Applications Note: AN_SY8008A/B/C
High Efficiency 1.5MHz, 0.6A/1A/1.2A
Synchronous Step Down Regulator
General Description
The SY8008A, SY8008B and SY8008C are high-
efficiency 1.5MHz synchronous step-down DC-DC
regulator ICs capable of delivering up to 1.2A output
currents. The SY8008 family 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.
Low output voltage ripple and small external inductor
and capacitor sizes are achieved with 1.5MHz
switching frequency. This along with small SOT-
23/TSOT-23 footprint provides small PCB area
application.
Features
Ordering Information
SY8008
□
(
□□
)
□
Temperature Code
Package Code
Optional Spec Code
Temperature Range:
-
40°C to 85°C
Ordering Number
Package type
SY8008AAAC
SOT23-5
SY8008BAAC
SOT23-5
SY8008CAAC
SOT23-5
SY8008AACC
TSOT23-5
SY8008BACC
TSOT23-5
Applications
Sil
er
g
Typical Applications
V
IN
EN
yC
or
p
L
C
1
(opt.)
.C
on
fid
Note
0.6A
1A
1.2A
0.6A
1A
en
t
V
OUT
R
1
C
OUT
IN
LX
C
IN
FB
GND
R
2
Figure 1. Schematic Diagram
Figure 2. Efficiency vs Load Current (SY8008B)
AN_SY8008 Rev. 1.0B
Silergy Corp. Confidential- Prepared for Customer Use Only
Efficiency (%)
ial
•
•
•
•
•
-P
Portable Navigation Device
Smart phone
USB Dongle
Set Top Box
Media Player
re
pa
re
•
Low R
DS(ON)
for internal switches (top/bottom)
ο
SY8008A: 300m Ω /250m Ω, 0.6A
ο
SY8008B: 250m Ω /200m Ω, 1A
ο
SY8008C: 200m Ω /150m Ω, 1.2A
•
2.5-5.5V input voltage range
•
1.5MHz switching frequency minimizes the
external components
•
Internal softstart limits the inrush current
•
100% dropout operation
•
RoHS Compliant and Halogen Free
•
Compact package: SOT23-5/ TSOT23-5 pin
d
fo
r
Fo
r
tu
n
1
tec
h
AN_SY8008A/B/C
Pinout (top view)
①
Part Number
Top Mark
SY8008AAAC
AAxyz
SY8008BAAC
ABxyz
SY8008CAAC
ACxyz
SY8008AACC
BIxyz
SY8008BACC
BGxyz
Note
① ：
x=year code, y=week code, z= lot number code.
(SOT23-5, TSOT23-5)
Package type
SOT23-5
SOT23-5
SOT23-5
TSOT23-5
TSOT23-5
Pin Name
EN
GND
LX
IN
FB
Pin Number
1
2
3
4
5
Pin Description
Enable control. Pull high to turn on. Do not float.
Ground pin.
Inductor pin. Connect this pin to the switching node of the inductor.
Input pin. Decouple this pin to the GND pin with at least 1uF ceramic
capacitor.
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:
Vout=0.6*(1+R1/R2).Add optional C
1
(10pF~47pF) to speed up the transient
response.
