Final Electrical Specifications
LTC1504
500mA Low Voltage
Step-Down Synchronous
Switching Regulator
FEATURES
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DESCRIPTION
The LTC
®
1504 is a self-contained, high efficiency syn-
chronous buck switching regulator. It includes a pair of
on-chip 1.5Ω power switches, enabling it to supply up to
500mA of load current. Efficiency peaks at 92%, minimiz-
ing heat and wasted power. The synchronous buck archi-
tecture allows the output to source or sink current as
required to keep the output voltage in regulation.
The LTC1504 is available in adjustable and fixed 3.3V
output versions. An adjustable current limit circuit pro-
vides protection from overloads. The internal 1% refer-
ence combined with a sophisticated voltage feedback loop
provides optimum output voltage accuracy and fast load
transient response. The LTC1504 is specified to operate
with input voltages between 4V and 10V. Contact the LTC
factory for guaranteed specifications at 2.7V supply.
The LTC1504 is available in a plastic SO-8 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
500mA Output Current at 3.3V Output
Up to 92% Peak Efficiency
Internal Reference Trimmed to 1%
Output Can Source or Sink Current
Requires as Few as Four External Components
Input Voltage Range: 4V to 10V
Adjustable Current Limit
Small SO-8 Package
200kHz Switching Frequency Can be
Synchronized Up to 500kHz
APPLICATIONS
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Small Portable Digital Systems
Control Outputs
Daisy-Chained
Active Termination
Auxiliary Output Voltage Supplies
Minimum Part Count/Size Switchers
TYPICAL APPLICATION
Minimum Part Count 5V to 3.3V Regulator
NC
I
MAX
5V
SHUTDOWN
SHDN
SW
L
EXT
3.3V AT 500mA
EFFICIENCY (%)
100
90
80
70
60
50
40
30
20
1504 • TA01
5V to 3.3V Efficiency
+
C
IN
V
CC
LTC1504-3.3
GND
SS
SENSE
COMP
1000pF
+
C
OUT
C
IN
: AVX TPSC226M016R0375
C
OUT
: AVX TAJC476M010
L
EXT
: COILTRONICS CTX50-1P
NC
10
0
10
100
LOAD CURRENT (mA)
500
1504 • TA02
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LTC1504
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER I FOR ATIO
TOP VIEW
I
MAX
1
V
CC
2
SW 3
GND 4
8
7
6
5
COMP
SS
SHDN
FB/SENSE*
Supply Voltage (V
CC
to GND) ................................... 10V
Peak Output Current (SW) .......................................
±1A
Input Voltage (All Other Pins) ......... – 0.3V to V
CC
+ 0.3V
Operating Temperature Range ..................... 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1504CS8
LTC1504CS8-3.3
S8 PART MARKING
1504
15043
S8 PACKAGE
8-LEAD PLASTIC SO
*FB FOR LTC1504CS8, SENSE FOR LTC1504CS8-3.3
T
JMAX
= 115°C,
θ
JA
= 90°C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC
V
FB
∆V
FB
V
SENSE
∆V
SENSE
I
CC
PARAMETER
Minimum Supply Voltage
Feedback Voltage
Feedback Voltage PSRR
Sense Pin Voltage
Sense Voltage PSRR
Supply Current
CONDITIONS
(Note 7)
LTC1504CS8
V
CC
= 5V, T
A
= 25°C unless otherwise specified. (Note 2)
MIN
q
q
q
q
q
q
q
q
q
q
q
q
TYP
1.265
1.1
3.30
1.2
3
0.3
1.0
MAX
1.28
1.6
3.40
1.8
0.6
20
250
2.0
0.8
UNITS
V
V
%
V
%
mA
mA
µA
kHz
Ω
V
V
µA
V
V
µA
µmho
dB
µmho
µA
µA
ns
%
4
1.25
3.20
Figure 1, 4V
≤
V
CC
≤
10V, LTC1504CS8
LTC1504CS8-3.3
Figure 1, 4V
≤
V
CC
≤
