SY8088 Datasheet. Www.s Manuals.com. Silergy

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Application Notes: AN_SY8088
High Efficiency 1.5MHz, 1A
Synchronous Step Down Regulator
Preliminary Specification
AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 1
General Description
SY8088 is a high efficiency 1.5MHz synchronous step
down DC/DC regulator IC capable of delivering up to
1A output current. It can operate over a wide input
voltage range from 2.5V to 5.5V and integrate main
switch and synchronous switch with very low R
DS (ON)
to minimize the conduction loss.
Ordering Information
Package Code
Temperature Code
Optional Spec Code
□
□□
□(□□
□□□□
□□)□
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□
SY8088
Package Code
Temperature Code
Optional Spec Code
□
□□
□(□□
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SY8088
Temperature Range:
-
40°C to 85°C
Features
•
Low R
DS(ON)
for internal switches (top/bottom)
260m
Ω
/170m
Ω
•
2.5~5.5V input voltage range
•
40
µ
A typical quiescent current
•
High light load efficiency
•
High switching frequency 1.5MHz minimizes the
external components
•
Internal soft-start limits the inrush current
•
100% dropout operation
•
RoHS Compliant and Halogen Free
•
Compact package: SOT23-5
Applications
•
Portable Navigation Device
•
Set Top Box
•
USB Dongle
•
Media Player
•
Smart phone
Typical Application
Efficiency vs. Load Current
Load Current (mA)
1 10 100 1000
70
75
80
85
90
95
VIN=4.2V,VOUT=1.8V
VIN=3.3V,VOUT=1.8V
VIN=5.0V,VOUT=1.8V
Figure1. Schematic Diagram Figure2. Efficiency
Ordering Number Package Type Note
SY8088AAC SOT23-5 1A
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AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 2
Pinout (Top View)
(SOT23-5)
Top Mark: LDxyz
(device code: LD, x=year code, y=week code, z= lot number code)
Pin Name Pin Number
Pin Description
EN 1 Enable control. Pull high to turn on. Do not float.
GND 2 Ground pin.
LX 3 Inductor pin. Connect this pin to the switching node of the inductor.
IN 4 Input pin. Decouple this pin to the GND pin with at least 4.7uF ceramic
capacitor.
FB 5 Output Feedback Pin. Connect this pin to the center point of the output resistor
divider (as shown in Figure 1) to program the output voltage:
V
OUT
=0.6*(1+R
1
/R
2
).Add optional C
1
(10pF~47pF) to speed up the transient
response.
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage -------------------------------------------------------------------------------------------------------- 6.0V
Enable, FB Voltage---------------------------------------------------------------------------------------------------- V
IN
+ 0.6V
Power Dissipation, P
D
@ T
A
= 25°C, SOT23-5--------------------------------------------------------------------------- 0.6W
Package Thermal Resistance (Note 2)
θ
JA
-------------------------------------------------------------------------------------------------------------- 170°C/W
θ
JC
---------------------------------------------------------------------------------------------------------- ----130°C/W
Junction Temperature Range ----------------------------------------------------------------------------------------------125°C
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------------------- 260°C
Storage Temperature Range -----------------------------------------------------------------------------------
-
65°C to 150°C
Recommended Operating Conditions
(Note 3)
Supply Input Voltage ----------------------------------------------------------------------------------------------- 2.5V to 5.5V
Junction Temperature Range -----------------------------------------------------------------------------------
-
40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------
-
40°C to 85°C
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AN_SY8088
AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 3
Electrical Characteristics
(V
IN
= 5V, V
OUT
= 2.5V, L = 2.2uH, C
OUT
= 10uF, T
A
= 25°C, unless otherwise specified)
Parameter Symbol Test Conditions Min
Typ Max
Unit
Input Voltage Range V
IN
2.5 5.5 V
Quiescent Current I
Q
I
OUT=
0
,
V
FB
=V
REF
⋅
105% 40 µA
Shutdown Current I
SHDN
EN=0 0.1 1 µA
Feedback Reference Voltage V
REF
0.588
0.6 0.612
V
PFET RON R
DS(ON)
,
P
260 mΩ
NFET RON R
DS(ON)
,
N
170 mΩ
PFET Current Limit I
LIM
1.3 A
EN rising threshold V
ENH
1.5 V
EN falling threshold V
ENL
0.4 V
Input UVLO threshold V
UVLO
2.5 V
UVLO hysteresis V
HYS
0.1 V
Oscillator Frequency F
OSC
1.5 MHz
Min ON Time 80 ns
Max Duty Cycle 100 %
Soft Start Time T
SS
1 ms
Thermal Shutdown Temperature T
SD
160 °C
Thermal Shutdown Hysteresis T
HYS
15 °C
Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are
for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for
extended periods may remain possibility to affect device reliability.
