Linear Technology LTC1430A Datasheet

LTC1430A

High Power Step-Down

Switching Regulator Controller

EATU

F

■

High Power 5V to 1.xV-3.xV Switching Controller:

RE

S

Can Exceed 10A Output

■

Maximum Duty Cycle > 90% Permits 3.3V to 2.xV
Conversion Using a Low Power 5V Supply

■

All N-Channel External MOSFETs

■

Fixed Frequency Operation—Small L

■

Excellent Output Regulation: ±1% Over Line, Load

and Temperature Variations

■

High Efficiency: Over 95% Possible

■

No Low Value Sense Resistor Needed

■

Outputs Can Drive External FETs with Up to
10,000pF Gate Capacitance

■

Quiescent Current: 350µA Typ, 1µA in Shutdown

■

Fast Transient Response

■

Adjustable or Fixed 3.3V Output

■

Available in 8-Lead SO and 16-Lead GN
and SO Packages

U

O

PPLICATI

A

■

Power Supply for Pentium® II and AMD-K6

S

®

Microprocessors

■

High Power 5V to 3.xV Regulators

■

Local Regulation for Dual Voltage Logic Boards

■

Low Voltage, High Current Battery Regulation

DUESCRIPTIO

The LTC®1430A is a high power, high efficiency switching
regulator controller optimized for 5V to 1.xV-3.xV applica­tions. It includes a precision internal reference and an
internal feedback system that can provide output regula­tion of ±1% over temperature, load current and line voltage
shifts. The LTC1430A uses a synchronous switching archi­tecture with two N-channel output devices, eliminating the
need for a high power, high cost P-channel device. Addi­tionally, it senses output current across the drain-source
resistance of the upper N-channel FET, providing an
adjustable current limit without an external low value sense
resistor.

The LTC1430A includes a fixed frequency PWM oscillator
for low output ripple under virtually all operating condi­tions. The 200kHz free-running clock frequency can be
externally adjusted from 100kHz to above 500kHz. The
LTC1430A’s maximum duty cycle is typically 93.5% com­pared to 88% for the LTC1430. This permits 3.3V to 2.xV
conversion using a low power 5V supply. The LTC1430A
features low 350µA quiescent current, allowing greater
than 90% efficiency operation in converter designs from
1A to greater than 50A output current. Shutdown mode
drops the LTC1430A supply current to 1µA.

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

Pentium is a registered trademark of Intel Corporation.
AMD-K6 is a registered trademark of Advanced Micro Devices, Inc.

4.7µF

U

O

A

PPLICATITYPICAL

TA = 25°C

= 5V

PV

CC

V

= 3.3V

OUT

Efficiency

LOAD CURRENT (A)

10

1430 TA02

Typical 5V to 3.3V, 10A Application

5V

+

C

IN

220µF
×4

Q1A, Q1B
2 IN PARALLEL

2.7µH/15A

+

Q2

C

OUT

330µF
×6

1430 TA01

3.3V
10A

CC2

LTC1430A

SENSE

SENSE

PV

PGND

–

CC1

I

MAX

GND

MBR0530T1

G1

I

FB

G2NC

+

FB NC

16k

0.1µF

1k

Q1A, Q1B, Q2: MOTOROLA MTD20N03HL

: AVX-TPSE227M010R0100

C

IN

: AVX-TPSE337M006R0100

C

OUT

0.1µF

+

0.1µF

SHUTDOWN

R

7.5k

0.01µF

C

C

C

4700pF

1µF

PV

V

CC

SS

FREQSET
SHDN
COMP

100Ω

+

C1
220pF

100

90

80

70

EFFICIENCY (%)

60

50

40

0.1 1

1

LTC1430A

A

W

O

LUTEXI TIS

S

A

WUW

U

ARB

G

Supply Voltage

VCC....................................................................... 9V

PV

.............................................................. 13V

CC1, 2

Input Voltage

IFB......................................................... –0.3V to 18V

All Other Inputs ...................... –0.3V to (VCC + 0.3V)

WU

/

PACKAGE

G1

PV

CC1

GND

FB

T

JMAX

O

RDER I FOR ATIO

TOP VIEW

1
2
3
4

S8 PACKAGE

8-LEAD PLASTIC SO

= 150°C, θJA = 150°C/W

ORDER

PART NUMBER

G2

8

/PV

V

7

CC

CC2

COMP

6

SHDN

5

LTC1430ACS8

S8 PART MARKING

1430A

(Note 1)

