Maximum Junction Temperature .......................... 125°C
Operating Junction Temperature Range (Note 2)
LT3573E ............................................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
GND
TEST
GND
SW
V
IN
BIAS
SHDN/UVLO
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GND
TC
R
REF
R
FB
V
C
R
ILIM
SS
GND
17
MSE PACKAGE
16-LEAD PLASTIC MSOP
θ
JA
= 50°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE CONNECTED TO GND
ORDER INFORMATION
LEAD FREE FINISH
LT3573EMSE#PBF
LT3573IMSE#PBF
TAPE AND REEL
LT3573EMSE#TRPBF
LT3573IMSE#TRPBF
PART MARKING*
3573
3573
PACKAGE DESCRIPTION
16-Lead Plastic MSOP
16-Lead Plastic MSOP
TEMPERATURE RANGE
–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.
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/
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Voltage Range
Quiescent Current
Soft-Start Current
SHDN/UVLO
Pin Threshold
SHDN/UVLO
Pin Hysteresis Current
Soft-Start Threshold
Maximum Switching Frequency
Switch Current Limit
Minimum Current Limit
Switch V
CESAT
R
REF
Voltage
R
REF
Voltage Line Regulation
R
REF
Pin Bias Current
I
REF
Reference Current
R
ILIM
= 10k
V
C
= 0V
I
SW
= 0.5A
V
IN
= 3V
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, unless otherwise noted.
CONDITIONS
l
MIN
3
TYP
3.5
0
7
MAX
40
1
1.29
3
UNITS
V
mA
µA
µA
V
µA
V
kHz
SS = 0V
V
SHDN/UVLO
= 0V
SS = 0.4V
UVLO Pin Voltage Rising
V
UVLO
= 1V
l
1.15
2
1.22
2.5
0.7
1000
1.25
1.55
200
150
1.85
250
1.25
1.25
0.03
600
A
mA
mV
V
%/ V
nA
µA
l
1.21
1.20
1.23
0.01
3V < V
IN
< 40V
(Note 3)
Measured at R
FB
Pin with R
REF
= 6.49k
l
100
190
3573fd
2
For more information
www.linear.com/LT3573
LT3573
ELECTRICAL CHARACTERISTICS
PARAMETER
Error Amplifier Voltage Gain
Error Amplifier Transconductance
Minimum Switching Frequency
TC Current into R
REF
BIAS Pin Voltage
V
IN
= 3V
DI
= 10µA, V
IN
= 3V
V
C
= 0.35V
R
TC
= 20.1k
I
BIAS
= 30mA
2.9
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, unless otherwise noted.
CONDITIONS
MIN
TYP
150
150
40
27.5
3
3.1
to 125°C operating junction temperature range are assured by design
characterization and correlation with statistical process controls. The
LT3573I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3:
Current flows out of the R
REF
pin.
MAX
UNITS
V/V
µmhos
kHz
µA
V
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 LT3573E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage
5.20
5.15
5.10
V
OUT
(V)
5.05
I
Q
(mA)
5.00
4.95
4.90
4.85
4.80
–50
–25
50
0
25
75
TEMPERATURE (°C)
100
125
7
6
5
4
3
2
1
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
V
IN
= 5V
V
IN
= 40V
T
A
= 25°C, unless otherwise noted.
Quiescent Current
3.2
3.0
BIAS VOLTAGE (V)
2.8
2.6
2.4
2.2
Bias Pin Voltage
V
IN
= 40V
V
IN
= 12V
100
125
2.0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3573 G01
3573 G02
3573 G03
3573fd
For more information
www.linear.com/LT3573
3
LT3573
TYPICAL PERFORMANCE CHARACTERISTICS
Switch V
CESAT
400
350
SWITCH V
CESAT
VOLTAGE (mV)
CURRENT LIMIT (A)
300
250
200
150
100
50
0
0
0.25
0.50 0.75 1.00
SWITCH CURRENT (A)
1.25
1.50
125°C
–50°C
25°C
T
A
= 25°C, unless otherwise noted.
