ST1S15
500 mA, 6 MHz synchronous step-down converter
Datasheet - production data
Description
Features
85% typical efficiency
500 mA output current capability
45 µA typical quiescent current
PFM or PWM operation for best efficiency
over whole load range
Ultra-fast load and line transient
Short-circuit and thermal protection
Small external components
Auto or forced PWM selection with
dedicated pin
Available in Flip Chip 6 package
The ST1S15 is a high efficiency miniaturized
step-down converter able to provide 500 mA
output current from an input voltage from 2.3 V to
5.5 V. This converter is specifically designed for
applications where high efficiency and small
application area are the key factors. Thanks to
6 MHz switching frequency, the ST1S15 can use
470 nH nominal values for the inductor and
4.7 µF for the output capacitor providing, at the
same time, very good performance in terms of
load and line transients. A PFM mode can be
selected for high efficiency under light load
conditions or PWM mode for tight regulation and
best dynamic performance. Short-circuit and
thermal protection are also included.
Table 1: Device summary
Order code
Output
voltage (V)
Package
ST1S15J18R
1.82
Flip Chip 6
Applications
DSP and multimedia processor core supply
Cell phones
PDAs
February 2015
DocID023280 Rev 4
This is information on a product in full production.
1/27
www.st.com
Contents
ST1S15
Contents
1
Application schematic .................................................................... 5
2
Pin configuration ............................................................................. 6
3
Maximum ratings ............................................................................. 7
4
5
Electrical characteristics ................................................................ 8
Typical performance characteristics ........................................... 10
6
Block schematic ............................................................................ 13
7
Detailed description ...................................................................... 14
8
7.1
General description ......................................................................... 14
7.2
Mode transition................................................................................ 14
7.3
Soft-start ......................................................................................... 15
7.4
Short-circuit protection .................................................................... 15
7.5
Undervoltage lockout (UVLO) ......................................................... 15
7.6
Thermal protection .......................................................................... 16
7.7
Overcurrent protection .................................................................... 16
7.8
Enable function ............................................................................... 16
Application information ................................................................ 17
8.1
Input and output capacitors ............................................................. 17
8.2
Inductor ........................................................................................... 17
8.3
Layout guidelines ............................................................................ 18
9
Different output voltage versions of the ST1S15 available on
request .................................................................................................... 19
10
11
2/27
Package information ..................................................................... 20
10.1
Flip Chip 6 package information ...................................................... 21
10.2
Packing information ......................................................................... 24
Revision history ............................................................................ 26
DocID023280 Rev 4
ST1S15
List of tables
List of tables
Table 1: Device summary ........................................................................................................................... 1
Table 2: Typical external components ........................................................................................................ 5
Table 3: Pin description .............................................................................................................................. 6
Table 4: Absolute maximum ratings ........................................................................................................... 7
Table 5: Thermal data ................................................................................................................................. 7
Table 6: ESD performance ......................................................................................................................... 7
Table 7: Electrical characteristics ............................................................................................................... 8
Table 8: Inductors ..................................................................................................................................... 17
Table 9: Flip Chip 6 mechanical data ....................................................................................................... 22
Table 10: Tape and reel mechanical data ................................................................................................ 25
Table 11: Document revision history ........................................................................................................ 26
DocID023280 Rev 4
3/27
List of figures
ST1S15
List of figures
Figure 1: ST1S15 application schematic .................................................................................................... 5
Figure 2: Pin connections (top view) ........................................................................................................... 6
Figure 3: Efficiency vs. output current ...................................................................................................... 10
Figure 4: Output voltage vs. input voltage ................................................................................................ 10
Figure 5: Supply current vs. input voltage in auto mode .......................................................................... 10
Figure 6: Supply current vs. input voltage in PWM mode ......................................................................... 10
Figure 7: Output voltage vs. output current .............................................................................................. 10
Figure 8: Frequency vs. input voltage ....................................................................................................... 10
Figure 9: Output voltage vs. output current VIN=3.6 V .............................................................................. 11
Figure 10: Mode transition vs. input voltage ............................................................................................. 11
Figure 11: Mode transition PFM to PWM.................................................................................................. 11
Figure 12: Output voltage ripple (no-load) ................................................................................................ 11
Figure 13: Output voltage ripple ............................................................................................................... 11
Figure 14: Line transient ........................................................................................................................... 11
Figure 15: Load transient IOUT = 50 to 250 mA ......................................................................................... 12
Figure 16: Load transient IOUT = 250 to 50 mA ......................................................................................... 12
Figure 17: Enable startup ......................................................................................................................... 12
Figure 18: VIN startup ................................................................................................................................ 12
Figure 19: Block schematic ....................................................................................................................... 13
Figure 20: PFM to PWM transition ............................................................................................................ 14
Figure 21: PWM to PFM transition ............................................................................................................ 15
Figure 22: Flip Chip layout recommended (not in scale) .......................................................................... 18
Figure 23: Flip Chip 6 package outline ..................................................................................................... 21
Figure 24: Flip Chip 6 footprint recommended data (mm) ........................................................................ 23
Figure 25: Tape and reel outline ............................................................................................................... 24
4/27
DocID023280 Rev 4
ST1S15
1
Application schematic
Application schematic
Figure 1: ST1S15 application schematic
Table 2: Typical external components
Component
Manufacturer
CIN
Part number
Size
4.7 µF
0402
470 nH
2.0 x 1.25 x 0.5 mm
GRM155R60J475ME87
GRM155R60G475ME87
COUT
Value
Murata
(1)
GRM155R60J475ME87
L
LQM21PNR47MC0D
Notes:
(1)
VOUT ≤ 1.82 V
All the above components refer to a typical application. The ST1S15 operation is
not limited to the choice of these external components.