Junction Temperature........................................... 150°C

Operating Temperature Range

LTC1430AC ............................................. 0°C to 70°C

LTC1430AI ........................................ – 40°C to 85°C

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

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

U

TOP VIEW

1

G1

2

PV

CC1

3

PGND

4

GND

–

SENSE

SENSE

16-LEAD PLASTIC SSOP

5
6

FB

+

7
8

SHDN

GN PACKAGE

T

= 150°C, θJA = 130°C/W (GN)

JMAX

T

= 150°C, θJA = 110°C/W (S)

JMAX

G2

16

PV

15

CC2

V

14

CC

I

13

FB

I

12

MAX

FREQSET

11

COMP

10

SS

9

S PACKAGE

16-LEAD PLASTIC SO

ORDER

PART NUMBER

LTC1430ACGN
LTC1430AIGN
LTC1430ACS

Consult factory for Military grade parts.

ELECTRICAL CHARACTERISTICS

VCC = 5V, T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS

V

CC

PV

CC

V

OUT

V

FB

∆V

OUT

I

VCC

I

PVCC

f

OSC

= 25°C (Note 2) unless otherwise noted.

A

LTC1430AC LTC1430AI

Supply Voltage ● 4848V
PV

, PV

CC1

Output Voltage Figure 1 3.30 3.30 V
Feedback Voltage SENSE+ and SENSE– Floating , ● 1.25 1.265 1.28 1.23 1.265 1.29 V

Output Load Regulation Figure 1, I
Output Line Regulation Figure 1, V

Supply Current (VCC Only) Figure 2, V

Supply Current (PVCC) Figure 2, PVCC = 5V, V

Internal Oscillator Frequency FREQSET Floating ● 140 200 260 130 200 300 kHz

Voltage ● 313313V

CC2

= 2.5V

V

COMP

= 0A to 10A 5 5 mV

OUT

= 4.75V to 5.25V 1 1 mV

CC

= V

SHDN

V

= 0V 1 10 1 10 µA

SHDN

V

= 0V 0.1 0.1 µA

SHDN

CC

= VCC (Note 3) 1.5 1.5 mA

SHDN

● 350 700 350 700 µA

2

LTC1430A

ELECTRICAL CHARACTERISTICS

VCC = 5V, T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS

V

IH

V

IL

I

IN

g

mV

g

mI

A

V

I

MAX

I

SS

tr, t

s

t

NOV

DC

MAX

= 25°C (Note 2) unless otherwise noted.

A

LTC1430AC LTC1430AI

SHDN Input High Voltage ● 2.4 2.4 V
SHDN Input Low Voltage ● 0.8 0.8 V
SHDN Input Current ● ±0.1 ±1 ±0.1 ±1 µA
Error Amplifier Transconductance ● 350 650 1100 300 650 1200 µmho
I

Amplifier Transconductance (Note 4) 2400 2400 µmho

LIM

Error Amplifier Open-Loop Gain (Note 5) ● 40 48 40 48 dB
I

Sink Current V

MAX

I(MAX)

= V

CC

● 8 12 16 8 12 17 µA

Soft Start Source Current VSS = 0V ● –8 –12 –16 –8 –12 –17 µA
Driver Rise/Fall Time Figure 3, PV
Driver Non-Overlap Time Figure 3, PV
Maximum Duty Cycle Figure 3, V

= 1.265V

V

FB

= PV

CC1

CC1

COMP

= 5V 80 250 80 250 ns

CC2

= PV

= 5V 25 130 250 25 130 250 ns

CC2

= VCC, ● 90 93.5 89 93.5 %

The ● denotes specifications which apply over the full operating
temperature range.

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a 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: Supply current in normal operation is dominated by the current
needed to charge and discharge the external FET gates. This will vary with

the LTC1430A operating frequency, operating voltage and the external
FETs used.

Note 4: The I
normal (not current limited) operation, the I

Note 5: The open-loop DC gain and transconductance from the FB pin
(SENSE

amplifier can sink but cannot source current. Under

LIM

+

and SENSE– floating) to COMP pin will be AV and gm

output current will be zero.

LIM

V

respectively.

