Linear Technology LTC1504 Datasheet

FEATURES

Final Electrical Specifications

LTC1504

500mA Low Voltage

Step-Down Synchronous

Switching Regulator

U

DESCRIPTION

■

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

U

APPLICATIONS

■

Small Portable Digital Systems

■

Active Termination

■

Auxiliary Output Voltage Supplies

■

Minimum Part Count/Size Switchers

Daisy-Chained Control Outputs

U

TYPICAL APPLICATION

The LTC®1504 is a self-contained, high efficiency syn­chronous 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%, minimiz­ing heat and wasted power. The synchronous buck archi­tecture 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 pro­vides protection from overloads. The internal 1% refer­ence 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.

Minimum Part Count 5V to 3.3V Regulator 5V to 3.3V Efficiency

5V

+

C

CIN: AVX TPSC226M016R0375

: AVX TAJC476M010

C

OUT

: COILTRONICS CTX50-1P

L

EXT

IN

SHUTDOWNNC

I

MAX

V

CC

LTC1504-3.3

GND

SS COMP

NC

100

90

SHDN

SENSE

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 represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

SW

1000pF

L

EXT

3.3V AT 500mA

+

C

OUT

1504 • TA01

80
70
60
50
40

EFFICIENCY (%)

30
20
10

0

10

LOAD CURRENT (mA)

100 500

1504 • TA02

1

LTC1504

WU

U

PACKAGE

/

O

RDER I FOR ATIO

WW

W

U

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Supply Voltage (VCC to GND)................................... 10V

Peak Output Current (SW) .......................................±1A

Input Voltage (All Other Pins) ......... –0.3V to VCC + 0.3V

Operating Temperature Range ..................... 0°C to 70°C

Storage Temperature Range ................. –65°C to 150°C

I

MAX

V

SW

GND

Lead Temperature (Soldering, 10 sec).................. 300°C

*FB FOR LTC1504CS8, SENSE FOR LTC1504CS8-3.3

Consult factory for Industrial and Military grade parts.

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

V

FB

∆V

FB

V

SENSE

∆V

SENSE

I

CC

f

OSC

R

SW

V

IH

V

IL

I

IN

V

OH

V

OL

IOH, I
g

mV

A

V

g

mI

I

MAX

ISSSoft Start Source Current VSS = 0V ● –8 –12 –16 µA
tr, t

f

DC

MAX

Minimum Supply Voltage (Note 7) ● 4V
Feedback Voltage LTC1504CS8 ● 1.25 1.265 1.28 V
Feedback Voltage PSRR Figure 1, 4V ≤ VCC ≤ 10V, LTC1504CS8 ● 1.1 1.6 %
Sense Pin Voltage LTC1504CS8-3.3 ● 3.20 3.30 3.40 V
Sense Voltage PSRR Figure 1, 4V ≤ VCC ≤ 10V, LTC1504CS8-3.3 ● 1.2 1.8 %
Supply Current Figure 1, V

Figure 1, V

= 0V ● 1.0 20 µA

V

SHDN

Internal Oscillator Frequency ● 150 200 250 kHz
Internal Switch Resistance ● 1.3 2.0 Ω
SHDN Input High Voltage ● 2.4 V
SHDN Input Low Voltage ● 0.8 V
SHDN Input Current ● ±0.1 ±1 µA
Error Amplifier Positive Swing Figure 2 ● 4.5 4.95 V
Error Amplifier Negative Swing Figure 2 ● 0.05 0.5 V
Error Amplifier Output Current Figure 2 ● ±50 ±100 ±200 µA

OL

Error Amplifier Transconductance (Note 5) ● 350 600 1100 µmho
Error Amplifier DC Gain (Note 5) ● 40 48 dB
I

Amplifier Transconductance (Note 6) 1000 2000 3000 µmho

LIM

I

Sink Current V

MAX

Output Switch Rise/Fall Time ● 550 ns
Maximum Duty Cycle V

IMAX

COMP

= V

= V

VCC = 5V, TA = 25°C unless otherwise specified. (Note 2)

SHDN
SHDN

CC

CC

= VCC, I
= VCC, I

= 0 (Note 4) 3 mA

OUT

= 0, VFB/V

OUT

SENSE

TOP VIEW

1




2

CC

3

4

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 115°C, θJA = 90°C/W

JMAX

= VCC (Note 4) ● 0.3 0.6 mA

COMP

8

SS

7

SHDN

6

FB/SENSE*

5

● 81216 µA

● 84 90 %

ORDER PART

NUMBER

LTC1504CS8
LTC1504CS8-3.3

S8 PART MARKING

1504
15043

2

ELECTRICAL CHARACTERISTICS

R

IMAX

(Ω)

10k

CURRENT LIMIT THRESHOLD (mA)

700

600

500

400

300

200

100

0

100k

1504 • TPC04

TA = 25°C
V

CC

= 5V

TEMPERATURE (°C)

–50 –25 0 25 50 75 100 125

SUPPLY CURRENT (mA)

10

1

0.1

1504 • TPC02



VFB = V

OUT

VFB = V

CC

VCC = 5V
I

OUT

= 0

LTC1504

The ● 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

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
lower than the specified values, due to the internal divider resistors.

Note 6: The I
(not current limited) operation, the I

Note 7: Contact factory for guaranteed specifications at 2.7V supply.

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

W

U

CC

TYPICAL PERFORMANCE CHARACTERISTICS

Supply Current vs Supply Voltage

14

TA = 25°C

= 0

I

OUT

12

10

8



6

VFB = V

OUT

and AV values 2.6 times

mV

amplifier can sink but not source current. Under normal

LIM

output current will be zero.

LIM

Supply Current vs Temperature

SUPPLY CURRENT (mA)

3.5

3.0

2.5

2.0



1.5

1.0

SWITCH ON-RESISTANCE (Ω)

0.5

4

2

0

2.5

VFB = V

CC

5

SUPPLY VOLTAGE (V)

Switch On-Resistance vs
Temperature

0

–50

–25 0

TEMPERATURE (°C)

50 100 125

25 75

7.5 10

1504 • TPC01

VCC = 3.3V

VCC = 5V

VCC = 10V

1504 • TPC03

Current Limit Threshold vs R

IMAX

3

LTC1504

SUPPLY VOLTAGE (V)

357

SHUTDOWN PIN THRESHOLD (V)

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

10

1504 • TPC07



W

U

TYPICAL PERFORMANCE CHARACTERISTICS

Current Limit Threshold vs
Temperature

500
450
400
350
300
250
200
150
100

CURRENT LIMIT THRESHOLD (mA)

50

0

–50

PIN FUNCTIONS

I

(Pin 1): Current Limit Set. Connect a resistor from

MAX

VCC to I
12µA current source from I
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

VCC (Pin 2): Power Supply Input. Connect to a power
supply voltage between 4V and 10V. VCC requires a low
impedance bypass capacitor to ground, located as close
as possible to the LTC1504. See the Applications Informa­tion 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
voltage. Avoid shorting SW to GND or VCC.

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

4

to set the current limit threshold. An internal

MAX

floating.

MAX

OUT

VCC = 5V

R

= 47k

IMAX

R

= 22k

IMAX

–25 0 25 50 75

TEMPERATURE (°C)

100

1504 • TPC05

125

UUU

to GND sets the voltage

MAX

and becomes the regulated output

Shutdown Threshold vs
Supply Voltage

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

to GND to set the regulated

OUT

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 1µ A. 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 0.1µ F) from SS to GND to limit the output rise time