STOD03AS
Dual DC-DC converter for powering AMOLED displays
Datasheet - production data
Applications
• Active matrix AMOLED power supply
• Cellular phones
• Camcorders and digital still cameras
• Multimedia players
DFN12L (3 x 3 mm)
Description
Features
• Step-up and inverter converters
• Operating input voltage range from 2.5 V to
4.5 V
• Synchronous rectification for both DC-DC
converters
• Minimum 200 mA output current
• 4.6 V fixed positive output voltage
• Programmable negative voltage by SWIRE from
-2.4 V to -5.4 V at 100 mV steps
• Typical efficiency: 85%
• Pulse skipping mode in light load condition
• 1.5 MHz PWM mode control switching
frequency
The STOD03AS is a dual DC-DC converter with
short-circuit protection for AMOLED display
panels. It integrates a step-up and an inverting
DC-DC converter making it particularly suitable
for battery operated products, in which the major
concern is overall system efficiency. It works in
pulse skipping mode during light load conditions
and PWM-MODE at 1.5 MHz frequency for
medium/high load conditions. The high frequency
allows the value and size of external components
to be reduced. The Enable pin allows the device
to be turned off, therefore reducing the current
consumption to less than 1 µA. The negative
output voltage can be programmed by an MCU
through a dedicated pin which implements singlewire protocol. Soft-start with controlled inrush
current limit and thermal shutdown are integrated
functions of the device.
• Enable pin for shutdown mode
• Low quiescent current in shutdown mode
• Soft-start with inrush current protection
• Overtemperature protection
• Temperature range: -40 °C to 85 °C
• True-shutdown mode
• Fast discharge outputs of the circuits after
shutdown
• Short-circuit protection
• Package DFN12L (3 x 3 mm) 0.6 mm height
Table 1. Device summary
Order code
Positive voltage
Negative voltage
Package
Packaging
STOD03ASTPUR
4.6V
-2.4V to -5.4V
DFN12L (3 x 3 mm)
3000 parts per reel
July 2013
This is information on a product in full production.
DocID022614 Rev 2
1/25
www.st.com
Contents
STOD03AS
Contents
1
Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5
Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6
Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1
6.2
7
7.2
SWIRE features and benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.2
SWIRE protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.3
SWIRE basic operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Negative output voltage levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
External passive components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1.1
Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1.2
Input and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Recommended PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1
2/25
6.1.1
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1
8
SWIRE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1.1
Multiple operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1.2
Pulse skipping operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1.3
Discontinuous conduction mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1.4
Continuous conduction mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.5
Enable pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.6
Soft-start and inrush current limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.7
Undervoltage lockout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
DocID022614 Rev 2
STOD03AS
Contents
8.1.8
Overtemperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.9
Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.10
Fast discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
10
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
DocID022614 Rev 2
3/25
25
Schematic
1
STOD03AS
Schematic
Figure 1. Application schematic
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Table 2. Typical external components
Comp.
Manufacturer
Part number
Value
Size
Ratings
L1 (1)
CoilCraft
Murata
SEMCO
ABCO
ABCO
LPS4012-472ML
LQH3NPN4R7MJ0
CIG22B4R7MNE
LPF2810T-4R7M
LPF2807T-4R7M
4.7µH
4.0 x 4.0 x 1.2
3.0 x 3.0 x 1.1
2.5 x 2.0 x 1.0
2.8 x 2.8 x 1.0
2.8 x 2.8 x 0.7
±20%, I = 1.7 A, R = 0.175Ω
±20%, I = 1.1 A, R = 0.156Ω
±20%, I = 1.1 A, R = 0.300Ω
±20%, I = 0.85 A, R = 0.33Ω
±20%, I = 0.70 A, R = 0.44Ω
L2 (2)
