SC493
EcoSpeedTM Step-down Controller
with I2C Interface
POWER MANAGEMENT
Features
Description
Input supply voltage range — 3.0V to 28V
Controller supply voltage range — 3.0V to 5.5V
All ceramic solution enabled
I2C interface
Output voltage fine adjust control
Output voltage margining
Supports dynamic voltage transitions via the I2C
interface
Programmable power-on delay time and soft-start time
EcoSpeedTM architecture with pseudo fixed-frequency
adaptive on-time control
Switching frequency programmable up to 1MHz
Selectable power save, including ultrasonic
Non-synchronous start-up into pre-biased loads
Over-voltage/under-voltage fault protection
Smart power save
Power good Output
Smart driveTM
Status register monitoring device operation
Ultra-thin package — 3 x 3 x 0.6 (mm), 20 pin MLPQ-UT
Lead-free and halogen-free
WEEE and RoHS compliant
The SC493 is a synchronous EcoSpeedTM buck power supply
controller. It features an I2C interface and a bootstrap switch in
a space-saving MLPQ 3X3-20 pin package. The SC493 uses
Semtech’s advanced patented adaptive on-time control architecture to provide excellent light load efficiency and fast transient response with small external components.
The I2C interface is used to program the output voltage
offset, the power-on delay time, the soft-start time, the
power save operating mode, and it can enable/disable the
controller. Additionally, a status register provides information on device state and faults.
The controller is capable of operating with all ceramic solutions and switching frequencies up to 1MHz. The programmable frequency and selectable power save mode offer the
flexibility to optimize the controller for high efficiency and
small size. The power save mode can be enabled to maximize
efficiency over the entire load range (PSAVE), or switched to
ultrasonic mode to set the minimum frequency to the desired
value (UPSAVE). Power save mode can be disabled for operation in continuous conduction mode at all loads.
Additional features include output voltage margining,
cycle-by-cycle current limit, output voltage soft-start, over
and under-voltage protection, controller over-temperature protection, and output voltage soft-shutdown when
disabled. The SC493 also provides a power good output.
Applications
Printers
Computer peripherals
Typical Application Circuit
VIN
VDD
CIN
Q1
ILIM
DH
VIN
RILIM
BST
EN
SDA
A0
A1
A2
PGND
SCL
VOUT
SCL
SDA
LX
SC493
FB
PGD
PGD
AGND
EN
PVDD
AVDD
R1 R2 R3
L
CBST
DL
Q2
VOUT
R4
COUT
R5
US Patent: 7,714,547 B2
June 10, 2010
© 2010 Semtech Corporation
SC493
VOUT
1
FB
2
AVDD
A0
A1
A2
ILIM
Ordering Information
AGND
Pin Configuration
20
19
18
17
16
15
PGOOD
14
PVDD
3
13
PGND
SDA
4
12
DL
SCL
5
11
NC
TOP VIEW
6
7
8
9
10
EN
VIN
DH
BST
LX
PAD
Device
Package
SC493ULTRT(1)(2)
MLPQ-UT-20 3X3
SC493EVB
Evaluation Board
Notes:
(1) Available in tape and reel only. A reel contains 3,000 devices.
(2) Lead-free packaging only. Device is WEEE and RoHS compliant,
and halogen-free.
MLPQ-UT-20 3X3, 20 LEAD
θJA=40°C/W
Marking Information
493
yyww
xxxxx
yyww = Date Code
xxxxx = Semtech Lot No.
Notice: All referenced brands, product names, service names and trademarks are the property of their respective owners.
SC493
Absolute Maximum Ratings
Recommended Operating Conditions
BST to LX (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0
Ambient Temperature (°C). . . . . . . . . . . . . . . . . . . . . -40 to +85
BST to PGND (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +35
Input Voltage VIN (V). . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 to 28
LX to PGND (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +30
Controller Supply Voltage AVDD, PVDD (V). . . . . 3.0 to 5.5
PVDD to PGND (V). . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0
Output Voltage (V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 to 5.0
VIN to PGND (V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +30
AVDD to AGND (V) . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0
Thermal Information
AGND to PGND (V). . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +0.3
Storage Temperature (°C). . . . . . . . . . . . . . . . . . . . -65 to +150
All other pins to AGND (V). . . . . . . . . . . . . . -0.3 to AVDD +0.3
ESD Protection Level(1) (kV). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Maximum Junction Temperature (°C). . . . . . . . . . . . . . . . 150
Operating Junction Temperature (°C). . . . . . . . . -40 to +125
Thermal Resistance, Junction to Ambient(2) (°C/W) . . . . . 40
Peak IR Reflow Temperature (10s to 30s) (°C). . . . . . . . . 260
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters
specified in the Electrical Characteristics section is not recommended.
NOTES:
(1) Tested according to JEDEC standard JESD22-A114-B.
(2) Calculated from package in still air, mounted to 3 x 4.5(in.) 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.
Electrical Characteristics
Test Condition (unless otherwise noted): VVDD(1)=5V, VIN=5V, TJ(MAX) = 125°C. Typ. values at 25°C, Min. and Max. at -40°C < TA < 85°C, VFBadj = 0%.
