Semtech Corporation SC1110CSTR Datasheet

SINK AND SOURCE DC/DC CONTROLLER FOR
TERMINATION POWER SUPPLY APPLICATIONS

SC1110

PRELIMINARY - October 9, 2000

TEL:[phone] FAX:[phone] WEB:http://www.semtech.com

DESCRIPTION

The SC1110 is a low-cost, full featured, synchronous
voltage-mode controller designed to generate termina­tion voltage in double data rate (DDR) memory sys­tems and other applications where wide data bus need
to be actively terminated. Synchronous control of the
MOSFET half bridge allows power flowing bi­directionally. The termination voltage can be tightly
regulated to track the chipset voltage, i.e. to be exactly
50% of that at all times.

The SC1110 is ideal for low cost implementation of ter­mination voltage supplies. SC1110 features include
temperature compensated voltage reference, triangle
wave oscillator and current sense comparator circuitry,
and allows the use of inexpensive N-channel power
switches.

The SC1110 operates at a fixed 250kHz, providing an
optimum compromise between efficiency, transient
performance, external component size, and cost.

FEATURES

•= Generates termination voltages for active termina-

tion schemes

•= 1% set point accuracy

•= For ±7A output current, transient regulation is bet-

ter than ±80mV

•= V

•= Buffered V

•= R

pin available

REFIN

sensing for over current protection in hiccup

DSON

for system usage

REFOUT

mode

•= Soft start and logic input enabling

•= 250kHz switching for best transient and efficiency

performance

•= Gate drive capable for 0.5A sourcing and sinking

APPLICATIONS

•= For DDR memory systems

•= For active termination schemes in high speed logic

systems

ORDERING INFORMATION

DEVICE

(1)

PACKAGE TEMP. RANGE (TJ)

TYPICAL APPLICATION CIRCUIT

REFOUT

SS/ENBL

PWRGD

C1

R1
5k

R2

0.01

1.24k

C3

0.1

C25

0.1

R3
10

C2

0.1

U1
SC1110

1

VCC

2

SS/ENBL

3

OCSET

4

PWRGD

5

GND

6

PHASE

7

DL

C10-14: Sanyo, 4SP560M
C8,9,15-24: TDK, CC3216AX5R0J106K
L1: Panasonic, ETQP6F0R8L or Falco, QPIP1205-809-3
Q1,Q2 options: Si9426DY, FDS6890A, IRF7401
D1: ON Semi (Motorola)

REFOUT

REFIN

SENSE

COMP

BSTL

BSTH

SC1110CSTR SO-14 0 - 125°C
Note:

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

+5Vcc

+

C10,11

C8,9

Q1

Si9426DY

Q2

Si9426DY

C7

1.0

C6

1.0

2 x 10uF

800 nH

L1

C12-14
3 x 560uF

2 x 560uF

R4

C4

1k

14

13

12

11

10

9

8

DH

0.022

R5
1k

C5

R6

0.047

4.7k

D1

MBRM120

R7

2.2

R8

2.2
C15-24

10 x 10uF

Vin 2.5V

_

+

Vout = 1.25V @ 7A

_

1

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

SINK AND SOURCE DC/DC CONTROLLER FOR

SC1110

TERMINATION POWER SUPPLY APPLICATIONS

PRELIMINARY - October 9, 2000

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Maximum Units

V

, BSTL to GND V

CC

IN

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

-0.5 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

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

= 2.5 ± 0.5V, VO = VIN/2 @ 0A 0.5 %

IN

CC

CC

UNDER VOLTAGE LOCKOUT

Turn-On Threshold TBD 4.2 TBD V
Turn-Off Threshold TBD 4.0 TBD V

ERROR AMPLIFIER

Transconductance 2 mS

BSTL

= 12V; V

BSTH-PHASE

= 12V; TJ = 25oC

4.4 12.6 V
8mA

Open Loop DC Gain 50 dB
Bandwidth -3dB 500 kHz
COMP Source Capability ±250 µA
Input Bias 58µA

OSCILLATOR

Oscillator Frequency 225 250 275 kHz
Oscillator Max Duty Cycle 90 95 %
Ramp Height 1V

