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PDF SC1154 Data sheet ( Hoja de datos )
| Número de pieza | SC1154 | |
| Descripción | PROGRAMMABLE SYNCHRONOUS DC/DC HYSTERETIC CONTROLLER FOR ADVANCED PROCESSORS | |
| Fabricantes | Semtech Corporation | |
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PROGRAMMABLE SYNCHRONOUS
DC/DC HYSTERETIC CONTROLLER
FOR ADVANCED PROCESSORS
SC1154
PRELIMINARY - March 1, 2000
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1154 is a synchronous-buck switch-mode con-
troller designed for use in single ended power supply
applications where efficiency is the primary concern.
The controller is a hysteretic type, with a user se-
lectable hysteresis. The SC1154 is ideal for imple-
menting DC/DC converters needed to power advanced
microprocessors such as Pentium® ll, in both single
and multiple processor configurations. Inhibit, under-
voltage lockout and soft-start functions are included for
controlled power-up.
SC1154 features include an integrated 5 bit D/A con-
verter, temperature compensated voltage reference,
current limit comparator, over-current protection, and
an adaptive deadtime circuit to prevent shoot-through
of the power MOSFET during switching transitions.
Power good signaling, logic compatible shutdown, and
over-voltage protection are also provided. The inte-
grated D/A converter provides programmability of out-
put voltage from 2.0V to 3.5V in 100mV increments
and 1.3V to 2.05V in 50mV increments with no external
components.
The SC1154 high side driver can be configured as ei-
ther a grounded reference or as a floating bootstrap
driver. High and low side drivers have a peak current
rating of 2 amps.
FEATURES
• Programmable hysteresis
• 5 bit DAC programmable output (1.3V-3.5V)
• On-chip power good and OVP functions
• Designed to meet latest Intel specifications
• Up to 95% efficiency
• +1% tolerance over temperature
APPLICATIONS
• Server Systems and Workstations
• Pentium® II Core Supply
• Multiple Microprocessor Supplies
• Voltage Regulator Modules
ORDERING INFORMATION
DEVICE(1) PACKAGE
SC1154CSW SO-28
TEMP. RANGE (TJ)
0 - 125°C
Note:
(1) Add suffix ‘TR’ for tape and reel.
PIN CONFIGURATION
Top View
SIMPLIFIED BLOCK DIAGRAM
(28-Pin SOIC)
© 2000 SEMTECH CORP.
Pentium is a registered trademark of Intel Corporation
1
652 MITCHELL ROAD NEWBURY PARK CA 91320
1 page  
PROGRAMMABLE SYNCHRONOUS
DC/DC HYSTERETIC CONTROLLER
FOR ADVANCED PROCESSORS
SC1154
PRELIMINARY - March 1, 2000
ELECTRICAL CHARACTERISTICS (cont.)
Unless specified: 0 < TJ < 125°C, VIN = 12V
PARAMETER
SYMBOL
CONDITIONS
SOFT START
Charge Current
Discharge Current
INHIBIT COMPARATOR
ICHG
Idischg
VSS = 0.5V, resistance from
VREFB pin to AGND = 20kΩ,
VREFB = 1.3V
Note: ICHG = (IVREFB / 5)
V(S/S) = 1V
Start Threshold
VIN12V UVLO
VstartINH
Start Threshold
Hysteresis
HYSTERETIC COMPARATOR
VstartUVLO
VhysUVLO
Input Offset Voltage
Input Bias Current
Hysteresis Accuracy
Hysteresis Setting
DROOP COMPENSATION
VosHYSCMP VDROOP pin grounded
IbiasHYSCMP
VHYS_ACC
VHYS_SET
Initial Accuracy
VDROOP_ACC VDROOP = 50mV
OVERCURRENT PROTECTION
OCP Trip Point
Input Bias Current
HIGH-SIDE VDS SENSING
VOCP
IbiasOCP
Gain
Initial Accuracy
IOUT Source
IOUT Sink Current
Output Voltage Swing
VIOUT_ACC VHISENSE = 12V, VIOUTLO = 11.9V
IsourceIOUT VIOUT = 0.5V, VHISENSE = 12V,
VIOUTLO = 11.5V
IsinkIOUT
VIOUT = 0.05V, VHISENSE = 12V,
VIOUTLO = 12V
VHISENSE = 11V,
RIOUT = 10k0hm
MIN
10.4
1
9.25
1.8
0.09
500
40
0
TYP
13
1
2.0
10
2
0.1
2
50
MAX
15.6
2.4
10.75
2.2
5
1
7
60
5
0.11
100
6
3.75
UNITS
µA
mA
V
V
V
mV
µA
mV
mV
mV
V
nA
V/V
mV
µA
µA
V
© 2000 SEMTECH CORP.
