Maximum Junction Temperature .......................... 125°C
Operating Junction Temperature Range (Note 2)
LT3575E, LT3575I .............................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
NC
V
IN
SW
SW
BIAS
SHDN/UVLO
SS
R
ILIM
1
2
3
4
5
6
7
8
17
GND
16
NC
15
NC
14 GND
13 TEST
12
TC
11
R
REF
10
R
FB
9
V
C
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 38°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE CONNECTED TO GND
ORDER INFORMATION
LEAD FREE FINISH
LT3575EFE#PBF
LT3575IFE#PBF
TAPE AND REEL
LT3575EFE#TRPBF
LT3575IFE#TRPBF
PART MARKING*
3575FE
3575FE
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. *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
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
4.5
0
7
MAX
40
1
1.32
3.2
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
2.2
1.22
2.8
0.7
1000
2.8
3.5
400
75
4.2
125
1.25
1.26
0.03
600
A
mA
mV
V
%/ V
nA
3575f
l
l
1.21
1.20
1.23
0.01
100
3V < V
IN
< 40V
(Note 3)
2
LT3575
ELECTRICAL CHARACTERISTICS
PARAMETER
I
REF
Reference Current
Error Amplifier Voltage Gain
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
Measured at R
FB
Pin with R
REF
= 6.49k
V
IN
= 3V
ΔI
= 10μA, V
IN
= 3V
V
C
= 0.35V
R
TC
= 20.1k
I
BIAS
= 30mA
2.9
MIN
TYP
190
150
150
40
27.5
3
3.1
MAX
UNITS
μA
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 LT3575E 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
LT3575I 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
I
Q
(mA)
5.00
4.95
4.90
4.85
4.80
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
8
7
6
T
A
= 25°C, unless otherwise noted.
Quiescent Current
3.2
V
IN
= 40V WITH BIAS = 20V
BIAS VOLTAGE (V)
3.0
2.8
2.6
2.4
2.2
Bias Pin Voltage
V
IN
= 40V
V
IN
= 12V
5
4
3
2
1
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
V
IN
= 5V WITH BIAS = 5V
2.0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3575 G01
3575 G02
3575 G03
3575f
3
LT3575
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
500
450
SWITCH V
CESAT
VOLTAGE (mV)
400
350
300
250
200
150
100
50
0
0
500
1000 1500 2000 2500
SWITCH CURRENT (mA)
3000
–50°C
CURRENT LIMIT (A)
25°C
125°C
4.5
4
3.5
3
2.5
2.0
1.5
1
0.5
0
–50
–25
0
MIN I
LIM
MAX I
LIM
SWITCH CURRENT LIMIT (A)
T
A
= 25°C, unless otherwise noted.
Switch Current Limit
4
3.5
3
2.5
2
1.5
1
0.5
75
100
125
0
Switch Current Limit vs R
ILIM
25
50
0
10
20
30
40
50
60
3575 G06
TEMPERATURE (°C)
3575 G05
R
ILIM
RESISTANCE (kΩ)
3575 G04
SHDN/UVLO
Falling Threshold
1.28
12
10
SS PIN CURRENT (μA)
–25
0
25
50
75
100
125
TEMPERATURE (°C)
3575 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)
3575 G08
1.24
1.22
1.20
1.18
–50
3575f
4
LT3575
PIN FUNCTIONS
NC (Pins 1, 15, 16):
No Connect Pins. Can be left open
or connected to any ground plane.
V
IN
(Pin 2):
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.
SW (Pins 3, 4):
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.
BIAS (Pin 5):
Bias Voltage. This pin supplies current to the
switch driver and internal circuitry of the LT3575. 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
(Pin 6):
Shutdown/Undervoltage Lockout.
A resistor divider connected to V
IN
is tied to this pin to
program the minimum input voltage at which the LT3575
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 7μA 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, 2.8μA will be pulled from the pin to
provide programmable hysteresis for UVLO.
SS (Pin 7):
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.
R
ILIM
(Pin 8):
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.
V
C
(Pin 9):
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
(Pin 10):
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
(Pin 11):
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.
TC (Pin 12):
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 (Pin 13):
This pin is used for testing purposes only
and must be connected to ground for the part to operate
properly.
GND (Pin 14, Exposed Pad Pin 17):
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
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