LINEAR TECHNOLOGY LTC2927 Technical data

FEATURES

LTC2927

Single Power Supply

Tracking Controller

U

DESCRIPTIO

n

Flexible Power Supply Tracking

n

Tracks Both Up and Down

n

Power Supply Sequencing

n

Supply Stability is Not Affected

n

Low Pin Count

n

Controls Single Supply without Series FETs

n

Adjustable Ramp Rate

n

Supply Shutdown Output

n

Available in 8-Lead ThinSOT™ and 8-Lead

(3mm × 2mm) DFN Packages

U

APPLICATIO S

n

V

n

Microprocessor, DSP and FPGA Supplies

n

Multiple Supply Systems

n

Point-of-Load Supplies

CORE

and V

Supply Tracking

I/O

U

TYPICAL APPLICATIO

The LTC®2927 provides a simple solution to power supply
tracking and sequencing requirements. By selecting a few
resistors, the supply can be confi gured to ramp-up and
ramp-down with differing ramp rates, voltage offsets, or
time delays relative to other supplies or a master signal.

By forcing current into a feedback node of an independent
supply, the LTC2927 causes the output to track a ramp
signal without inserting any pass element losses. Because
the current is controlled in an open-loop manner, the
LTC2927 does not affect the transient response or stabil­ity of the supply. The compact solution at point of load
minimizes the trace length of the DC/DC circuit sensitive
FB node. Furthermore, it presents a high impedance when
power-up is complete, effectively removing it from the
DC/DC circuit.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Patents Pending.

EARLY V

EARLY V

3.3V

3.3V

IN

IN

138k

100k

16.5k

13k

887k

412k

V

ON RAMP

RAMPBUF

TRACK

ON RAMP

RAMPBUF

TRACK

CC

LTC2927

GND

V

CC

LTC2927

GND

SDO RUN/SSFBIN

SDO RUN/SSFBIN

2927 TA01a

0.1μF

0.1μF

35.7k

0.1μF

412k

V

IN

DC/DC

FB = 1.235V OUT

16.5k

V

IN

DC/DC

FB = 0.8V OUT

887k

1.8V

2.5V

Track-Up and Track-Down Waveforms

1V/DIV

10ms/DIV

RAMP
(3.3V)

2.5V

1.8V

10ms/DIV

RAMP
(3.3V)

2.5V

1.8V

2927 TA01b

1V/DIV

2927 TA01c

2927fb

1

LTC2927

WW

W

ABSOLUTE AXI U RATI GS

U

(Note 1)

Supply Voltage (VCC) ................................. –0.3V to 10V

Input Voltages

ON ......................................................... –0.3V to 10V

TRACK .........................................–0.3V to V

+ 0.3V

CC

Output Voltages

FB, SDO ................................................. –0.3V to 10V

RAMP, RAMPBUF .........................–0.3V to V

+ 0.3V

CC

PIN CONFIGURATION

TOP VIEW

1ON

RAMP

2

RAMPBUF

8-LEAD (3mm × 2mm) PLASTIC DFN

EXPOSED PAD (PIN 9) PCB GND, CONNECTION OPTIONAL

3

TRACK

4

DDB PACKAGE

= 125°C, θJA = 76°C/W

T

JMAX

8

V

CC

SDO

7

9

FB

6

GND

5

Average Current

TRACK .................................................................5mA

FB ........................................................................5mA

RAMPBUF ............................................................5mA

Operating Temperature Range

LTC2927C ................................................ 0°C to 70°C

LTC2927I.............................................. –40°C to 85°C

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

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

TOP VIEW

VCC 1

SDO 2

FB 3

GND 4

TS8 PACKAGE

8-LEAD PLASTIC TSOT-23

T

= 125°C, θJA = 250°C/W

JMAX

8 ON
7 RAMP
6 RAMPBUF
5 TRACK

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC2927CDDB#PBF LTC2927CDDB#TRPBF LBQH

LTC2927IDDB#PBF LTC2927IDDB#TRPBF LBQH

LTC2927CTS8#PBF LTC2927CTS8#TRPBF LTBQJ 8-Lead Plastic TSOT-23 0°C to 70°C

LTC2927ITS8#PBF LTC2927ITS8#TRPBF LTBQJ 8-Lead Plastic TSOT-23 –40°C to 85°C

LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC2927CDDB LTC2927CDDB#TR LBQH

LTC2927IDDB LTC2927IDDB#TR LBQH

LTC2927CTS8 LTC2927CTS8#TR LTBQJ 8-Lead Plastic TSOT-23 0°C to 70°C

LTC2927ITS8 LTC2927ITS8#TR LTBQJ 8-Lead Plastic TSOT-23 –40°C to 85°C

Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
For more information on lead free part marking, go to:

For more information on tape and reel specifi cations, go to:

http://www.linear.com/leadfree/

http://www.linear.com/tapeandreel/

8-Lead (3mm × 2mm) Plastic DFN
8-Lead (3mm × 2mm) Plastic DFN

8-Lead (3mm × 2mm) Plastic DFN
8-Lead (3mm × 2mm) Plastic DFN

0°C to 70°C

–40°C to 85°C

0°C to 70°C

–40°C to 85°C

2927fb

2

LTC2927

2

0

1

ELECTRICAL CHARACTERISTICS

The
temperature range, otherwise specifi cations are at T

= 25°C. 2.9V < VCC < 5.5V unless otherwise noted (Note 2).

A

l denotes the specifi cations which apply over the full operating

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

I

CC

V

CC(UVLO)

ΔV

CC(UVHYST)

V

ON(TH)

ΔV

ON(HYST)

I

ON

I

RAMP

V

RAMPBUF(OL)

V

RAMPBUF(OH)

V

OS

I

ERROR(%)

V

TRACK

I

FB(LEAK)

V

FB(CLAMP)

V

SDO(OL)

Supply Voltage

Supply Current IFB = 0mA, I

I

= –1mA, I

FB

TRACK

Supply Undervoltage Lockout VCC Rising

Supply Undervoltage Lockout Hysteresis 25 mV

ON Pin Threshold Voltage VON Rising

ON Pin Hysteresis

ON Pin Input Current VON = 1.2V, VCC = 5.5V

RAMP Pin Input Current 0V < V

0V < V

RAMPBUF Output Low Voltage I

RAMPBUF Output High Voltage,
V

RAMPBUF(OH)

= VCC – V

RAMPBUF

Ramp Buffer Offset,
V

= V

OS

IFB to I

TRACK

I

ERROR(%)

– V

RAMPBUF

Current Mismatch

= (IFB – I

TRACK

RAMP

)/I

TRACK

TRACK Pin Voltage I

RAMPBUF

I

RAMPBUF

V

RAMP

I

TRACK

I

TRACK

TRACK

I

TRACK

< VCC, Ramp On –9 –10 –11 μA

RAMP

< VCC, Ramp Off 9 10 11 μA

RAMP

= 1mA

= –1mA

= VCC/2, I

= –10μA

= –1mA

= –10μA

= –1mA

FB Pin Leakage Current VFB = 2V, VCC = 5.5V

FB Pin Clamp Voltage 1μA < IFB < 1mA
SDO Output Low Voltage I

= 1mA, VCC = 2.3V

SDO

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

= 0mA

TRACK

RAMPBUF

= –1mA, I

= 0mA –30 0 30 mV

RAMPBUF

= –1mA

Note 2: All currents into the device pins are positive; all currents out of
device pins are negative. All voltages are referenced to ground unless
otherwise specifi ed.

l

2.9 5.5 V

l

0.25 0.56 1.2 mA

l

3 3.6 4.2 mA

l

2.2 2.5 2.7 V

l

1.210 1.230 1.250 V

l

30 75 150 mV

l

l

l

l

l

l

0.77 0.800 0.82 V

l

0.77 0.800 0.82 V

l

l

1.5 2 2.3 V

l

0 ±100 nA

20 100 mV

45 150 mV

0±5 %

0±5 %

±1 ±100 nA

0.1 0.4 V

reliability and lifetime.

TYPICAL PERFORMANCE CHARACTERISTICS

750

700

650

(μA)

CC

I

600

550

500

ICC vs V

CC

I

= IFB = 0mA

TRACK

= 0mA

I

RAMBUF

3.0 3.5 4.0 4.5

2.5
VCC (V)

6.05.55.0

2927 G0

ICC vs V

I

TRACK

I

RAMBUF

CC

= IFB = –1mA

= –2mA

VCC (V)

4.70

4.65

4.60

(mA)

CC

I

4.55

4.50

4.45

2.5 3.0 3.5 4.0 4.5 6.

V

vs Temperature

TRACK

820

810

800

(mV)

TRACK

790

V

780

5.55.0

2927 G0

770

–25 0 25 50

–50

TEMPERATURE (°C)

75 100

2927 G03

2927fb

3

LTC2927

0

7

4

0

6

UW

TYPICAL PERFOR A CE CHARACTERISTICS

1.240

1.235

1.230

(V)

1.225

ON(TH)

V

1.220

1.215

1.210

(mA)

I

60

50

40

TRACK

30

vs Temperature

ON(TH)

–25 0 25 50

–50

MAX I

V

TRACK

TEMPERATURE (°C)

TRACK

= 0V

vs V

CC

75 10

2927 G0

V

RAMPBUF(OL)