3

LTC1430A

TEMPERATURE (°C)

–40

70

DUTY CYCLE (%)

75

85

90

95

0

40

60

1430 G03

80

–20 20

80

100

100

V

COMP

= V

CC

VFB = 1.265V

LOAD CURRENT (A)

0

–1.0

∆V

OUT

(mV)

–0.8

–0.4

–0.2

0

0.4

1

5

7

1460 G06

–0.6

0.2

4

9

10

2

3

68

TA = 25°C
V

OUT

= 3.3V

V

CC

= 5V

FIGURE 4

UW

TYPICAL PERFOR A CE CHARACTERISTICS

I

Pin Sink Current

MAX

vs Temperature

14.0
VCC = 5V

13.5

Oscillator Frequency
vs Temperature

240

VCC = 5V
FREQSET FLOATING

230

Maximum Duty Cycle
vs Temperature

13.0

12.5

12.0

CURRENT (µA)

MAX

I

11.5

11.0

10.5

–40

–20 0

TEMPERATURE (°C)

40 80 100

20 60

Error Amplifier Transconductance
vs Temperature

850
800
750
700
650
600
550
500
450

TRANSCONDUCTANCE (µmho)

400
350

gm =

–20 20

–40

∆I

COMP

∆V

FB

0

TEMPERATURE (°C)

40

60 100

1430 G01

80

1430 G04

220

210

200

190

OSCILLATOR FREQUENCY (kHz)

180

170

(mV)

FB

∆V

–10

–40

–20 0

∆V

vs Temperature

FB

10

VCC = 5V

8
6
4
2

0
–2
–4
–6
–8

–20 0 40

–40

20 60

TEMPERATURE (°C)

20

TEMPERATURE (°C)

40 80 100

1430 G02

Load Regulation

60 80 100

1430 G05

4

OUTPUT VOLTAGE (V)

Output Voltage vs Load Current
with Current Limit

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

R

= 10k R

I(MAX)

TA = 25°C

= 5V

V

CC

FIGURE 4

0

24 8

0

LOAD CURRENT (A)

= 16k

I(MAX)

6

Supply Current
vs Oscillator Frequency

1000

TA = 25°C

= 5V

V

CC

FIGURE 4

100

10

SUPPLY CURRENT (mA)

1

12

10

1430 G07

0.1
0 200 300 400

100

OSCILLATOR FREQUENCY (kHz)

IV

CC

IPVCC (LOADED

WITH 10,000pF,

= 12V)

PV

CC

(NO LOAD,

IPV

CC

= 12V)

PV

CC

IPVCC (NO LOAD,

= 5V)

PV

CC

500

1430 G08

UU U

PI FU CTIO S

LTC1430A

(16-Lead Package/8-Lead Package)

G1 (Pin 1/Pin 1): Driver Output 1. Connect this pin to the

gate of the upper N-channel MOSFET, Q1. This output will
swing from PV

to PGND. It will always be low when G2

CC1

is high.

PV

(Pin 2/Pin 2): Power VCC for Driver 1. This is the

CC1

power supply input for G1. G1 will swing from PGND to
PV

. PV

CC1

PVCC + V

must be connected to a potential of at least

CC1

(Q1). This potential can be generated using

GS(ON)

an external supply or a simple charge pump connected to
the switching node between the upper MOSFET and the
lower MOSFET; see Applications Information for details.

PGND (Pin 3/Pin 3): Power Ground. Both drivers return to
this pin. It should be connected to a low impedance ground
in close proximity to the source of Q2. 8-lead parts have
PGND and GND tied together at Pin 3.

GND (Pin 4/Pin 3): Signal Ground. All low power internal
circuitry returns to this pin. To minimize regulation errors
due to ground currents, GND should be connected to
PGND right at the LTC1430A. 8-lead parts have PGND and
GND tied together internally at Pin 3.

SENSE–, FB, SENSE+ (Pins 5, 6, 7/Pin 4): These three
pins connect to the internal resistor divider and to the
internal feedback node. To use the internal divider to set
the output voltage to 3.3V, connect SENSE+ to the positive
terminal of the output capacitor and SENSE– to GND. FB
should be left floating in applications that use the internal
divider. To use an external resistor divider to set the output
voltage, float SENSE+ and SENSE– and connect the exter­nal resistor divider to FB.

COMP (Pin 10/Pin 6): External Compensation. The COMP
pin is connected directly to the output of the error amplifier
and the input of the PWM. An RC network is used at this
node to compensate the feedback loop to provide opti­mum transient response. See Applications Information for
compensation details.

FREQSET (Pin 11/NA): Frequency Set. This pin is used to
set the free running frequency of the internal oscillator.
With the pin floating, the oscillator runs at about 200kHz.
A resistor from FREQSET to ground will speed up the
oscillator; a resistor to VCC will slow it down. See Applica­tions Information for resistor selection details.

