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PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1185 combines a synchronous voltage mode controller with two low-dropout linear regulators providing most of the circuitry necessary to implement three DC/DC converters for powering (R) advanced microprocessors such as Pentium II . The SC1185 switching section features an integrated 5 bit D/A converter, pulse by pulse current limiting, integrated power good signaling, and logic compatible shutdown. The SC1185 switching section operates at a fixed frequency of 140kHz, providing an optimum compromise between size, efficiency and cost in the intended application areas. The integrated D/A converter provides programmability of output voltage from 2.0V to 3.5V in 100mV increments and 1.30V to 2.05V in 50mV increments with no external components. The SC1185 linear sections are low dropout regulators supplying 1.5V for GTL bus and 2.5V for nonGTL I/O. The Reference voltage is made available for external linear regulators.
FEATURES * Synchronous design, enables no heatsink solution * 95% efficiency (switching section) * 5 bit DAC for output programmability * On chip power good function * Designed for Intel Pentium(R) ll requirements * 1.5V, 2.5V @ 1% for linear section * 1.265V 1.5% Reference available APPLICATIONS * Pentium(R) ll microprocessor supplies * Flexible motherboards * 1.3V to 3.5V microprocessor supplies * Programmable triple power supplies ORDERING INFORMATION
Part Number
(1)
Package
Linear Voltage
Temp. Range (TJ)
SC1185CSW SC1185ACSW
(2)
SO-24 SO-24
1.5V/2.5V 0 to 125C 1.5V/2.5V 0 to 125C
Note: (1) Add suffix `TR' for tape and reel. (2) SC1185A provides improved output tolerance. See Output Voltage Table.
PIN CONFIGURATION
BLOCK DIAGRAM
VCC CSCS+ EN BSTH
Top View
VID4
REF. DH
AGND GATE1 LDOS1 LDOS2 VCC REF PWRGOOD CSCS+ PGNDH DH PGNDL
1 2 3 4 5 6 7 8 9 10 11 12
24 23 22 21 20 19 18 17 16 15 14 13
GATE2 LDOV VID0 VID1 VID2 VID3 VID4 VOSENSE EN BSTH BSTL DL
VID3 VID2 VID1 VID0
D/A PGNDH
VOSENSE
PWRGOOD BSTL
DL
(24 Pin SOIC)
LDOS1 FET CONTROLLER 2.5V/ADJ. 1.265V REF. FET CONTROLLER 1.5V/ADJ. GATE1
PGNDL
LDOV
REF
GATE2
LDOS2
AGND
Pentium is a registered trademark of Intel Corporation
1
(c) 1999 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
ABSOLUTE MAXIMUM RATINGS
Parameter VCC to GND PGND to GND BST to GND Operating Temperature Range Junction Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 seconds Thermal Impedance Junction to Ambient Thermal Impedance Junction to Case Symbol VIN Maximum -0.3 to +7 1 -0.3 to +15 0 to +70 0 to +125 -65 to +150 300 80 25 Units V V V C C C C C/W C/W
TA TJ TSTG TL JA JC
ELECTRICAL CHARACTERISTICS
Unless specified: VCC = 4.75V to 5.25V; GND = PGND = 0V; VOSENSE = VO; 0mV < (CS+-CS-) < 60mV; LDOV = 11.4V to 12.6V; TA = 0 to 70C
PARAMETER Switching Section Output Voltage Supply Voltage Supply Current Load Regulation Line Regulation Current Limit Voltage Oscillator Frequency Oscillator Max Duty Cycle Peak DH Sink/Source Current Peak DL Sink/Source Current Gain (AOL) VID Source Current VID Leakage Power good threshold voltage Dead time Linear Sections Quiescent current Output Voltage LDO1 Output Voltage LDO2 Reference Voltage Gain (AOL) Load Regulation Line Regulation Output Impedance Gate Pulldown Impedance VOSENSE Impedance
CONDITIONS IO = 2A in Application Circuit VCC VCC = 5.0V IO = 0.8A to 15A
MIN
TYP
MAX
UNITS
