ST ST1S15 User Manual
500 mA, 6 MHz synchronous step-down converter
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
■ Tiny external components
■ Auto or forced PWM selection with dedicated
pin
■ Available in Flip Chip 6 and DFN6 (2 x 2 mm)
packages
Applications
■ DSP and multimedia processors core supply
■ Cell phones
■ PDAs
ST1S15
Datasheet − preliminary data
Flip Chip 6
inductor and 4.7 µF for the output capacitor,
providing, at the same time, very good
performance in terms of load and line transients.
It is possible to select a PFM mode 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.
DFN6 (2 x 2 mm)
Description
The ST1S15 is a high efficiency miniaturized
step-down converter able to provide 500 mA
output current from an input voltage from 2.3 to
5.5. This converter is specifically designed for
applications where high efficiency and small a
application area are the key factors. With an
output voltage as low as 0.6 V the device
supports low voltage DSPs and processors core
supply. Due to the 6 MHz switching frequency the
ST1S15 can use nominal values of 470 nH for the
Table 1. Device summary
Order codes Output voltages (V) Packages
ST1S15J18R 1.82 Flip Chip 6
ST1S15J28R 2.8 Flip Chip 6
ST1S15TPU18R 1.82 DFN6 (2 x 2 mm)
June 2012 Doc ID 023280 Rev 1 1/27
This is preliminar y information on a new product now in development or undergoing evaluation. Details are subject to
change without notice.
www.st.com
27
Contents ST1S15
Contents
1 Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6 Block schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7 Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1 General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.2 Mode transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.3 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.5 Undervoltage lockout (UVLO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.6 Thermal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.7 Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.8 Enable function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8 Application Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1 Input and output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.2 Inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.3 Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10 Different output voltage versions of the ST1S15
available on request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2/27 Doc ID 023280 Rev 1
ST1S15 Application schematic
1 Application schematic
Figure 1. ST1S15 application schematic
V
IN
VIN
C
IN
ST1S15
EN
MODE
SW
FB
GND
L
C
OUT
Table 2. Typical external components
Component Manufacturer Part number Value Size
Murata GRM155R60J475ME87 4.7 µF 0402
Murata
GRM155R60G475ME87
GRM155R60J475ME87
(1)
4.7 µF 0402
C
1. For V
C
IN
OUT
L Murata LQM21PNR47MC0D 470 nH 2.0 x 1.25 x 0.5 mm
≤ 1.82 V.
OUT
V
OUT
AM11904v1
Note: All the above components refer to a typical application. Operation of the ST1S15 is not
limited to the choice of these external components.
Doc ID 023280 Rev 1 3/27
Pin configuration ST1S15
2 Pin configuration
Figure 2. Pin connections (top view)
MARKING VIEW
A1 A2
B1 B2
C1 C2
BUMPS VIEW
A2 A1
B2 B1
C2 C1
AM11909v1
Table 3. Pin description
Pin name Flip Chip DFN6 Description
V
IN
EN B2 2
GND C2 3 Power and IC supply ground.
FB C1 4 Feedback input.
SW B1 5 Inductor connection to internal PFET and NFET.
MODE A1 6
A2 1 High-side switch connection and IC supply.
ENABLE pin with positive logic. The IC goes into shutdown if pulled
low. Do not leave this pin floating.
Operation mode selection:
- LOW => Automatic operation PFM or PWM according to output
load;
- HIGH => Forced PWM operation.
Do not leave this pin floating.
AM11911v1
Epad - Epad Exposed pad to be connected to ground
4/27 Doc ID 023280 Rev 1
ST1S15 Maximum ratings
3 Maximum ratings
Table 4. Absolute maximum ratings
Symbol Parameter Value Unit
V
IN
EN, MODE Logic input pins - 0.3 to + 6.0 V
FB, SW Feedback and switching pins -0.3 to V
T
AMB
T
J
T
STG
Power and signal supply voltage - 0.3 to + 6.0 V
+ 0.3 V
IN
Operating ambient temperature - 40 to 85 °C
Junction temperature - 40 to 150 °C
Storage temperature - 65 to 150 °C
Note: 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 DFN6 Flip Chip Unit
R
thJA
Thermal resistance junction-ambient 80 130 °C/W
Table 6. ESD performance
Symbol Parameter Value Unit
ESD
Human body model ±
Machine model ± 100
2000
V
Doc ID 023280 Rev 1 5/27
Electrical characteristics ST1S15
4 Electrical characteristics
- 40 °C < TA < 85 °C, CIN = 4.7 µF nominal, C
values are at T
Table 7. Electrical characteristics
= 25 °C, V
A
= VIN unless otherwise specified.