I

(Pin 12/NA): Current Limit Set. I

MAX

sets the thresh-

MAX

old for the internal current limit comparator. If IFB drops
below I
limit. I

with G1 on, the LTC1430A will go into current

MAX

has a 12µA pull-down to GND. It can be adjusted

MAX

with an external resistor to PVCC or an external voltage
source.

IFB (Pin 13/NA): Current Limit Sense. Connect to the
switched node at the source of Q1 and the drain of Q2
through a 1k resistor. The 1k resistor is required to prevent
voltage transients from damaging IFB. This pin can be
taken up to 18V above GND without damage.

VCC (Pin 14/Pin 7): Power Supply. All low power internal
circuits draw their supply from this pin. Connect to a clean
power supply, separate from the main PVCC supply at the

drain of Q1. This pin requires a 4.7µF or greater bypass
capacitor. 8-lead parts have VCC and PV

tied together

CC2

at Pin 7 and require at least a 10µF bypass to GND.

SHDN (Pin 8/Pin 5): Shutdown. A TTL compatible low
level at SHDN for longer than 50µs puts the LTC1430A into
shutdown mode. In shutdown, G1 and G2 go low, all
internal circuits are disabled and the quiescent current
drops to 10µA max. A TTL compatible high level at SHDN
allows the part to operate normally.

SS (Pin 9/NA): Soft Start. The SS pin allows an external
capacitor to be connected to implement a soft start func­tion. An external capacitor from SS to ground controls the
start-up time and also compensates the current limit loop,
allowing the LTC1430A to enter and exit current limit
cleanly. See Applications Information for more details.

PV

(Pin 15/Pin 7): Power VCC for Driver 2. This is the

CC2

power supply input for G2. G2 will swing from GND to
PV

. PV

CC2

supply. 8-lead parts have VCC and PV

is usually connected to the main high power

CC2

tied together at

CC2

Pin 7 and require at least a 10µF bypass to GND.
G2 (Pin 16/Pin 8): Driver Output 2. Connect this pin to the

gate of the lower N-channel MOSFET, Q2. This output will
swing from PV

to PGND. It will always be low when G1

CC2

is high.