DocID023280 Rev 4
5/27
Pin configuration
2
ST1S15
Pin configuration
Figure 2: Pin connections (top view)
MARKING VIEW
BUMP VIEW
A1
A2
A2
A1
B1
B2
B2
B1
C1
C2
C2
C1
GIPG0901151142LM
Table 3: Pin description
Pin
Flip Chip
VIN
A2
High-side switch connection and IC supply.
EN
B2
ENABLE pin with positive logic. The IC shuts down if pulled
low. Do not leave this pin floating.
GND
C2
Power and IC supply ground.
FB
C1
Feedback input.
SW
B1
Inductor connection to internal PFET and NFET.
A1
Operation mode selection:
LOW = automatic operation PFM or PWM according to
output load.
HIGH = forced PWM operation.
Do not leave this pin floating.
MODE
6/27
Description
DocID023280 Rev 4
ST1S15
3
Maximum ratings
Maximum ratings
Table 4: Absolute maximum ratings
Symbol
Parameter
Value
Unit
VIN
Power and signal supply voltage
- 0.3 to + 6.0
V
Logic input pins
- 0.3 to + 6.0
V
-0.3 to VIN + 0.3
V
Operating ambient temperature
- 40 to 85
°C
Junction temperature
- 40 to 150
°C
EN, MODE
FB, SW
TAMB
TJ
Feedback and switching pins
Absolute maximum ratings are those values beyond which damage to the device
may occur. Functional operation under these conditions is not implied.
Table 5: Thermal data
Symbol
Parameter
Flip Chip
Unit
RthJA
Thermal resistance junction-ambient
130
°C/W
Flip Chip
Unit
Table 6: ESD performance
Symbol
ESD
Parameter
Human body model
±2000
Machine model
±100
DocID023280 Rev 4
V
7/27
Electrical characteristics
4
ST1S15
Electrical characteristics
- 40 °C < TA < 85 °C, CIN = 4.7 µF nominal, COUT = 4.7 µF nominal, L = 470 nH, typical
values are at TA = 25 °C, VEN = VIN unless otherwise specified.
Table 7: Electrical characteristics
Symbol
Parameter
Test conditions
Min.
Typ.
Max.
