Linear Technology LTC1553L Datasheet

FEATURES

■

5-Bit Digitally Programmable 1.8V to 3.5V Fixed
Output Voltage

■

Provides All Features Required by the

Intel
Pentium® II Processor VRM 8.2 DC/DC
Converter Specification

■

Flags for Power Good, Over-Temperature and
Overvoltage Fault

■

19A Output Current Capability from a 5V Supply

■

Dual N-Channel MOSFET Synchronous Driver

■

Initial Output Accuracy: ±1.5%

■

Excellent Output Accuracy: ±2% Typ Over Line,
Load and Temperature Variations

■

High Efficiency: Over 95% Possible

■

Adjustable Current Limit Without External Sense
Resistors

■

Fast Transient Response

■

Available in 2O-Lead SSOP and SW Packages

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APPLICATIONS

■

Power Supply for Pentium II, SPARC, ALPHA and
PA-RISC Microprocessors

■

High Power 5V to 1.8V-3.5V Regulators

LTC1553L

5-Bit Programmable

Synchronous Switching

Regulator Controller for

®

Pentium

II Processor

U

DESCRIPTION

The LTC®1553L is a high power, high efficiency switching
regulator controller optimized for a 5V input to 1.8V-3.5V
output applications. It features a digitally programmable
output voltage, a precision internal reference and an internal
feedback system that provides output accuracy of ±1.5% at
room temperature and typically ±2% over-temperature, load
current and line voltage shifts. The LTC1553L uses a syn­chronous switching architecture with two external N-channel
output devices, providing high efficiency and eliminating the
need for a high power, high cost P-channel device. Addition­ally, it senses the output current across the on-resistance of
the upper N-channel FET, providing an adjustable current
limit without an external low value sense resistor.

The LTC1553L free-runs at 300kHz and can be synchronized
to a faster external clock if desired. It includes all the inputs
and outputs required to implement a power supply conform­ing to the

Converter Specification

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

Pentium is a registered trademark of Intel Corporation.

Intel Pentium® II Processor VRM 8.2 DC/DC

.

TYPICAL APPLICATION

5.6k

5.6k

PENTIUM® II

SYSTEM

C1
150pF

5

U

5.6k

R

8.2k



C

CC

0.01µF

+

0.1µF

10µF CIN**

PWRGD
FAULT
OT
VID0 TO VID4
OUTEN
COMP

C

SS

0.1µF

V

SS SGND GND SENSE



CC

LTC1553L

PV

CC

12V

2.7k

I

MAX

0.1µF

PV

CC

G1

I



FB

G2



0.1µF

Figure 1. 5V to 1.8V-3.5V Supply Application

V

IN

5V

+

10µF

Q1*

20Ω

Q2*

 *SILICONIX SUD50N03-10
**SANYO 10MV1200GX



†

COILTRONICS CTX02-13198 OR

 PANASONIC 12TS-2R5SP

††

AVX TPSE337M006R0100



+

L

2µH
18A

1200µF
× 4

O†

††



C

+

OUT

330µF

× 7

V

OUT

1.8V TO

3.5V
14A

1553L F01



1

LTC1553L

WW

W

U

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Supply Voltage

VCC........................................................................ 7V

PVCC................................................................... 14V

Input Voltage

IFB (Note 2)............................................ PVCC + 0.3V

I

........................................................ – 0.3V to 9V

MAX

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

Digital Output Voltage................................. – 0.3V to 9V

IFB Input Current (Notes 2, 3) .......................... –100mA

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

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

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

ELECTRICAL CHARACTERISTICS

VCC = 5V, PVCC = 12V, TA = 25°C, unless otherwise noted. (Note 3)

U

W

PACKAGE/ORDER INFORMATION

TOP VIEW

1

G2

2

PV



CC

3

GND

4

SGND

5

V



CC

6

SENSE

7

I



MAX

8

I



FB

9

SS

10

COMP

G PACKAGE

20-LEAD PLASTIC SSOP

T

= 125°C, θJA = 100°C/ W (G)

JMAX

= 125°C, θJA = 100°C/ W (SW)

T

JMAX

20-LEAD PLASTIC SO

G1

20

OUTEN

19

VID0

18

VID1

17

VID2

16

VID3

15

VID4

14

PWRGD

13

FAULT

12

OT

11





SW PACKAGE



Consult factory for Industrial and Military grade parts.