EN
= 4.7 µF nominal, L = 470 nH, typical
OUT
Symbol Parameter Test conditions Min. Typ. Max. Unit
General section
V
V
UVLO
Operating input voltage range 2.3 5.5 V
IN
V
rising 2.1 2.2 V
Undervoltage lockout threshold
IN
V
falling 1.8 1.9
IN
PFM mode quiescent current No load 45 60 µA
I
PWM mode quiescent current No load 15 mA
Q
f
SW
I
OUT
I
SC
I
PFM-
PWM
η
t
ON
Shutdown current V
Switching frequency 5.4 6 6.6 MHz
Continuous output current
Short-circuit current
(1)
(2)
PFM to PWM transition
PWM to PFM transition 100
Efficiency (V
= 3.6 V, V
IN
OUT
=
1.82 V)
Startup time
= 0 0.5 5 µA
EN
VIN ≥ V
+ 0.40 V 500 mA
OUT
1200 mA
200
= 3.6V, V
V
IN
I
= 10 mA PFM mode 80
OUT
I
= 150 mA 83
OUT
from low to high, V
V
EN
OUT
= 1.82 V
V, V
OUT
= 1.82 V
IN
= 3.6
260 µs
Thermal shutdown 125 °C
T
SHDN
Hysteresis 30 °C
mA
%
Output voltage
V
Accuracy (ST1S15x18R)
Load regulation
OUT
Accuracy (ST1S15x28R)
Load regulation
2.3 ≤ VIN ≤ 5.5 V, I
PWM mode, -40 ≤ T
2.3 ≤ V
≤ 5.5 V, I
IN
PFM mode, -40 ≤ T
2.3 ≤ VIN ≤ 5.5 V, V
= 0 to 500 mA, PWM
I
OUT
mode, -40 ≤ T
3.2 ≤ VIN ≤ 5.5 V, I
PWM mode, -40 ≤ T
3.2 ≤ V
≤ 5.5 V, I
IN
PFM mode, -40 ≤ T
3.2 ≤ V
I
OUT
≤ 5.5 V, V
IN
= 0 to 500 mA, PWM
mode, - 40 ≤ T
OUT
OUT
≤ 85 °C
A
OUT
OUT
≤ 85 °C
A
A
A
OUT
A
A
OUT
6/27 Doc ID 023280 Rev 1
= 10 mA,
≤ 85 °C
= 10 mA,
≤ 85 °C
=1.82 V,
= 10 mA,
≤ 85 °C
= 10 mA,
≤ 85 °C
= 2.8 V,
1.78 1.82 1.86
V
1.78 1.82 1.86
-1.5 %
2.74 2.8 2.86
V
2.74 2.8 2.86
-1.5 %
ST1S15 Electrical characteristics
Table 7. Electrical characteristics (continued)
Symbol Parameter Test conditions Min. Typ. Max. Unit
V
OUT_Rip
I
LKFB
Peak-to-Peak output voltage
ripple
ple
FB pin leakage current V
Line transient response.
Output voltage variation over
V
IN_TR
nominal DC level.
t
R
Case 1: V
Case 2: V
Load transient response
t
R=tF
I
OUT_TR
Case 1: V
Case 2: V
Case 3: V
Logic Inputs
V
V
Low-level input voltage (EN,
IL
MODE pins)
High-level input voltage (EN,
IH
MODE pins)
= tF = 10 µs
IN
IN
=0.1µs.
=2.5 V
IN
=3.6 V
IN
=4.5 V
IN
= 2.5 to 3.1 V
= 3.9 to 4.5 V
PWM mode, I
= 3.6 V, V
V
IN
PFM mode, I
= 3.6 V, V
V
IN
= 5.5 V 9 µA
FB
I
= 50 mA, V
OUT
OUT
OUT
= 150 mA,
OUT
OUT
OUT
= 150 mA,
= 1.82 V
= 1.82 V
= 1.82 V
10 mV
30 mV
±50 mV
I
= 250 mA, V
OUT
= 0 to 150 mA,
I
OUT
= 1.82 V
V
OUT
= 50 to 250 mA,
I
OUT
V
= 1.82 V
OUT
= 150 to 400 mA,
I
OUT
= 1.82 V
V
OUT
OUT
= 1.82 V
±50
±70
±70
0.4 V
1.2 V
mV
I
Input leakage current (EN, MODE
LK-I
pins)
= V
V
EN
= 5.5 V 0.01 1 µA
MODE
Power Switches
P-channel MOSFET onresistance
R
DSON
N-channel MOSFET onresistance
I
LPEAK
I
LKG-P
I
LKG-N
1. Not tested in production. This value is guaranteed by correlation with R
2. Not tested in production. This parameter is guaranteed by peak current limit.
P-channel peak current limit Over input voltage range 900 1000 1200 mA
P-channel leakage current V
N-channel leakage current V
= 5.5 V, VEN= 0 1 µA
IN
= 5.5 V, VEN= 0 1 µA
SW
DSON
300 400
mΩ
350 450
, peak current limit and operating input voltage.
