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Simple, Synchronous Voltage Mode PWM Controller
POWER MANAGEMENT Description
The SC1104A/B is a versatile voltage-mode PWM controller designed for use in single ended DC/DC power supply applications. A simple, fixed frequency high efficiency buck regulator can be implemented using the SC1104A/B with a minimum of external components. Internal level shift and drive circuitry eliminates the need for an expensive P-channel, high-side switch. The small device footprint allows for compact circuit design. SC1104A/B features include temperature compensated voltage reference, triangle wave oscillator, current limit comparator and an externally compensated error amplifier. Current limit is implemented by sensing the voltage drop across the top .ETs RDS(ON).. The SC1104A/B operates at a fixed frequency of 300/ 600 kHz, providing an optimum compromise between efficiency, external component size, and cost. 600kHz switching frequency is typically reserved for the 5V operation only. SC1104A/B has a thermal protection circuit, which is activated if the junction temperature exceeds 150C.
SC1104A/B
PRELIMINARY
.eatures
K K K K K K K K
+5V or +12V operation High efficiency (>90%) 1% Reference voltage accuracy Hiccup mode over current protection Robust output drive RDS(ON) Current sensing Industrial temperature range SO-8 package
Applications
K K K K K
Termination supplies Low cost microprocessor supplies Peripheral card supplies Industrial power supplies High density DC/DC conversion
Typical Application Circuit
Typical Distributed Power Supply
R2 10 C3 0.1 D1 MBRA130L U1 SC1104A/B 1 COMP/SS SENSE 8 R3 1.00k R5 200-1k C8 0.1-0.22
2.32k
+
C4 10.0 C5 47/16V C6 47/16V C7 47/16V
C1 220-680pF
Vin 5 to 12V
_
R1 2k
C2 0.01
R4
2
GND
VCC
7
3
DL
PHASE
6
4
DH
BST
5 R8 10 R6 1-5.1 Q1 Si4884DY C9 0.1 L1 1.5-3uH
Q2 Si4874DY R7 1-5.1 D2 (opt) C10 220/4V C11 220/4V C12 220/4V C13 220/4V C14-17 1.0
+
3.3V
_
.igure 1
Revision 3, October 2001 1 www.semtech.com
SC1104A/B
POWER MANAGEMENT Absolute Maximum Ratings
Parameter VCC to GND BST to PHASE PHASE to GND DH to PHASE DL to GND COMP/SS to GND SENSE to GND Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 Sec. JC J A TA TSTG TLead Symbol Maximum 15 15 -1 to 15 15 15 7 7 40 160 -40 to +85 -65 to +150 300
PRELIMINARY
Units V V V V V V V C/W C/W C C C
Electrical Characteristics
Unless specified: A: VCC = 12 0.6V, VBST = 23 1V, VOUT = 3.3V, TA = 25oC.B: VCC = 5 0.25V, VBST = 12 0.6V, VOUT = 2.0V, TA = 25oC
Parameter Pow er Supply Supply Voltage
Symbol
Conditions
Min
Typ
Max
Units
V CC V CC
FSW = 300kHz (nom.), (SC1104A) FSW = 600kHz (nom.), (SC1104B) VCOMP 0.4V
4.2 4.2 11
12.6 V 7 14 mA
Supply Current Error Amplifier E/A Transconductance Input Bias Current Output Sink Current Source Current Oscillator Switching Frequency
ICC
gm IFB ISIK ISC VSENSE 1.1V; VCOMP = 1.5V VSENSE 0.9V; VCOMP = 1.5V
10 1 0.7 3
mS A mA
1.1
FOSC
VCC = 12V 0.6V VCC = 5V 0.25V
270 540
300 600 2.0
330 660 kHz V
Ramp Peak Voltage
VP-K
4.75V VCC 12.6V
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SC1104A/B
POWER MANAGEMENT Electrical Characteristics
Parameter Ramp Valley Voltage Maximum Duty Cycle Symbol VV dcMAX Conditions 4.75V VCC 12.6V VCC = 12V (300kHz) VCC = 5V (600kHz) MOSFET Drivers DH Sink/Source Current SC1104A DL Sink/Source Current SC1104A DH Sink/Source Current SC1104B DL Sink/Source Current SC1104B DH Rise/Fall Time DL Rise/Fall Time Dead Time DH Minimum Off Time Reference Section Reference Voltage Reference Accuracy Current Limit Trip Voltage Soft-Start/Enable SS Source Current SS Sink Current Enable Input Threshold Enable Input Current Under Voltage Lockout UVLO Threshold Thermal Shutdow n Over Temperature Trip Point TOTP 150 C Vth -40< TA < 85C 3.9 4.15 4.5 V VCOMP = 0.8V ISRC ISNK VCOMP < 2.5V VCOMP > 0.5V 1.5 1.5 1 2 V mA A Vtrp 4.75V < Vcc < 12.6V Vtrp = Vcc - VPHASE 180 200 220 mV VREF 4.75V Vcc 12.6V -40 < TA < 85C 0.990 -1 1.000 1.010 1 V % IDH IDL IDH IDL tr, tf tr, tf tdt tOFF d.c. < 2%, tPW < 100s VGS = 4.5V (src) VGS = 2.5V (snk) d.c. < 2%, tPW < 100s VGS = 4.5V (src) VGS = 2.5V (snk) CL = 3000pF, See Fig. 2 CL = 4000pF, See Fig. 2 S ee F i g. 2 4.75V Vcc 12.6V 0.7 0.7 0.5 0.5 50 50 80 160 ns ns A A Min Typ 1.0 95 90
PRELIMINARY
Unless specified: A: VCC = 12 0.6V, VBST = 23 1V, VOUT = 3.3V, TA = 25oC.B: VCC = 5 0.25V, VBST = 12 0.6V, VOUT = 2.0V, TA = 25oC
Max
Units V %
Note: 1. This device is ESD sensitive. Use of standard ESD handling precautions is required.
