSE#PBF
LT3999EDD#PBF
LT3999IDD#PBF
TAPE AND REEL
LT3999EMSE#TRPBF
LT3999IMSE#TRPBF
LT3999HMSE#TRPBF
LT3999MPMSE#TRPBF
LT3999EDD#TRPBF
LT3999IDD#TRPBF
PART MARKING*
LTGKR
LTGKR
LTGKR
LTGKR
LGKQ
LGKQ
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead (3mm
×
3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–55°C to 150°C
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on nonstandard 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/
2
3999fa
For more information
www.linear.com/LT3999
LT3999
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V
PARAMETER
Input Supply and Shutdown
V
IN
Minimum Operating Voltage
V
IN
Overvoltage Lockout
V
IN
Supply Current
V
IN
Shutdown Current
UVLO Threshold (Rising)
UVLO Hysteresis
UVLO Pin Current
OVLO/DC Threshold (Rising)
OVLO/DC Hysteresis
OVLO/DC Pin Current
Power Switches (SWA, SWB)
Switch Saturation Voltage
Switch Current Limit
Non Overlap Time
Switch Base Drive Current
Oscillator/Sync
Switching Frequency
R
T
= 316k
R
T
= 49.9k
R
T
= 12.1k
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP
MAX
2.7
UNITS
V
V
mA
μA
V
mV
nA
V
mV
nA
mV
Internal, Rising
(Note 3)
V
UVLO
= 0.3V
l
36
40
4.3
0.1
42
1
1.35
100
1.35
100
l
1.15
1.25
125
10
V
UVLO
= 1.25V
l
1.15
1.25
125
10
350
V
OVLO/DC
= 1.25V
I
SW
= 1A
Internal Default
I
SW
= 1A
l
1.0
1.4
70
35
50
300
1000
1.5
200
1.7
A
ns
mA
kHz
kHz
kHz
kHz
V
kΩ
280
100
320
1000
Synchronization Frequency Range
SYNC Voltage Threshold
SYNC Pin Input Resistance
ILIM/SS
SWA and SWB Current Limit
ILIM/SS Pin Current
Duty Cycle
Switch Duty Cycle
OVLO/DC = 0.8V, R
DC
= 24.3k, R
T
= 49.9k
OVLO/DC = 0.612V, R
DC
= 24.3k, R
T
= 49.9k
OVLO/DC = 0.3V, R
DC
= 24.3k, R
T
= 49.9k
l
R
ILIM/SS
= 43.2k
l
0.4
0.5
10
20
25
48
0.6
A
μA
%
%
%
22
30
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 the device
reliability and lifetime.
Note 2:
The LT3999E 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
LT3999I Is guaranteed over the –40°C to 125°C operating junction
temperature range. The LT3999H is guaranteed over the full –40°C to
150°C operating junction temperature range. The LT3999MP is 100%
tested and guaranteed over the –55°C to 150°C junction temperature
range. High junction temperatures degrade operating lifetimes; operating
lifetime is derated for junction temperatures greater than 125°C.
Note 3:
Supply current specification does not include switch drive
currents. Actual supply currents will be higher.
