Semtech Corporation SC1102CSTR, SC1102EVB Datasheet

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

SC1102

September 5, 2000

TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com

DESCRIPTION

The SC1102 is a low-cost, full featured, synchronous voltage-mode controller designed for use in single ended power supply applications where efficiency is of primary concern. Synchronous operation allows for the elimination of heat sinks in many applications. The SC1102 is ideal for implementing DC/DC converters needed to power advanced microprocessors in low cost systems, or in distributed power applications where efficiency is important. Internal level-shift, highside drive circuitry, and preset shoot-thru control, allows the use of inexpensive N-channel power switches.

SC1102 features include temperature compensated voltage reference, triangle wave oscillator and current sense comparator circuitry. Power good signaling, shutdown, and over voltage protection are also provided.

The SC1102 operates at a fixed 200kHz, providing an optimum compromise between efficiency, external component size, and cost.

APPLICATION CIRCUIT

Typical Distributed Power Supply

FEATURES

•

1.265V Reference available

•

Synchronous operation

•

Over current fault monitor

•

On-chip power good and OVP functions

•

Small size with minimum external components

•

Soft Start

•

R

Current sensing

DS(ON)

APPLICATIONS

•

Microprocessor core supply

•

Low cost synchronous applications

•

Voltage Regulator Modules (VRM)

ORDERING INFORMATION

DEVICE

SC1102CSTR SO-14 0 - 125°C

SC1102EVB Evaluation Board

Note: (1) Only available in tape and reel packaging. A reel contains 2500 devices.

(1)

PACKAGE TEMP. RANGE (TJ)

PWRGD

OVP

+5V

R4

R1

R2

1k

C1

0.1

C2

0.1

R3 1k

D1

MBR0520

U1

10

SC1102

1

VCC

2

PWRGD

3

OVP

4

OCSET

5

PHASE

6

DRVH

7

PGND

GND

SS/SHDN

VREF

SENSE

BSTH

BSTL

DRVL

14

C3

0.1

13

12

11

10

9

8

SHDN

VREF

+12V

C4

1.0

R5

3.9

R6

2.2

Q1

STP40NE

Q2

STP40NE

L1 2uH

NOTE:

*) Vout = 1.265 x (1+R8/R7)

C6 680/6.3V

R8 124*

C10 180/4V

C7 680/6.3V

C11 180/4V

C5

10.0

R7 127

C9 180/4V

C8 680/6.3V

+

Vin 5V

_

C12 180/4V

C13 180/4V

+

Vout=2.5V*

_

Figure 1.

1

SYNCHRONOUS DC/DC CONTROLLER FOR

SC1102

DISTRIBUTED POWER SUPPLY APPLICATIONS

September 5, 2000

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Maximum Units

V

, BSTL to GND V

CC

IN

PGND to GND ± 0.5 V PHASE to GND -0.3 to 18 V BSTH to PHASE 14 V

-0.3 to 14 V

Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Operating Temperature Range T Storage Temperature Range T

Lead Temperature (Soldering) 10 sec T

θ

JC

θ

JA

STG

LEAD

A

45 °C/W

115 °C/W

0 to 70 °C

-65 to +150 °C 300 °C

ESD Rating (Human Body Model) ESD 2 kV

ELECTRICAL CHARACTERISTICS

Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; V

PARAMETER CONDITIONS MIN TYP MAX UNITS POWER SUPPLY

Supply Voltage V Supply Current EN = V Line Regulation V

CC

= 2.5V 0.5 %

O

ERROR AMPLIFIER

Gain (AOL) 35 dB Input Bias 58µA

OSCILLATOR

BSTL

= 12V; V

BSTH-PHASE

= 12V; TJ = 25oC

4.2 12.6 V 610mA

Oscillator Frequency 180 200 220 kHz Oscillator Max Duty Cycle 90 95 %

MOSFET DRIVERS

DH Source/Sink Current BST DL Source/Sink Current BST

- DH = 4.5V / DH - PHASE = 2V 1 A

H

- DL = 4.5V / DL - PGNDL = 2V 1 A

L

PROTECTION

OVP Threshold Voltage 20 % OVP Source Current V

= 3V 10 mA

OVP

Power Good Threshold 88 112 % Dead Time 45 100 ns Over Current Set Isource

2.0V ≤ V

OCSET

≤ 12V

180 200 220 µA

NOTE:

(1) Specification refers to application circuit (Figure 1).