CoilCraft
Murata
TOKO
ABCO
TDK
LPS4012-472ML
LQH3NPN4R7MJ0
DFE252012C1239AS-H4R7N 4.7µH
LPF3510T-4R7M
VLF4014AT-4R7M1R1
4.0 x 4.0 x 1.2
3.0 x 3.0 x 1.1
2.5 x 2.0 x 1.2
3.5 x 3.5 x 1.0
3.7 x 3.5 x 1.4
±20%, I = 1.7 A, R = 0.175Ω
±20%, I = 1.1 A, R = 0.156Ω
±30%, I = 1.2 A, R = 0.252Ω
±20%, I = 0.83 A, R = 0.25Ω
±20%, I = 1.1 A, R = 0.140Ω
CIN
Murata
Taiyo Yuden
GRM219R61A106KE44
LMK212BJ106KD-T
2x
10µF
0805
0805
±10%, X5R, 10V
±10%, X5R, 10V
CMID
Murata
Taiyo Yuden
GRM219R61A106KE44
LMK212BJ106KD-T
10µF
0805
0805
±10%, X5R, 10V
±10%, X5R, 10V
CO2
Murata
Taiyo Yuden
GRM219R61A106KE44
LMK212BJ106KD-T
2x
10µF
0805
0805
±10%, X5R, 10V
±10%, X5R, 10V
CREF
Murata
Taiyo Yuden
GRM185R60J105KE26
JMK107BJ105KK-T
1µF
0603
0603
±10%, X5R, 6.3V
±10%, X5R, 6.3V
1. A 200 mA load can be provided with inductor saturation current as a minimum of 0.5 A.
2. At -5.4 V, a 200 mA load can be provided with inductor saturation current as a minimum of 1 A. See Section 7.1.1.
Note:
4/25
All the above components refer to the typical application performance characteristics.
Operation of the device is not limited to the choice of these external components. Inductor
values ranging from 3.3 µH to 6.8 µH can be used together with the STOD03AS.
DocID022614 Rev 2
STOD03AS
Schematic
Figure 2. Block schematic
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DocID022614 Rev 2
$0 Y
5/25
25
Pin configuration
2
STOD03AS
Pin configuration
Figure 3. Pin configuration (top view)
Table 3. Pin description
Pin name
Pin n°
Description
Lx1
1
Switching node of the step-up converter
PGND
2
Power ground pin
VMID
3
Step-up converter output voltage (4.6V)
NC
4
Not internally connected
AGND
5
Signal ground pin. This pin must be connected to the power ground pin
VREF
6
Voltage reference output. 1µF bypass capacitor must be connected
between this pin and AGND
SWIRE
7
Negative voltage setting pin
EN
8
Enable control pin. ON = VINA. When pulled low it puts the device in
shutdown mode
VO2
9
Inverting converter output voltage (Default - 4.9V)
Lx2
10
Switching node of the inverting converter
VIN A
11
Analogic input supply voltage
ViN P
12
Power input supply voltage
Internally connected to AGND. Exposed pad must be connected to AGND
Exposed
and PGND in the PCB layout in order to guarantee proper operation of the
pad
device
6/25
DocID022614 Rev 2
STOD03AS
3
Maximum ratings
Maximum ratings
Table 4. Absolute maximum ratings
Symbol
Parameter
VINA, VINP
DC supply voltage
EN, SWIRE
Logic input pins
Value
Unit
-0.3 to 6
V
-0.3 to 4.6
V
ILX2
Inverting converter switching current
Internally limited
A
LX2
Inverting converter switching node voltage
- 10 to VINP + 0.3
V
VO2
Inverting converter output voltage
- 10 to AGND + 0.3
V
VMID
Step-up converter and LDO output voltage
-0.3 to 6
V
LX1
Step-up converter switching node voltage
-0.3 to VMID + 0.3
V
ILX1
Step-up converter switching current
Internally limited
A
VREF
Reference voltage
-0.3 to 3
V
PD
Power dissipation
Internally limited
mW
-65 to 150
°C
150
°C
2
kV
TSTG
TJ
ESD
Note:
Storage temperature range
Maximum junction temperature
ESD protection HBM
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
RthJA
RthJC
Parameter
Thermal resistance junction-ambient
Thermal resistance junction-case (FR-4 PCB)
(1)
Value
Unit
48.8
°C/W
2.6
°C/W
1. The package is mounted on a 4-layer (2S2P) JEDEC board as per JESD51-7.
DocID022614 Rev 2
7/25
25
Electrical characteristics
4
STOD03AS
Electrical characteristics
TJ = 25 °C, VINA = VINP = 3.7 V, IMID,O2 = 30 mA, CIN = 2 x 10 µF, CMID = 10 µF,
CO2 = 2 x 10 µF, CREF = 1 µF, L1 = L2 = 4.7 µH, VEN = 2 V, VMID = 4.6 V, VO2= -4.9 V unless
otherwise specified.
