Programmable Synchronous DC/DC
Controller for Advanced Processors
POWER MANAGEMENT
Description
The SC1157 is a low-cost, full featured, synchronous
voltage-mode controller designed for use in single ended
power supply applications where efficiency is of primary
concern. Synchronous operation allows for the
elimination of heat sinks in many applications. The
SC1157 is ideal for implementing DC/DC converters
needed to power advanced microprocessors such as
the Pentium
®
ll , in both single and multiple
processor configurations. Internal level-shift, high-side drive
circuitry, and preset shoot-thru control, allows for use of
inexpensive N-channel power switches.
SC1157 features include an integrated 4-bit VID DAC,
temperature compensated voltage reference, triangle
wave oscillator, current limit comparator, frequency shift
over-current protection, and an internally compensated
error amplifier.
The SC1157 operates at a fixed 140KHz, providing an
optimum compromise between efficiency, external
component size, and cost.
SC1157
Features
u
u
u
u
u
Low cost / full featured
Synchronous operation
4 Bit VID DAC programmable output (1% tolerance)
Designed to meet Intel VRM8.2 (Pentium
®
II)
1.5% Reference
Applications
u
u
u
u
u
Pentium® II Core Supply
Multiple Microprocessor Supplies
Voltage Regulator Modules (VRM)
Programmable Power Supplies
High Efficiency DC/DC Conversion
Typical Application Circuit
12V
5V
1500uF
C3
+
C2
1500uF
1500uF
C5
0.1uF
EN
VID0
VID1
VID2
VID3
3
11
16
15
14
13
U1
VCC
EN
VID0
VID1
BSTH
VID2
DH
VID3
BSTL
12V
C12
0.01uF
2
1
REF
GND
SC1157CS
C13
0.1uF
3.3V
Q6 IRLR024N
3
2
8
+
-
U2A
1
LM358
0
R19
18.7
R15
+
C25
330uF
+
R20
100
4
C24
330uF
1.5V
DL
PGND
9
8
6
CS+
CS-
VOSENSE
5
4
12
10
7
Q3
Si4410
R8
2.2
Q4
Si4410
R9
2.2
Q5
Si4410
R10
2.2
Q1
Si4410
R3
2.2
Q2
Si4410
R4
2.2
PHASE
L1
2uH
R13
See Table
R12
See Table
C9
C7
+
+
C8
+
C17
+
C11
0.1uF
R16
1k
1500uF 1500uF 1500uF
1500uF 1500uF 1500uF
R7
R5
1.00k
R6
2.32k
5mOhm
VCCP
R1
10
C15
+
C4
0.1uF
C6
0.1uF
5V
+
C1
0.1uF
C10
+
C21
+
Q7 IRLR024N
5
6
8
+
-
U2B
7
LM358
0
R21
97.6
R14
+
C27
330uF
2.5V
R22
100
4
Revision 4/01
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SC1157
POWER MANAGEMENT
Absolute Maximum Ratings
Parameter
VCC to GND
PGND to GND
BST to GND
Thermal Impedance Junction to Case
Thermal Resistance Junction to Ambient
Operating Temperature Range
Storage Temperature Range
Lead Temperature (Soldering) 10 Sec.
ESD Rating (Human Body Model)
θ
JC
θ
JA
T
A
T
STG
T
LEAD
ESD
Symbol
V
IN
Maximum
-0.3 to 7
±1
-0.3 to 15
30
130
0 to 70
-65 to +150
300
1.5
Units
V
V
V
°C/W
°C/W
°C
°C
°C
kV
Electrical Characteristics
Unless specified: VCC = 4.75V to 5.25V; GND = PGND = 0V; FB = V
O
; 0mV < (CS+ - CS-) < 60mV; T
J
= 25
o
C
Parameter
Output Voltage
Supply Voltage
Supply current
Load Regulation
Line Regulation
Gain (AOL)
Current Limit Voltage
Oscillator Frequency
Buffered Reference Voltage
Oscillator Max Duty Cycle
DH Sink/SourceCurrent
DL Sink/Source Current
Dead Time
VID Pin Source current
VIDx
≤
2.4V
I
REF
≤
1mA
VCC
VCC = 5.0V
Conditions
Min
Typ
Max
Units
See VID Table.