10V, LTC1504CS8-3.3
Figure 1, V
SHDN
= V
CC
, I
OUT
= 0 (Note 4)
Figure 1, V
SHDN
= V
CC
, I
OUT
= 0, V
FB
/V
SENSE
= V
CC
(Note 4)
V
SHDN
= 0V
f
OSC
R
SW
V
IH
V
IL
I
IN
V
OH
V
OL
I
OH
, I
OL
g
mV
A
V
g
mI
I
MAX
I
SS
t
r
, t
f
DC
MAX
Internal Oscillator Frequency
Internal Switch Resistance
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Input Current
Error Amplifier Positive Swing
Error Amplifier Negative Swing
Error Amplifier Output Current
Error Amplifier Transconductance
Error Amplifier DC Gain
I
LIM
Amplifier Transconductance
I
MAX
Sink Current
Soft Start Source Current
Output Switch Rise/Fall Time
Maximum Duty Cycle
V
COMP
= V
CC
Figure 2
Figure 2
Figure 2
(Note 5)
(Note 5)
(Note 6)
V
IMAX
= V
CC
V
SS
= 0V
150
2.4
200
1.3
±0.1
4.5
±50
350
40
1000
8
–8
84
4.95
0.05
±100
600
48
2000
12
– 12
5
90
±1
0.5
±200
1100
3000
16
– 16
50
q
q
q
q
q
q
q
q
q
2
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LTC1504
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
Note 3:
This parameter is guaranteed by correlation and is not tested
directly.
Note 4:
LTC1504 quiescent current is dominated by the gate drive current
drawn by the onboard power switches. With FB or SENSE pulled to V
CC
the output stage will stop switching and the static quiescent current can be
observed. With FB or SENSE hooked up normally, the output stage will be
switching and total dynamic supply current can be measured.
Note 5:
Fixed output parts will appear to have g
mV
and A
V
values 2.6 times
lower than the specified values, due to the internal divider resistors.
Note 6:
The I
LIM
amplifier can sink but not source current. Under normal
(not current limited) operation, the I
LIM
output current will be zero.
Note 7:
Contact factory for guaranteed specifications at 2.7V supply.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Supply Voltage
14
12
SUPPLY CURRENT (mA)
T
A
= 25°C
I
OUT
= 0
SUPPLY CURRENT (mA)
10
8
6
4
2
V
FB
= V
CC
0
2.5
7.5
5
SUPPLY VOLTAGE (V)
10
1504 • TPC01
Switch On-Resistance vs
Temperature
3.5
700
CURRENT LIMIT THRESHOLD (mA)
3.0
SWITCH ON-RESISTANCE (Ω)
2.5
2.0
1.5
1.0
0.5
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
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Supply Current vs Temperature
10
V
CC
= 5V
I
OUT
= 0
V
FB
= V
OUT
V
FB
= V
OUT
1
V
FB
= V
CC
0.1
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1504 • TPC02
Current Limit Threshold vs R
IMAX
600
500
400
300
200
100
0
10k
R
IMAX
(Ω)
1504 • TPC03
1504 • TPC04
T
A
= 25°C
V
CC
= 5V
V
CC
= 3.3V
V
CC
= 5V
V
CC
= 10V
100
125
100k
3
LTC1504
TYPICAL PERFORMANCE CHARACTERISTICS
Current Limit Threshold vs
Temperature
500
CURRENT LIMIT THRESHOLD (mA)
450
400
350
300
250
200
150
100
50
0
–50 –25
0
25
50
75
TEMPERATURE (°C)
R
IMAX
= 22k
R
IMAX
= 47k
SHUTDOWN PIN THRESHOLD (V)
PIN FUNCTIONS
I
MAX
(Pin 1):
Current Limit Set. Connect a resistor from
V
CC
to I
MAX
to set the current limit threshold. An internal
12µA current source from I
MAX
to GND sets the voltage
drop across this resistor. This voltage is compared to the
voltage drop across the internal high-side switch (Q1)
while it is turned on. See the Applications Information
section for more information. To disable current limit,
leave I
MAX
floating.
