ST1S03
1.5A, 1.5 MHZ ADJUSTABLE,
STEP-DOWN SWITCHING REGULATOR IN DFN6
I
I
I
I
I
I
I
I
I
STEP-DOWN CURRENT MODE PWM
(1.5MHz) DC-DC CONVERTER
2% DC OUTPUT VOLTAGE TOLERANCE
INTERNAL SOFT START FOR START-UP
CURRENT LIMITIATION AND POWER ON
DELAY OF 50-100µs
TYPICAL EFFICIENCY: > 70% OVER ALL
OPERATING CONDITIONS
1.5A OUTPUT CURRENT CAPABILITY
NOT SWITCHING QUIESCENT CURRENT:
MAX 2.5mA OVER TEMPERATURE RANGE
SWITCH V
DS
: MAX 350mV @ISW=750mA
USES TINY CAPACITORS AND INDUCTORS
AVAILABLE IN DFN 3x3 EXPOSED PAD
DFN6 (3x3)
DESCRIPTION
The ST1S03 is a step down DC-DC converter
optimized for powering low-voltage digital core in
HDD applications and, generally, to replace the
high current linear solution when the power
dissipation may cause an high heating of the
application environment. It provides up to 1.5A
over an input voltage range of 3V to 16V. An high
Figure 1: Schematic Diagram
switching frequency (1.5MHz) allows the use of
tiny surface-mount components: as well as the
resistor divider to set the output voltage value,
only an inductor, a schottky diode and two
capacitors are required. Besides, a low output
ripple is guaranteed by the current mode PWM
topology and by the use of low E.S.R. SMD
ceramic capacitors. The device is thermal
protected and current limited to prevent damages
due to accidental short circuit. The ST1S03 is
available in DFN6 package.
March 2005
Rev. 3
1/11
ST1S03
Table 1: Order Codes
SYMBOL
ST1S03
DFN6
ST1S03PM
(Tape & Reel)
ST1S03RPM
Figure 2: Pin Connection
(top through view)
Table 2: Pin Description
PIN N°
1
2
3
4
5
6
Symbol
V
FB
GND
SW
V
IN_SW
V
IN_A
N.C.
Voltage of Feedback
Sistem Ground
Output of the internal Power Swithch
Power Supply for the MOSFET Switch
Power Supply for the Analog Circuit
Not Connected
Name and Function
Table 3: Absolute Maximum Ratings
Symbol
V
I_SW
V
I_SW
SWITCH
Voltage
V
FB
I
VFB
T
J
T
STG
T
LEAD
Parameter
Positive Power Supply Voltage
Positive Power Supply Voltage
Max Voltage of output pin
Feedback Voltage
Common mode input voltage
Max Junction Temperature
Storage Temperature Range
Lead Temperature (Soldering) 10 Sec.
Value
-0.3 to 16
-0.3 to 16
-0.3 to 16
2.5
±1
150
-25 to 150
300
Unit
V
V
V
V
mA
°C
°C
°C
Absolute Maximum Ratings are those beyond which damage to the device may occur. Functional operation under these condition is not im-
plied.