Parameter
Symbol
Condition
Min
Typ
Max
Units
5.5
V
Input Supply
VDD(1) Input Voltage
VDD
VDD(1) UVLO Threshold
VDDUVLO
VDD(1) UVLO Hysteresis
VDDUVLO_HYS
VDD(1) Supply Current
IVDD
3.0
VDD rising
2.8
V
0.2
V
Shut down, EN pin = 0V
0.1
I2C Standby, controller disabled
150
No switching, PSAVE, FB>0.5V
1000
fsw = 25kHz, UPSAVE
2
Operating fsw= 250kHz, no load
10
2
µA
mA
Switch-mode Controller
FB On-Time Threshold
VVFB_TON
Static VIN and Load, no offset via I2C
0.496
0.5
0.504
V
On-Time Accuracy
tON
Deviation from the ideal on-time to meet
the set switching frequency
-10
10
%
Minimum On Time
tON_MIN
100
ns
Minimum Off Time
tOFF_MIN
250
ns
SC493
Electrical Characteristics (continued)
Parameter
Symbol
Condition
Initialization Time (2)
tINIT
Delay before the I2C bus and the Power-on
delay ramp are enabled
Soft-Start Time Accuracy
tSS
Power-on Delay Time Accuracy
tDLY
Min
Typ
Max
Units
1
ms
-20
+20
%
-20
+20
%
Startup
Powersave
Zero-Crossing Detector Threshold
VTZC
VLX - PGND
-3
0
+3
mV
UPSV mode Frequency
fUPSV
UPSV enabled, UPSV1 = 1, UPSV0 = 1
20
25
30
kHz
PGD Rising Threshold
VTPGD_RISE
FB with respect to set point, under voltage,
and over voltage
90/120
%
PGD Falling Threshold
VTPGD_FALL
FB with respect to set point, under voltage,
and over voltage
80/110
%
PGD Leakage
ILEAKPGD
Device operating, no fault, VPGD=VVDD(1)
1
µA
PGD Output Low Voltage
VPGD_LOW
IPGD=3mA
0.4
V
11
μA
Power Good
Fault Protection
ILIM Source Current
ILIM Temperature Coefficient
ILIM Comparator Offset
ILIM
9
TCILIM
10
3000
VOFFILIM
-10
0
ppm
+10
mV
VTUV
FB with respect to set point,
8 consecutive switching cycles
70
%
Output Over-Voltage Fault
VTOV
FB with respect to set point rising/ falling
120
%
Over-Voltage Fault Delay(2)
tDLY_OV
5
μs
Output Under-Voltage Fault
Smart Power-save Protection Threshold(2)
VTSMRTPSV
FB with respect to set point rising
110
%
Over-Temperature Shutdown
TOT
Rising TJ
160
°C
Over-Temperature Hysteresis
TOT_HYS
10
°C
Analog Inputs and Outputs
VOUT Input Resistance
RVOUT
Controller enabled
500k
Controller disabled/internal load enabled
10
Ω
SC493
Electrical Characteristics (continued)
Parameter
Symbol
Condition
Min
1.6
Typ
Max
Units
Digital Input Electrical Specifications (A0, A1, A2, EN)
Input High Threshold
VIH
VVDD(1) = 5.5V
Input Low Threshold
VIL
VVDD(1) = 3.0V
Input High Current
IIH
VVDD(1) = 5.5V
Input Low Current
IIL
VVDD(1) = 5.5V
V
0.4
V
-1
+1
μA
-1
+1
μA
I2C Interface
Interface complies with slave mode I2C interface as described by Philips I2C specifications version 2.1 dated January, 2000
Digital Input Voltage Low
VB-IL
Digital Input Voltage High
VB-IH
SDA Output Low Level
VSDA_LOW
0.4
1.6
V
V
IDN(SDA) ≤ 3mA
0.4
V
+0.2
μA
Digital Input Current
IB-IN
Hysteresis of Schmitt Trigger Inputs
VHYS
0.1
V
Maximum Glitch Pulse
Rejection
tSP
50
ns
I/O Pin Capacitance
CIN
10
pF
Clock Frequency
fSCL
400
SCL Low Period (2)
tLOW
1300
ns
SCL High Period (2)
tHIGH
600
ns
Data Hold Time (2)
tHD_DAT
0
ns
Data Setup Time (2)
tSU_DAT
100
ns
Setup Time for Repeated START
Condition (2)
tSU_STA
600
ns
Hold Time for Repeated START
Condition (2)
tHD_STA
600
ns
Setup Time for STOP Condition (2)
tSU_STO
600
ns
tBUF
1300
ns
-0.2
I2C Timing
Bus-Free Time Between STOP and START
(2)
440
kHz
SC493
Electrical Characteristics (continued)
Parameter
Symbol
Condition
Min
Typ
tPROT
DH or DL Rising
30
RDL_DOWN
DL Low
0.3
DL Sink Current
IDL_SINK
VDL = 2.5V
8.3
DL Pull-Up Resistance
RDL_UP
DL High
1
DL Source Current
IDL_SOURCE
VDL = 2.5V
2.5
DH Pull-Down Resistance
RDH_DOWN
DH Low, BST-LX = 5V
0.6
DH Sink Current
IDH_SINK
VDH - LX = 2.5V
4.2
DH Pull-Up Resistance
RDH_UP
DH High, BST-LX = 5V
1
IDH_SOURCE
VDH - LX = 2.5V
2.5
Max
Units
Gate Drivers
Shoot-Through Protection Delay(2)
DL Pull-Down Resistance
DH Source Current
ns
0.6
Ω
A
2
Ω
A
1.2
Ω
A
2
Ω
A
Note:
(1) VDD refers to both AVDD and PVDD
(2) Guaranteed by design.
SC493
Typical Characteristics
Switching Frequency vs. Load — CCM
Efficiency vs Load — CCM and PSAVE
100
VOUT = 1.8V, VIN = 5V, fSW = 1MHz
1200
VOUT = 1.8V, VIN = 5V, fSW = 1MHz
1150
PSAVE
Switching Frequency (kHz)
Efficiency (%)
90
80
CCM
70
60
1100
1050
1000
950
900
850
50
1
0.1
Output Current (A)
10
800
100
5
0
VOUT = 1.8V, VIN = 5V, fSW = 250kHz
1.9
+1%
1.82
1.78
-1%
1.74
VOUT = 1.8V, VIN = 5V, fSW = 250kHz
+1%
1.82
1.78
-1%
1.74
0
5
10
15
Output Current (A)
20
1.7
25
0
Output Voltage vs. Margin — CCM
2
10
15
Output Current (A)
20
25
VOUT = 1.8V, VIN = 5V, fSW = 1MHz
VOUT = 1.8V, VIN = 5V, fSW = 1MHz
2
1.9
Output Voltage (V)
Output Voltage (V)
5
Output Voltage vs. VFBadj — CCM
1.9
1.8
1.8
1.7
1.6
25
1.86
Output Voltage (V)
Output Voltage (V)
1.86
1.7
20
Load Regulation — PSAVE
Load Regulation — CCM
1.9
10
15
Output Current (A)
1.7
-10
-5
0
Margin Command (%)
5
10
1.6
-10
-5
0
VFBadjust Command(%)
5
10
SC493
Typical Characteristics (continued)
Soft Start — EN Pin
Soft Start — I2C
VIN = 5V, VOUT = 1.8V, Soft Start = 1ms, Power-on Delay = 0ms
VIN = 5V, VOUT = 1.8V, Soft Start = 2ms, Power-on Delay = 2ms
EN (5V/div)
SCL (5V/div)
VOUT (500mV/div)
VOUT (500mV/div)
PGOOD (5V/div)
PGOOD (5V/div)
Time (500μs/div)
Load Transient Response
Time (1ms/div)
Output Over Current Response — Normal Operation
VIN = 5V, VOUT = 1.2V, fSW = 1MHz, L = 0.2μH, C = 220μF
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, L = 0.2μH, C = 1000μF
IOUT = 20A
IL (10A/div)
IOUT
(5A/div)
VOUT (1V/div)
VOUT (20mV/div)
LX (5V/div)
PGOOD (5V/div)
Time (500μs/div)
Time (20μs/div)
Switching — Forced Continuous Mode
Switching — Ultrasonic PSAVE Mode
VIN = 5V, VOUT = 1.8V, fSW = 500kHz, No load
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, Load = 3A
VOUT (20mV/div)
LX (5V/div)
VFB (20mV/div)
DH (5V/div)
VOUT (20mV/div)
DL (5V/div)
Time (1μs/div)
Time (4μs/div)
SC493
Typical Characteristics (continued)
Slew-Up — CCM, No Load, EnIntLd=0/1
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, VFBadj command change -9% to +9%
Slew-Down — CCM, No Load, EnIntLd=0
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, VFBadj command change +9% to -9%
SCL (5V/div)
SCL (5V/div)
VOUT (100mV/div)
VOUT (100mV/div)