V
CC
(Pin 2):
Power Supply Input. Connect to a power
supply voltage between 4V and 10V. V
CC
requires a low
impedance bypass capacitor to ground, located as close
as possible to the LTC1504. See the Applications Informa-
tion section for details on capacitor selection and
placement.
SW (Pin 3):
Power Switch Output. This is the switched
node of the buck circuit. Connect SW to one end of the
external inductor. The other end of the inductor should be
connected to C
OUT
and becomes the regulated output
voltage. Avoid shorting SW to GND or V
CC
.
GND (Pin 4):
Ground. Connect to a low impedance ground.
The input and output bypass capacitors and the feedback
resistor divider (adjustable parts only) should be grounded
as close to this pin as possible. Pin 4 acts as a heat sink
in the LTC1504 S0-8 package and should be connected to
as large a copper area as possible to improve thermal
dissipation. See the Thermal Considerations section for
more information.
FB (LTC1504CS8) (Pin 5):
Feedback. Connect FB to a
resistor divider from V
OUT
to GND to set the regulated
output voltage. The LTC1504CS8 feedback loop will servo
the FB pin to 1.265V.
SENSE (LTC1504CS8-3.3) (Pin 5):
Output Voltage Sense.
Connect directly to the output voltage node. The
LTC1504CS8-3.3 feedback loop will servo SENSE to 3.3V.
SENSE is connected to an internal resistor divider which
will load any external dividers. For output voltages other
than 3.3V, use the LTC1504CS8.
SHDN (Pin 6):
Shutdown, Active Low. When SHDN is at a
logic High, the LTC1504 will operate normally. When
SHDN is Low, the LTC1504 ceases all internal operation
and supply current drops below 1µA. In shutdown, the SW
pin is pulled low. This ensures that the output is actively
shut off when SHDN is asserted, but it prevents other
supplies from providing power to the output when the
LTC1504 is inactive. See the Applications Information
section for more details.
SS (Pin 7):
Soft Start. Connect an external capacitor
(usually 0.1µF) from SS to GND to limit the output rise time
4
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Shutdown Threshold vs
Supply Voltage
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
100
125
3
5
7
SUPPLY VOLTAGE (V)
10
1504 • TPC07
V
CC
= 5V
1504 • TPC05
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LTC1504
PIN FUNCTIONS
during power-up. C
SS
also compensates the current limit
loop, allowing the LTC1504 to enter and exit current limit
cleanly. See the Applications Information section for more
details.
COMP (Pin 8):
External Compensation. An external RC
network should be connected to COMP to compensate the
feedback loop. COMP is connected to the output of the
internal error amplifier.
BLOCK DIAGRAM
SHDN
COMP
12V
SS
I
MAX
+
–
V
REF
1.265V
Figure 3. Block Diagram
TEST CIRCUITS
NC
I
MAX
V
CC
SHDN
SW
LTC1504
GND
SS
FB/SENSE
COMP
L
EXT
V
OUT
A
B
FB/SENSE
LTC1504
+
C
IN
1µF
V
CC
+
C
OUT
0.1µF
C
IN
: AVX TPSE107M016R0125
C
OUT
: SANYO 16CV220GX
L
EXT
: COILCRAFT D03316-473
7.5k
0.01µF
220pF
1504 • TC01
Figure 1
+
–
12V
W
U
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TO INTERNAL BLOCKS
V
CC
SAW
–
PWM
Q1
SW
+
Q2
I
LIM
FB
MIN
MAX
–
+
+
–
+
–
+
–
FB
(ADJ ONLY)
40mV
20.4k
12.6k
1504 • BD
40mV
+
–
SENSE
(–3.3V ONLY)
–
COMP
+
V
REF
A: TEST V
OL
, I
OL
B: TEST V
OH
, I
OH
1504 • TC02
Figure 2
5
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