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SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

September 5, 2000

ELECTRICAL CHARACTERISTICS (CONT)

SC1102

Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; V

BSTL

= 12V; V

BSTH-PHASE

= 12V; TJ = 25oC

PARAMETER CONDITIONS MIN TYP MAX UNITS REFERENCE

Reference Voltage 1.252 1.265 1.278 V Accuracy -1 +1 %

SOFT START

Charge Current V Discharge Current V

= 1.5V 8.0 10 12 µA

SS

= 1.5V 1.3 2 2.4 µA

SS

BLOCK DIAGRAMPIN CONFIGURATION

Top View

(14-Pin SOIC)

3

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

September 5, 2000

PIN DESCRIPTION

Pin # Pin Name Pin Function

1 VCC Chip supply voltage 2 PWRGD Logic high indicates correct output voltage 3 OVP Over voltage protection. 4 OCSET Sets the converter overcurrent trip point 5 PHASE Input from the phase node between the MOSFET’S 6 DH High side driver output 7 PGND Power ground 8 DL Low side driver output

9 BSTL Bootstrap, low side driver. 10 BSTH Bootstrap, high side driver. 11 SENSE Voltage sense input

SC1102

12 VREF Buffered band gap voltage reference. 13 SS/SHDN Soft start. A capacitor to ground sets the slow start time. 14 GND Signal ground

NOTE:

(1) All logic level inputs and outputs are open collector TTL compatible.

CHARACTERISTIC CURVES

SC1102 Voltage Regulation, Vin=5V

2%

1%

0%

-1%

-2% 0123456789101112

Current, A

3.3V

2.5V

2.0V

1.3V

100%

90%

80%

70%

60%

0123456789101112

SC1102 Effiency, Vin=5V

Current, A

3.3V

2.5V

2.0V

1.3V

4

September 5, 2000

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

Gate Drive WaveformsOutput Ripple Voltage

SC1102

1. VIN = 5V; VO = 3.3V; I

Ch1: Vo_rpl

2. V

= 5V; V

IN

= 1.3V; I

OUT

= 12A

Ch1: Top FET Ch2: Bottom FET

= 12A

Ch1: Vo_rpl Ch1: Top FET

Ch2: Bottom FET

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September 5, 2000

Start Up

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

Ch1: Vin Ch2: Vss Ch3: Top Gate Ch4: Vout

Vin = 5V Vout = 3.3V Iout = 2A Vbst = 12V

SC1102

Hiccup Mode

Ch1: Vin Ch2: Vss Ch3: Top Gate Ch4: Vout

Vin = 5V Vout = 3.3V Vbst = 12V

Iout = S.C.

6

September 5, 2000

THEORY OF OPERATION

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

SC1102

Synchronous Buck Converter

Primary V

power is provided by a synchronous,

CORE

voltage-mode pulse width modulated (PWM) controller. This section has all the features required to build a high efficiency synchronous buck converter, including “Power Good” flag, shut-down, and cycle-by-cycle current limit.

The output voltage of the synchronous converter is set and controlled by the output of the error amplifier. The external resistive divider reference voltage is derived from an internal trimmed-bandgap voltage reference (See Fig. 1). The inverting input of the error amplifier receives its voltage from the SENSE pin.

The internal oscillator uses an on-chip capacitor and trimmed precision current sources to set the oscillation frequency to 200kHz. The triangular output of the oscillator sets the reference voltage at the inverting input of the comparator. The non-inverting input of the comparator receives it’s input voltage from the error amplifier. When the oscillator output voltage drops below the error amplifier output voltage, the comparator output goes high. This pulls DL low, turning off the low-side FET, and DH is pulled high, turning on the high-side FET (once the cross-current control allows it). When the oscillator voltage rises back above the error amplifier output voltage, the comparator output goes low. This pulls DH low, turning off the high-side FET, and DL is pulled high, turning on the low-side FET (once the cross-current control allows it).

As SENSE increases, the output voltage of the error amplifier decreases. This causes a reduction in the ontime of the high-side MOSFET connected to DH, hence lowering the output voltage.

Under Voltage Lockout

The under voltage lockout circuit of the SC1102 assures that the high-side MOSFET driver outputs remain in the off state whenever the supply voltage drops below set parameters. Lockout occurs if V

4.1V. Normal operation resumes once V

falls below

CC

rises above

CC

4.2V.

Over-Voltage Protection

The over-voltage protection pin (OVP) is high only when the voltage at SENSE is 20% higher than the target value programmed by the external resistor divider. The OVP pin is internally connected to a PNP’s collector.

Power Good

The power good function is to confirm that the regulator outputs are within +/-10% of the programmed level. PWRGD remains high as long as this condition is met. PWRGD is connected to an internal open collector NPN transistor.