Note 2:
θ
JA is measured in the natural convection at T
A
= 25°C on a low effective single layer thermal conductivity
test board of JEDEC 51-3 thermal measurement standard. Exposed Paddle of DFN package is the case position for
θ
JC measurement.
Note 3: The device is not guaranteed to function outside its operating conditions.
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AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 4
Typical Performance Characteristics
Efficiency vs. Load Current
Load Current (mA)
1 10 100 1000
65
70
75
80
85
90
95
VIN=5.0V,VOUT=1.2V
VIN=3.3V,VOUT=1.2V
VIN=4.2V,VOUT=1.2V
Efficiency vs. Load Current
Load Current (mA)
1 10 100 1000
70
75
80
85
90
95
VIN=4.2V,VOUT=1.8V
VIN=3.3V,VOUT=1.8V
VIN=5.0V,VOUT=1.8V
Efficiency vs. Load Current
Load Current (mA)
1 10 100 1000
70
75
80
85
90
95
100
VIN=5V,VOUT=3.3V
VIN=4.2V,VOUT=3.3V
Output Ripple
∆Vout 20mV/div
LX2.0V/div
(VIN=5.0V, VOUT=1.8V, ILOAD=0A)
Time (400ns/div)
IL0.5A/div
Output Ripple
∆Vout 20mV/div
LX2.0V/div
(VIN=5.0V, VOUT=1.8V, ILOAD=0.2A)
Time (400ns/div)
IL0.5A/div
Output Ripple
∆Vout 20mV/div
LX2.0V/div
(VIN=5.0V, VOUT=1.8V, ILOAD=1A)
Time (400ns/div)
IL1.0A/div
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Time (400µs/div)
Startup from Enable
(VIN=5.0V, VOUT=1.8V, ILOAD=1.0A)
LX5.0V/div
VOUT 1.0V/div
EN 5.0V/div
IL1.0A/div
Time (40µs/div)
Shutdown from Enable
(VIN=5.0V, VOUT=1.8V, ILOAD=1.0A)
LX5.0V/div
VOUT 1.0V/div
EN 5.0V/div
IL1.0A/div
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AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 6
Operation
The SY8088 is a high-efficiency 1.5MHz synchronous
step-down DC-DC converters capable of delivering up
to 1A output current. It operates over a wide input
voltage range from 2.5V to 5.5V and integrates main
switch and synchronous switch with very low R
DS(ON)
to minimize the conduction loss.
Applications Information
Because of the high integration in the SY8088 IC, the
application circuit based on this regulator IC is rather
simple. Only input capacitor C
IN
, output capacitor C
OUT
,
output inductor L and feedback resistors (R1 and R2)
need to be selected for the targeted applications
specifications.