BSTH-DH = 4.5V, DH-PGNDH = 3.1V DH-PGNDH = 1.5V BSTL-DL = 4.5V, DL-PGNDL = 3.1V DL-PGNDL = 1.5V VOSENSE to VO VIDx 2.4V VIDx = 5V
See Output Voltage Table 4.5 7 V 8 15 mA 1 % 0.15 % 60 70 85 mV 125 140 160 kHz 90 95 % 1 A 100 mA 1 100 1 88 40 35 10 10 112 100 A mA dB A A % ns mA V V V dB % % k k k 2
LDOV = 12V
Iref 100A LDOS (1,2) to GATE (1,2) IO = 0 to 8A VGATE = 6.5V GATE(1,2)-AGND;VCC=LDOV=0V
5 2.469 2.500 2.531 1.481 1.500 1.519 1.246 1.265 1.284 90 0.3 0.3 1 1.5 80 10 300 750
(c) 1999 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
PIN DESCRIPTION
Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Pin Name AGND GATE1 LDOS1 LDOS2 VCC REF PWRGOOD CSCS+ PGNDH DH PGNDL DL BSTL BSTH (1) EN VOSENSE (1) VID4 (1) VID3 (1) VID2 (1) VID1 (1) VID0 LDOV GATE2
(1)
Pin Function Small Signal Analog and Digital Ground Gate Drive Output LDO1 Sense Input for LDO1 Sense Input for LDO2 Input Voltage Buffered Reference Voltage output Open collector logic output, high if VO within 10% of setpoint Current Sense Input (negative) Current Sense Input (positive) Power Ground for High Side Switch High Side Driver Output Power Ground for Low Side Switch Low Side Driver Output Supply for Low Side Driver Supply for High Side Driver Logic low shuts down the converter; High or open for normal operation. Top end of internal feedback chain Programming Input (MSB) Programming Input Programming Input Programming Input Programming Input (LSB) +12V for LDO section Gate Drive Output LDO2
Top View
AGND GATE1 LDOS1 LDOS2 VCC REF PWRGOOD CSCS+ PGNDH DH PGNDL 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 GATE2 LDOV VID0 VID1 VID2 VID3 VID4 VOSENSE EN BSTH BSTL DL
(24 Pin SOIC)
Note: (1) All logic level inputs and outputs are open collector TTL compatible.
3 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
OUTPUT VOLTAGE
Unless specified: 4.75V < VCC < 5.25V; GND = PGND = 0V; VOSENSE = VO; 0mV < (CS+-CS-) < 60mV; = 0C < Tj < 85C
PARAMETER Output Voltage
VID 43210 01111 01110 01101 01100 01011 01010 01001 01000 00111 00110 00101 00100 00011 00010 00001 00000 11111 11110 11101 11100 11011 11010 11001 11000 10111 10110 10101 10100 10011 10010 10001 10000
MIN 1.277 1.326 1.375 1.424 1.478 1.527 1.576 1.625 1.675 1.724 1.782 1.832 1.881 1.931 1.980 2.030 1.970 2.069 2.167 2.266 2.364 2.463 2.561 2.660 2.758 2.842 2.940 3.038 3.136 3.234 3.332 3.430
Standard TYP 1.300 1.350 1.400 1.450 1.500 1.550 1.600 1.650 1.700 1.750 1.800 1.850 1.900 1.950 2.000 2.050 2.000 2.100 2.200 2.300 2.400 2.500 2.600 2.700 2.800 2.900 3.000 3.100 3.200 3.300 3.400 3.500
MAX 1.323 1.374 1.425 1.476 1.523 1.573 1.624 1.675 1.726 1.776 1.818 1.869 1.919 1.970 2.020 2.071 2.030 2.132 2.233 2.335 2.436 2.538 2.639 2.741 2.842 2.958 3.060 3.162 3.264 3.366 3.468 3.570
"A" Version MIN TYP MAX 1.287 1.337 1.386 1.436 1.485 1.535 1.584 1.634 1.683 1.733 1.782 1.832 1.881 1.931 1.980 2.030 1.970 2.069 2.167 2.266 2.364 2.463 2.561 2.660 2.758 2.842 2.940 3.038 3.136 3.234 3.332 3.430 1.300 1.350 1.400 1.450 1.500 1.550 1.600 1.650 1.700 1.750 1.800 1.850 1.900 1.950 2.000 2.050 2.000 2.100 2.200 2.300 2.400 2.500 2.600 2.700 2.800 2.900 3.000 3.100 3.200 3.300 3.400 3.500 1.313 1.364 1.414 1.465 1.515 1.566 1.616 1.667 1.717 1.768 1.818 1.869 1.919 1.970 2.020 2.071 2.030 2.132 2.233 2.335 2.436 2.538 2.639 2.741 2.842 2.958 3.060 3.162 3.264 3.366 3.468 3.570
UNITS V
4 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
12V
(c) 1999 SEMTECH CORP.