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SC1104A/B
POWER MANAGEMENT Electrical Characteristics PRELIMINARY
.igure 2
Block Diagram
.igure 3
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SC1104A/B
POWER MANAGEMENT Pin Configuration
Top View
PRELIMINARY Ordering Information
Device
(2)
P ackag e SOIC-8
Temp Range (TJ) -40 to 125C
SC1104XISTR (1)
Note: (1) In place of "X": A = 300kHz; B = 600kHz. (2) Only available in tape and reel packaging. A reel contains 2500 devices.
(8-Pin SOIC)
Pin Descriptions
Pin # 1 2 3 4 5 6 7 8 Pin Name COMP/SS GND DL DH BST PHASE VC C SENSE Pin Function Error amplifier output. Compensation, soft start/enable. Ground. Low side driver output High side driver output Bootstrap, high side driver. Input from the phase node between the MOSFETs. Chip bias supply voltage. Output voltage sense input.
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SC1104A/B
POWER MANAGEMENT Theory of Operation PRELIMINARY
The circuit will be in steady state when Vout =3.3V , Vsense = 1V, Icomp = 0 . The COMP voltage and duty cycle depend on Vin. Under Voltage Lockout The under voltage lockout circuit of the SC1104A/B assures that both high-side and low-side MOS.ET driver outputs remain in the off state whenever the supply voltage drops below set parameters. Lockout occurs if VCC falls below 4.2V typ. RDS(ON) Current Limiting In case of a short circuit or overload, the high-side (HS) .ET will conduct large currents. To prevent damage, in this situation, large currents will generate a fault condition and begin a soft start cycle. While the HS driver is on, the phase voltage is compared to the Vcc pin voltage. If the phase voltage is 200mV lower than Vcc, a fault is latched and the soft start cycle begins. The voltages are compared during the middle of the HS pulse, to prevent transients from affecting the accuracy. Soft Start The soft start (or hiccup) circuitry is activated when a fault occurs. .aults occur for three reasons: 1) Under voltage (VCC < 4.2V) 2) Over temperature (die temperature > 150C) 3) Over current in high side .ET. All faults are handled the same way. Both DH and DL are forced low. The error amplifier is turned off, but a 2A current flows into the comp pin (soft start current). The sink current reduces the Comp voltage down to 0.6V over a period of a few milliseconds. When Vcomp ~ 0.6V, the fault is cleared and the DL goes high. Also, the soft start current changes polarity and begins to increase the voltage on the Comp capacitor. The DH remains low, because Vcomp is less than the lowest excursion of the oscillator ramp (1.0V). After a few ms, the Vcomp increases to about 1.0V and the DH will start to switch. The duty cycle will gradually increase, and Vsns will increase. When Vsns ~ 1.00V, the error amplifier turns on again. The circuit has now reached its operating point. If a fault occurs during the soft start, the cycle will begin again (drivers low, Vcomp decreasing down to 0.6V).
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Synchronous Buck Converter The output voltage of the synchronous converter is set and controlled by the output of the error amplifier. The inverting input of the error amplifier receives its voltage from the SENSE pin. The non-inverting input of the error amplifier is connected to an internal 1V reference. The error amplifier output is connected to the COMPensation pin. The error amplifier generates a current proportional to (Vsense 1V), which is the COMP pin output current (Transconductance ~ 10mS). The voltage on the COMP pin is the integral of the error amplifier current. The COMP voltage is the non-inverting input to the PWM comparator and controls the duty cycle of the MOS.ET drivers. The size of capacitor Ccomp controls the stability and transient response of the regulator. The larger the capacitor, the slower the COMP voltage changes, and the slower the duty cycle changes. The inverting input voltage of the PWM comparator is the triangular output of the oscillator. When the oscillator output voltage drops below the COMP voltage, the comparator output goes high. This pulls DL low, turning off the low-side .ET. After a short delay (dead time), DH is pulled high, turning on the high-side .ET. 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 .ET, and after a dead time delay, DL is pulled high, turning on the lowside .ET. The dead time delay is determined by a monostable on the chip. The triangle wave minimum is about 1V, and the maximum is about 2V. Thus, if Vcomp = 0.9V, high side duty cycle is the minimum (~0%) , but if Vcomp is 2.0V, duty cycle is at maximum ( ~80%).The internal oscillator uses an on-chip capacitor and trimmed precision current sources to set the oscillation frequency to 300/600kHz. .igure 1 shows a 3.3V output converter. If the Vout <3.3V, then the SENSE voltage < 1V. In this case the error amplifier will be sourcing current into the COMP pin so that COMP voltage and duty cycle will gradually increase. If Vout > 3.3V, the error amplifier will sink current and reduce the COMP voltage, so that duty cycle will decrease.
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SC1104A/B
POWER MANAGEMENT Outline Drawing - SO-8 PRELIMINARY
Land Pattern - SO-8
Contact Information
Semtech Corporation Power Management Products Division 652 Mitchell Rd., Newbury Park, CA 91320 Phone: (805)498-2111 .AX (805)498-3804
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