Doc ID 023280 Rev 1 7/27
Typical performance characteristics ST1S15
5 Typical performance characteristics
Figure 3. Efficiency vs. output current
100
90
80
70
60
50
40
30
Efficiency [%]
20
10
0
1 10 100 1000
VEN = VIN, I
(V
= 1.82 V)
OUT
= 1 mA to 500 mA
OUT
Figure 4. Efficiency vs. output current
(V
= 2.8 V)
100
90
80
Vin= 2.5V PWM Mode
Vin= 2.5V PFM Mode
Vin= 3.6V PWM Mode
Vin= 3.6V PFM Mode
Vin= 4.5V PWM Mode
Vin= 4.5V PFM Mode
Vin= 5.5V PWM Mode
Vin= 5.5V PFM Mode
I
[mA]
OUT
70
60
50
40
30
Efficiency [%]
20
10
0
1 10 100 1000
VEN = VIN, I
OUT
= 1 mA to 500 mA
OUT
Vin= 3.2V PWM Mode
Vin= 3.2V PFM Mode
Vin= 3.6V PWM Mode
Vin= 3.6V PFM Mode
Vin= 4.2V PWM Mode
Vin= 4.2V PFM Mode
Vin= 5.0V PWM Mode
Vin= 5.0V PFM Mode
I
[mA]
OUT
Figure 5. Output voltage vs. input voltage Figure 6. Supply current vs. input voltage in
2.00
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
Output Voltage [V]
0.20
0.00
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
T=85°C
T=55°C
T=25°C
T=0°C
T= -25°C
T= -40°C
Input Voltage [V]
65
60
55
50
ISupply [µA]
45
40
35
2 2.5 3 3.5 4 4.5 5 5.5 6
auto mode
T= 85°C
T= 25°C
T= 0°C
T= -40° C
Input Voltage [V]
VIN = 0 to 5.5 V (step 0.1 V), I
= V
V
EN
IN
= 500 mA, Mode = GND,
OUT
Figure 7. Supply current vs. input voltage in
100
10
ISupply [mA]
1
2 2.5 3 3.5 4 4.5 5 5.5 6
VIN = 2.3 V to 5.5 V, Mode = VIN, V
PWM mode
Input Voltage [V]
= 1.82 V, VEN = V
OUT
T= 85°C
T= 25°C
T= 0°C
T= -40 °C
VIN = 2.5 V to 5.5 V, Mode = GND, V
Figure 8. Output voltage vs. output current
1.85
1.84
1.83
1.82
1.81
Output Voltage [V]
1.8
1.79
0 50 100 150 200 250 300 350 400 450 500 550
VEN = VIN, Mode = VIN, V
IN
8/27 Doc ID 023280 Rev 1
Output Current [mA ]
= 1.82 V
OUT
= 1.82 V, VEN = V
OUT
IN
Vin = 2.5 V
Vin = 3.6 V
Vin = 4.5 V
ST1S15 Typical performance characteristics
Figure 9. Frequency vs. input voltage Figure 10. Output voltage vs. output current
7.5
7
6.5
T= 85°C
T= 25°C
T= 0°C
T= - 40°C
6
5.5
Frequency [MHz]
5
4.5
22.5 33.5 44.5 55.5 6
Inp ut Voltage [V]
VIN = 2.3 V to 5.5 V, I
Figure 11. Mode transition vs. input voltage Figure 12. Mode transition PFM to PWM
250
200
150
100
Output Current [ mA ]
50
0
2 2.5 3 3.5 4 4.5 5 5.5 6
= 10 mA, Mode = V
OUT
IN, VEN
= V
PFM t o PWM
PWM to PFM
IN
1.89
1.87
1.85
1.83
1.81
1.79
Output Voltage [V]
1.77
1.75
0 50 100 150 200 250 300 350 400 450 500 550
Output Cur rent [ mA ]
VIN = 3.6 V, I
= 0 to 500 mA, Mode = GND, VEN = V
OUT
Mode
V
IN
V
OUT
I
L
Inpu t Voltage [V]
T= 85°C
T= 25°C
T= 0°C
T= - 40°C
IN
VIN = Enable, V
Figure 13. Mode transition PWM to PFM Figure 14. Output voltage ripple
= 1.82 V, Mode = GND
OUT
VIN = 3.6 V, V
= 1.82 V, Mode = 0 to 3.6 V, Load = 180 Ω
OUT
Mode
V
IN
V
OUT
I
L
VIN = 3.6 V, V
= 1.82 V, Mode = 3.6 to 0 V, Load = 180 Ω
OUT
VIN = 3.6 V, V
load
= 1.82 V, Mode = GND, VEN = V
OUT
Doc ID 023280 Rev 1 9/27
IN,
No
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