4.5
8
1
±0.15
35
60
125
70
140
1.25
90
BSTH - DH = 4.5V, DH-PGNDH = 3V
BSTL - DL = 4.5V, DL =PGNDL = 3V
1
1
50
30
100
100
95
80
155
7
15
V
mA
%
%
dB
mV
kHz
V
%
A
A
ns
µA
I
O
= 0.3A to 15A
(1)
All VID codes
(1)
VOSENSE to VCCP
Note:
(1) Specification refers to Eval Board Schematic.
(2) This device is ESD sensitive. Use of standard ESD handling precautions is required.
©
2000 Semtech Corp.
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SC1157
POWER MANAGEMENT
Pin Configuration
TOP VIEW
GND
REF
VCC
CS-
CS+
PGND
DH
DL
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VID0
VID1
VID2
VID3
VOSENSE
EN
BSTH
BSTL
Ordering Information
Device
(1)
P ackag e
SO-16NB
Temp Range (T
J
)
0 to125°C
SC1157CS.TR
Note:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
(2) “NB” indicates 150 MIL body.
(16 Pin SOIC)
Pin Descriptions
Pin #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Pin Name
GND
REF
VCC
CS-
CS+
PGND
DH
DL
BSTL
BSTH
EN
VOSENSE
VID3
(1)
VID2
(1)
VID1
(1)
VID0
(1)
Small Signal Analog and Digital Ground
Buffered Reference output
Chip Supply voltage
Current Sense Input (negative)
Current Sense Input (positive)
Power Ground for High and Low Side Drivers
High Side Driver Output
Low Side Driver Output
Supply for Low Side Driver (Boost)
Supply for High Side Driver (Boost)
Enable Pin, 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 (LSB)
Pin Function
NOTE:
(1) All logic level inputs and outputs are open collector TTL compatible.
©
2000 Semtech Corp.
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SC1157
POWER MANAGEMENT
Block Diagram
VCC
CS- CS+
CURRENT
LIMIT
REF
EN
70mV
+
-
LEVEL SHIFT AND
HIGH SIDE DRIVE
BSTH
VID3
VID2
VID1
VID0
VOSENSE
DH
+
D/A
-
-
ERROR
AMP
+
R
OSCILLATOR
Q
S
SHOOT-THRU
CONTROL
AGND
BSTL
SYNCHRONOUS
MOSFET DRIVE
DL
PGND
Theory of Operation
The voltage at the VOSENSE pin is applied, through the
internal precision resistor feedback chain, to the inverting
input of the error amplifier. The non-inverting input of the
error amplifier is supplied with a DC voltage derived by
the DAC from the internal trimmed bandgap voltage ref-
erence. The output of the error amplifier is compared to
the triangular output of the internal oscillator to generate
a fixed frequency, variable duty cycle pulse train. The in-
ternal oscillator uses an on-chip capacitor and precision
trimmed current sources to set the frequency to 140 kHz.
The generated pulse train is gated with the output of the
current limit latch and the inhibit signal to produce a drive
signal for the upper FET. It is also inverted to produce a
drive signal for the lower FET. These FET drive signals are
modified by the shoot-through control circuitry so that
the top FET turn-on is delayed until the bottom FET has
turned off, and visa-versa.
The current limit latch is set (ending the upper FET drive
pulse early) if the current limit comparator indicates an
overcurrent condition. The latch is reset at the start of each
oscillator period.
©
2000 Semtech Corp.
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SC1157
POWER MANAGEMENT
VID Table
Unless specified: VCC = 4.75V to 5.25V; GND = PGND = 0V; FB = V
O
; 0mV < (CS+ - CS-) < 60mV;
T
J
=0°C to 85°C
Parameter
Output Voltage
(1)
Conditions
I
O
= 2A in Evaluation Board
Vid
3210
1111
1110
1101
1100
1011
1010
1001
1000
0111
0110
0101
0100
0011
0010
0001
0000
Min
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
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
Max
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
2.070
Units
V
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2000 Semtech Corp.
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