Linear Technology LTC1159IS-5, LTC1159IS-3.3, LTC1159IS, LTC1159CS-5, LTC1159CS-3.3 Datasheet

FEATURES

■

Operation from 4V to 40V Input Voltage

■

Ultrahigh Efficiency: Up to 95%

■

20µA Supply Current in Shutdown

■

High Efficiency Maintained Over Wide Current Range

■

Current Mode Operation for Excellent Line and Load
Transient Response

■

Very Low Dropout Operation: 100% Duty Cycle

■

Short-Circuit Protection

■

Synchronous FET Switching for High Efficiency

■

Adaptive Non-Overlap Gate Drives

■

Available in SSOP and SO Packages

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APPLICATIO S

■

Step-Down and Inverting Regulators

■

Notebook and Palmtop Computers

■

Portable Instruments

■

Battery-Operated Digital Devices

■

Industrial Power Distribution

■

Avionics Systems

■

Telecom Power Supplies

LTC1159

LTC1159-3.3/LTC1159- 5

High Efficiency Synchronous

Step-Down Switching Regulators

U

DESCRIPTIO

The LTC®1159 series is a family of synchronous step-down
switching regulator controllers featuring automatic Burst
ModeTM operation to maintain high efficiencies at low
output currents. These devices drive external complemen­tary power MOSFETs at switching frequencies up to 250kHz
using a constant off-time current-mode architecture.

A separate pin and on-board switch allow the MOSFET
driver power to be derived from the regulated output
voltage providing significant efficiency improvement when
operating at high input voltages. The constant off-time
current-mode architecture maintains constant ripple cur­rent in the inductor and provides excellent line and load
transient response. The output current level is user pro­grammable via an external current sense resistor.

The LTC1159 automatically switches to power saving
Burst Mode operation when load current drops below
approximately 15% of maximum current. Standby current
is only 300µA while still regulating the output and shut-
down current is a low 20µA.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

V

IN

+

3.3µF

0V = NORMAL

>2V = SHUTDOWN

3300pF

1k

C

T

300pF

CAP

V

CC

V

CC

SHDN1
SHDN2
I

TH

C

T

S-GND

0.15µF

Figure 1. High Efficiency Step-Down Regulator

P-GATE

P-DRIVE

EXTV

LTC1159-5

SENSE

SENSE

N-GATE

P-GND

U

V

IN

+

C

R

SENSE

0.05Ω

IN

100µF
100V

21

4

+

V

OUT

5V/2A

C

OUT

220µF

100

FIGURE 1 CIRCUIT

90

80

EFFICIENCY (%)

70

60

0.02

LTC1159-5 Efficiency

VIN = 10V

VIN = 20V

0.2 2

LOAD CURRENT (A)

LTC1159 • TA01

1N4148

Si9435DY

0.1µF

CC

+

–

D1

MBRS140T3

0.01µF

LTC1159 • F01

L*

33µH

3

Si9410DY

*COILTRONICS CTX33-4-MP

1

LTC1159
LTC1159-3.3/LTC1159-5

A

W

O

LUTEXI TIS

S

A

WUW

U

ARB

G

(Note 1)