Feedback resistor dividers R1 and R2:
Choose R1 and R2 to program the proper output
voltage. To minimize the power consumption under
light loads, it is desirable to choose large resistance
values for both R1 and R2. A value of between 100kΩ
and 1MΩ is highly recommended for both resistors. If
R2=120kΩ is chosen, then R1 can be calculated to be:
2
OUT
1
(V 0.6V) R
R
0.6V
− ⋅
=
Input capacitor C
IN
:
A typical X7R or better grade ceramic capacitor with
6V rating and greater than 4.7uF capacitance is
recommended. To minimize the potential noise
problem, place this ceramic capacitor really close to the
IN and GND pins. Care should be taken to minimize
the loop area formed by C
IN
, and IN/GND pins.
Output capacitor C
OUT
:
The output capacitor is selected to handle the output
ripple noise requirements. Both steady state ripple and
transient requirements must be taken into consideration
when selecting this capacitor. For the best performance,
it is recommended to use X7R or better grade ceramic
capacitor with 6V rating and greater than 4.7uF
capacitance.
Output inductor L:
There are several considerations in choosing this
inductor.
1) Choose the inductance to provide the desired
ripple current. It is suggested to choose the ripple
current to be about 40% of the maximum output
current. The inductance is calculated as:
OUT OUT IN,MAX
SW OUT,MAX 40%
V (1 V /V )
LF I
×
−
=×
where Fsw is the switching frequency and Iout,max is
the maximum load current.
The SY8088 regulator IC is quite tolerant of different
ripple current amplitude. Consequently, the final choice
of inductance can be slightly off the calculation value
without significantly impacting the performance.
2) The saturation current rating of the inductor must
be selected to be greater than the peak inductor
current under full load conditions.
OUT OUT IN MAX
SAT MIN OUT MAX
SW
V (1-V /V , )
I , I ,
2 F L
> +
⋅ ⋅
3) The DCR of the inductor and the core loss at the
switching frequency must be low enough to achieve the
desired efficiency requirement. It is desirable to choose
an inductor with DCR<50mohm to achieve a good
overall efficiency.
Layout Design:
The layout design of SY8088 regulator is relatively
simple. For the best efficiency and minimum noise
problems, we should place the following components
close to the IC: C
IN
, L, R1 and R2.
1) It is desirable to maximize the PCB copper area
connecting to GND pin to achieve the best thermal and
noise performance. If the board space allowed, a
ground plane is highly desirable.
2) C
IN
must be close to Pins IN and GND. The loop
area formed by C
IN
and GND must be minimized.
3) The PCB copper area associated with LX pin must
be minimized to avoid the potential noise problem.
4) The components R1 and R2, and the trace
connecting to the FB pin must NOT be adjacent to the
LX net on the PCB layout to avoid the noise problem.
5) If the system chip interfacing with the EN pin has a
high impedance state at shutdown mode and the IN pin
is connected directly to a power source such as a LiIon
battery, it is desirable to add a pull down 1Mohm
resistor between the EN and GND pins to prevent the
noise from falsely turning on the regulator at shutdown
mode.
Load Transient Considerations:
The SY8088 regulator IC integrates the compensation
components to achieve good stability and fast transient
responses. In some applications, adding a 22pF ceramic
cap in parallel with R1 may further speed up the load
transient responses and is thus recommended for
applications with large load transient step requirements.
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AN_SY8088
AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 7
SOT23-5 Package outline & PCB layout design
2.40
0.80
0.55
0.95 TYP
2.40
0.80
0.55
0.95 TYP
1.50 - 1.70
0.30 - 0.50
2.80 - 3.10
2.70 - 3.00
1.50 - 1.70
0.30 - 0.50
2.80 - 3.10
2.70 - 3.00
Recommended Pad Layout
0.1 - 0.15
0.25 REF
0.3 - 0.6
0.1 - 0.15
0.25 REF
0.3 - 0.6
1.0 - 1.3
0.01 - 0.1
1.90 TYP
0.95 TYP
1.0 - 1.3
0.01 - 0.1
1.90 TYP
0.95 TYP
Notes: All dimensions are in millimeters.
All dimensions don’t include mold flash & metal burr.
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