sc1406a Semtech Corporation, sc1406a Datasheet - Page 9

• Manufacturer Part Number: sc1406a
• Description: Portable Pentium Ii & Iii Power Supply Controller
• Manufacturer: Semtech Corporation

January 28, 2000
FUNCTIONAL DESCRIPTION
SUPPLY
The chip is optimized to operate from a 3.3V + 5% rail
but is also designed to work up to 6V maximum supply
voltage. If V
the quiescent current will increase somewhat and
slight degradation of line regulation is expected.
UNDER VOLTAGE LOCK-OUT CIRCUIT
The under voltage lockout circuit consists of two com-
parators, the low battery and low V
age) comparators. The output of the comparator
gated with the Enable signal turns on or off the inter-
nal bias, enables or disables the CO output, and
initiates or resets the soft start timers.
POWER GOOD GENERATOR
If the chip is enabled but not in UVLO condition, and
the core voltage gets within + 10% of the VID pro-
grammed value, then a high level Power Good signal
is generated on the PWRGD pin to trigger the CPU
power up sequence. If the chip is either disabled or
enabled in UVLO condition, then PWRGD stays low.
This condition is satisfied by the presence of an inter-
nal 200k pull-down resistor connected from PWRGD
to ground.
During soft start, PWRGD stays low independently
from the status of Vcore voltage. During this time,
PWRGD status is “don’t care”.
BAND GAP REFERENCE
A better than + 1% precision band gap reference acts
as the internal reference voltage standard of the chip,
which all critical biasing voltages and currents are de-
rived from. All references to VREF in the equations to
follow will assume V
CORE CONVERTER CONTROLLER
Precision VID DAC Reference
The 5-bit digital to analog converter (DAC) serves as
the programmable reference source of the core com-
parator. Programming is accomplished by CMOS logic
level VID code applied to the DAC inputs. The VID
code vs. the DAC output is shown in the Output Volt-
age Table. The accuracy of the VID DAC is main-
tained on the same level as the band gap reference.
There is a 10µA pull-up current on each DAC input
while EN is high.
© 2000 SEMTECH CORP.
CC
is out of the 3.3V + 5% voltage range,
REF
= 1.7V.
CC
(low supply volt-
PORTABLE PENTIUM
POWER SUPPLY CONTROLLER
652 MITCHELL ROAD
Core Comparator
This is an ultra-fast hysteretic comparator with a typi-
cal propagation delay of approximately 20ns at a
20mV overdrive. Its hysteresis is determined by the
resistance ratio of two external resistors, R
and the high accuracy internal reference voltage, V
This chip can be used in standard hysteretic mode
controller configuration and in DSPS (Dynamic Set
Point Switching) hysteretic controller scheme.
In standard hysteretic controller configuration, the
core comparator compares the output voltage of the
core converter, V
DAC voltage, V
The core voltage ramps up and down between the two
thresholds determined by the hysteresis of the com-
parator:
In DSPS hysteretic controller configuration, the
core comparator compares the core voltage, V
not to the DAC voltage, V
voltage less than the DAC voltage by a DSPS voltage,
V
V
The DSPS voltage is a function of the load current. It
is generated from the current sense voltage, V
developed across a sense resistor, R
serted in series with the main buck inductor and also
used for current sensing for the cycle-by-cycle current
limiting. The sense voltage is scaled up by the DSPS
gain, A
external resistors, R
DSPS
CORE
V
DSPS
Pentium is a registered trademark of Intel Corporation
.
(t) = V
(
DSPS
) t
, which is set by the resistance ratio of two
A
DAC
DSPS
V
HYS
V
-
®
DAC
CORE
V
V
V
II & III
CORE
.
HCORE
LCORE
DSPS
V
DAC
(t) = V
R
CS
R
to the VID code programmed
(t) + V
HYS
OH
(
and R
= V
= V
) t
NEWBURY PARK CA 91320
DAC
DAC
DAC
DAC
1 (
V
HYST
directly but rather to a
REF
CORE
+ V
+ V
-
R
R
(t)
V
.
CORE
DAC
HYST
HYST
HYST
CS,
(t)
)
which is in-
R
SC1406A
CS
HYS
and R
CS
CORE
i
CORE
,
,
REF
(
) t
OH
9
.
,