Soft Start

Initially, SS/SHDN sources 10µA of current to charge an external capacitor. The outputs of the error amplifiers are clamped to a voltage proportional to the voltage on SS/SHDN. This limits the on-time of the highside MOSFETs, thus leading to a controlled ramp-up of the output voltages.

Current Limiting

R

DS(ON)

The current limit threshold is set by connecting an external resistor from the V

supply to OCSET. The

CC

voltage drop across this resistor is due to the 200µA internal sink sets the voltage at the pin. This voltage is compared to the voltage at the PHASE node. This comparison is made only when the high-side drive is high to avoid false current limit triggering due to uncontributing measurements from the MOSFET’s offvoltage. When the voltage at PHASE is less than the voltage at OCSET, an overcurrent condition occurs and the soft start cycle is initiated. The synchronous switcher turns off and SS/SHDN starts to sink 2µA. When SS/SHDN reaches 0.8V, it then starts to source 10µA and a new cycle begins.

Hiccup Mode

During power up, the SS/SHDN pin is internally pulled low until VCC reaches the undervoltage lockout level of 4.2V. Once V

has reached 4.2V, the

CC

SS/SHDN pin is released and begins to source 10µA of current to the external soft-start capacitor. As the soft-start voltage rises, the output of the internal error amplifier is clamped to this voltage. When the error signal reaches the level of the internal triangular oscillator, which swings from 1V to 2V at a fixed frequency of 200 kHz, switching occurs. As the error signal crosses over the oscillator signal, the duty cycle of the PWM signal continues to increase until the output comes into regulation. If an over-current condition has not occurred the soft-start voltage will continue to rise and level off at about 2.2V.

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September 5, 2000

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

SC1102

THEORY OF OPERATION (CON’T)

An over-current condition occurs when the high-side drive is turned on, but the PHASE node does not reach the voltage level set at the OCSET pin. The PHASE node is sampled only once per cycle during the valley of the triangular oscillator. Once an over-current occurs, the high-side drive is turned off and the lowside drive turns on and the SS/SHDN pin begins to sink 2uA. The soft-start voltage will begin to decrease as the 2uA of current discharges the external capacitor. When the soft-start voltage reaches 0.8V, the SS/ SHDN pin will begin to source 10uA and begin to charge the external capacitor causing the soft-start voltage to rise again. Again, when the soft-start voltage reaches the level of the internal oscillator, switching will occur.

APPLICATION CIRCUIT

Typical 12V Application Circuit with Bootstrapped BSTH

+5V

PWRGD

OVP

R1

R2

1k

1.74k

C1

0.1

C2

0.1

R3 1k

D1

MBR0520

R4 10

U1

SC1102

1

VCC

2

PWRGD

3

OVP

4

OCSET

5

PHASE

6

DRVH

7

PGND

GND

SS/SHDN

VREF

SENSE

BSTH

BSTL

DRVL

14

C3

SHDN

0.1

13

12

11

10

9

8

VREF

C4

1.0

R6

2.2

If the over-current condition is no longer present, normal operation will continue. If the over-current condition is still present, the SS/SHDN pin will again begin to sink 2uA. This cycle will continue indefinitely until the over-current condition is removed.

In conclusion, below is shown a typical “12V Application Circuit” which has a BSTH voltage derived by bootstrapping input voltage to the PHASE node through diode D1. This circuit is very useful in cases where only input power of 12V is available.

In order to prevent substrate glitching, a small-signal diode should be placed in close proximity to the chip with cathode connected to PHASE and anode connected to PGND.

+

C6

R8 127

C10 180/4V

270/16V

R9

205*

C11 180/4V

C7 270/16V

C8 270/16V

C12 180/4V

Vin 12V

_

C13 180/4V

C5

D2

MBRA130

Q1

R5

3.9

STP40NE

Q2

STP40NE

10.0

C9

L1

1.0 4uH

D3 MBRD1035

Optional

C14 180/4V

+

Vout=3.3V*

_

NOTE:

*) Vout = 1.265 x (1+R9/R8)

8

September 5, 2000 Top component side view

Top copper view

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

SC1102

Bottom copper view

9

September 5, 2000

OUTLINE DRAWING SO-14

SYNCHRONOUS DC/DC CONTROLLER FOR DISTRIBUTED POWER SUPPLY APPLICATIONS

SC1102

LAND PATTERN SO-14

ECN00-1311

10

Semtech Corporation SC1102CSTR, SC1102EVB Datasheet

Specifications and Main Features

Frequently Asked Questions

User Manual