Input Supply Voltage (Pin 2) ..................... –15V to 60V

VCC Output Current (Pin 3) .................................. 50mA

Continuous Pin Currents (Any Pin)...................... 50mA

Sense Voltages ......................................... –0.3V to 13V

Shutdown Voltages................................................... 7V

EXTVCC Input Voltage ............................................. 15V

Junction Temperature (Note 2)............................ 125°C

WU

/

PACKAGE

P-GATE

V

IN

V

CC

P-DRIVE
P-DRIVE

V

CC

V

CC

C

T

I

TH

–

SENSE

T

O

RDER I FOR ATIO

TOP VIEW

1
2
3
4
5
6
7
8
9

10

G PACKAGE

20-LEAD PLASTIC SSOP

JMAX

= 125°C, θ

= 135°C/W

JA

20
19
18
17
16
15
14
13
12
11

CAP
SHDN2
EXTV
PGND
N-GATE
PGND
SGND
SHDN1
V

FB

SENSE

ORDER PART

NUMBER

CC

LTC1159CG
LTC1159CG-3.3
LTC1159CG-5

+

Operating Temperature Range

LTC1159C .............................................. 0°C to 70°C

LTC1159I........................................... –40°C to 85°C

Extended Commercial

Temperature Range ............................... – 40°C to 85°C

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

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

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ORDER PART

NUMBER

LTC1159CN
LTC1159CN-3.3
LTC1159CN-5
LTC1159CS
LTC1159CS-3.3
LTC1159CS-5
LTC1159IS
LTC1159IS-3.3
LTC1159IS-5

1

P-GATE

2

V

IN

3

V

CC

P-DRIVE

SENSE

4
5

V

CC

6

C

T

7

I

TH

–

8

N PACKAGE

16-LEAD PDIP

*FIXED OUTPUT VERSIONS

T

= 125°C, θ

JMAX

T

= 125°C, θ

JMAX

TOP VIEW

S PACKAGE

16-LEAD PLASTIC SO

= 80°C/ W (N)

JA

= 110°C/ W (S)

JA

16
15
14
13
12
11
10

9

CAP
SHDN2
EXTV
N-GATE
PGND
SGND
V

(SHDN1)*

FB

SENSE

CC

+

Consult LTC Marketing for parts specified with wider operating temperature ranges.

LECTRICAL C CHARA TERIST

E

ICS

temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

FB

I

FB

V

OUT

∆V

OUT

I

IN

I

EXTVCC

Feedback Voltage (LTC1159 Only) ● 1.21 1.25 1.29 V
Feedback Current (LTC1159 Only) ● 0.2 µA
Regulated Output Voltage VIN = 9V

LTC1159-3.3 I

LTC1159-5 I
Output Voltage Line Regulation VIN = 9V to 40V –40 0 40 mV
Output Voltage Load Regulation

LTC1159-3.3 5mA < I

LTC1159-5 5mA < I
Burst Mode Output Ripple I
VIN Pin Current (Note 4)

Normal Mode V

Shutdown VIN = 12V, V

EXTVCC Pin Current (Note 4) EXTVCC = 5V, Sleep Mode 250 µA

LOAD
LOAD

LOAD

IN

V

IN

V

IN

The ● denotes specifications which apply over the full operating

= 0V (Note 3), unless otherwise noted.

SHDN1

= 700mA ● 3.23 3.33 3.43 V
= 700mA ● 4.90 5.05 5.20 V

< 2A ● 40 65 mV

LOAD

< 2A ● 60 100 mV

LOAD

= 0A 50 mV

= 12V, EXTVCC = 5V 200 µA
= 40V, EXTVCC = 5V 300 µA

= 2V 15 µA

= 40V, V

SHDN2

= 2V 25 µA

SHDN2

P-P

2

LTC1159

LTC1159-3.3/LTC1159- 5

LECTRICAL C CHARA TERIST

E

ICS

temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, V

The ● denotes specifications which apply over the full operating

= 0V (Note 3), unless otherwise noted.

SHDN1

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

VIN – V
V

– V

EXT

V

P-GATE

Internal Regulator Voltage VIN = 12V to 40V, EXTVCC = 0V, ICC = 10mA ● 4.25 4.5 4.75 V
VCC Dropout Voltage VIN = 4V, EXTVCC = Open, ICC = 10mA 300 400 mV