5
652 MITCHELL ROAD NEWBURY PARK CA 91320
5 Page 
PROGRAMMABLE SYNCHRONOUS
DC/DC HYSTERETIC CONTROLLER
FOR ADVANCED PROCESSORS
SC1154
PRELIMINARY - March 1, 2000
FUNCTIONAL DESCRIPTION
Reference/Voltage Identification
The reference/voltage identification (VID) section con-
sists of a temperature compensated bandgap refer-
ence and a 5-bit voltage selection network. The 5 VID
pins are TTL compatable inputs to the VID selection
network. They are internally pulled up to +5V gener-
ated from the +12V supply by a resistor divider, and
provide programmability of output voltage from 2.0V to
3.5V in 100mV increments and 1.3V to 2.05V in 50mV
increments.
Refer to the Output Voltage Table for the VID code
settings. The output voltage of the VID network, VREF
is within 1% of the nominal setting over the full input
and output voltage range and junction temperature
range. The output of the reference/VID network is indi-
rectly brought out through a buffer to the REFB pin.
The voltage on this pin will be within 3mV of VREF. It
is not recommended to drive loads with REFB other
than setting the hysteresis of the hysteretic compara-
tor, because the current drawn from REFB sets the
charging current for the soft start capacitor. Refer to
the soft start section for additional information.
Hysteretic Comparator
The hysteretic comparator regulates the output voltage
of the synchronous-buck converter. The hysteresis is
set by connecting the center point of a resistor divider
from REFB to AGND to the HYST pin. The hysteresis
of the comparator will be equal to twice the voltage dif-
ference between REFB and HYST, and has a maxi-
mum value of 60mV. The maximum propagation delay
from the comparator inputs to the driver outputs is
250ns.
Low Side Driver
The low side driver is designed to drive a low RDS(ON) N-
channel MOSFET, and is rated for 2 amps source and
sink. The bias for the low side driver is provided inter-
nally from VDRV.
High Side Driver
The high side driver is designed to drive a low RDS(ON)
N-channel MOSFET, and is rated for 2 amps source
and sink. It can be configured either as a ground refer-
enced driver or as a floating bootstrap driver. When
configured as a floating driver, the bias voltage to the
driver is developed from the DRV regulator. The inter-
nal bootstrap diode, connected between the DRV and
BOOT pins, is a Schottky for improved drive efficiency.
The maximum voltage that can be applied between the
BOOT pin and ground is 25V. The driver can be refer-
enced to ground by connecting BOOTLO to PGND,
and connecting +12V to the BOOT pin.
Deadtime Control
Deadtime control prevents shoot-through current from
flowing through the main power FETs during switching
transitions by actively controlling the turn-on times of
the FET drivers. The high side driver is not allowed to
turn on until the gate drive voltage to the low-side FET
is below 2 volts, and the low side driver is not allowed
to turn on until the voltage at the junction of the 2 FETs
(VPHASE) is below 2 volts. An internal low-pass filter
with an 11MHz pole is located between the output of
the low-side driver (DL) and the input of the deadtime
circuit that controls the high-side driver, to filter out
noise that could appear on DL when the high-side
driver turns on.
Current Sensing
Current sensing is achieved by sampling and holding
the voltage across the high side FET while it is turned
on. The sampling network consists of an internal 50Ω
switch and an external 0.1µF hold capacitor. Internal
logic controls the turn-on and turn-off of the sample/
hold switch such that the switch does not turn on until
VPHASE transitions high and turns off when the input
to the high side driver goes low. Thus sampling will
occur only when the high side FET is conducting cur-
rent. The voltage at the IO pin equals 2 times the
sensed voltage. In applications where a higher accu-
racy in current sensing is required, a sense resistor
can be placed in series with the high side FET and the
voltage across the sense resistor can be sampled by
the current sensing circuit.
Droop Compensation
The droop compensation network reduces the load
transient overshoot/undershoot at VOUT, relative to
VREF. VOUT is programmed to a voltage greater than
VREF (equal to VREF x (1+R5/R6)) by an external re-
sistor divider from VOUT to the VSENSE pin to reduce
the undershoot on VOUT during a low to high load
current transient. The overshoot during a high to low
load current transient is reduced by subtracting the
voltage that is on the DROOP pin from VREF. The
voltage on the IO pin is divided down with an external
© 2000 SEMTECH CORP.
11
652 MITCHELL ROAD NEWBURY PARK CA 91320
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet SC1154.PDF ] | |
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