ORDER PART

NUMBER

LTC1553LCG
LTC1553LCSW

U

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V
PV
V
V

CC

CC

FB

OUT

Supply Voltage ● 4.5 6 V
Supply Voltage for G1, G2 ● 13.2 V
Internal Feedback Voltage (Note 4) 1.260 V

1.8V Initial Output Voltage With Respect to Rated Output Voltage (Figure 2) – 27 (– 1.5%) 27 (+1.5%) mV

2.8V Initial Output Voltage – 42 (–1.5%) 42 (+ 1.5%) mV

3.5V Initial Output Voltage – 52 (–1.5%) 52 (+1.5%) mV

1.8V Initial Output Voltage

2.8V Initial Output Voltage

3.5V Initial Output Voltage

∆V

OUT

Output Load Regulation I
Output Line Regulation V

V

PWRGD

Positive Power Good Trip Point % Above Output Voltage (Figure 2) ● 57 %
Negative Power Good Trip Point % Below Output Voltage (Figure 2)

V

FAULT

I

CC

FAULT Trip Point % Above Output Voltage (Figure 2) ● 12 15 20 %
Operating Supply Current OUTEN = VCC = 5V (Note 5)(Figure 3) ● 800 1200 µA

Shutdown Supply Current OUTEN = 0, VID0 to VID4 Floating (Figure 3)

I

PVCC

f

OSC

V

SAWL

V

SAWH

G

ERR

g

mERR

BW

ERR

Supply Current PVCC = 12V, OUTEN = VCC (Note 6) (Figure 3) 15 mA

Internal Oscillator Frequency (Figure 4) ● 250 300 350 kHz
V

at Minimum Duty Cycle (Note 4) 1.8 V

COMP

V

at Maximum Duty Cycle (Note 4) 2.8 V

COMP

Error Amplifier Open-Loop DC Gain (Note 7) ● 40 53 dB
Error Amplifier Transconductance (Note 7) ● 0.9 1.6 2.3 millimho
Error Amplifier –3dB Bandwidth COMP = Open (Note 4) 400 kHz

= 0 to 14A (Note 4) (Figure 2) –5 mV

OUT

= 4.75V to 5.25V, I

IN

= 12V, OUTEN = 0, VID0 to VID4 Floating 1 µA

PV

CC

= 0 (Note 4)(Figure 2) ±1mV

OUT

● – 36 (–2%) 36 (+2%) mV

● – 56 (–2%) 56 (+2%) mV

● – 70 (–2%) 70 (+2%) mV

● –7 –5 %

● 130 250 µA

2

LTC1553L

ELECTRICAL CHARACTERISTICS

VCC = 5V, PVCC = 12V, TA = 25°C, unless otherwise noted. (Note 3)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

IMAX

I

SS

I

SSIL

I

SSHIL

I

Sink Current V

MAX

Soft Start Source Current VSS = 0V, V
Maximum Soft Start Sink Current V

IMAX

SENSE

= V

= V

CC

IMAX

OUT

Under Current Limit (Notes 8, 9), V
Soft Start Sink Current Under Hard V

SENSE

= 0V, V

= 0V, V

, V

IMAX

= V

SS

IMAX

IFB

= VCC, V

CC

= VCC, V

● 150 180 220 µA

= V

CC

= 0V ● 30 60 150 µA

IFB

= 0V ● 20 45 mA

IFB

● –15 –11 –8 µA

Current Limit

t

SSHIL

t

PWRGD

t

PWRBAD

t

FAULT

t

OT

V

OT

V

OTDD

V

SHDN

tr, t

f

t

NOL

DC

MAX

V

IH

V

IL

R

IN

Hard Current Limit Hold Time V
Power Good Response Time↑ V
Power Good Response Time↓ V
FAULT Response Time V