Unit
5.5
V
General section
VIN
VUVLO
IQ
Operating input voltage range
Undervoltage lockout
threshold
VIN rising
PFM mode quiescent current
No load
45
PWM mode quiescent current
No load
15
Shutdown current
VEN = 0
VIN falling
fSW
Switching frequency
IOUT
Continuous output current
ISC
IPFM-PWM
h
tON
TSHDN
2.3
Short-circuit current
2.1
1.8
5.4
(1)
VIN ≥ VOUT + 0.40 V
2.2
1.9
60
mA
5
µA
6
6.6
MHz
500
mA
1200
200
VIN = 3.6 V, VOUT = 1.82 V
PWM to PFM transition
µA
0.5
(2)
PFM to PWM transition
V
mA
mA
100
IOUT = 10 mA PFM mode
80
IOUT = 150 mA
83
VEN from low to high,
VIN = 3.6 V, VOUT = 1.82 V
260
µs
Thermal shutdown
125
°C
Hysteresis
30
°C
Efficiency
(VIN = 3.6 V, VOUT = 1.82 V)
Start-up time
%
Output voltage
Accuracy (ST1S15J18)
VOUT
ILKFB
8/27
Peak-to-peak output voltage
ripple
FB pin leakage current
1.78
2.3 ≤ VIN ≤ 5.5 V,
IOUT= 10 mA, PFM mode,
-40 ≤ TA ≤ 85 °C
1.78
2.3 ≤ VIN ≤ 5.5 V,
VOUT=1.82 V, IOUT = 0 to
500 mA, PWM mode,
-40 ≤ TA ≤ 85 °C
Load regulation
VOUT_Ripple
2.3 ≤ VIN ≤ 5.5 V,
IOUT= 10 mA, PWM mode,
-40 ≤ TA ≤ 85 °C
1.82
1.86
V
1.82
1.86
-1.5
%
PWM mode,
IOUT = 150 mA, VIN = 3.6 V,
VOUT = 1.82 V
10
mV
PFM mode,
IOUT = 150 mA, VIN = 3.6 V,
VOUT = 1.82 V
30
mV
VFB = 5.5 V
DocID023280 Rev 4
9
µA
ST1S15
Electrical characteristics
Symbol
Parameter
Test conditions
VIN_TR
Line transient response.
Output voltage variation over
the nominal DC level
tR = tF = 10 µs
case 1: VIN = 2.5 to 3.1 V
case 2: VIN = 3.9 to 4.5 V
IOUT_TR
Load transient response
tR= tF= 0.1 µs
case 1: VIN = 2.5 V
case 2: VIN = 3.6 V
case 3: VIN = 4.5 V
Min.
Typ.
Max.
Unit
IOUT = 50 mA,
VOUT = 1.82 V
±50
IOUT = 250 mA,
VOUT = 1.82 V
IOUT = 0 to 150 mA,
VOUT = 1.82 V
±50
IOUT = 50 to 250 mA,
VOUT = 1.82 V
±70
IOUT = 150 to 400 mA,
VOUT = 1.82 V
±70
mV
mV
Logic inputs
VIL
Low-level input voltage
(EN, MODE pins)
VIH
High-level input voltage
(EN, MODE pins)
ILK-I
Input leakage current
(EN, MODE pins)
0.4
V
1.2
VEN = VMODE = 5.5 V
V
0.01
1
µA
P-channel MOSFET
on-resistance
300
400
N-channel MOSFET
on-resistance
350
450
1000
1200
mA
Power switches
RDS(on)
mΩ
ILPEAK
P-channel peak current limit
Over the input voltage
range
ILKG-P
P-channel leakage current
VIN = 5.5 V, VEN= 0
1
µA
ILKG-N
N-channel leakage current
VSW = 5.5 V, VEN= 0
1
µA
900
Notes:
(1)
(2)
Not tested in production. This value is guaranteed by correlation with RDS(on), peak current limit and operating input voltage.
Not tested in production. This parameter is guaranteed by peak current limit.
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Typical performance characteristics
5
ST1S15
Typical performance characteristics
Figure 3: Efficiency vs. output current
(VOUT = 1.82 V)
Figure 4: Output voltage vs. input voltage
Figure 5: Supply current vs. input voltage in auto
mode
Figure 6: Supply current vs. input voltage in PWM
mode
Figure 7: Output voltage vs. output current
Figure 8: Frequency vs. input voltage
10/27
DocID023280 Rev 4
ST1S15
Typical performance characteristics
Figure 10: Mode transition vs. input voltage
Figure 9: Output voltage vs. output current VIN=3.6 V
Figure 11: Mode transition PFM to PWM
Figure 12: Output voltage ripple (no-load)
Figure 13: Output voltage ripple
Figure 14: Line transient
DocID023280 Rev 4
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Typical performance characteristics
ST1S15
Figure 15: Load transient IOUT = 50 to 250 mA
Figure 16: Load transient IOUT = 250 to 50 mA
Figure 17: Enable startup
Figure 18: VIN startup
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DocID023280 Rev 4
ST1S15
6
Block schematic
Block schematic
Figure 19: Block schematic
EN
Enable and
soft-start
V - I reference
and
prereg + UVLO
VIN
Current limit and short protection
MODE
PFM- analog timing
PFM - PWM
Switch control logic
Oscillator
and
sawtooth
Driver
and
anti X - cond
SW
Thermal protection
Vref_PFM
FB
PW M comparator
R1
GND
Error amp and comp.