Table 6. Electrical characteristics
Symbol
Parameter
Test conditions
Min.
Typ.
Max.
Unit
2.3
3.7
4.5
V
2.22
2.25
V
General section
VINA, VINP
Supply input voltage
UVLO_H
Undervoltage lockout HIGH
VINA rising
UVLO_L
Undervoltage lockout LOW
VINA falling
Input current
No load condition
IQ_SH
Shutdown current
VEN=GND
TJ=-40°C to +85°C
VEN H
Enable high threshold
VEN L
Enable low threshold
IEN
Enable input current
VEN=VINA=4.5V
TJ=-40°C to +85°C
fS
Switching frequency
PWM mode
D1MAX
Step-up maximum duty cycle
No load
87
%
D2MAX
Inverting maximum duty cycle No load
87
%
IMID,O2=10 to 30mA,
VMID=4.6V, VO2=-4.9V
80
%
IMID,O2=30 to 150mA,
VMID=4.6V, VO2=-4.9V
85
%
I_VI
h
Total system efficiency
VINA=2.5V to 4.5V,
TJ=-40°C to +85°C
VREF
Voltage reference
IREF=10µA
IREF
Voltage reference current
capability
At 98.5% of no load
reference voltage
1.9
2.18
1.3
V
1.7
mA
1
µA
1.2
V
0.4
1.2
1.208
1.5
1.22
1
µA
1.7
MHz
1.232
100
V
µA
Step-up converter section
VMID
VINA=VINP=2.5V to 4.5V;
Positive voltage total variation IMID=5mA to 150mA, IO2 no
load, TJ=-40°C to +85°C
Temperature accuracy
8/25
VINA=VINP=3.7V; IMID=5mA;
IO2 no load; TJ=-40°C to
+85°C
DocID022614 Rev 2
4.55
4.6
±0.5
4.65
V
%
STOD03AS
Electrical characteristics
Table 6. Electrical characteristics (continued)
Symbol
ΔVMID LT
ΔVMIDT
Parameter
Line transient
Load transient regulation
Test conditions
Min.
Typ.
Max.
Unit
VINA,P=3.5V to 3.0V,
IMID=100mA; TR=TF=50µs
-12
mV
IMID=3 to 30mA and IMID=30
to 3mA, TR=TF=30µs
±20
mV
IMID=10 to 100mA and
IMID=100 to 10mA,
TR=TF=30µs
±25
mV
±20
mV
VMID-PP
TDMA noise line transient
regulation
IMID=5 to 100mA; VINA,P
=2.9V to 3.4V; F=200Hz;
TR=TF=50µs; IO2 no load
IMID MAX
Max. step-up load current
VINA,P=2.9V to 4.5V
200
I-L1MAX
Step-up inductor peak current
VMID 10% below of nominal
value
0.9
RDSONP1
P-channel static drain-source
ON resistance
VINA,P=3.7V, ISW=100mA
RDSONN1
N-channel static drain-source
ON resistance
VINA,P=3.7V, ISW=100mA
mA
1.1
A
1.0
2.0
W
0.4
1.0
W
-2.4
V
-4.83
V
Inverting converter section
31 different values set by the
Output negative voltage range SWIRE pin
(see Section 6.1.2)
-5.4
Output negative voltage total
variation on default value
VINA=VINP=2.5V to 4.5V;
IO2=5mA to 150mA, IMID no
load, TJ=25°C
Temperature accuracy
VINA=VINP=3.7V; IO2=5mA,
IMID no load,
TJ=-40°C to +85°C
±0.5
%
Line transient
VINA,P=3.5V to 3.0V,
IO2=100mA, TR=TF=50µs
+12
mV
Load transient regulation
IO2=3 to 30mA and IO2=30 to
3mA, TR=TF=100µs
±20
mV
Load transient regulation
IO2=10 to 100mA and
IO2=100 to 10mA,
TR=TF=100µs
±25
mV
VO2-PP
TDMA noise line transient
regulation
IO2=5 to 100mA; VINA,P
=2.9V to 3.4V; F=200Hz;
TR=TF=50µs; IMID no load
±25
mV
IO2
Maximum inverting output
current
VINA,P=2.9V to 4.5V
-200
Inverting peak current
VO2 below 10% of nominal
value
-1.2
P-channel static drain-source
ON resistance
VINA,P=3.7V, ISW=100mA
VO2
ΔVO2 LT
ΔVO2T
I-L2MAX
RDSONP2
DocID022614 Rev 2
-4.97
-4.9
mA
-0.9
0.42
A
W
9/25
25
Electrical characteristics
STOD03AS
Table 6. Electrical characteristics (continued)
Symbol
Parameter
RDSONN2
N-channel static drain-source
ON resistance
Test conditions
VINA,P=3.7V, ISW=100mA
Min.