Table 4: Thermal Data
Symbol
R
THJ-C
R
THJ-A
Parameter
Thermal Resistance Junction-case
Thermal Resistance Junction-ambient
DFN6
10
55
Unit
°C/W
°C/W
2/11
ST1S03
Table 5: Electrical Characteristics
(V
IN_SW
= V
IN_A
= 5V, C
I
= 4.7µF, C
O
= 22µF, L1 = 3.3µH, T
J
= 0 to
125°C, unless otherwise specified. Typical values are referred to 25°C)
Symbol
FB
PSRR
I
FB
BW
I
Q
I
OUT
I
MIN
%V
OUT
/
∆V
IN
%V
OUT
/
∆I
OUT
PWM f
S
D
MAX
I
SWL
V
DS
E
T
SHDN
T
HYS
∆V
OUT
/
∆I
OUT
Parameter
Feedback Voltage
Feedback PSRR
V
FB
Pin Bias Current
Bandwidth of Error Amplifier Closed Loop
Quiescent Current
No Switching
Output Current
Minimum Output Current
Reference Line Regulation
Reference Load Regulation
PWM Switching Frequency
(1)
Maximum Duty Cycle
Switching Current Limitation
Switch V
DS
Efficiency
Thermal Shut Down (1)
Thermal Shut Down
Hysteresis (1)
Load Transient Response
(1)
I
SW
= 750 mA
I
OUT
=
10mA to 1.2A
70
130
150
15
I
OUT
= 100mA to 700mA
t
R
= t
F
≥
100ns, T
A
= 25°C
I
OUT
= 10mA to short, T
A
= 25°C
-5
+5
+5
V
IN
= 3V to 16V
I
OUT
= 10mA to 1.2A
V
FB
= 0.8V, T
A
=25°C
1.2
V
IN
=3V to 16V
1.5
1
0.032
0.0014
1.5
87
1.65
200
350
0.06
0.003
1.8
300
2.5
Test Conditions
1Hz < Frequency V
IN
Min.
784
Typ.
800
-60
Max.
816
600
Unit
mV
dB
nA
KHz
mA
A
mA
%V
OUT
/∆V
IN
%V
OUT
/mA
MHz
%
A
mV
%
°C
°C
%V
O
%V
O
Short Circuit Removal
∆V
OUT
/
Response (1)
∆I
OUT
@I
O
= short
NOTE 1: Guaranteed by design, not tested in production.
3/11
ST1S03
APPLICATION NOTES
The ST1S03 is an adjustable current mode PWM
step-down DC/DC converter with internal 1.5A
power switch, packaged in a 6-lead DFN 3x3.
It’s a complete 1.5A switching regulator with its
internal compensation eliminating additional
component.
The constant frequency, current mode, PWM
architecture and stable operation with ceramic
capacitors results in low, predictable output ripple.
However, in order to keep the output regulated,
the devices goes in pulse skipping mode when a
very light load is required.
To clamp the error amplifier reference voltage a
Soft Start control block generating a voltage ramp,
has been implemented. Besides an On-Chip
Power on Reset of 50 = 100µs ensure the proper
operation when switching on the power supply.
Other circuits fitted to the device protection are the
Thermal Shut down block which turn off the
regulator when the junction temperature exceeds
150°C typically and the Cycle-by-cycle Current
Limiting that provides protection against shorted
outputs.
Being the ST1S03 an adjustable regulator, the
output voltage is determined by an external
Figure 3: Application Circuit
resistor divider. The desired value is given by the
following equation:
V
OUT
= V
FB
[1+R1/R2]
To make the device working, only other four
external components are required: a Schottky
diode, an inductor and two capacitors. The chosen
inductor must be able to not saturate at the peak
current level. Besides, its value can be selected
keeping in account that a large inductor value
increases the efficiency at low output current and
reduces output voltage ripple, while a smaller
inductor can be chosen when it is important to
reduce the package size and the total cost of the
application. Finally, the ST1S03 has been
designed to work properly with X5R or X7R SMD
ceramic capacitors both at the input and at the
output. this kind of capacitors, thanks to their very
low series resistance (ESR), minimize the output
voltage ripple. Other low ESR capacitors can be
used according to the need of the application
without invalidating the right functioning of the
device. Due to the high switching frequency and
peak current, it is important to optimize the
application environment reducing the length of the
PCB traces and placing all the external
component near the device.
4/11
ST1S03
TYPICAL CHARACTERISTICS
(C
IN
= 4.7µF, C
O
= 22µF, L1 = 3.3µH, unless otherwise specified)
Figure 4:
Load Voltage Feedback vs
Temperature
Figure 7:
Line Voltage Feedback vs Temperature
Figure 5:
Voltage Feedback vs Temperature
Figure 8:
Voltage Feedback vs Output Current
Figure 6:
Line Output Voltage Regulation vs
Temperature
Figure 9:
PWM Switching Frequency vs
Temperature
5/11
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