5V
+
R1 10 0.1uF U1 5
VCC REF VID0 VID1 VID2 VID3 EN AGND PGNDL GATE2 GATE1 LDOS2 LDOS1 LDOV BSTL DL PGNDH DH BSTH VID4 PWRGOOD VO SENSE CSCS+
+
R16 10k C13 1.00k 2.32k R6 R5
PRELIMINARY - January 6, 1999
APPLICATION CIRCUIT
C1 0.1uF
C2 1500uF C3 1500uF 9 8 17 7 18 15 11 10 13 14 23 3 C14 1500uF Q2 IRL34025 4uH L1 R4 5mOhm C15 1500uF Q1 IRL34025 6 22 21 20 19 EN 16 C5 0.1uF 12 24 2 4 1 REF VID0 VID1 VID2 VID3 VID4 SC1185CSW PWRGD Q3 IRLML2803
C17 1500uF
VCC_CORE
+ + +
+
C18 0.1uF GND C16 1500uF
2.5V
+
C11 330uF
3.3V
1.5V
+
330uF
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
C21
Q4 IRFZ14S
+
C9 1000uF
5
652 MITCHELL ROAD NEWBURY PARK CA 91320
SC1185 SC1185A
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
MATERIALS LIST
Qty. Reference 4 6 1 2 1 2 1 1 1 1 1 1 1 Part/Description Vendor Various SANYO MV-GX or equiv. Low ESR Notes
C1,C5,C13,C18 0.1F Ceramic C2,C3,C14-C17 1500F/6.3V C9 C11,C21 L1 Q1,Q2 Q3 Q4 R4 R5 R6 R1 U1 1000F 330F/6.3V 4H See notes IRLML2803 IRFZ14S 5m 2.32k, 1%, 1/8W 1k, 1%, 1/8W 10, 5%, 1/8W SC1185CSW
Various 8 Turns 16AWG on MICROMETALS T50-52D core See notes IR IR IRC Various Various Various SEMTECH FET selection requires trade-off between efficiency and cost. Absolute maximum RDS(ON) = 22 m for Q1,Q2 .25 30V SOT23 (or equavilent) Or equivalent OAR-1 Series
6 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
95% 95%
SC1185 SC1185A
90%
90%
Efficiency
Efficiency
85%
85%
80% 3.5V Std 3.5V Sync 3.5V Sync Lo Rds
80% 2.8V Std 2.8V Sync 2.8V Sync Lo Rds
75%
75%
70% 0 2 4 6 8 Io (Amps) 10 12 14 16
70% 0 2 4 6 8 Io (Amps) 10 12 14 16
Typical Efficiency at Vo=3.5V
95%
Typical Efficiency at Vo=2.8V
95%
90%
90%
Efficiency
Efficiency
85%
85%
80% 2.5V Std 2.5V Sync 2.5V Sync Lo Rds
80% 2.0V Std 2.0V Sync 2.0V Sync Lo Rds
75%
75%
70% 0 2 4 6 8 Io (Amps) 10 12 14 16
70% 0 2 4 6 8 Io (Amps) 10 12 14 16
Typical Efficiency at Vo=2.5V
Typical Efficiency at Vo=2.0V
Typical Ripple, Vo=2.8V, Io=10A
Transient Response Vo=2.8V, Io=300mA to 10A
7 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
LAYOUT GUIDELINES
Careful attention to layout requirements are necessary for successful implementation of the SC1185 PWM controller. High currents switching at 140kHz are present in the application and their effect on ground plane voltage differentials must be understood and minimized. 1). The high power parts of the circuit should be laid out first. A ground plane should be used, the number and position of ground plane interruptions should be such as to not unnecessarily compromise ground plane integrity. Isolated or semi-isolated areas of the ground plane may be deliberately introduced to constrain ground currents to particular areas, for example the input capacitor and bottom FET ground. 2). The loop formed by the Input Capacitor(s) (Cin), the Top FET (Q1) and the Bottom FET (Q2) must be kept
as small as possible. This loop contains all the high current, fast transition switching. Connections should be as wide and as short as possible to minimize loop inductance. Minimizing this loop area will a) reduce EMI, b) lower ground injection currents, resulting in electrically "cleaner" grounds for the rest of the system and c) minimize source ringing, resulting in more reliable gate switching signals. 3). The connection between the junction of Q1, Q2 and the output inductor should be a wide trace or copper region. It should be as short as practical. Since this connection has fast voltage transitions, keeping this connection short will minimize EMI. The connection between the output inductor and the sense resistor should be a wide trace or copper area, there are no fast voltage or current transitions in this connection and length is not so important, however adding unnecessary impedance will reduce efficiency.