Typ.
Max.
Unit
0.43
W
Thermal shutdown
OTP
Overtemperature protection
140
°C
OTPHYST
Overtemperature protection
hysteresis
15
°C
400
W
8
ms
Discharge resistor
RDIS
Resistor value
No load
TDIS
Discharge time
No load, VMID-VO2 at 10% of
nominal value
10/25
DocID022614 Rev 2
STOD03AS
5
Typical performance characteristics
Typical performance characteristics
VO2 = - 4.9 V; TA = 25 °C; See Table 1 for external components used in the tests below.
Figure 4. Efficiency vs. input voltage
Figure 5. Efficiency vs. output current
90%
90%
88%
85%
86%
84%
80%
75%
Efficiency [%]
80%
78%
76%
74%
Io=50mA
72%
Io=100mA
70%
Io=150mA
2.7
2.9
3.1
3.3
3.5
3.7
3.9
VIN=3.2V
VIN=3.7V
VIN=4.2V
55%
66%
2.5
VIN=2.7V
65%
60%
Io=200mA
68%
70%
4.1
4.3
50%
4.5
0
VIN [V]
20
40
60
80
100
120
140
160
180
200
IOUT [mA]
Figure 7. Max. power output vs. VIN,
TA = 25 °C
IOUT [mA]
Figure 6. Input current vs. VIN no load
500
4.0
450
3.5
400
3.0
350
2.5
300
2.0
250
POUT [W]
Efficiency [%]
82%
1.5
max IOUT at VO2 = -4.9V
200
max POUT
150
1.0
0.5
100
0.0
2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5
VIN [V]
Figure 8. Fast discharge VIN = 3.7 V, no load
Figure 9. Startup and inrush VIN = 3.7 V, no load
EN
VMID
VO2
IIN
DocID022614 Rev 2
11/25
25
Typical performance characteristics
STOD03AS
Figure 10. Step-up CCM operation
VEN = VINA = VINP = 3.7 V, IMID = 100 mA, TA = 25 °C
Figure 12. Line transient
Figure 11. Inverting CCM operation
VEN = VINA = V INP = 3.7 V, IO2 = 100 mA, TA = 25 °C
Figure 13. Output voltage vs. input voltage
IO = 200 mA, VO2 = - 4.9 V
10.00
9.00
VIN
8.00
VO1+VO2 [V]
7.00
VMID
-40 °C
25 °C
85 °C
6.00
5.00
4.00
3.00
VO2
2.00
1.00
0.00
1.6
VINA = VINP = 2.9 to 3.4 V, IMID,O2 = 100 mA, TR = TF = 50 µs
12/25
DocID022614 Rev 2
1.8
2
2.2
2.4
VIN [V]
2.6
2.8
3
STOD03AS
Detailed description
6
Detailed description
6.1
SWIRE
6.1.1
6.1.2
6.1.3
•
Protocol: to digitally communicate over a single cable with single-wire components
•
Single-wire's 3 components:
1.
an external MCU
2.
wiring and associated connectors
3.
the STOD03AS device with a dedicated single-wire pin.
SWIRE features and benefits
•
Fully digital signal
•
No handshake needed
•
Protection against glitches and spikes though an internal low pass filter acting on falling
edges
•
Uses a single wire (plus analog ground) to accomplish both communication and power
control transmission
•
Simplified design with an interface protocol that supplies control and signaling over a
single-wire connection to set the output voltages.
SWIRE protocol
•
Single-wire protocol uses conventional CMOS/TTL logic levels (maximum 0.6 V for
logic “zero” and a minimum 1.2 V for logic “one”) with operation specified over a supply
voltage range of 2.5 V to 4.5 V
•
Both master (MCU) and slave (STOD03AS) are configured to permit bit sequential data
to flow only in one direction at a time; master initiates and controls the device
•
Data is bit-sequential with a START bit and a STOP bit
•
Signal is transferred in real time
•
System clock is not required; each single-wire pulse is self-clocked by the oscillator
integrated in the master and is asserted valid within a frequency range of 250 kHz
(maximum).
