SC1480A Datasheet, PDF (1/23 Pages) Semtech Corporation – DDR and DDR Memory VTT power Supply Controller

SC1480A
DDR and DDR2 Memory VTT
Power Supply Controller
POWER MANAGEMENT
Description
.eatures
The SC1480A is a single output, constant on-time
synchronous-buck, pseudo fixed frequency, PWM
controller intended for use in notebook computers and
other battery operated portable devices. .eatures
include high efficiency and fast dynamic response with
no minimum on time, a reference input and a buffered
RE.OUT pin capable of sourcing 3mA. The excellent
transient response means that SC1480A 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. After the transient event, the controller
frequency will return to steady state operation.
The SC1480A incorporates two power-reducing states,
standby and shutdown. In standby mode, the switcher
output is shutdown but the buffered reference output
stays up, reducing quiescent current to a low 125µA. This
is particularly useful for reducing battery draw in systems
which implement a suspend-to-RAM (S3) state. The
SC1480A can be completely shut down, drawing less than
10µA.
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.
Typical Application Circuit
K Compatible with DDR & DDR2 memory power
requirements
K Constant on-time for fast dynamic response
K Programmable VOUT based on external reference
K VBAT range = 1.8V – 25V
K DC current sense using low-side RDS(ON) sensing
or sense resistor
K 3mA reference output buffer
K Low power S3 state
K Resistor programmable frequency
K Cycle-by-cycle current limit
K Digital soft start
K Output current source-sink capability
K Overvoltage/under-voltage fault protection and
PGOOD output
K Under 10uA typical shutdown current
K Low quiescent power dissipation
K 14 Lead TSSOP
K Industrial temperature range
K Integrated gate drivers with soft switching
K Efficiency >80%
Applications
K Notebook computers
K CPU I/O supplies
K Handheld terminals and PDAs
K LCD monitors
K Network power supplies
VDDQ VBAT
5VSUS
5VRUN
VBAT
R1
10k0
REFOUT
VTT
PGOOD
C8
R6
0u1 10k0
R2
R3
RTON
C3
1u
C6
R7
1n
10R
R4
10R
U1
1
REFIN
SC1480A
14
BST
2 _TON
DH ¹³
3 _REFOUT
LX ¹²
4 _VCCA
ILIM ¹¹
5 _FB
VDDP ¹⁰
6
PGD
9
DL
C7
7 _VSSA
PGND ⁸
1u
D1
C1 0u1
Q1
Q2
R5 RLIM
C5
1u
C2
10u
L1
VTT
C4
+
Revision: December 8, 2004
1
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