12V IN 5V
10 1 2 3 4 0.1uF 5 6 0.1uF 7 8 9 10 11 12
AGND GATE1 LDOS1 LDOS2 VCC REF PWRGOOD CSCS+ PGNDH DH PGNDL GATE2 LDVO VID0 VID1 VID2 VID3 VID4 VOSENSE EN BSTH BSTL DL
24 23 22 Cin 21 20 19 18 17 16 15 14 13 Q2 Cout 4uH + Q1 + 1.00k 5mOhm Vout 2.32k
SC1185
Heavy lines indicate
3.3V Q3 + Cin Lin Cout Lin1 + Vo Lin1
high current paths.
Vo Lin2 Q4 Cout Lin2 +
Layout diagram for the SC1185
8 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999 4) The Output Capacitor(s) (Cout) should be located as close to the load as possible, fast transient load currents are supplied by Cout only, and connections between Cout and the load must be short, wide copper areas to minimize inductance and resistance. 5) The SC1185 is best placed over a quiet ground plane area, avoid pulse currents in the Cin, Q1, Q2 loop flowing in this area. PGNDH and PGNDL should be returned to the ground plane close to the package. The AGND pin should be connected to the ground side of (one of) the output capacitor(s). If this is not possible, the AGND pin may be connected to the ground path between the Output Capacitor(s) and the Cin, Q1, Q2 loop. Under no circumstances should AGND be returned to a ground inside the Cin, Q1, Q2 loop. 6) Vcc for the SC1185 should be supplied from the 5V
SC1185 SC1185A
supply through a 10 resistor, the Vcc pin should be decoupled directly to AGND by a 0.1F ceramic capacitor, trace lengths should be as short as possible. 7) The Current Sense resistor and the divider across it should form as small a loop as possible, the traces running back to CS+ and CS- on the SC1185 should run parallel and close to each other. The 0.1F capacitor should be mounted as close to the CS+ and CS- pins as possible. 8) Ideally, the grounds for the two LDO sections should be returned to the ground side of (one of) the output capacitor(s).
5V
+
Vout +
Currents in various parts of the power section
9 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
COMPONENT SELECTION
SWITCHING SECTION OUTPUT CAPACITORS - Selection begins with the most critical component. Because of fast transient load current requirements in modern microprocessor core supplies, the output capacitors must supply all transient load current requirements until the current in the output inductor ramps up to the new level. Output capacitor ESR is therefore one of the most important criteria. The maximum ESR can be simply calculated from:
fast enough to reduce the voltage dropped across the ESR at a faster rate than the capacitor sags, hence ensuring a good recovery from transient with no additional excursions. We must also be concerned with ripple current in the output inductor and a general rule of thumb has been to allow 10% of maximum output current as ripple current. Note that most of the output voltage ripple is produced by the inductor ripple current flowing in the output capacitor ESR. Ripple current can be calculated from:
R ESR
V t It
ILRIPPLE=
VIN 4L fOSC
Where Vt = Maximum transient voltage excursion It = Transient current step
For example, to meet a 100mV transient limit with a 10A load step, the output capacitor ESR must be less than 10m. To meet this kind of ESR level, there are three available capacitor technologies.