SWIRE basic operations
•
The negative output voltage levels are selectable within a wide range (steps of 100 mV)
•
The device can be enabled / disabled via SWIRE in combination with the Enable pin.
DocID022614 Rev 2
13/25
25
Detailed description
6.2
STOD03AS
Negative output voltage levels
Table 7. Negative output voltage levels
Pulse
VO2
Pulse
VO2
Pulse
VO2
1
-5.4
11
-4.4
21
-3.4
2
-5.3
12
-4.3
22
-3.3
3
-5.2
13
-4.2
23
-3.2
4
-5.1
14
-4.1
24
-3.1
5
-5.0
15
-4.0
25
-3.0
(1)
-4.9
16
-3.9
26
-2.9
7
-4.8
17
-3.8
27
-2.8
8
-4.7
18
-3.7
28
-2.7
9
-4.6
19
-3.6
29
-2.6
10
-4.5
20
-3.5
30
-2.5
31
-2.4
6
1. Default output voltage.
Table 8. Enable and SWIRE operation table (1)
Enable
SWIRE
Action
Low
Low
Device off
Low
High
Negative output set by SWIRE
High
Low
Default negative output voltage
High
High
Default negative output voltage
1. The Enable pin must be set to AGND while using the SWIRE function.
14/25
DocID022614 Rev 2
STOD03AS
Application information
7
Application information
7.1
External passive components
7.1.1
Inductor selection
Magnetic shielded low ESR power inductors must be chosen as the key passive
components for switching converters.
For the step-up converter an inductance between 4.7 µH and 6.8 µH is recommended.
For the inverting stage the suggested inductance ranges from 3.3 µH to 4.7 µH.
It is very important to select the right inductor according to the maximum current the inductor
can handle to avoid saturation. The step-up and the inverting peak current can be calculated
as follows:
Equation 1
IPEAK −BOOST =
VMID × IOUT VINMIN × (VMID − VINMIN )
+
η1× VINMIN
2 × VMID × fs × L1
Equation 2
I PEAK - INVERTING =
(VIN M IN - VO 2 M IN ) x I OUT
VIN M IN x VO 2 MIN
+
η 2 x VIN M IN
2 x (VO 2 MIN - VIN M IN ) x fs xL 2
where
VMID: step-up output voltage, fixed at 4.6 V;
VO2: inverting output voltage including sign (minimum value is the absolute maximum
value);
IO: output current for both DC-DC converters;
VIN: input voltage for the STOD03AS;
fs: switching frequency. Use the minimum value of 1.2 MHz for the worst case;
η1: efficiency of step-up converter. Typical value is 0.85;
η2: efficiency of inverting converter. Typical value is 0.75.
The negative output voltage can be set via SWIRE at - 5.4 V. Accordingly, the inductor peak
current, at the maximum load condition, increases. A proper inductor, with a saturation
current as a minimum of 1 A, is preferred.
7.1.2
Input and output capacitor selection
It is recommended to use X5R or X7R low ESR ceramic capacitors as input and output
capacitors in order to filter any disturbance present in the input line and to obtain stable
operation for the two switching converters. A minimum real capacitance value of 6 µF must
be guaranteed for CMID and CO2 in all conditions. Considering tolerance, temperature
variation and DC polarization, a 10 µF, 10 V ±10% capacitor as CMID and 2 x 10 µF, 10 V
±10% as CO2, can be used to achieve the required 6 µF.
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Application information
7.2
STOD03AS
Recommended PCB layout
The STOD03AS is high frequency power switching device and therefore requires a proper
PCB layout in order to obtain the necessary stability and optimize line/load regulation and
output voltage ripple.
Analog input (VINA) and power input (VINP) must be kept separated and connected together
at the CIN pad only. The input capacitor must be as close as possible to the IC.
In order to minimize the ground noise, a common ground node for power ground and a
different one for analog ground must be used. In the recommended layout, the AGND node
is placed close to CREF ground while the PGND node is centered at CIN ground. They are
connected by a separated layer routing on the bottom through vias.
The exposed pad is connected to AGND through vias.