R2
Vref_PW M
GIPG1401151127LM
DocID023280 Rev 4
13/27
Detailed description
ST1S15
7
Detailed description
7.1
General description
The ST1S15 is a fixed voltage mode PWM step-down DC-DC converter, which operates
with typically 6 MHz fixed frequency pulse width modulation (PWM) at moderate and heavy
load currents. At light load currents the converter can automatically enter PFM (pulse
frequency mode) mode.
Few components are required: an inductor and two capacitors. It can work properly with
X5R or X7R SMD ceramic capacitors both at the input and at the output. These kinds of
capacitors, thanks to their very low series resistance (ESR), minimize the output voltage
ripple. In addition, the chosen inductor must not saturate at the peak current level.
7.2
Mode transition
The ST1S15 can work in PWM mode or in PFM mode according to the different operating
conditions. If the MODE pin is pulled high, the device works in PWM mode only even at
light or no-load. If the MODE pin is low, the operation changes according to the average
input current handled by the device. At low output current the device works in PFM mode
so to obtain very low power consumption and very good efficiency. When the output current
increases, the device automatically switches to PWM mode in order to deliver the power
needed by the load.
The ST1S15 passes from PFM to PWM when 3 consecutive PFM pulses occur. This
means that the PFM has reached its maximum current capability and the device needs to
go into PWM mode. The whole PWM circuitry starts after a transition time. During this time
the duration of the PFM pulses rises about 350 ns so to provide higher current capability.
After the PWM circuitry startup, the ST1S15 switches to PWM operation.
Figure 20: PFM to PWM transition
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ST1S15
Detailed description
The transition from PWM to PFM mode occurs when the load current decreases and the
coil current becomes negative. After the zero-crossing output goes up for 127 consecutive
times the device switches to PFM mode.
Figure 21: PWM to PFM transition
7.3
Soft-start
The internal soft-start is enabled after VIN reaches the UVLO threshold and the EN pin is
high or for startup after enable. An overtemperature shutdown event or over short-circuit
event also activates the soft-start sequence.
It eliminates the in-rush current problem during the start-up phase. During the soft-start the
device always works in PWM regardless of the status of the MODE pin.
7.4
Short-circuit protection
The short-circuit protection begins when there is a short between the device output and
ground. In this case the output voltage value is lower than the voltage reference and the
overcurrent protection comparator output is high.
When this happens the power stage (P-channel and N-channel) turns off and a soft-start
phase starts. The device repeats the soft-start sequence during the short-circuit condition.
7.5
Undervoltage lockout (UVLO)
The UVLO circuit prevents the device from malfunctioning when the input voltage is not
high enough. The device is in shutdown mode, when the input voltage is below the UVLO
threshold. The hysteresis of 200 mV prevents unstable operation when the input voltage is
close to the UVLO threshold.
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Detailed description
7.6
ST1S15
Thermal protection
The device also has thermal shutdown protection, which is active when the junction
temperature reaches 125 °C. In this case both the high and low-side MOSFETs turn off.
Once the junction temperature goes back below 95 °C, the device resumes normal
operation.
7.7
Overcurrent protection
The overcurrent protection limits the maximum inductor current. This current, flowing
through the P-channel of the power stage, causes a voltage drop, across its R DS(on), at the
switching node. A comparator compares the switching node voltage with a reference
voltage VR. To generate the VR voltage a current generator is used, which causes a drop
across a P-channel of the same kind as the power stage. When the switching node voltage
is lower than VR, the comparator output goes high and the power P-channel turns off.
7.8
Enable function
The ST1S15 features an enable function (B2). When the EN voltage is higher than 1.2 V
the device is ON, and if it is lower than 0.4 V the device is OFF. In shutdown mode the
consumption is lower than 5 µA. The EN pin does not have an internal pull-up, which
means that the EN pin cannot be left floating. If the enable function is not used, the EN pin
must be connected to VIN.
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ST1S15
Application information
8
Application information
8.1
Input and output capacitors
Ceramic capacitors with X5R or X7R dielectric and low ESR should be used. The input
capacitor filters any disturbance present in the input line so to obtain a stable operation.
The output capacitor satisfies the output voltage ripple requirement. The output voltage
ripple (VOUT_RIPPLE), in continuous mode, is calculated as follows:
Equation 1
VOUT_RIPPLE = IL
VIN ESL
1
ESR + ---------------------------------------- + --------------------------8 C OUT f SW
L
where ΔIL is the ripple current and fSW is the switching frequency. The use of ceramic
capacitors with voltage ratings higher than 1.5 times the maximum input or output voltage
is recommended.
