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PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER

SC1186

PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1186 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 ® advanced microprocessors such as Pentium II & III. The SC1186 switching section features an integrated 5 bit D / A converter, latched drive output for enhanced noise immunity, pulse by pulse current limiting and logic compatible shutdown. The SC1186 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 SC1186 linear sections are low dropout regulators with short circuit protection, supplying 1.5V for GTL bus and 2.5V for non-GTL I / O. The Reference voltage is made available for external linear regulators.
APPLICATIONS
Pentium ll & III microprocessor supplies Flexible motherboards 1.3V to 3.5V microprocessor supplies Programmable triple power supplies
ORDERING INFORMATION
Part Number
Package
Linear Voltage
Temp. Range (T J)
SC1186CSW
SO-24
1.5V / 2.5V 0° to 125°C
PIN CONFIGURATION
BLOCK DIAGRAM
CURRENT LIMIT
Top View
AGND GATE1 LDOS1 LDOS2 VCC REF LDOEN CSCS+ PGNDH DH PGNDL
GATE2 LDOV VID0 VID1 VID2 VID3 VID4 VOSENSE EN BSTH BSTL DL
VID4 VID3 VID2 VID1 VID0 VOSENSE
LEVEL SHIFT AND HIGH SIDE DRIVE
+ ERROR AMP +
PGNDH
OSCILLATOR
SHOOT-THRU CONTROL
LDOEN LDOS1
2.5V FET CONTROLLER 1.5V FET CONTROLLER SYNCHRONOUS MOSFET DRIVE
(24 Pin SOIC)
GATE1
1.265V REF
PGNDL LDOV REF GATE2 LDOS2
Pentium is a registered trademark of Intel Corporation
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
ABSOLUTE MAXIMUM RATINGS
TA TJ TSTG TL JA JC
ELECTRICAL CHARACTERISTICS
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
UNITS
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
ELECTRICAL CHARACTERISTICS (Cont.)
PARAMETER LDOV Undervoltage Lockout LDOEN Threshold LDOEN Sink Current Overcurrent Trip Voltage Power-up Output Short Circuit Immunity Output Short Circuit Glitch Immunity Gate Pulldown Impedance VOSENSE Impedance
CONDITIONS
MIN 6.5 1.3
TYP 8.0 0.01 -200 40 5 4 300
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 LDOEN CSCS+ PGNDH DH PGNDL DL BSTL BSTH (1) EN VOSENSE (1) VID4 (1) VID3 (1) VID2 (1) VID1 (1) VID0 LDOV GATE2 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 LDO Supply Monitor. 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 LDOEN CSCS+ PGNDH DH PGNDL
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.
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
OUTPUT VOLTAGE
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
UNITS V
5V + R1 10 0.1uF U1 5
VCC REF VID0 VID1 VID2 VID4 LDOEN VOSENSE CSCS+
+ R6 C13 1.00k 2.32k R5
APPLICATION CIRCUIT
C1 0.1uF
PRELIMINARY - September 22, 1999
C2 1500uF C3 1500uF 9 8 17 7 18 4uH 15 11 10 13 14 23 3 C14 1500uF + Q2 IRL34025 L1 R4 5mOhm C15 1500uF Q1 IRL34025 6 22 21 20 19
VID3 EN AGND PGNDL GATE2 GATE1 LDOS2 LDOS1 LDOV BSTL DL PGNDH DH BSTH
C17 1500uF
EN 16 C5 0.1uF 12 24 2 4 1 REF VID0 VID1 VID2 VID3 VID4 SC1186CSW
+ C18 0.1uF GND C16 1500uF
2.5V Q3 IRLML2803 C11 330uF
+ 330uF
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
Q4 IRFZ14S
C9 1000uF
SC1186
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
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
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
Output Voltage
Output Current 5A / div
2.5V Linear Short circuit output response
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
LAYOUT GUIDELINES
Careful attention to layout requirements are necessary for successful implementation of the SC1186 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
AGND GATE1 LDOS1 LDOS2 VCC REF LDOEN CSCS+ PGNDH DH PGNDL GATE2 LDOV 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
SC1186
Heavy lines indicate
3.3V Q3 + Cin Lin Cout Lin1 + Vo Lin1
high current paths.
Vo Lin2 Q4 + Cout Lin2
Layout diagram for the SC1186
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 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 SC1186 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 SC1186 should be supplied from the
SC1186
5V supply through a 10 resistor, the Vcc pin should be decoupled directly to AGND by a 0.1µF 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 SC1186 should run parallel and close to each other. The 0.1µF 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).
Vout +
Currents in various parts of the power section
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
COMPONENT SELECTION
VIN 4L fOSC
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 (µF) 330 330 1500 ESR (m) 60 25 44 Qty. Rqd. 6 3 5 Total C (µF) 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:
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:
or more generally,
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:
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:
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 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
SC1186
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:
SHORT CIRCUIT PROTECTION - LINEARS
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
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 circuit board material, thermal impedances of o 2 o 40 C / W 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
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.
PROGRAMMABLE SYNCHRONOUS DC / DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER
PRELIMINARY - September 22, 1999
SC1186
OUTLINE DRAWING
JEDEC MS-013AD B17104B
ECN99-600