= 0V, V

SENSE

↑ from 0V to Rated V

SENSE

↓ from Rated V

SENSE

↑ from Rated V

SENSE

IMAX

= 4V, V

↓ from 5V (Note 4) 500 µs

IFB

OUT

to 0V ● 200 500 1000 µs

OUT

to V

OUT

CC

● 0.5 1 2 ms

● 200 500 1000 µs

OT Response Time OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3) ● 15 40 60 µs
Over-Temperature Trip Point OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3) ● 1.9 2 2.12 V
Over-Temperature Driver Disable OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3) ● 1.6 1.7 1.8 V
Shutdown OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3) ● 0.8 V
Driver Rise and Fall Time (Figure 4) ● 90 150 ns
Driver Nonoverlap Time (Figure 4) ● 30 100 ns
Maximum G1 Duty Cycle (Figure 4) ● 77 85 90 %
VID0 to VID4 Input High Voltage ● 2V
VID0 to VID4 Input Low Voltage ● 0.8 V
VID0 to VID4 Internal Pull-Up ● 10 20 kΩ

Resistance

I

SINK

Digital Output Sink Current ● 10 mA

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: When I

is taken below GND, it will be clamped by an internal

FB

diode. This pin can handle input currents greater than 100mA below GND
without latchup. In the positive direction, it is not clamped to V

or PVCC.

CC

Note 3: All currents into device pins are positive; all currents out of the
device pins are negative. All voltages are referenced to ground unless
otherwise specified.

Note 4: This parameter is guaranteed by correlation and is not tested
directly.

Note 5: The LTC1553L goes into the shutdown mode if VID0 to VID4 are
floating. Due to the internal pull-up resistors, there will be an additional

0.25mA/pin if any of the VID0 to VID4 pins are pulled low.

Note 6: Supply current in normal operation is dominated by the current
needed to charge and discharge the external FET gates. This will vary with
the LTC1553L operating frequency, supply voltage and the external FETs
used.

Note 7: The open-loop DC gain and transconductance from the SENSE pin to
COMP pin will be (G

)(1.260/3.3) and (g

ERR

)(1.260/3.3) respectively.

mERR

Note 8: The current limiting amplifier can sink but cannot source current.
Under normal (not current limited) operation, the output current will be zero.

Note 9: Under typical soft current limit, the net soft start discharge current
will be 60µA (I

) + [–11µA(ISS)] ≅ 50µA. The soft start sink-to-source

SSIL

current ratio is designed to be 5.5:1.
Note 10: When VID0 to VID4 are all HIGH, the LTC1553L will be forced to

shut down internally. The OUTEN trip voltages are guaranteed by design for
all other input codes.

3

LTC1553L

TEMPERATURE (°C)

–50

OVER-TEMPERATURE TRIP POINT (V)

1.96

2.08

2.10

2.12

0

50

75

1553L G06

1.92

2.04

2.00

1.94

2.06

1.90

2.02

1.98

–25

25

100

125

TEMPERATURE (°C)

–50

40

ERROR AMPLIFIER OPEN-LOOP DC GAIN (dB)

45

50

55

60

–25 0 25 50

1553L G09

75 100 125

UW

TYPICAL PERFORMANCE CHARACTERISTICS

Typical 2.8V V

140

TOTAL SAMPLE SIZE = 1500

120

100

80

60

NUMBER OF UNITS

40

20

0

2.775

2.785

25°C 100°C

OUTPUT VOLTAGE (V)

Distribution Load Regulation

OUT

2.795

2.805 2.815

2.825

1553L G01

Efficiency vs Load Current

100

90

A

B

80

70

REFER TO TYPICAL APPLICATION

60

CIRCUIT FIGURE 1

= 5V, PVCC = 12V, V

V

50

IN

= 330µF ×7, LO = 2µH

C

OUT

40

EFFICIENCY (%)

A: Q1 = 1 × SUD50N03-10
Q2 = 1 × SUD50N03-10

30

B: Q1 = 2 × SUD50N03-10

20

Q2 = 1 × SUD50N03-10
NO FAN

10

Q1 IS MOUNTED ON 1IN


0



0

2

0.3

4

LOAD CURRENT (A)

Line Regulation Output Temperature Drift

2.825
REFER TO TYPICAL APPLICATION 

2.820

CIRCUIT FIGURE 1
OUTPUT = NO LOAD

2.815

2.810

2.805

2.800

2.795

2.790

OUTPUT VOLTAGE (V)

