SC1486 Datasheet, PDF (1/17 Pages) Semtech Corporation – Dual Synchronous Buck Pseudo Fixed Frequency DDR Power Supply Controller

SC1486
Dual Synchronous Buck Pseudo Fixed
Frequency DDR Power Supply Controller
POWER MANAGEMENT
Description
Features
The SC1486 is a dual output constant on synchronous-
buck PWM controller optimized for cost effective mobile
DDR applications. Features include high efficiency, a fast
dynamic response with no minimum on time, a REFIN
input and a buffered REFOUT pin capable of sourcing
3mA. The excellent transient response means that
SC1486 based solutions will require less output
capacitance than competing fixed frequency converters.
The frequency is constant until a step in load or line voltage
occurs at which time the pulse density and frequency will
increase or decrease to counter the change in output or
input voltage.
The output voltage of the first controller can be adjusted
from 0.5V to VCCA. In DDR applications, this voltage is
set to 2.5 volts. A resistor divider from the 2.5 volt supply
is used to drive the REFIN pin of the second controller. A
unity gain buffer drives the REFOUT pin to the same
potential as REFIN. The second controller regulates its
output to REFOUT. Two frequency setting resistors set
the on-time for each buck controller. The frequency can
thus be tailored to minimize crosstalk. The integrated
gate drivers feature adaptive shoot-through protection
and soft switching. Additional features include cycle-by-
cycle current limit, digital soft-start, overvoltage and
under-voltage protection, and a PGOOD output for each
controller.
Typical Application Circuit
‹ Constant on-time for fast dynamic response
‹ VIN range = 1.8V – 25V
‹ DC current sense using low-side RDS(ON) sensing
or sense resistor
‹ Integrated reference buffer for VTT
‹ Low power S3 state
‹ Resistor programmable frequency
‹ Cycle-by-cycle current limit
‹ Digital soft-start
‹ PSAVE option for VDDQ
‹ Over-voltage/under-voltage fault protection
‹ <20uA shutdown current
‹ Low quiescent power dissipation
‹ Two separate PGOOD indicators
‹ Separate enable of each switcher
‹ Integrated gate drivers with soft switching
‹ Efficiency >90%
‹ 1% Internal reference
‹ 28 Lead TSSOP
‹ Industrial temperature range
Applications
‹ Notebook computers
‹ CPU I/O supplies
‹ Handheld terminals and PDAs
‹ LCD monitors
‹ Network power supplies
VDDQ/2
VBAT
VDDQ, 2.5V
R11
R10
L1
+ C7
R4
PGND1
R5
R1
R2
REFOUT
EN1
Q1
R3
Q2
23 _TON1
9 _TON2
8 _REFIN
10 _REFOUT
22 _EN/PSV1
6 _DH1
5 _LX1
4 _ILIM1
2 _DL1
1 _PGND1
SC1486
PGOOD1 ²⁷
PGOOD2 ¹³
DH2 ²⁰
LX2 ¹⁹
ILIM2 ¹⁸
DL2 ¹⁶
PGND2 ¹⁵
FBK2 ¹²
FBK1 ²⁶
PGOOD2
PGOOD1
Q4
R8
Q3
VBAT
L2
+ C8
PGND1
VTT, 1.25V
Revision 3, October 2002
1
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