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SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS
PRELIMINARY - October 9, 2000
SC1110
TEL:805-498-2111 FAX:805-498-3804 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*= 1% set point accuracy *= For 7A output current, transient regulation is bet*= VREFIN pin available *= Buffered VREFOUT for system usage *= RDSON sensing for over current protection in hiccup *= Soft start and logic input enabling *= 250kHz switching for best transient and efficiency *= Gate drive capable for 0.5A sourcing and sinking APPLICATIONS *= For DDR memory systems *= For active termination schemes in high speed logic
systems performance mode ter than 80mV tion schemes
ORDERING INFORMATION
DEVICE
(1)
PACKAGE SO-14
TEMP. RANGE (TJ) 0 - 125C
SC1110CSTR Note:
TYPICAL APPLICATION CIRCUIT
REFOUT
(1) Only available in tape and reel packaging. A reel contains 2500 devices.
+5Vcc
+
R1 5k
C1 0.01
R2 1.24k C2 0.1
R3 10
U1 SC1110 VCC REFOUT 14
R4 1k
C4 0.022
C7 1.0
C8,9 2 x 10uF
C10,11 2 x 560uF
Vin 2.5V
_
1 SS/ENBL 2 C3 0.1 PWRGD 4 C25 0.1 5
SS/ENBL
REFIN
13 R5 1k
3
OCSET
SENSE
12 R6 4.7k C5 0.047
PWRGD
COMP
11
GND
BSTL
10 D1 MBRM120
6
PHASE
BSTH
9 R7 2.2 R8 2.2 Q1 Si9426DY Q2 Si9426DY C12-14 3 x 560uF C15-24 10 x 10uF C6 1.0 L1 800 nH
7
DL
DH
8
+
Vout = 1.25V @ 7A
_
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)
1 (c) 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
SC1110
ABSOLUTE MAXIMUM RATINGS
Parameter VCC, BSTL to GND PGND to GND PHASE to GND BSTH to PHASE Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 sec JC JA TA TSTG TLEAD Symbol VIN Maximum -0.5 to 14 0.5 -0.5 to 18 14 45 115 0 to 70 -65 to +150 300 Units V V V V C/W C/W C C C
ELECTRICAL CHARACTERISTICS
Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25oC PARAMETER POWER SUPPLY Supply Voltage Supply Current Line Regulation UNDER VOLTAGE LOCKOUT Turn-On Threshold Turn-Off Threshold ERROR AMPLIFIER Transconductance Open Loop DC Gain Bandwidth -3dB COMP Source Capability Input Bias OSCILLATOR Oscillator Frequency Oscillator Max Duty Cycle Ramp Height TIMING Minimum Off-Time Dead Time 80 100 ns ns 225 90 250 95 1 275 kHz % V 2 50 500 250 5 8 mS dB kHz A A TBD TBD 4.2 4.0 TBD TBD V V VCC EN = VCC VIN = 2.5 0.5V, VO = VIN/2 @ 0A 4.4 8 0.5 12.6 V mA % CONDITIONS MIN TYP MAX UNITS
2 (c) 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
SC1110
ELECTRICAL CHARACTERISTICS
Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25oC PARAMETER MOSFET DRIVERS Peak DH Sink/Source Current BSTH - DH = 4.5V, DH - PHASE = 3.0V DH - PHASE = 1.5V Peak DL Sink/Source Current BSTL - DL = 4.5V, DL - GND = 3.0V DL - GND = 1.5V PROTECTION Over Current Set Isource SOFT START Charge Current Discharge Current POWER GOOD Upper Threshold Lower Threshold PWRGD Voltage Low REFERENCE REFOUT Source Current Input Bias
NOTE: (1) Specification refers to application circuit (Figure 1.).
CONDITIONS
MIN
TYP
MAX
UNITS
0.5 0.1 0.5 0.1
A
A
VOCSET = 4.5V VSS = 1.5V VSS = 1.5V
180
200
220
A
10 2
A A
112 88 IPWRGD = 2mA 3 5 8 0.5
% % V
mA A
BLOCK DIAGRAM
3 (c) 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
SC1110
PIN CONFIGURATION
Top View
(14-Pin SOIC)
PIN DESCRIPTION
Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NOTE: (1) All logic level inputs and outputs are open collector TTL compatible. Pin Name VCC SS/ENBL OCSET PWRGD GND PHASE DL DH BSTH BSTL COMP SENSE REFIN REFOUT Pin Function Chip supply voltage. Soft start/Enable. Current limit set point. Logic high indicates correct output. Ground. Phase node connection between MOSFET's. Low side driver output. High side driver output. High side drive supply. Low side drive supply. Error amplifier output, compensation. Error amplifier negative input. Error amplifier positive input. Buffered reference voltage.
4 (c) 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
SC1110
THEORY OF OPERATION
Synchronous Buck Converter VTERMINATION power is provided by a synchronous, 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. 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 drops below set parameters. Lockout occurs if VCC falls below 4.0V. Normal operation resumes once VCC rises above 4.2V. Soft Start Initially, SS/ENABLE sources 10A 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.
RDS(ON) Current Limiting The current limit threshold is set by connecting an external resistor from the VCC supply to OCSET. The voltage drop across this resistor is due to the 200A 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 2A. When SS/ENABLE reaches 0.8V, it then starts to source 10A and a new cycle begins. Hiccup Mode During power up, the SS/ENABLE pin is internally pulled low until VCC reaches the undervoltage lockout level of 4.2V. Once VCC has reached 4.2V, the SS/ENABLE pin is released and begins to source 10A 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
(c) 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
SC1110
SIMULATION WAVEFORMS
2.5V and 1.25V ramp up
Output current of the VTT supply
6 (c) 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
SC1110
OUTLINE DRAWING SO-14
ECN00-1363
7 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

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