TIMING

Minimum Off-Time 100 ns
Dead Time 80 ns

2

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

SINK AND SOURCE DC/DC CONTROLLER FOR

SC1110

TERMINATION POWER SUPPLY APPLICATIONS

PRELIMINARY - October 9, 2000

ELECTRICAL CHARACTERISTICS

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

PARAMETER CONDITIONS MIN TYP MAX UNITS
MOSFET DRIVERS

Peak DH Sink/Source Current BSTH - DH = 4.5V, DH - PHASE = 3.0V 0.5 A

DH - PHASE = 1.5V 0.1

Peak DL Sink/Source Current BSTL - DL = 4.5V, DL - GND = 3.0V 0.5 A

DL - GND = 1.5V 0.1

PROTECTION

BSTL

= 12V; V

BSTH-PHASE

= 12V; TJ = 25oC

Over Current Set Isource V

= 4.5V 180 200 220 µA

OCSET

SOFT START

Charge Current V
Discharge Current V

= 1.5V 10 µA

SS

= 1.5V 2 µA

SS

POWER GOOD

Upper Threshold 112 %
Lower Threshold 88 %
PWRGD Voltage Low I

= 2mA 0.5 V

PWRGD

REFERENCE

REFOUT Source Current 3 mA
Input Bias 58µA

NOTE:

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

BLOCK DIAGRAM

3

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

PRELIMINARY - October 9, 2000

PIN CONFIGURATION

Top View

(14-Pin SOIC)

SINK AND SOURCE DC/DC CONTROLLER FOR
TERMINATION POWER SUPPLY APPLICATIONS

SC1110

PIN DESCRIPTION

Pin # Pin Name Pin Function

1 VCC Chip supply voltage.
2 SS/ENBL Soft start/Enable.
3 OCSET Current limit set point.
4 PWRGD Logic high indicates correct output.
5 GND Ground.
6 PHASE Phase node connection between MOSFET’s.
7 DL Low side driver output.
8 DH High side driver output.

9 BSTH High side drive supply.
10 BSTL Low side drive supply.
11 COMP Error amplifier output, compensation.
12 SENSE Error amplifier negative input.
13 REFIN Error amplifier positive input.
14 REFOUT Buffered reference voltage.

NOTE:

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

4

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

SINK AND SOURCE DC/DC CONTROLLER FOR
TERMINATION POWER SUPPLY APPLICATIONS

PRELIMINARY - October 9, 2000

THEORY OF OPERATION

Synchronous Buck Converter

V

TERMINATION

voltage-mode pulse width modulated (PWM) controller.
This section has all the features required to build a
high efficiency synchronous buck converter for termi­nation of power application.

The output voltage of the synchronous converter is set
and controlled by the output of the error amplifier. The
resistive divider generates reference voltage for the
error amplifier from an external chipset voltage which
is usually 2.5V. The inverting input of the error amplifier
receives its voltage from the SENSE pin.

power is provided by a synchronous,

SC1110

R

Current Limiting

DS(ON)

The current limit threshold is set by connecting an ex­ternal resistor from the V
age 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/ENABLE starts to sink 2µA.
When SS/ENABLE reaches 0.8V, it then starts to
source 10µA and a new cycle begins.

supply to OCSET. The volt-

CC

The internal oscillator uses an on-chip capacitor and
trimmed precision current sources to set the oscillation
frequency to 250kHz. The triangular output of the os­cillator sets the reference voltage at the inverting input
of the PWM 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 low­side FET, and DH is pulled high, turning on the high­side 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 SC1110 as­sures that both the high-side MOSFET driver outputs
remain in the off state whenever the supply voltage

CC

falls

CC

rises

drops below set parameters. Lockout occurs if V
below 4.0V. Normal operation resumes once V
above 4.2V.

Soft Start

Initially, SS/ENABLE 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/ENABLE. This limits the on-time of the
high-side MOSFETs, thus leading to a controlled ramp­up of the output voltages.

Hiccup Mode

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

has reached 4.2V, the SS/EN-

CC

ABLE pin is released and begins to source 10µA of
current to the external soft-start capacitor. As the soft­start 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 250
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.

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, both the high-side and low-side drivers turn off
and the SS/ENABLE pin begins to sink 2uA. The soft­start voltage will begin to decrease as the 2uA of cur­rent discharges the external capacitor. When the soft­start voltage reaches 0.8V, the SS/ENABLE 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.

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

5

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

PRELIMINARY - October 9, 2000

SIMULATION WAVEFORMS

2.5V and 1.25V ramp up

SINK AND SOURCE DC/DC CONTROLLER FOR
TERMINATION POWER SUPPLY APPLICATIONS

SC1110

Output current of the VTT supply

6

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

PRELIMINARY - October 9, 2000

OUTLINE DRAWING SO-14

SINK AND SOURCE DC/DC CONTROLLER FOR
TERMINATION POWER SUPPLY APPLICATIONS

SC1110

ECN00-1363

7

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320