Switch Current Limit
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–50
–25
MINIMUM CURRENT LIMIT
RILIM = 10k
CURRENT LIMIT (A)
MAXIMUM CURRENT LIMIT
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
100
125
0
Switch Current Limit vs R
ILIM
0
25
50
75
0
10
20
30
40
50
3573 G06
TEMPERATURE (°C)
3573 G04
3573 G05
R
ILIM
RESISTANCE (k)
SHDN/UVLO
Falling Threshold
1.28
12
10
SS PIN CURRENT (µA)
3573 G07
SS Pin Current
SHDN/UVLO
VOLTAGE (V)
1.26
8
6
4
2
0
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
3573 G08
1.24
1.22
1.20
1.18
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
3573fd
4
For more information
www.linear.com/LT3573
LT3573
PIN FUNCTIONS
GND:
Ground.
TEST:
This pin is used for testing purposes only and must
be connected to ground for the part to operate properly.
SW:
Collector Node of the Output Switch. This pin has
large currents flowing through it. Keep the traces to the
switching components as short as possible to minimize
electromagnetic radiation and voltage spikes.
V
IN
: Input Voltage. This pin supplies current to the internal
start-up circuitry and as a reference voltage for the DCM
comparator and feedback circuitry. This pin must be locally
bypassed with a capacitor.
BIAS:
Bias Voltage. This pin supplies current to the switch
driver and internal circuitry of the LT3573. This pin must
be locally bypassed with a capacitor. This pin may also be
connected to V
IN
if a third winding is not used and if V
IN
≤ 15V. If a third winding is used, the BIAS voltage should
be lower than the input voltage for proper operation.
SHDN/UVLO:
Shutdown/Undervoltage Lockout. A resistor
divider connected to V
IN
is tied to this pin to program the
minimum input voltage at which the LT3573 will operate.
At a voltage below ~0.7V, the part draws no quiescent
current. When below 1.22V and above ~0.7V, the part will
draw 10µA of current, but internal circuitry will remain off.
Above 1.25V, the internal circuitry will start and a 10µA
current will be fed into the SS pin. When this pin falls
below 1.25V, 2.5µA will be pulled from the pin to provide
programmable hysteresis for UVLO.
R
ILIM
: Maximum Current Limit Adjust Pin. A resistor
should be tied to this pin to ground to set the current
limit. Use a 10k resistor for the full current capabilities
of the switch.
SS:
Soft-Start Pin. Place a soft-start capacitor here to
limit start-up inrush current and output voltage ramp
rate. Switching starts when the voltage at this pin reaches
~0.7V.
V
C
: Compensation Pin for Internal Error Amplifier. Connect
a series RC from this pin to ground to compensate the
switching regulator. A 100pF capacitor in parallel helps
eliminate noise.
R
FB
: Input Pin for External Feedback Resistor. This pin is
connected to the transformer primary (V
SW
). The ratio
of this resistor to the R
REF
resistor, times the internal
bandgap reference, determines the output voltage (plus
the effect of any non-unity transformer turns ratio). The
average current through this resistor during the flyback
period should be approximately 200µA. For nonisolated
applications, this pin should be connected to V
IN
.
R
REF
: Input Pin for External Ground-Referred Reference
Resistor. This resistor should be in the range of 6k, but
for convenience, need not be precisely this value. For
nonisolated applications, a traditional resistor voltage
divider may be connected to this pin.
T
C
: Output Voltage Temperature Compensation. Connect
a resistor to ground to produce a current proportional to
absolute temperature to be sourced into the R
REF
node.
I
TC
= 0.55V/R
TC
.
Exposed Pad:
Ground. The Exposed Pad of the package
provides both electrical contact to ground and good thermal
contact to the printed circuit board. The Exposed Pad must
be soldered to the circuit board for proper operation and
should be well connected with many vias to an internal
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