2.785

2.780

2.775

4.75

T

A

= 25°C

4.85

5.05

4.95

INPUT VOLTAGE (V)

5.15

5.25

1553L G04

2.860

2.850

2.840

2.830

2.820

2.810

2.800

2.790

2.780

OUTPUT VOLTAGE (V)

2.770

2.660

2.750

2.740
–50

–25

0

TEMPERATURE (°C)

= 2.8V, 

OUT

2

COPPER AREA

6 8 10 12 14

1533L G02

50

25

75

100

1553L G05

2.825

2.820

2.815

2.810

2.805

2.800

2.795

2.790

OUTPUT VOLTAGE (V)

2.785

2.780

2.775

125

REFER TO TYPICAL APPLICATION
CIRCUIT FIGURE 1

= 5V, PVCC = 12V, TA = 25°C

V

IN

123

0

4

67891011121314

5

OUTPUT CURRENT (A)

Over-Temperature Trip Point
vs Temperature

1533L G03

Over-Temperature Driver Disable
vs Temperature

1.80

1.78

1.76

1.74

1.72

1.70

1.68

1.66

1.64

1.62

OVER-TEMPERATURE DRIVER DISABLE (V)

1.60

4

–50

–25

0

TEMPERATURE (°C)

25

50

Error Amplifier Transconductance
vs Temperature

2.3

2.1

1.9

1.7



1.5

1.3

1.1

100

125

1553L G07

75

0.9

ERROR AMPLIFIER TRANSCONDUCTANCE (millimho)

–50

–25 0

TEMPERATURE (°C)

50 100 125

25 75

1553L G08

Error Amplifier Open-Loop
DC Gain vs Temperature

UW

TEMPERATURE (°C)

–50

SOFT START SOURCE CURRENT (µA)

–9

–8

25 75

1553L G12

–10

–11

–25 0

50 100 125

–12

–13

–14

–15

TEMPERATURE (°C)

–50

V

CC

SHUTDOWN SUPPLY CURRENT (mA)

225

25

1553L G15

150

100

–25 0 50

75

50

250

200

175

125

75 100 125

TYPICAL PERFORMANCE CHARACTERISTICS

LTC1553L

Oscillator Frequency
vs Temperature

350
340
330
320
310
300
290
280
270

OSCILLATOR FREQUENCY (kHz)

260
250

–50

–25

25

0

TEMPERATURE (°C)

Maximum G1 Duty Cycle
vs Temperature

92

OSCILLATOR FREQUENCY = 300kHz

90

G1, G2 CAPACITANCE = 1100pF

88

86

84

82

80

MAXIMUM G1 DUTY CYCLE (%)

78

–50

–25 0

5500pF
7700pF

25 75

TEMPERATURE (°C)

50

75

50 100 125

100

1553L G10

2200pF
3300pF

1553L G13

125

I

Sink Current

MAX

vs Temperature

220

210

200

190

180

SINK CURRENT (µA)

170

MAX

I

160

150

–50

0

–25

TEMPERATURE (°C)

25

VCC Operating Supply Current
vs Temperature

1.2
VCC = 5V

= 300kHz

f

OSC

1.1

1.0

0.9



0.8

0.7

OPERATING SUPPLY CURRENT (mA)

0.6

CC

V

0.5

–50

–25 0

25 75

TEMPERATURE (°C)

75

50 125

50 100 125

100

1553L G11

1553L G14

Soft Start Source Current
vs Temperature

VCC Shutdown Supply Current
vs Temperature

PVCC Supply Current
vs Gate Capacitance

70

PVCC = 12V

= 25°C

T

A

60

50

40

30

SUPPLY CURRENT (mA)

20

CC

PV

10

0

2000 4000 8000

0

GATE CAPACITANCE (pF)

6000

1553L G16

Output Over Current Protection

3.0

Q1 CASE = 90°C, V

2.5

Q1 = 2 × MTD20N03HDL
Q2 = 1 × MTD20N03HDL

2.0

1.5

1.0

OUTPUT VOLTAGE (V)

0.5

= 2.7k, R

R

IMAX

SS CAP = 0.01µF

SHORT-CIRCUIT

CURRENT

0

26

0

4

OUTPUT CURRENT (A)

= 2.8V

OUT

= 20Ω,

IFB

10 18

8

Transient Response

50mV/DIV

5A/DIV

100µs/DIV

14

12

16

1553L G17

1553L G18

5

LTC1553L

UUU

PIN FUNCTIONS

G2 (Pin 1): Gate Drive for the Lower N-Channel MOSFET,
Q2. This output will swing from PVCC to GND. It will always
be low when G1 is high or when the output is disabled. To
prevent undershoot during a soft start cycle, G2 is held low
until G1 first goes high.

