Maximum Junction Temperature .......................... 125°C
Operating Junction Temperature Range
(Note 2).................................................. –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
VC
R
ILIM
SS
GND
MS PACKAGE
16-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 120°C/W,
θ
JC
= 21°C/W
orDer inForMation
LEAD FREE FINISH
LT3574EMS#PBF
LT3574IMS#PBF
TAPE AND REEL
LT3574EMS#TRPBF
LT3574IMS#TRPBF
PART MARKING*
3574
3574
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
Error Amplifier Voltage Gain
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
R
ILIM
= 10k
V
C
= 0V
I
SW
= 0.5A
V
IN
= 3V
l
0.65
0.9
100
150
1.1
250
1.25
1.25
0.03
600
A
mA
mV
V
%/ V
nA
µA
V/V
1.21
1.20
1.23
0.01
3V < V
IN
< 40V
(Note 3)
Measured at R
FB
Pin with R
REF
= 6.49k
V
IN
= 3V
l
100
190
150
3574f
LT3574
electrical characteristics
PARAMETER
Error Amplifier Transconductance
Minimum Switching Frequency
TC Current into R
REF
BIAS Pin Voltage
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
DI
= 10µA, V
IN
= 3V
V
C
= 0.35V
R
TC
= 20.1k
I
BIAS
= 30mA
2.9
MIN
TYP
150
40
27.5
3
3.1
MAX
UNITS
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 LT3574E 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
LT3574I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3:
Current flows out of the R
REF
pin.
typical perForMance characteristics
Output Voltage
5.20
5.15
5.10
V
OUT
(V)
5.05
5.00
4.95
4.90
4.85
4.80
–50
–25
50
0
25
75
TEMPERATURE (°C)
100
125
QUIESCENT CURRENT (mA)
6
5
4
3
2
1
0
–50 –25
V
IN
= 40V
BIAS = 20V
T
A
= 25°C, unless otherwise noted.
Bias Pin Voltage
3.2
3.0
BIAS VOLTAGE (V)
2.8
2.6
2.4
2.2
2.0
–50
V
IN
= 40V
V
IN
= 12V
Quiescent Current
V
IN
= 5V
BIAS = 5V
50
25
75
0
TEMPERATURE (°C)
100
125
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3574 G01
3574 G02
3574 G03
3574f
LT3574
typical perForMance characteristics
Switch Saturation Voltage
300
250
200
150
125°C
100
50
0
25°C
–50°C
1200
1000
CURRENT LIMIT (mA)
800
600
400
200
0
–50 –25
MINIMUM CURRENT LIMIT
50
25
75
0
TEMPERATURE (°C)
100
125
MAXIMUM CURRENT LIMIT
T
A
= 25°C, unless otherwise noted.
Switch Current Limit vs R
ILIM
Switch Current Limit
R
ILIM
= 10k
SWITCH CURRENT LIMIT (A)
1.2
1.0
0.8
0.6
0.4
0.2
0
SWITCH V
CESAT
VOLTAGE (mV)
0 100 200 300 400 500 600 700 800 900
SWITCH CURRENT (mA)
3574 G04
1
10
20
30
40
R
ILIM
RESISTANCE (k )
50
3574 G06
3574 G05
SHDN/UVLO
Falling Threshold
1.28
12
10
SS PIN CURRENT (µA)
3574 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)
3574 G08
1.24
1.22
1.20
1.18
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
3574f
LT3574
pin Functions
BIAS:
Bias Voltage. This pin supplies current to the switch
driver and internal circuitry of the LT3574. 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.
GND:
Ground.
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
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.
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.
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 LT3574 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 1.22V, the internal circuitry will start and a 7µA
current will be fed into the SS pin. When this pin falls
below 1.22V, 2.5µA will be pulled from the pin to provide
programmable hysteresis for UVLO.
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.
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.
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
.
TEST:
This pin is used for testing purposes only and must
be connected to ground for the part to operate properly.
VC:
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.
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
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