CC

EXTVCC Switch Drop VIN = 12V, EXTVCC = 5V, I

CC

= 10mA 250 350 mV

SWITCH

– VINP-Gate to Source Voltage (Off) VIN = 12V –0.2 0 V

VIN = 40V –0.2 0 V

+

V

– Current Sense Threshold Voltage

SENSE

V

SENSE

V

SNDN1

–

LTC1159 V

LTC1159-3.3 V

LTC1159-5 V

SHDN1 Threshold

–

= 5V, VFB = 1.32V (Forced) 25 mV

SENSE

–

V

= 5V, VFB = 1.15V (Forced) ● 130 150 170 mV

SENSE

–

= 3.4V (Forced) 25 mV

SENSE

–

= 3.1V (Forced) ● 130 150 170 mV

V

SENSE

–

= 5.2V (Forced) 25 mV

SENSE

–

= 4.7V (Forced) ● 130 150 170 mV

V

SENSE

LTC1159CG, LTC1159-3.3, LTC1159-5 0.5 0.8 2 V

V

SHDN2

I

SHDN2

I

CT

t

OFF

tr, t

f

SHDN2 Threshold 0.8 1.4 2 V
Shutdown 2 Input Current V
CT Pin Discharge Current V

Off-Time (Note 5) CT = 390pF, I

= 5V 12 20 µA

SHDN2

in Regulation 50 70 90 µA

OUT

= 0V 2 10 µA

V

OUT

= 700mA, VIN = 10V 4 5 6 µs

LOAD

Driver Output Transition Times CL = 3000pF (Pins P-Drive and N-Gate), VIN = 6V 100 200 ns

–40°C ≤ TA ≤ 85°C (Note 6)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

FB

V

OUT

I

IN

I

EXTVCC

V

CC

+

V

SENSE

–

V

SENSE

V

SHDN2

t

OFF

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: T
dissipation P

LTC1159CG, LTC1159CG-3.3, LTC1159CG-5: T
LTC1159CN, LTC1159CN-3.3, LTC1159CN-5: T
LTC1159CS, LTC1159CS-3.3, LTC1159CS-5: T

Feedback Voltage (LTC1159 Only) 1.2 1.25 1.3 V
Regulated Output Voltage VIN = 9V

LTC1159-3.3 I

LTC1159-5 I

= 700mA 3.17 3.30 3.43 V

LOAD

= 700mA 4.85 5.05 5.25 V

LOAD

VIN Pin Current (Note 4)

Normal V

= 12V, EXTVCC = 5V 200 µA

IN

VIN = 40V, EXTVCC = 5V 300 µA

Shutdown VIN = 12V, V

VIN = 40V, V

= 2V 15 µA

SHDN2

= 2V 25 µA

SHDN2

EXTVCC Pin Current (Note 4) EXTVCC = 5V, Sleep Mode 250 µA
Internal Regulator Voltage VIN = 12V to 40V, EXTVCC = 0V, ICC = 10mA 4.5 V

– Current Sense Threshold Voltage Low Threshold (Forced) 25 mV

High Threshold (Forced) 125 150 175 mV
SHDN2 Threshold 0.8 1.4 2 V
Off-Time (Note 5) CT = 390pF, I

= 700mA, VIN = 10V 3.5 5 6.5 µs

LOAD

Note 3: On LTC1159 versions which have a SHDN1 pin, it must be at
ground potential for testing.

is calculated from the ambient temperature TA and power

J

according to the following formulas:

D

= TA + (PD • 135°C/W)

J

= TA + (PD • 80°C/W)

J

= TA + (PD • 110°C/W)

J

Note 4: The LTC1159 V
MOSFET driver currents. When V

, the input current increases by (I

EXTV

CC

and EXTVCC current measurements exclude

IN

power is derived from the output via

CC

• Duty Cycle)/(Efficiency).

GATECHG

See Typical Performance Characteristics and Applications Information.
Note 5: In applications where R

is placed at ground potential, the off-

SENSE

time increases approximately 40%.