8.2
Inductor
The inductor is the key passive component for switching converters. The internal
compensation is optimized to operate with an output filter of L=0.47 µH and COUT=4.7 µF.
In addition to the inductance value, in order to avoid saturation, the maximum saturation
current of the inductor must be higher than IPEAK.
The peak current of the inductor has to be calculated as follows:
Equation 2
IPEAK = I
V OUT V IN_MAX – V OUT
OUT + --------------------------------------------------------------------2 V IN_MAX fSW L
The following inductor part numbers from different suppliers have been tested in the
ST1S15 converters.
Table 8: Inductors
Manufacturer
Murata
TDK
Part numbers
Dimension (mm)
LQM21PNR47MC0D
2.0 x 1.25 x 0.5
LQM21PNR54MG0D
2.0 x 1.25 x 0.5
LQH32PNR47NN0L
3.2 x 2.7 x 1.55
MLP2012SR47T
2.0 x 1.25 x 0.5
VLS2010ET-1R0N
2.0 x 2.0 x 1.0
DocID023280 Rev 4
17/27
Application information
8.3
ST1S15
Layout guidelines
Due to the high switching frequency and peak current, the layout is an important design
step for all switching power supplies. If the layout is not fulfilled carefully, important
parameters such as: stability, efficiency, line and load regulation and output voltage ripple
may be compromised. Short, wide traces must be implemented for main current and for
power ground paths. The input capacitor must be placed as close as possible to the device
pin as well as the inductor and output capacitor. The feedback pin (FB) is a high
impedance node, so the interference can be minimized by placing the routing of the
feedback node as far as possible from the high current paths. A common ground node
minimizes ground noise.
Figure 22: Flip Chip layout recommended (not in scale)
VOUT
EN
GND
COUT
CIN
L
VIN
MODE
GIPG1401151337LM
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DocID023280 Rev 4
ST1S15
9
Different output voltage versions of the ST1S15
available on request
Different output voltage versions of the ST1S15
available on request
Options available on request:
0.8 V
1V
1.05 V
1.2 V
1.25 V
1.5 V
1.8 V
1.85 V
1.875 V
2.5 V
2.8 V
3.0 V
3.3 V
DocID023280 Rev 4
19/27
Package information
10
ST1S15
Package information
In order to meet environmental requirements, ST offers these devices in different grades of
®
®
ECOPACK packages, depending on their level of environmental compliance. ECOPACK
specifications, grade definitions and product status are available at: www.st.com.
®
ECOPACK is an ST trademark.
20/27
DocID023280 Rev 4
ST1S15
10.1
Package information
Flip Chip 6 package information
Figure 23: Flip Chip 6 package outline
1
2
A B C
GIPG2301151335LM
DocID023280 Rev 4
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Package information
ST1S15
Table 9: Flip Chip 6 mechanical data
mm
Dim.
Min.
Typ.
Max.
A
0.52
0.56
0.6
A1
0.17
0.20
0.23
A2
0.35
0.36
0.37
b
0.23
0.25
0.29
D
1.16
1.19
1.22
D1
0.8
e
0.4
E
0.905
0.935
E1
0.4
fD
0.267
fE
0.195
SE
0.2
ccc
0.075
0.965
The terminal A1 on the bump side is identified by a distinguishing feature (for
instance by a circular "clear area" typically 0.1 mm diameter) and/or a missing
bump. The terminal A1 on the backside of the product is identified by a
distinguishing feature (for instance by a circular "clear area" typically 0.5 mm
diameter).
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ST1S15
Package information
Figure 24: Flip Chip 6 footprint recommended data (mm)
DocID023280 Rev 4
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Package information
10.2
ST1S15
Packing information
Figure 25: Tape and reel outline
Drawing not in scale
24/27
DocID023280 Rev 4
ST1S15
Package information
Table 10: Tape and reel mechanical data
mm
Dim.
Min.
Typ.
A
Max.
180
C
12.8
D
20.2
N
60
13.2
T
14.4
Ao
1.01
1.06
1.11
Bo
1.26
1.31
1.36
Ko
0.61
0.66
0.71
Po
3.9
4.1
P
3.9
4.1
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Revision history
11
ST1S15
Revision history
Table 11: Document revision history
26/27
Date
Revision
Changes
07-Jun-2012
1
Initial release.
4-Mar-2013
2
Modified: D1 and E1 values in table 9.
27-Aug-2013
3
Updated: table 1, table 7, section 9 and Package
mechanical data.
24-Feb-2015
4
Deleted DFN package.
DocID023280 Rev 4
ST1S15
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