PGOOD (5V/div)
PGOOD (5V/div)
Time (500μs/div)
Slew-Up — CCM, No Load, EnIntLd=0/1
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, Margin command change -10% to +10%
Time (500μs/div)
Slew-Down — CCM, No Load, EnIntLd=1
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, Margin command change +10% to -10%
SCL (5V/div)
SCL (5V/div)
VOUT (100mV/div)
VOUT (100mV/div)
PGOOD (5V/div)
PGOOD (5V/div)
Time (500μs/div)
Time (500μs/div)
Slew-Up — CCM, 3A Load, EnIntLd=0/1
Slew-Down — CCM, 3A Load, EnIntLd=0/1
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, Margin command change -10% to +10%
VIN = 5V, VOUT = 1.8V, fSW = 1MHz, Margin command change +10% to -10%
SCL (5V/div)
SCL (5V/div)
VOUT (100mV/div)
VOUT (100mV/div)
PGOOD (5V/div)
PGOOD (5V/div)
Time (500μs/div)
Time (500μs/div)
SC493
Pin Descriptions
Pin #
Pin Name
Pin Function
1
VOUT
Output voltage
2
FB
3
AVDD
Chip supply voltage
4
SDA
I2C data input/output
5
SCL
I2C clock input
6
EN
Enable pin
7
VIN
Power stage input voltage
8
DH
High side gate driver pin
9
BST
Bootstrap pin — a capacitor is connected from BST to LX to develop the bias voltage for the high side gate
drive.
10
LX
Switching (phase) node — connect to the switching side of the power inductor.
11
NC
No Connect
12
DL
Low side gate driver pin
13
PGND
Power ground
14
PVDD
Supply voltage for driver
15
PGOOD
16
ILIM
17
A2
Input for bit 2 of the I2C device address
18
A1
Input for bit 1 of the I2C device address
19
A0
Input for bit 0 of the I2C device address
20
AGND
PAD
Feedback pin
Power good
Current limit sense point — to program the current limit connect a resistor from ILIM to LX
Analog ground
Thermal pad for heat sinking purposes — connect to ground plane using multiple vias — not connected
internally.
10
SC493
Block Diagram
VIN
EN
SCL
SDA
A2
A1
A0
PGOOD
PVDD
7
6
5
4
17
18
19
15
14
PVDD
2
Control, Status, and I C Interface
Reference
Feedback Adjustment
Output Voltage Margining
Power On Delay
Soft Start Time
Frequency Setting
Current Limit Setting
Power Save Mode
Status Register
DL
9
BST
8
DH
10
LX
12
DL
16
ILIM
13
PGND
Soft Start &
Slew Control
AVDD
AVDD
3
+
-
On-time
Generator
Gate Drive
Control
Comparator
AGND
20
FB
2
Zero Cross Detector
PVDD
Valley Current Limit
1
VOUT
11
SC493
Applications Information
General Description
The SC493 is a step down synchronous buck DC-DC
controller optimized for use in 3.3V/5V input small formfactor applications. It has the following key features:
•
•
•
•
•
•
•
I2C control over output voltage offset, margining, power-on delay, switching frequency, softstart duration, and power save mode.
Integrated bootstrap switch
Programmable switching frequency from 250kHz
to 1MHz to optimize board space and efficiency.
Protection features — over-current, over-voltage,
under-voltage, and over-temperature
Power save operation — low quiescent current
and ultrasonic power save
Status and flag bits for diagnosis and protection
purposes
Supports 25A operation
I2C Compatible Interface Functions
The I2C interface can be used to read & write the following
functions:
•
•
•
•
•
Shutdown/Start-up of output
Power-on delay and soft-start duration
Output voltage offset and margining
Power save mode
Switching frequency
Additionally, the I2C interface can be used to read status
and flag bits for the following functions:
•
•
•
•
•
•
•
•
Under voltage
Over voltage
Over temperature
Current limit
Brown out
Did not start
Discontinuous mode
Power good
Status and Flag Bits
The status and flag bits are used to indicate the status of
the converter. The status bits always indicate the current
state of the converter — the status bit becomes high
when the specified condition happens and turns low
when the specified condition disappears. The flag bits also
become high when the specified condition happens, but
will not turn low when the specified condition disappears.
For the above mentioned status and flag bits, only discontinuous mode and power good are status bits, the rest of
them are all flag bits. The flag bits remain set until one of
the following events occurs:
•
•
•
The input voltage is cycled
EN pin is cycled
CLF bit is set
Enable/Disable
The converter is enabled by applying power to VDD
(VDD when used refers to AVDD and PVDD together) and
VIN, and pulling the EN pin high. The output voltage will
rise to the voltage programmed by the FB pin and the
external FB network. Pulling the EN pin low turns the
converter off and clears all flag bits. The converter can
also be turned on/off via the I2C interface. When the EN
pin is high, setting the ENSW bit low will turn off the
converter, but the flag bits will not be cleared. Setting the
ENSW bit back high will turn on the converter again.
Diagnosis and Protection Features
When the device detects fault conditions, the SC493 sets
the flag bits indicating what fault conditions have
occurred. In addition, depending upon what kind of faults
have been detected, the SC493 will provide appropriate
actions to safeguard the device from catastrophic failures.
The following paragraphs describe how these fault conditions are handled by the SC493.
Did Not Start Indication
If the FB voltage does not rise to 90% of nominal voltage
after the converter is enabled, the soft-start duration has
passed, and the power good delay has elapsed, the Did
Not Start (DNS) flag bit is set. Note that the converter does
not latch off just because this bit is set.
Output Over Voltage Protection
When the FB pin voltage exceeds 120% of the nominal
voltage, DL goes high, forcing the low-side MOSFET on,
and the OVO flag bit is set. The low side MOSFET stays on
(and the high side MOSFET remains off ) until the output
voltage comes back into regulation. However, the CLF bit
will successfully clear the OVO flag as soon as the FB falls
below 120% of the normal voltage. The converter does not
12
SC493
Applications Information (continued)
latch off just because this bit is set. The PGD output is
driven low when the FB pin is above 120% of the nominal
voltage and returns to high when the FB pin is below 110%
of the nominal voltage.