5

LTC1430A

–

+

–

+

I

LIM

FB MIN

PWM

MAX

+

40mV

20k

+

1.265V

12µA

+

40mV

12µA

12.4k

PV

CC1

SHDN

FREQSET

COMP

SS

I

MAX

V

CC

PV

CC2

G1

G2

PGND

I

FB

FB

SENSE

+

SENSE

–

1430 BD

INTERNAL
SHUTDOWN

50µs

DELAY

BLOCK DIAGRAM

W

TEST CIRCUITS

4.7µF

6

= 12V

PV

CC1

PV

CC2

= 5V

+

0.01µF

R

C

7.5k
C

4700pF

1µF

PV

CC2

V

CC

SS

LTC1430A

FREQSET
SHDN
COMP

C

SENSE

100Ω

+

C1
220pF

0.1µF

SHUTDOWN

PV

CC1

I

MAX

PGND

GND

SENSE

–

+

1µF

G1

I

FB

G2NC

+

FB NC

+

C

IN

220µF
×4

Q1A, Q1B
2 IN PARALLEL

2.7µH/15A

+

Q2

Q1A, Q1B, Q2: MOTOROLA MTD20N03HL
C

: AVX-TPSE227M010R0100

IN

C

: AVX-TPSE337M006R0100

OUT

Figure 1

C

OUT

330µF
×6

3.3V

LTC1430A

SENSE

FB MEASUREMENT

+

SENSE

FB

–

NC

NC

V

OUT

1430 F01

1.61k

1k

TEST CIRCUITS

V

SHDN

SHDN

NC
NC
NC
NC

I

MAX

FREQSET
COMP
SS

GND PGND SENSE

V

CC

V

CCPVCC2

LTC1430A

PV

SENSE

PV

CC

CC1IFB

–

LTC1430A

5V

+

10µF

PV

PV

V

CC1

CC

V

G1
G2

FB

NC
NC
NC

+

COMP

COMP

LTC1430A

V

FB

FB

GND

CC2

PGND

G1

10,000pF

G2

10,000pF

0.1µF

G1 RISE/FALL

G2 RISE/FALL

4.7µF

+

Figure 2

100Ω

0.1µF

SHUTDOWN

C1
220pF

+

0.01µF

R

C

7.5k
C

4700pF

1430 F02

1430 F03

Figure 3

V

CC

PV

CC1

I

MAX

PGND

GND

SENSE

–

1N4148

G1

I

FB

G2NC

+

FB NC

0.1µF

16k

1k

Q1A, Q1B, Q2: MOTOROLA MTD20N03HL

: AVX-TPSE227M010R0100

C

IN

C

: AVX-TPSE337M006R0100

OUT

1µF

PV

CC2

V

CC

SS

LTC1430A

FREQSET
SHDN
COMP

C

SENSE

0.1µF

V

= 5V

IN

Q1A, Q1B
2 IN PARALLEL

2.7µH/15A

Q2

+

C

IN

220µF
×4

+

C

OUT

330µF
×6

3.3V

1430 F04

Figure 4

7

LTC1430A

U

WUU

APPLICATIONS INFORMATION

OVERVIEW

T

he LTC1430A is a voltage feedback PWM switching
regulator controller (see Block Diagram) designed for use
in high power, low voltage step-down (buck) converters.
It includes an onboard PWM generator, a precision refer­ence trimmed to ±0.5%, two high power MOSFET gate
drivers and all necessary feedback and control circuitry to
form a complete switching regulator circuit. The PWM
loop nominally runs at 200kHz.

The 16-lead versions of the LTC1430A include a current
limit sensing circuit that uses the upper external power
MOSFET as a current sensing element, eliminating the
need for an external sense resistor.

Also included in the 16-lead version is an internal soft start
feature that requires only a single external capacitor to
operate. In addition, 16-lead parts feature an adjustable
oscillator which can run at frequencies from 50kHz to
500kHz, allowing added flexibility in external component
selection. The 8-lead version does not include current
limit, internal soft start or frequency adjustability.

THEORY OF OPERATION

Primary Feedback Loop

The LTC1430A senses the output voltage of the circuit at
the output capacitor with the SENSE+ and SENSE– pins
and feeds this voltage back to the internal transconduc­tance amplifier FB. FB compares the resistor-divided out­put voltage to the internal 1.265V reference and outputs an
error signal to the PWM comparator. This is then com­pared to a fixed frequency sawtooth waveform generated
by the internal oscillator to generate a pulse width modu­lated signal. This PWM signal is fed back to the external
MOSFETs through G1 and G2, closing the loop. Loop
compensation is achieved with an external compensation
network at COMP, the output node of the FB transconduc­tance amplifier.

MIN, MAX Feedback Loops

Two additional comparators in the feedback loop provide
high speed fault correction in situations where the FB
amplifier may not respond quickly enough. MIN compares
the feedback signal to a voltage 40mV (3%) below the

internal reference. At this point, the MIN comparator
overrides the FB amplifier and forces the loop to full duty
cycle, set by the internal oscillator at about 93.5%. Simi­larly, the MAX comparator monitors the output voltage at
3% above the internal reference and forces the output to
0% duty cycle when tripped. These two comparators
prevent extreme output perturbations with fast output
transients, while allowing the main feedback loop to be
optimally compensated for stability.

Current Limit Loop

The 16-lead LTC1430A devices include yet another feed­back loop to control operation in current limit. The current
limit loop is disabled in the 8-lead device. The I
fier monitors the voltage drop across external MOSFET Q1
with the IFB pin during the portion of the cycle when G1 is
high. It compares this voltage to the voltage at the I
As the peak current rises, the drop across Q1 due to its
R
that Q1’s drain current has exceeded the maximum level,
I

LIM

capacitor, cutting the duty cycle and controlling the output
current level. At the same time, the I
generates a signal to disable the MIN comparator to
prevent it from conflicting with the current limit circuit. If
the internal feedback node drops below about 0.8V, indi­cating a severe output overload, the circuitry will force the
internal oscillator to slow down by a factor of as much as

100. If desired, the turn on time of the current limit loop
can be controlled by adjusting the size of the soft start
capacitor, allowing the LTC1430A to withstand short
overcurrent conditions without limiting.

By using the R
the current limit circuit eliminates the sense resistor that
would otherwise be required and minimizes the number of
components in the external high current path. Because
power MOSFET R
with temperature, the LTC1430A current limit is not de­signed to be accurate; it is meant to prevent damage to the
power supply circuitry during fault conditions. The actual
current level where the limiting circuit begins to take effect
may vary from unit to unit, depending on the power
MOSFETs used. See Soft Start and Current Limit for more
details on current limit operation.

increases. When IFB drops below I

DS(ON)

starts to pull current out of the external soft start

of Q1 to measure the output current,

DS(ON)

is not tightly controlled and varies

DS(ON)

MAX

LIM

ampli-

LIM

pin.

MAX

, indicating

comparator

8