3

LTC1159

LOAD CURRENT (A)

0

–100

∆V

OUT

(mV)

–80

–60

–40

–20

0

20

0.5 1.0 1.5 2.0

LTC1159 • TPC03

2.5

FIGURE 1 CIRCUIT
V

IN

= 24V

LTC1159-3.3/LTC1159-5

LECTRICAL C CHARA TERIST

E

ICS

Note 6: The LTC1159C, LTC1159C-3.3, and LTC1159C-5 are not tested
and not quality assurance sampled at –40°C and 85°C. These
specifications are guaranteed by design and/or correlation. The LTC1159I,
LTC1159I-3.3 and LTC1159I-5 are guaranteed and tested over the –40°C

Note 7: The logic-level power MOSFETs shown in Figure 1 are rated for
V

= 30V. For operation at VIN > 30V, use standard threshold

DS(MAX)

MOSFETs with EXTV
Information.

to 85°C operating temperature range.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Efficiency vs Input Voltage

100

FIGURE 1 CIRCUIT
I

= 1A

LOAD

95

90

EFFICIENCY (%)

85

80

0

5101520

INPUT VOLTAGE (V)

NOTE 6

25 30 35 40

LTC1159 • TPC01

Line Regulation

60

FIGURE 1 CIRCUIT

= 1A

I

LOAD

40

20

(mV)

0

OUT

∆V

–20

–40

–60

0

515

10 20

INPUT VOLTAGE (V)

30

25

NOTE 6

35

LT1159 • TPC02

powered from a 12V supply. See Applications

CC

Load Regulation

40

Operating Frequency

EXTVCC Pin Current

10

FIGURE 1 CIRCUIT

8

I

= 1A

LOAD

6

CURRENT (mA)

4

CC

I

= 100mA

EXTV

2

0

0

510

LOAD

I

= 0

LOAD

20

15 25 40

INPUT VOLTAGE (V)

NOTE 6

30 35

LTC1159 • TPC04

VIN Pin Current

500

FIGURE 1 CIRCUIT

400

300

200

SUPPLY CURRENT (µA)

100

0

0

510

INPUT VOLTAGE (V)

NORMAL

V

= 2V

SHDN2

20

15 25 40

NOTE 6

30 35

LTC1159 • TPC05

vs (VIN – V

2.0
V

= 5V

OUT

1.5

1.0

0.5

NORMALIZED FREQUENCY

0

0

5

(VIN – V

OUT

10

OUT

)

T = 0°C

T = 70°C

15

) VOLTAGE (V)

T = 25°C

20

25

LTC1159 • TPC06

4

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC1159

LTC1159-3.3/LTC1159- 5

EXTVCC Switch Drop Current Sense Threshold Voltage

600

500

400

(mV)

CC

300

– V

CC

200

EXTV

100

0

0

5101520
SWITCH CURRENT (mA)

LTC1159 • TPC07

U

UU

Off-Time vs V

80

70

60

50

40

30

OFF-TIME (µs)

20

10

0

0

OUT

LTC1159-3.3

1

2

OUTPUT VOLTAGE (V)

LTC1159-5

34

LTC1159 • TPC08

5

160

140

120

100

80

60

SENSE VOLTAGE (mV)

40

20

0

0

20

MAXIMUM

THRESHOLD

THRESHOLD

60 80

40

TEMPERATURE (°C)

PI FU CTIO S

VIN: Main Supply Input Pin.
SGND: Small-Signal Ground. Must be routed separately

from other grounds to the (–) terminal of C

OUT

.

PGND: Driver Power Grounds. Connect to source of N­channel MOSFET and the (–) terminal of CIN.

VCC: Outputs of internal 4.5V linear regulator, EXTV
switch, and supply inputs for driver and control circuits.
The driver and control circuits are powered from the higher
of the 4.5V regulator or EXTVCC voltage. Must be closely
decoupled to power ground.

SENSE+: The (+) Input for the Current Comparator. A built­in offset between the SENSE+ and SENSE– pins, in conjunc­tion with R

, sets the current trip threshold.

SENSE

N-Gate: High Current Drive for the Bottom N-Channel
MOSFET. The N-Gate pin swings from ground to VCC.

P-Gate: Level-Shifted Gate Drive Signal for the Top

CC

P-Channel MOSFET. The voltage swing at the P-gate pin is
from VIN to VIN – VCC.