Output Over Current Protection
The SC493 features adjustable current limit capability.
The RDS(ON) of the external low side MOSFET is used as the
current sensing element. The over current limit is set by
RILIM (connected externally). Internally there is a 10μA
current source that feeds the ILIM pin when the low side
MOSFET has turned on. This current flows through the RILIM
resistor and creates a voltage drop across it. When the low
side MOSFET turns on, the inductor current flowing
through it creats a voltage across the MOSFET due to its
RDS(ON). If this voltage drop exceeds the voltage across the
RILIM resistor, current limit will activate. This prevents the
high side MOSFET from turning on until the voltage drop
across the low side MOSFET falls below the voltage across
the RILIM resistor. This effectively sets a valley current limit
of RILIM x 10μA/RDS(ON). Please note that RDS(ON) of the MOSFET
is dependent on the VGS voltage (equals to PVDD applied
to SC493). The ILIM flag bit is set whenever current limit
occurs. The converter does not latch off just because this
bit is set.
Output Under Voltage Protection
The output under voltage condition occurs with or without
current limit. The output under voltage without current
limit is normally a result of low input voltage. The controller will look at the inductor current to differentiate these
two situations and respond accordingly. After PGD is
asserted, if the FB voltage falls below the PGD falling
threshold (80%) and current limit does not happen simultaneously, the Brown Out (BO) flag bit is set. This indicates
an output under voltage has happened because of low
input voltage. The converter does not latch off just
because the BO bit is set. After PGD is asserted, if FB
voltage falls below 70% of the nominal voltage for 8 consecutive current limited switching cycles, the UVO flag bit
is set. This latches the converter off, with both the high
side and low side MOSFETs turned off.
To restart, either the EN pin or ENSW register bit must be
set low and then back to high.
Over Temperature Protection
When the temperature of the device reaches the over
temperature rising threshold, the OT flag bit is set, turning
off both high side and low side MOSFETs. After the
temperature of the device drops to the over temperature
falling threshold, the converter restarts as if the device
has been enabled. The converter will go through poweron delay and soft start.
Synchronous Buck Converter Operation, Benefits, and Features
The SC493 employs pseudo-fixed frequency adaptive ontime control. This control method allows fast transient
response thereby lowering the size of the power
components needed in the system.
The on time is determined by an internal one-shot with a
period proportional to the output voltage and inversely
proportional to the input voltage. The output ripple
voltage generated by the ESR of the output capacitance is
used as the PWM ramp signal. This ripple voltage
determines the off time for the controller.
For the SC493 the operating frequency range is from 250kHz
to 1MHz , programmable via the I2C interface.
Adaptive on-time control has significant advantages over
traditional control methods. Some of the advantages of
the adaptive on-time control are:
•
•
•
•
No error amplifier, which reduces external components used for compensation
Predictable frequency spread because of adaptive on-time architecture
Fast transient response — operation with
minimum output capacitance
Overall superior performance compared to fixed
frequency architectures
On-Time One-Shot Generator (TON)
Adaptive on-time controllers like the SC493 have an
internal on-time one-shot generator. The one-shot timer
uses an internal comparator and a capacitor. The positive
input of the comparator is a voltage proportional to the
output voltage and the negative input is connected to the
capacitor charged by a current proportional to the input
voltage. The TON time is the time required to charge this
13
SC493
Applications Information (continued)
capacitor from 0V to the voltage at the positive input. This
makes the on-time proportional to the output voltage and
inversely proportional to the input voltage, providing a nearconstant switching frequency when the input and output
voltage vary. A second comparator compares the voltage at
the feedback pin to a fixed internal reference voltage to
determine when to turn on the high side MOSFET.
Power-on Delay Programming
The power-on delay is programmable via the I2C interface.
The power-on delay is defined as the time from when the
ENSW bit is set to when the PWM control is enabled and the
part begins switching. At the end of the power-on delay time,
the PWM control circuit is enabled in a phased manner to
ensure proper operation. The phased enabling of internal
circuitry adds up to 48μs to the power-on delay time. On startup (controller enabled by applying power and driving the EN
pin high). The controller can take up to 1ms for internal
initialization following which the power-on delay is applied.
Soft-Start Operation and Programming
Soft-start is achieved in the PWM controller by using an
internal voltage ramp as the reference for the FB Comparator.
The voltage ramp is generated using an internal charge
pump which drives the reference from zero to 500mV in ~
2mV increments, using an internal oscillator. When the
ramp voltage reaches 500mV, the ramp is ignored and the
FB comparator switches over to a fixed 500mV threshold.
During soft-start the output voltage tracks the internal
ramp, which limits the start-up inrush current and provides
a controlled soft-start profile for a wide range of applications. Soft-start programmability is achieved by changing
the frequency of the oscillator. The soft-start ramp reaches
500mV in 90% of the programmed soft-start time. The
remaining 10% of the programmed soft-start time is used
to allow the system to stabilize before enabling the PGOOD
comparator to drive the PGOOD pin high.
During soft-start the controller turns off the low-side
MOSFET on any cycle if the inductor current falls to zero.
This prevents negative inductor current, allowing the
device to start into a pre-biased output.
Frequency Programming
The nominal switching frequency in continuous
conduction mode is programmable via the I2C interface.
The switching frequency is changed to the programmed
value by scaling the on time as needed.
Power Save Mode Programming
The SC493 provides selectable power-save operation at
light loads. When register bits PSV1,0 are set to 01 or 10
the power save mode is enabled. With power save
enabled, the zero crossing comparator monitors the
inductor current via the voltage across the low-side
MOSFET. If the inductor current falls to zero for 8 consecutive cycles then the controller enters power save and turns
off the low-side FET on each subsequent cycle as long as
the current crosses zero. If the inductor current does not
reach zero for 8 consecutive switching cycles the controller immediately exits power save. The controller counts
zero crossings and therefore the converter can sink current
as long as the current does not cross zero on 8 consecutive consecutive cycles. This allows the output voltage to
recover quickly in response to negative load steps.
The SC493 can also be operated in forced Continuous
Conduction Mode (CCM) by setting PSV1,0 = 00 or 11.
With these settings the device will not enter PSAVE and
operates at programmed frequency even at light loads.
This feature provides user flexibility for system design.
Figure 1 shows operation under power save and continuous conduction mode at light loads.
FB Ripple
Voltage
(VFB)
Dead time varies
according to load
FB threshold
(500mV)
Inductor
Current
Zero (0A)
On-time (TON)
DH
DH On-time is triggered when
VFB reaches the FB Threshold.
DL
DL drives high when on-time is completed.
DL remains high until inductor current reaches zero.