PVCC (Pin 2): Power Supply for G1 and G2. PVCC must be
connected to a potential of at least VIN + V
VIN = 5V, PVCC can be generated using a simple charge
pump connected to the switching node between Q1 and
Q2 (see Figure 7), or it can be connected to an auxiliary 12V
supply if one exists.

GND (Pin 3): Power Ground. GND should be connected to
a low impedance ground plane in close proximity to the
source of Q2.

SGND (Pin 4): Signal Ground. SGND is connected to the
low power internal circuitry and should be connected to
the negative terminal of the output capacitor where it
returns to the ground plane. GND and SGND should be
shorted right at the LTC1553L.

VCC (Pin 5): Power Supply. Power for the internal low
power circuity. VCC should be wired separately from the
drain of Q1 if they share the same supply. A 10µ F bypass
capacitor is recommended from this pin to SGND.

SENSE (Pin 6): Output Voltage Pin. Connect to the positive
terminal of the output capacitor. There is an internal 120k
resistor connected from this pin to SGND. SENSE is a very
sensitive pin; for optimum performance, connect an exter­nal 0.1µ F capacitor from this pin to SGND. By connecting
a small external resistor between the output capacitor and
the SENSE pin, the initial output voltage can be raised
slightly. Since the internal divider has a nominal imped­ance of 120kΩ, a 1200Ω series resistor will raise the
nominal output voltage by 1%. If an external resistor is
used, the value of the 0.1µF capacitor on the SENSE pin
must be greatly reduced or loop phase margin will suffer.
Set a time constant for the RC combination of approxi­mately 0.1µ s. So, for example, with a 1200Ω resistor, set
C = 83pF. Use a standard 100pF capacitor.

GS(ON)Q1

. If

I

(Pin 7): Current Limit Threshold. Current limit is set

MAX

by the voltage drop across an external resistor connected
between the drain of Q1 and I
pull-down at I

IFB (Pin 8): Current Limit Sense Pin. Connect to the
switching node between the source of Q1 and the drain of
Q2. If IFB drops below I
will go into current limit. The current limit circuit can be
disabled by floating I
an external 10k resistor.

SS (Pin 9): Soft Start. Connect to an external capacitor to
implement a soft start function. During moderate overload
conditions, the soft start capacitor will be discharged
slowly in order to reduce the duty cycle. In hard current
limit, the soft start capacitor will be forced low immedi­ately and the LTC1553L will rerun a complete soft start
cycle. CSS must be selected such that during power-up the
current through Q1 will not exceed the current limit value.

COMP (Pin 10): External Compensation. The COMP pin is
connected directly to the output of the error amplifier and
the input of the PWM comparator. An RC+C network is
used at this node to compensate the feedback loop to
provide optimum transient response.

OT (Pin 11): Over-Temperature Fault. OT is an open-drain
output and will be pulled low if OUTEN is less than 2V. If
OUTEN = 0, OT pulls low.

FAULT (Pin 12): Overvoltage Fault. FAULT is an open­drain output. If V
output voltage, FAULT will go low and G1 and G2 will be
disabled. Once triggered, the LTC1553L will remain in this
state until the power supply is recycled or the OUTEN pin
is toggled. If OUTEN = 0, FAULT floats or is pulled high by
an external resistor.

PWRGD (Pin 13): Power Good. This is an open-drain
signal to indicate validity of output voltage. A high indi­cates that the output has settled to within ±5% of the rated
output for more than 1ms. PWRGD will go low if the output
is out of regulation for more than 500µs. If OUTEN = 0,
PWRGD pulls low.

MAX

.

MAX

and shorting IFB to VCC through

MAX

reaches 15% above the nominal

OUT

. There is a 180µ A internal

MAX

when G1 is on, the LTC1553L

6