Each Capacitor Technology Low ESR Tantalum OS-CON Low ESR Aluminum C (F) 330 330 1500 ESR (m) 60 25 44 Qty. Rqd. 6 3 5 Total C (F) 2000 990 7500 ESR (m) 10 8.3 8.8
Ripple current allowance will define the minimum permitted inductor value. POWER FETS - The FETs are chosen based on several criteria with probably the most important being power dissipation and power handling capability. TOP FET - The power dissipation in the top FET is a combination of conduction losses, switching losses and bottom FET body diode recovery losses. a) Conduction losses are simply calculated as:
2 PCOND = IO R DS ( on )
where = duty cycle VO VIN
b) Switching losses can be estimated by assuming a switching time, if we assume 100ns then:
The choice of which to use is simply a cost/performance issue, with Low ESR Aluminum being the cheapest, but taking up the most space. INDUCTOR - Having decided on a suitable type and value of output capacitor, the maximum allowable value of inductor can be calculated. Too large an inductor will produce a slow current ramp rate and will cause the output capacitor to supply more of the transient load current for longer - leading to an output voltage sag below the ESR excursion calculated above. The maximum inductor value may be calculated from:
PSW = IO VIN 10 - 2
or more generally,
PSW =
IO VIN ( t r + t f ) fOSC 4
L
R ESR C (VIN - VO ) It
c) Body diode recovery losses are more difficult to estimate, but to a first approximation, it is reasonable to assume that the stored charge on the bottom FET body diode will be moved through the top FET as it starts to turn on. The resulting power dissipation in the top FET will be:
PRR = Q RR VIN f OSC
To a first order approximation, it is convenient to only consider conduction losses to determine FET suitability. For a 5V in; 2.8V out at 14.2A requirement, typical FET losses would be:
The calculated maximum inductor value assumes 100% duty cycle, so some allowance must be made. Choosing an inductor value of 50 to 75% of the calculated maximum will guarantee that the inductor current will ramp
10 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999 Using 1.5X Room temp RDS(ON) to allow for temperature rise. FET type IRL34025 IRL2203 Si4410 RDS(on) (m) PD (W) 15 10.5 20 1.69 1.19 2.26 Package D PAK D PAK SO-8
2 2
SC1185 SC1185A
INPUT CAPACITORS - since the RMS ripple current in the input capacitors may be as high as 50% of the output current, suitable capacitors must be chosen accordingly. Also, during fast load transients, there may be restrictions on input di/dt. These restrictions require useable energy storage within the converter circuitry, either as extra output capacitance or, more usually, additional input capacitors. Choosing low ESR input capacitors will help maximize ripple rating for a given size.
BOTTOM FET - Bottom FET losses are almost entirely due to conduction. The body diode is forced into conduction at the beginning and end of the bottom switch conduction period, so when the FET turns on and off, there is very little voltage across it, resulting in low switching losses. Conduction losses for the FET can be determined by:
2 PCOND = IO RDS(on) (1- )
For the example above: FET type IRL34025 IRL2203 Si4410 RDS(on) (m) PD (W) 15 10.5 20 1.33 0.93 1.77 Package D PAK D PAK SO-8
2 2
Each of the package types has a characteristic thermal impedance, for the TO-220 package, thermal impedance is mostly determined by the heatsink used. For the surface mount packages on double sided FR4, 2 oz printed o circuit board material, thermal impedances of 40 C/W 2 o for the D PAK and 80 C/W for the SO-8 are readily achievable. The corresponding temperature rise is detailed below: Temperature rise ( C) FET type IRL34025 IRL2203 Si4410 Top FET 67.6 47.6 180.8 Bottom FET 53.2 37.2 141.6
o
It is apparent that single SO-8 Si4410 are not adequate for this application, but by using parallel pairs in each position, power dissipation will be approximately halved and temperature rise reduced by a factor of 4.
11 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - January 6, 1999
SC1185 SC1185A
OUTLINE DRAWING
JEDEC MS-013AD B17104B
12 (c) 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

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