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage ---------------------------------------------------------------------------------------------------------- 6.0V
Enable, FB, LX Voltage--------------------------------------------------------------------------------------
-
0.3V to V
IN
+ 0.6V
Power Dissipation, P
D
@ T
A
= 25°C, SOT23-5, TSOT23-5 ------------------------------------------------------------- 0.6W
Package Thermal Resistance (Note 2)
SOT23-5, TSOT23-5,
θ
JA
------------------------------------------------------------------------------------- 170°C/W
SOT23-5, TSOT23-5,
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
ESD Susceptibility (Note 2)
HBM (Human Body Mode) ---------------------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ---------------------------------------------------------------------------------------------------------- 200V
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
AN_SY8008 Rev. 1.0B
Silergy Corp. Confidential- Prepared for Customer Use Only
2
AN_SY8008A/B/C
Electrical Characteristics
(V
IN
= 5V, V
OUT
= 2.5V, L = 2.2uH, C
OUT
= 10uF, T
A
= 25°C, I
MAX
= 1A unless otherwise specified)
Parameter
Input Voltage Range
Shutdown Current
Feedback Reference
Voltage
FB Input Current
PFET RON
Symbol
V
IN
I
SHDN
V
REF
I
FB
R
DS(ON)
,
P
Test Conditions
EN=0
Min
2.5
0.588
Typ
0.1
0.6
Max
5.5
1
0.612
50
Unit
V
µA
V
nA
mΩ
mΩ
mΩ
mΩ
mΩ
mΩ
A
A
A
V
V
V
V
MHz
ns
%
°C
NFET RON
R
DS(ON)
,
N
PFET Current Limit
I
LIM
V
FB
=V
IN
SY8008A
SY8008B
SY8008C
SY8008A
SY8008B
SY8008C
SY8008A
SY8008B
SY8008C
-50
300
250
200
250
200
150
0.8
1.2
1.5
1.5
EN Rising Threshold
EN Falling Threshold
Input UVLO Threshold
UVLO Hysteresis
Oscillator Frequency
Min ON Time
Max Duty Cycle
Thermal Shutdown
Temperature
V
ENH
V
ENL
V
UVLO
V
HYS
F
OSC
0.4
2.5
I
OUT
=100mA
100
0.1
1.5
50
160
T
SD
Note 1:
Stresses listed as the above “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 TA = 25°C on a low effective single layer thermal
conductivity test board of JEDEC 51-3 thermal measurement standard. Pin 2 of SOT23-5/TSOT23-5 packages is the
case position for
θ
JC measurement. Test condition: Device mounted on 2” x 2” FR-4 substrate PCB, 2oz copper,
with minimum recommended pad on top layer and thermal vias to bottom layer ground plane
Note 3:
The device is not guaranteed to function outside its operating conditions.
AN_SY8008 Rev. 1.0B
Silergy Corp. Confidential- Prepared for Customer Use Only
3
AN_SY8008A/B/C
Typical Performance Characteristics (SY8008B)
Efficiency vs Load Current
92%
96%
Efficiency vs Load Current
98%
Efficiency vs Load Current
Vout=3.3V
96%
94%
E ffi ency a
ci
92%
90%
88%
86%
84%
Vin=5.0V
Vin=4.2V
Vin=3.6V
Vout=1.2V
90%
88%
E ffi en cy a
ci
E ffi en cy a
ci
94%
92%
90%
88%
86%
84%
82%
Vout=1.8V
86%
84%
82%
80%
78%
Vin=5.0V
Vin=3.6V
Vin=2.7V
Vin=5.0V
Vin=3.6V
Vin=2.7V
76%
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Load C urrent (A )
80%
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Load C urrent (A )
82%
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Load C urrent (A )
Oscillator Frequency vs Vin
1.70
1.65
F requncy(M H z) a
1.60
1.55
1.50
1.45
1.40
1.35
1.30
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
I
nput V ol
tage (V )
AN_SY8008 Rev. 1.0B
Silergy Corp. Confidential- Prepared for Customer Use Only
4
AN_SY8008A/B/C
Operation
SY8008A/B/C is a synchronous buck regulator IC that integrates the PWM control, top and bottom switches on the
same die to minimize the switching transition loss and conduction loss. With ultra low Rds(on) power switches and
proprietary PWM control, this regulator IC can achieve the highest efficiency and the highest switch frequency
simultaneously to minimize the external inductor and capacitor size, and thus achieving the minimum solution
footprint. The internal softstart time is about 1ms.
Applications Information
Because of the high integration in the SY8008 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 100k and 1M is highly
recommended for both resistors. If R2=120k is chosen, then R1 can be calculated to be:
R1
=
(V
OUT
−
0.6 V)
⋅
(R2)
0.6V
Input capacitor C
IN
:
With the maximum load current at 1.2A (SY8008C), the maximum ripple current through the input capacitor is
about 0.6Arms. A typical X7R or better grade ceramic capacitor with 6V rating and greater than 4.7uF capacitance
can handle this ripple current well. 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:
V (1
−
V
OUT
/V
IN, MAX
)
L
=
OUT
F
SW
×
I
OUT, MAX
×
40%
where Fsw is the switching frequency and I
OUT
,
MAX
is the maximum load current.
The SY8008 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.
V
OUT
(1-V
OUT
/V
IN
,
MAX
)
I
SAT
,
MIN
>
I
OUT
,
MAX
+
2
⋅
F
SW
⋅
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 SY8008 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 allows, a ground plane is highly desirable.
AN_SY8008 Rev. 1.0A
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