Figure 1 — Power-save Operation
14
SC493
Applications Information (continued)
Ultrasonic Power-save
When ultrasonic PSAVE is enabled (PSV1,0 =10) the
minimum operating frequency in power save for the
SC493 is set by UPSV1,0 bits . This is accomplished by
using a built-in timer that detects the time between consecutive high-side gate pulses.
UVLO and POR
Under-Voltage Lockout (UVLO) circuitry inhibits switching
and tri-states the output until VDD rises above 2.8V. An
internal Power-On Reset (POR) occurs until VDD exceeds
2.8V, which resets the internal registers, enables the I 2C
interface, and resets the soft-start circuitry.
As soon as the time exceeds the the programmed upper
limit, the bottom gate is turned on. This prevents the controller from going below the set limit in frequency when
the power save is enabled. Figure 2 shows ultrasonic
power-save operation.
Smart Power-save Protection
Active loads may leak current from a higher voltage into
the switcher output. Under light load conditions with
power-save enabled, this can force VOUT to slowly rise and
reach the over-voltage threshold. Smart power-save prevents this condition. When the FB voltage exceeds 10%
above nominal (exceeds 550mV), the device immediately
disables power-save, and DL drives high to turn on the
low-side MOSFET. This draws current from VOUT through
the inductor and causes VOUT to fall. When VFB drops back
to the 500mV trip point, a normal TON switching cycle
begins. This method prevents an OVP fault and also cycles
energy from VOUT back to VIN. The device will return to
power-save operation on the next switching cycle if the
load remains light. Smart Power-Save allows the user to
minimize operating power by allowing the use of power
save mode in load conditions that would normally require
the use of forced continuous conduction mode. Figure 3
shows typical waveforms for the Smart Power-save
feature.
Minimum FSW ~ 20kHz
FB Ripple
Voltage (VFB)
FB threshold
(500mV)
(0A)
Inductor
Current
On-time
(TON)
DH On-Time is triggered when
VFB reaches the FB Threshold
DH
40µsec time-out
DL
After the 40µsec time-out, DL drives high if VFB
has not reached the FB threshold.
Figure 2 — Ultrasonic Power-save (UPSV 1,0 = 11)
Power Good Output
The Power Good (PGD) output is an open-drain output
which requires a pull-up resistor. When the FB voltage falls
lower than 80% (typical) of the nominal voltage, PGD is
pulled low. It is held low until the FB voltage rises above
90% (typical) of the nominal voltage. PGD is held low
during start-up and will not be allowed to transition high
until soft-start is completed. PGD also transitions low if the
FB voltage rises above 120% (typical) of the nominal
voltage, it is held low until the FB voltage drops below 110%
(typical) of the nominal voltage.
VOUT drifts up to due to leakage
current flowing into COUT
Smart Power Save
Threshold (550mV)
VOUT discharges via inductor
and low-side MOSFET
Normal VOUT ripple
FB
threshold
DH and DL off
High-side
Drive (DH)
Single DH on-time pulse
after DL turn-off
Low-side
Drive (DL)
DL turns on when Smart
PSAVE threshold is reached
Normal DL pulse after DH
on-time pulse
DL turns off when FB
threshold is reached
Figure 3 — Smart Power-save
15
SC493
Applications Information (continued)
Dynamic Output Voltage Control
SC493 allows changing the output voltage when the part
is already switching. Whenever the output voltage is
changed via margining or by fine adjust, the controller
changes the internal reference by small intermediate steps
using 32us per step. This ensures that the output keeps up
with internal slewing and excessive current does not build
up in the inductor. The faults are blanked till the end of the
slewing. Blanking is released when 8 switching cycles
occur after the end of internal slewing since the switching
cycles indicate that the part is in regulation. The part is
enabled to operate in DCM mode to prevent negative
current build up in the inductor when slewing down. The
part returns to the previous operational state (DCM or
CCM) at the end of blanking.
Since the controller operates in DCM, it depends on the
load to discharge the output when slewing down. Therefore,
no switching cycles may occur if the load is very light and
the output will not keep pace with the internal slew. In such
cases, the blanking at the end of slewing will end after a
1ms timeout whether any switching cycles occur or not and
the part will return to its previous operational state.
For applications that need to have the output slew down at
the same rate as the internal slewing, register bit Enable
Internal Load (EnIntLd) can be set. This activates an internal
10Ω pull down on Vout when the part is slewing down. This
resistance discharges the output capacitor and helps the
output keep pace with internal slewing. To help maximize
efficiency, the pulldown will not activate when slewing up
even if the feature is enabled via register settings.
When the internal pull down is enabled, it is active only for
the time it takes the internal reference to reach its target.
For example, when slewing from VFBadjust of +9% to 0%,
the pull down is active only for 12 x 32µs = 384µs. In applications with large output capacitors, this time may not be
sufficient to discharge the output to keep up with the
internal reference. Therefore, the output can be higher
than the desired regulation value at the end of the slewing
sequence. If the part was in DCM before slewing began,
the output will stay at the higher value at the end of the
sequence. If there is no load, the output will return to the
desired value very slowly. In such applications, to ensure
that the controller quickly brings the output voltage into
regulation, it is recommended that either PSAVE be dis-
abled or set to ultrasonic before the output is slewed. This
will ensure that the low side MOSFET will turn back on at
the end of the slewing sequence even if there is no load
and bring the output voltage back into regulation. Figure
4 demonstrates this with a 1000µF output capacitor and
with psave disabled before slewing from VFBadj = +9% to
VFBadj = -9%.
SCL (5V/div)
VOUT (100mV/div)
PGOOD (5V/div)
Time (500μs/div)
Figure 4 — Slew Down in CCM with Large Output
Capacitors
Soft-shutdown
SC493 features a soft-shutdown feature: whenever switching is disabled, an internal 10Ω pull-down activates on the
Vout pin which discharges the output capacitor and holds
Vout low. The pull-down stays active even if the EN pin is
subsequently driven low. Note that the pull-down will not
activate if EN pin has not been high after power has been
applied or power is cycled with EN pin low.
SmartDriveTM
For each DH pulse, the DH driver initially turns on the
high-side MOSFET at a slower speed, allowing a softer,
smooth turn-off of the low-side diode. Once the diode is
off and the LX voltage has risen 0.5V above PGND, the
SmartDrive circuit automatically drives the high-side
MOSFET on at a rapid rate. This technique reduces switching noise while maintaining high efficiency, reducing the
need for snubbers or series resistors in the gate drive.
16
SC493
Applications Information (continued)
Power Stage Design Procedure
When designing a switch mode supply the input voltage
range, load current, switching frequency, and inductor
ripple current must be specified.
implemented is calculated according to the next
equation.