3999fa
For more information
www.linear.com/LT3999
3
LT3999
TYPICAL PERFORMANCE CHARACTERISTICS
V
IN
Shutdown Current
2.5
400
375
SHUTDOWN CURRENT (µA)
2.0
1.5
FREQUENCY (kHz)
SWITCH V
CESAT
(mV)
0
25 50 75 100 125 150
TEMPERAURE (°C)
3999 G02
Switching Frequency
400
350
300
250
200
150
100
50
0
V
CESAT
vs Switch Current
350
325
300
275
250
225
1.0
0.5
0
–50 –25
0
25 50
75 100 125 150
TEMPERATURE (°C)
3999 G01
200
–50 –25
0 100 200 300 400 500 600 700 800 900 1000
SWITCH CURRENT (mA)
3999 G03
Switch V
CESAT
600
SWITCH CURRENT = 1A
3.0
2.5
SWITCH CURRENT (µA)
Switch Leakage Current
2000
1800
1600
CURRENT LIMIT (mA)
1400
1200
1000
800
600
400
200
0
25 50 75 100 125 150
TEMPERATURE (°C)
3999 G05
Switch Current Limit
500
SWITCH V
CESAT
(mV)
400
R
ILIM/SS
= OPEN
R
ILIM/SS
= 80.6k
2.0
1.5
1.0
0.5
0
–50 –25
300
R
ILIM/SS
= 43.2k
200
100
–50 –25
0
25 50
75 100 125 150
TEMPERATURE (°C)
3999 G04
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3999 G06
UVLO Threshold Voltage
1.40
1.35
1.30
UVLO PIN VOLTAGE (V)
1.25
1.20
1.15
1.10
1.05
1.00
0.95
0.90
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3999 G07
OVLO Threshold Voltage
1.40
1.35
OVLO PIN VOLTAGE (V)
UVLO RISING
1.30
1.25
1.20
1.15
1.10
1.05
1.00
0.95
0.90
–50 –25
0
OVLO RISING
UVLO FALLING
OVLO FALLING
25 50 75 100 125 150
TEMPERATURE (°C)
3999 G08
4
3999fa
For more information
www.linear.com/LT3999
LT3999
TYPICAL PERFORMANCE CHARACTERISTICS
Soft-Start (ILIM/SS) Current
14
13
SOFT-START CURRENT (µA)
12
DUTY CYCLE (%)
11
10
9
8
7
6
5
4
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3999 G09
Switch Duty Cycle
40
35
30
25
20
15
10
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3999 G10
PIN FUNCTIONS
SWA, SWB (Pin 1, Pin 10):
SWA and SWB pins are the
open-collector nodes of the power switches. These pins
drive the transformer and are connected to the outer ter-
minals of the center tapped transformer. Large currents
flow through these pins so keep PCB traces short and wide.
RBIAS (Pin 2):
The RBIAS pin sets the bias current of
the power switches (SWA and SWB). Connect the pin to
a 49.9k resistor to GND.
V
IN
(Pin 3):
The V
IN
pin is the main supply pin for the
switch driver and internal regulator. Short duration, high
current pulses are produced during the turn on and turn
off of the power switches. Connect a low ESR capacitor
of 4.7µF or greater.
UVLO (Pin 4):
The UVLO pin has a precision threshold
with hysteresis to implement an accurate V
IN
undervolt-
age lockout. The UVLO function disables switching and
sets the part into a low current shutdown mode. Connect
the UVLO pin directly to V
IN
or to a resistor divider string.
OVLO/DC (Pin 5):
The OVLO/DC pin has a precision thresh-
old with hysteresis to implement an accurate V
IN
overvolt-
age lockout. The OVLO function disables the switching.
Connect OVLO/DC pin to ground to disable the function
or to a resistor divider string to program the duty cycle.
RDC (Pin 6):
The RDC pin is the duty cycle control pin. A
resistor to ground sets the duty cycle. If unused leave the
pin floating or connect to the OVLO/DC pin.
RT (Pin 7):
The RT pin sets the switching frequency of
the power switches.
SYNC (Pin 8):
The SYNC pin synchronizes the part to an
external clock. Set the internal oscillator frequency below
the external clock frequency. Synchronizing the clock to
an external reference is useful for creating more stable
positioning of the switcher voltage or current harmonics.
Connect the SYNC pin to ground if not used.
ILIM/SS (Pin 9):
The ILIM/SS pin sets a threshold level
for the cycle by cycle maximum switch current. Imple-
ment soft-start with a capacitor, C
SS
, placed on this pin to
ground. An internal current source charges the capacitor.
The R
ILIM
, C
SS
time constant sets the soft-start time and
ramps the maximum switch current threshold at start-up.
If the ILIM/SS function is not used, float this pin and the
current limit will default to the internal limit.
GND (Pin 11):
The ground pin is the exposed pad of the
package. Solder the exposed pad directly to the ground
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