28

26

24

22

(mV)

20

18

RAMPBUF(OL)

16

V

14

12

10

–25 0 25 50

–50

TEMPERATURE (°C)

Tracking Cell Error vs I

5

ERROR = •

4

3

ERROR (%)

2

V

TRACK

0.8V

vs Temperature V

70

65

60

(mV)

55

RAMPBUF(OH)

50

V

45

40

1.0

0.8

0.6

(V)

SDO(OL)

0.4

V

I

I

TRACK

75 100

2927 G05

TRACK

FB

–1

RAMPBUF(OH)

–25 0 25 50

–50

V

SDO(OL)

TEMPERATURE (°C)

vs V

vs TemperatureV

CC

I

SDO

75 100

2927 G0

= 5mA

20

10

2.5 3.0 3.5 4.0 4.5 6.05.55.0
V

(V)

CC

PIN FUNCTIONS

2927 G0

TSOT/DFN Packages

1

0

1

234

I

TRACK

VCC (Pin 1/Pin 8): Supply Voltage Input. Operating range
is from 2.9V to 5.5V. An undervoltage lockout asserts SDO
until V

> 2.5V. VCC should be bypassed to GND with a

CC

0.1μF capacitor.
SDO (Pin 2/Pin 7): Slave Supply Shutdown Output. SDO

is an open-drain output that holds the shutdown (RUN/SS)
pin of the slave supply low until the V

pin is pulled above

CC

2.5V, and the ON pin is pulled above 1.23V, or RAMP is
above 200mV. SDO is pulled low again when both RAMP
< 200mV and ON < 1.23V. If the slave supply is capable
of operating with an input supply that is lower than the
LTC2927’s minimum operating voltage of 2.9V, the SDO

0.2

I

= 10μA

SDO

1234

VCC (V)

5

2927 G

(mA)

2927 G0

5

0.0
0

pin can be used to hold off the slave supply. Tie the SDO
pin to GND if unused.

FB (Pin 3/Pin 6): Feedback Control Output. FB pulls up
on the feedback node of the slave supply. Tracking is
achieved by mirroring the current from TRACK into FB.
A resistive divider connecting RAMPBUF and TRACK will
force the output voltage of the slave supply to track RAMP.
To prevent damage to the slave supply, the FB pin will not
force the slave’s feedback node above 2.3V. In addition,
the LTC2927 will not actively sink current from this node,
even when it is unpowered.

2927fb

4

UUU

PI FU CTIO S

LTC2927

TSOT/DFN Packages

GND (Pin 4/Pin 5): Device Ground.

TRACK (Pin 5/Pin 4): Tracking Control Input. A resistive

voltage divider between RAMPBUF and TRACK determines
the tracking profi le of the slave supply. TRACK servos to

0.8V, and the current supplied at TRACK is mirrored at FB.
The TRACK pin is capable of supplying at least 1mA when

= 2.9V. Under short circuit conditions, the TRACK pin

V

CC

is capable of supplying up to 70mA. Do not connect to
GND for extended periods. Limit the capacitance at the
TRACK pin to less than 25pF.

RAMPBUF (Pin 6/Pin 3): Ramp Buffer Output. Provides
a low impedance buffered version of the signal on the
RAMP pin. This buffered output drives the resistive volt­age divider that connects to the TRACK pin. Limit the
capacitance at the RAMPBUF pin to less than 100pF. Float
RAMPBUF if unused.

UU

W

FU CTIO AL BLOCK DIAGRA

RAMP (Pin 7/Pin 2): Ramp Buffer Input. The RAMP pin is
the input to the voltage buffer whose output drives a resis­tive voltage divider connected to the TRACK pin. Connect
this input to a capacitor to set the ramp voltage generated
from internal 10μA pull-up or pull-down currents. RAMP
can also be connected to an external ramping signal for
tracking. Ground RAMP if unused.

ON (Pin 8/Pin 1): On Control Input. The voltage level of
the ON pin relative to its 1.23V threshold (with 75mV
hysteresis) controls the tracking direction of the LTC2927.
An active high causes a 10μA pull-up current to fl ow at
the RAMP pin, which charges an external capacitor. An
active low at the ON pin causes a 10μA pull-down cur­rent at the RAMP pin to discharge the external capacitor
relative to GND.

Exposed Pad (NA/Pin 9): Exposed pad may be left open
or connected to device ground.

RAMPBUF

5

ON

5

1.23V

TRACK

5

2.5V

V

5

V

CC

1x

+

–

–

+

+

–

CC

UVLO

V

GND

CC

+

0.8V

–

5

V

10μA

10μA

0.2V

RAMP

SDO

FB

2927 BD

5

5

5

2927fb

CC

5