DMAX
t ON
t ON t OFF(MIN)
The maximum input voltage (VINMAX) is the highest specified input voltage. The minimum input voltage ( VINMIN) is
determined by the lowest input voltage after evaluating
the voltage drops due to connectors, fuses, switches, and
PCB traces.
If a maximum load step occurs instantly, the voltage
undershoot can be derived by the next equation.
The following parameters define the design:
For load release, the worst case happens when the
maximum load release occurs at the same time as the high
side turns on. The over-shoot in this situation can be
derived by the next equation.
•
•
•
•
Nominal output voltage (VOUT )
Static or DC output tolerance
Transient response
Maximum load current (IOUT )
There are two values of load current to evaluate — continuous load current and peak load current. Continuous
load current relates to thermal limitations which drive the
selection of the inductor and input capacitors. Peak load
current determines instantaneous component stresses
and filtering requirements such as inductor saturation,
output capacitors, and design of the current limit circuit.
Inductor Selection
Low inductor values result in smaller size but create higher
ripple current, and are less efficient because of that ripple
current flowing in the inductor. Higher inductor values
will reduce the ripple current/voltage and are more efficient, but are larger and more costly. The inductor selection is based upon the ripple current which is typically set
between 20% and 50% of the maximum load current.
Cost, size, output ripple, and efficiency are all used in the
selection process. The equation for determining the inductance is shown by the next equation.
L
( VIN VOUT ) u t ON
IRIPPLE
Output Capacitor Selection
Two parameters need to be determined in order to select
the output capacitor — the output capacitance and the
capacitor ESR. These two parameters are determined
based upon the dynamic and the static regulation requirements. On a load step, the maximum duty ratio that is
VUV
VOV
'I2 u L
2 u C u DMAX u VIN VOUT 'I u t ON
L u 'I
2 u C u VOUT
2uC
2
Using the previous two equations, the output capacitor
can be calculated based upon the required performance
metrics (under-shoot or over-shoot voltage during the
transient). Note that the above equations show the worst
case analysis. In practice, the load normally changes with
certain slew rate limits, so the required capacitance value
may be much smaller than the value calculated using
these equations.
Input Capacitor Selection
The input capacitor should be chosen to handle the RMS
ripple current of a synchronous buck converter. This value
is shown by the next equation.
IRMS
2
(I D) u IIN D u (IOUT IIN )2
where
D
VOUT
, IIN
VIN
VOUT u IOUT
VIN
When the input voltage is also used as VDD, it is desirable to
limit the input voltage ripple to less than 20mV. The input
voltage ripple can be calculated by the next equation.
VIN _ RIPPLE
IOUT IIN u t ON
CIN
17
SC493
Applications Information (continued)
Stability Considerations
Unstable operation occurs in two related but distinctly different ways — double-pulsing and fast-feedback loop instability. Double-pulsing occurs due to switching noise seen at
the FB input or because the FB ramp voltage is too low. This
causes the high side to turn on prematurely after the 250ns
minimum off-time has been completed. Double-pulsing
will result in higher ripple voltage at the output, but in most
applications will not adversely affect operation. However, In
some cases double-pulsing can indicate the presence of
loop instability, which is caused by insufficient ESR.
The best method for checking stability is to apply a zero-tofull load transient and observe the output voltage ripple
envelope for overshoot and ringing. Over one cycle of
ringing after the initial step is an indication that the ESR
should be increased. One simple way to solve this problem
is to add trace resistance in the high current output path. A
side effect of adding trace resistance is output voltage
droop with load.
The on-time control regulates the valley of the output
ripple voltage. This ripple voltage consists of a term generated by the ESR of the output capacitor and a term based
upon the capacitance charging and discharging during
the switching cycle. A minimum ESR is required to generate the required ripple voltage for regulation. For stability
the ESR zero of the output capacitor should be lower than
approximately one-third of the switching frequency. The
formula for minimum ESR is shown by the next equation.
ESRMIN
3
2 u S u COUT u fSW
Where fSW is the switching frequency.
For applications using ceramic output capacitors, the ESR
is normally too small to meet the above ESR criteria. In
these applications it is necessary to add a small virtual ESR
network composed of two capacitors and one resistor, as
shown in the Figure 5.
L
High-side
CL
RL
R1
CC
Low-side
COUT
R2
FB
pin
Figure 5 – Virtual ESR Network
This network creates a ramp voltage across CL which is
analogous to the ramp voltage generated across the ESR
of a standard capacitor. This ramp is then capacitively
coupled into the FB pin via capacitor CC. This circuit is analyzed as follows. The AC equivalent circuit used to calculate the injected signal at FB pin is shown in Figure 6
(without considering the output ripple voltage).
VSW
VRIPPLE
RL
CL
CC
R1
VINJ
FB pin
R2
Figure 6 – AC Equivalent Circuit
The DC voltage at VRIPPLE is the same as VSW, which is the
same as VOUT. The current through resistance RL during the
on time is shown by the next equation.
18
SC493
Applications Information (continued)
IINJ
VIN VOUT
RL
The following describes one way to design the virtual ESR
circuit.
1
CL t CC !!
§ R u R2 ·
¸¸
2S u fSW u ¨¨ 1
© R1 R 2 ¹
The current through resistance RL will all go through CL and
the voltage change through capacitor CL will be shown by
the next equation.
VINJ |
VIN VOUT t ON
u
RL
CL
All of this voltage will be coupled into the FB pin if the
rules previously stated are followed. Note that the output
ripple voltage has not been taken into account. The
output voltage ripple will also be coupled through the CL
and CC path into the FB pin. The ripple voltage at the
output due to the output capacitance (ignoring the
capacitance ESR) is shown by the next equation.
VCOUT _ RIPPLE |
IRIPPLE
8 u COUT u fSW
The ripple due to the capacitance ESR alone is shown
by the next equation.
VESR_RIPPLE = IRIPPLE x RESR
The output ripple voltage due to output capacitance has
a 90° phase lag with respect to the ripple voltage generated by the virtual ESR. The actual ripple voltage seen at
the FB pin (VFB_RIPPLE) can be approximated by the next
equation.
VFB _ RIPPLE
( VINJ VESR _ RIPPLE )2 VCOUT _ RIPPLE
2
Resistor Divider Selection
The DC voltage at the FB pin is shown by the next equation.
VFB | 0.5 V VFB _ RIPPLE
2
The resistor divider value should be selected using the
next equation.
VOUT
VFB
R1 R 2
R2
19
SC493
Applications Information (continued)
Layout Guidelines
The switching converter can be an EMI source if the circuitry is not properly laid out on the PCB. The suggested
layout guidelines are shown in Figure 7. The following are
several simple rules that should be followed to prevent
EMI issues.
The ground connection between the input capacitor,
the output capacitor, and the MOSFET ground should
use a short and wide trace. This can reduce the
resistive losses and high frequency ringing due to stray
inductance.