P-Drive: High Current Gate Drive for the Top P-Channel
MOSFET. The P-drive pin(s) swing(s) from VCC to ground.

MINIMUM

100

LTC1159 • TPC09

CT: External capacitor CT from this pin to ground sets the
operating frequency. (The frequency is also dependent on
the ratio V

OUT/VIN

.)

ITH: Gain Amplifier Decoupling Point. The current com­parator threshold increases with the I

pin voltage.

TH

VFB: For the LTC1159 adjustable version, the VFB pin
receives the feedback voltage from an external resistive
divider used to set the output voltage.

SENSE–: Connects to internal resistive divider which sets
the output voltage in fixed output versions. The SENSE– pin
is also the (–) input of the current comparator.

CAP: Charge Compensation Pin. A capacitor to VCC pro-
vides charge required by the P-gate level-shift capacitor
during supply transitions.

pacitor must be larger than the gate drive capacitor

SHDN1: This pin shuts down the control circuitry only (V

The charge compensation ca-

.

CC

is not affected). Taking SHDN1 pin high turns off the
control circuitry and holds both MOSFETs off. This pin
must be at ground potential for normal operation.

SHDN2: Master Shutdown Pin. Taking SHDN2 high shuts
down VCC and all control circuitry.

5

LTC1159
LTC1159-3.3/LTC1159-5

U

U

W

FU CTIO AL DIAGRA

V

IN

SHDN2

EXTV

LOW DROPOUT

4.5V REGULATOR

CC

LOW DROP SWITCH

SLEEP

+

S

V

–

TH2

CAP

V

CC

V

C

T

Internal divider broken at VFB for adjustable versions.

550k

PGND

–

V

+

25mV TO 150mV

13k

SGND

TH

TH1

Q

–

T

+

OFF-TIME
CONTROL

R

S

–

SENSE

–

C

+

I

V

CC

G

550k

–

+

1.25V

REFERENCE

SENSE

P-GATE

P-DRIVE

N-GATE

+

V

OS

SHDN1

–

SENSE

100k

LTC1159 • FD

V

FB

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OPERATIO

The LTC1159 uses a current mode, constant off-time
architecture to synchronously switch an external pair of
complementary power MOSFETs. Operating frequency is
set by an external capacitor at the CT pin.

The output voltage is sensed either by an internal voltage
divider connected to the SENSE– pin (LTC1159-3.3 and
LTC1159-5) or an external divider returned to the VFB pin
(LTC1159). A voltage comparator V, and a gain block G,
compare the divided output voltage with a reference volt­age of 1.25V. To optimize efficiency, the LTC1159 auto­matically switches between two modes of operation, burst
and continuous.

A low dropout 4.5V regulator provides the operating volt­age VCC for the MOSFET drivers and control circuitry during
start-up. During normal operation, the LTC1159 family
powers the drivers and control from the output via the
EXTVCC pin to improve efficiency. The N-GATE pin is
referenced to ground and drives the N-channel MOSFET
gate directly. The P-channel gate drive must be referenced
to the main supply input VIN, which is accomplished by

(Refer to Functional Diagram)

level-shifting the P-drive signal via an internal 550k resistor
and external capacitor.

During the switch “ON” cycle in continuous mode, current
comparator C monitors the voltage between the SENSE

+

and SENSE– pins connected across an external shunt in
series with the inductor. When the voltage across the shunt
reaches its threshold value, the P-gate output is switched
to VIN, turning off the P-channel MOSFET. The timing
capacitor CT is now allowed to discharge at a rate deter­mined by the off-time controller. The discharge current is
made proportional to the output voltage to model the
inductor current, which decays at a rate which is also
proportional to the output voltage. While the timing
capacitor is discharging, the N-gate output is high, turning
on the N-channel MOSFET.

When the voltage on CT has discharged past V

, compara-

TH1

tor T trips, setting the flip-flop. This causes the N-gate output
to go low (turning off the N-channel MOSFET) and the P­gate output to also go low (turning the P-channel MOSFET
back on). The cycle then repeats. As the load current

6