COUT
CLDO3
AGND
VOUT
ILIM
A1
A2
A0
AGND
RPGOOD
PGOOD
PVDD
FB
SC493
VDD
PGND
PGND
LX
NC
BST
SCL
DH
DL
VIN
SDA
EN
C2
VOUT
C1
1.
2. Both the high side loop and low side loop should use
short traces. The high side loop includes the input
capacitors, the high side MOSFET, the inductor, and the
output capacitors. The low side loop includes the low
side MOSFET, the inductor, and the output capacitors.
3. The LX trace should be short, since it is the main
noise source of the circuit. All sensitive analog signals
should be routed away from the LX trace.
4. Standard techniques such as snubbers can also be
used to remove the high frequency ringing at the
phase node.
RILIM
CBST
LX
PGND
MOSFETs
VIN
CIN
Figure 7 — Suggested Layout Guidelines
20
SC493
Register Map
Address
D7
D6
D5
D4
D3
D2
D1
D0
Access
Reset
Description
00h
PGD
DCM
DNS
BO
ILIM
OT
OVO
UVO
RO
40h
Status Register
01h
0(1)
0(1)
0(1)
0(1)
0(1)
EnIntLd
CLF
ENSW
R/W
01h
Control Register 1
02h
0(1)
0(1)
UPSV0
POD2
POD1
POD0
Freq1
Freq0
R/W
20h
Control Register 2
03h
0(1)
0(1)
UPSV1
SST2
SST1
SST0
PSV1
PSV0
R/W
2Eh
Control Register 3
04h
0(1)
0(1)
0(1)
VFBadj4
VFBadj3
VFBadj2
VFBadj1
VFBadj0
R/W
0Fh
Control Register 4
06h
0(1)
0(1)
1(2)
1 (2)
1 (2)
Margin2
Margin1
Margin0
R/W
3Bh
Control Register 6
Notes:
(1) Always write 0
(2) Always write 1
Definition of Registers and Bits
Status and Flag Bits Description — Register 0
A status bit reflects the current state of the converter. It becomes high when the specified condition has occurred and
turns low when the specified condition has disappeared. A flag bit becomes high when the specified condition has
occurred and will not turn low when the specified condition has disappeared.
Name
Bit
Definition
Description
UVO
00h[0]
Under Voltage Output Flag
Flag bit when high indicates that the output voltage fell below 70% of the regulation level
while being current limited.
OVO
00h[1]
Over Voltage Output Flag
Flag bit when high indicates output voltage has been above the regulation level by 20%.
OT
00h[2]
Over Temperature Flag
ILIM
00h[3]
Output Current Limit Flag
BO
00h[4]
Brown Out Flag
Flag bit when high indicates that the FB voltage has fallen below PGD falling threshold (80%)
with the device not in current limit. This normally means the output under voltage has been
caused by low input voltage.
DNS
00h[5]
Did Not Start Flag
Flag bit when high indicates that the FB voltage did not reach the power good rising threshold (90%) within the predetermined time. This time interval is the programmed soft start time.
The power good delay is 10% of the programmed soft start time.
DCM
00h[6]
Discontinuous Mode
Status
PGD
00h[7]
Power Good Status
Flag bit when high indicates that the over temperature circuit has tripped.
Flag bit when high indicates that the inductor current threshold has been reached.
Status bit when high indicates that the part is operating in discontinuous mode. The part is
only permitted to operate in DCM if PSAVE or UPSAVE is enabled. The part also enters into
DCM mode before the soft start process is complete. Therefore, in the shut down state and
during the soft start process, this bit is also set.
Status bit when high indicates that the PGD pin is not being pulled low and therefore the
output is within regulation by +20%.
21
SC493
Definition of Registers and Bits (continued)
Switching and Status Control — Register 1
Name
Bit
Description
Description
ENSW
01h[0]
Enable Switching
This bits controls whether the output is enabled or not.
0: The output is disabled, both high side and low side switches are off.
1: power-on delay and soft start process can start when this bit is 1 and the EN pin is pulled
high.
CLF
01h[1]
Clear Fault Status
Set to clear fault indicator flags (UVO, OVO, OT, ILIM, BO, & DNS). This bit is self clearing.
EnIntLd
01h{2}
Enable Internal Load
Set to enable internal pull down on VOUT when slewing down.
Timing Control — Registers 2 and 3
These registers provide software control over key timing parameters of the controller: frequency setting (Freq), PowerOn Delay (POD) time, Soft-Start Time (SST) setting, power save (PSV) mode control, and minimum switching frequency
in Ultrasonic Power Save (UPSV) mode. The details of each setting are listed in the table below.
Name
Freq1
Freq0
POD2
POD1
POD0
SST2
SST1
SST0
PSV1
PSV0
Bit
02h
[1:0]
02h
[4:2]
03h
[4:2]
03h
[1:0]
Definition
Frequency Setting
Description
2 bits that control the switching frequency from 250kHz to 1MHz.
00 : 250kHz
01 : 500kHz
10 : 750kHz
11 : 1MHz
Power-on Delay Time
3 bits that control the power-on delay from 0μs to 16ms.
000 : 0μs
001 : 250μs
010 : 500μs
011 : 1000μs
100 : 2ms
101 : 4ms
110 : 8ms
111 : 16ms
Soft Start Time Setting
3 bits that control the soft start time from 250μs to 16ms.
000 : 250μs
001 : 500μs
010 : 1000μs
011 : 2ms
100 : 4ms
101 : 8ms
110 : 16ms
111 : 16ms
Power Save Mode Control
These bits control whether the device is permitted to enter power save when input, output,
and load conditions dictate. If permitted to enter power save, they also control what mode of
power save the part can enter.
00 : PSAVE is disabled
01 : PSAVE enabled (low IQ , no ultrasonic mode)
10 : UPSAVE enabled (ultrasonic mode)
11 : PSAVE is disabled
22
SC493
Definition of Registers and Bits (continued)
Name
Bit
Definition
UPSV1
UPSV0
03h
[5]
02h
[5]
Ultrasonic Power Save
Frequency
Description
2 bits that control the nominal minimum switching frequency in ultrasonic mode.
00 : 6.25kHz
01 : 12.5kHz
10 : 18.75kHz
11 : 25kHz
Output Voltage Control — Registers 4 and 6
These registers provide fine & coarse control over the output voltage. Margin bits can vary the the output by +/-10% in
5% steps. VFBadj can move the output by +/-9% in 0.75% steps. When both registers are used together, the change in
the output voltage is determined by the multiplication of the 2 settings, i.e., setting Margin to +10% with +9% VFBadj
will change the output by +19.9% whereas a setting Margin to +10% with -9% VFBadj will change the output by
+0.1%.
Name
VFBadj4
VFBadj3
VFBadj4
VFBadj1
VFBadj0
Margin1
Margin0
Bit
04h[4:0]
06h[2:0]
Definition
Description
Output Voltage
Adjustment
000xx : -9%
00100 : -8.25%
00101 : -7.50%
00110 : -6.75%
00111 : -6%
01000 : -5.25%
01001 : -4.50%
01010 : -3.75%
01011 : -3%
01100 : -2.25%
01101 : -1.50%
01110 : -0.75%
01111 : -0%
10000 : -0%
10001 : +0.75%
10010 : +1.50%
10011 : +2.25%
10100 : +3%
10101 : +3.75%
10110 : +4.50%
10111 : +5.25%
11000 : +6%
11001 : +6.75%
11010 : +7.50%
11011 : +8.25%
111xx : +9%
Margin Control
These bits control whether margining is disabled, set to high or set to low.
000 : Margining disabled
001 : Set output to 10% below set value
010 : Set output to 5% below set value
011 : Margining disabled
100 : Margining disabled
101 : Set output to 5% above set value
110 : Set output to 10% above set value
111 : Margining disabled
23
SC493
Serial Interface
The I2C General Specification
The SC493 is a read-write slave-mode I C device and complies with the Philips I 2C standard Version 2.1, dated
January 2000. The SC493 has six user-accessible internal
8-bit registers. The I2C interface has been designed for
program flexibility, supporting direct format for write
operation. Read operations are supported on both combined format and stop separated format. While there is
no auto increment/decrement capability in the SC493 I2C
logic, a tight software loop can be designed to randomly
access the next register independent of which register
was accessed first. The start and stop commands frame
the data-packet and the repeat start condition is allowed
if necessary.
2
SC493 Limitations to the I2C Specifications
The SC493 only recognizes seven bit addressing. This
means that ten bit addressing and CBUS communication
are not compatible. The device can operate in either standard mode (100kbit/s) or fast mode (400kbit/s).
Slave Address Assignment
The seven bit slave address is 0001A2A1A0x, where A2A1A0
are set by the respective pins on the device. Bit 8 is the
data direction bit: 0001A2A1A00 is used for a write operation, and 0001A2A1A01 is used for a read operation.
Supported Formats
The supported formats are described in the following
subsections.
Direct Format — Write
The simplest format for an I2C write is direct format. After
the start condition [S], the slave address is sent, followed
by an eighth bit indicating a write. The I2C logic then
acknowledges that it is being addressed, and the master
responds with an 8 bit data byte consisting of the register
address. The slave acknowledges and the master sends
the appropriate 8 bit data byte. Once again the slave
acknowledges and the master terminates the transfer with
the stop condition [P].
Combined Format — Read
After the start condition [S], the slave address is sent, followed by an eighth bit indicating a write. The I2C logic
then acknowledges that it is being addressed, and the
master responds with an 8 bit data byte consisting of the
register address. The slave acknowledges and the master
sends the repeated start condition [Sr]. Once again, the
slave address is sent, followed by an eighth bit indicating
a read. The slave responds with an acknowledge and the
previously addressed 8 bit data byte; the master then
sends a non-acknowledge (NACK). Finally, the master terminates the transfer with the stop condition [P].
Stop Separated Reads
Stop-separated reads can also be used. This format allows
a master to set up the register address pointer for a read
and return to that slave at a later time to read the data. In
this format the slave address followed by a write command
are sent after a start [S] condition. The SC493 then
acknowledges it is being addressed, and the master
responds with the 8-bit register address. The master sends
a stop or restart condition and may then address another
slave. After performing other tasks, the master can send a
start or restart condition to the SC493 with a read
command. The device acknowledges this request and
returns the data from the register location that had previously been set up.
24
SC493
Serial Interface (continued)
I2C Direct Format Write
S
Slave Address
W
A
Register Address
S – Start Condition
W – Write = ‘0’
A – Acknowledge (sent by slave)
P – Stop condition
A
Data
A
P
Slave Address – 7-bit
Register address – 8-bit
Data – 8-bit
I2C Stop Separated Format Read
Master Addresses
other Slaves
Register Address Setup Access
S Slave Address W A Register Address A P S
S – Start Condition
W – Write = ‘0’
R – Read = ‘1’
A – Acknowledge (sent by slave)
NAK – Non-Acknowledge (sent by master)
Sr – Repeated Start condition
P – Stop condition
Slave Address B
Register Read Access
S/Sr
Slave Address
R A
Data
NACK P
Data
NACK P
Slave Address – 7-bit
Register address – 8-bit
Data – 8-bit
I2C Combined Format Read
S
Slave Address
W A
Register Address
S – Start Condition
W – Write = ‘0’
R – Read = ‘1’
A – Acknowledge (sent by slave)
NAK – Non-Acknowledge (sent by master)
Sr – Repeated Start condition
P – Stop condition
A Sr
Slave Address
R
A
Slave Address – 7-bit
Register address – 8-bit
Data – 8-bit
25
SC493
Outline Drawing - MLPQ-UT-20 3x3
A
D
PIN 1
INDICATOR
(LASER MARK)
DIMENSIONS
INCHES
MILLIMETERS
DIM
MIN NOM MAX MIN NOM MAX
B
E
A2
A
aaa C
C
A1
SEATING
PLANE
A
A1
A2
b
D
D1
E
E1
e
L
N
aaa
bbb
.020
.000
-
.024
.002
(.006)
.006 .008 .010
.114 .118 .122
.061 .067 .071
.114 .118 .122
.061 .067 .071
.016 BSC
.012 .016 .020
20
.003
.004
0.50
0.00
-
0.60
0.05
(0.1524)
0.15 0.20 0.25
2.90 3.00 3.10
1.55 1.70 1.80
2.90 3.00 3.10
1.55 1.70 1.80
0.40 BSC
0.30 0.40 0.50
20
0.08
0.10
D1
e
LxN
E/2
E1
2
1
N
D/2
bxN
bbb
C A B
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS .
3. DAP is 1.90 x 190mm.
26
SC493
Land Pattern - MLPQ-UT-20 3x3
H
R
(C)
DIMENSIONS
K
G
Y
X
P
Z
DIM
INCHES
MILLIMETERS
C
G
H
K
P
R
X
Y
Z
(.114)
(2.90)
.083
.067
.067
.016
.004
.008
.031
.146
2.10
1.70
1.70
0.40
0.10
0.20
0.80
3.70
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
3.
THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD
SHALL BE CONNECTED TO A SYSTEM GROUND PLANE.
FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR
FUNCTIONAL PERFORMANCE OF THE DEVICE.
27
SC493
© Semtech 2010
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Contact Information
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28