Figure 14. Top layer and silk-screen (top view, not to scale)
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Figure 15. Bottom layer and silk-screen (top view, not to scale)
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Detailed description
STOD03AS
8
Detailed description
8.1
General description
The STOD03AS is a high efficiency dual DC-DC converter which integrates a step-up and
inverting power stage suitable for supplying AMOLED panels. Thanks to the high level of
integration it needs only 6 external components to operate and it achieves very high
efficiency using a synchronous rectification technique for each of the two DC-DC
converters.
The controller uses an average current mode technique in order to obtain good stability and
precise voltage regulation in all possible conditions of input voltage, output voltage, and
output current. In addition, the peak inductor current is monitored in order to avoid saturation
of the coils.
The STOD03AS implements a power saving technique in order to maintain high efficiency at
very light load and it switches to PWM operation as the load increases in order to guarantee
the best dynamic performances and low noise operation.
The STOD03AS avoids battery leakage thanks to the true-shutdown feature and it is self
protected from overtemperature. Undervoltage lockout and soft-start guarantee proper
operation during startup.
8.1.1
Multiple operation modes
Both the step-up and the inverting stage of the STOD03AS operate in three different modes:
pulse skipping (PS), discontinuous conduction mode (DCM) and continuous conduction
mode (CCM). It switches automatically between the three modes according to input voltage,
output current, and output voltage conditions.
8.1.2
Pulse skipping operation
The STOD03AS works in pulse skipping mode when the load current is below some tens of
mA. The load current level at which this way of operation occurs depends on input voltage
only for the step-up converter and on input voltage and negative output voltage (VO2) for the
inverting converter.
8.1.3
Discontinuous conduction mode
When the load increases above a few mA, the STOD03AS enters DCM operation. In order
to obtain this type of operation the controller must avoid the inductor current going negative.
The discontinuous mode detector (DMD) blocks sense the voltage across the synchronous
rectifiers (P1B for the step-up and N2 for the inverting) and turn off the switches when the
voltage crosses a defined threshold which, in turn, represents a certain current in the
inductor. This current can vary according to the slope of the inductor current which depends
on input voltage, inductance value, and output voltage.
8.1.4
Continuous conduction mode
At medium/high output loads, the STOD03AS enters full CCM at constant switching
frequency mode for each of the two DC-DC converters.
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8.1.5
Detailed description
Enable pin
The device operates when the EN pin is set high. If the EN pin is set low, the device stops
switching, and all the internal blocks are turned off. In this condition the current drawn from
VINP/VINA is below 1 µA in the whole temperature range. In addition, the internal switches
are in an OFF state so the load is electrically disconnected from the input, this avoids
unwanted current leakage from the input to the load.
When the EN is pulled high, the P1B switch is turned on for 100 µs. In normal operation,
during this time, apart of a small drop due to parasitic resistance, VMID reaches VIN.
If, after this 100 µs, VMID stays below VIN, the P1B is turned off and stays off until a new
pulse is applied to the EN. This mechanism avoids the STOD03AS starting if a short-circuit
is present on VMID.
8.1.6
Soft-start and inrush current limiting
After the EN pin is pulled high, or after a suitable voltage is applied to VINP, VINA and EN, the
device initiates the startup phase.
As a first step, the CMID capacitor is charged and the P1B switch implements a current
limiting technique in order to keep the charge current below 400 mA. This avoids the battery
overloading during startup.
After VMID reaches the VINP voltage level, the P1B switch is fully turned on and the soft-start
procedure for the step-up is started. After around 2 ms the soft-start for the inverting is
started. The positive and negative voltages are under regulation at around 6 ms after the
EN pin is asserted high.
8.1.7
Undervoltage lockout
The undervoltage lockout function avoids improper operation of the STOD03AS when the
input voltage is not high enough. When the input voltage is below the UVLO threshold the
device is in shutdown mode. The hysteresis of 50mV avoids unstable operation when the
input voltage is close to the UVLO threshold.
8.1.8
Overtemperature protection
An internal temperature sensor continuously monitors the IC junction temperature. If the IC
temperature exceeds 140 °C, typical, the device stops operating. As soon as the
temperature falls below 125 °C, typical, normal operation is restored.
8.1.9
Short-circuit protection
When short-circuit occurs, the device is able to detect the voltage difference between VIN
and VMID. Overshoots on LX1 are limited, decreasing the inductor current. After that, the
output stages of the device are turned off. This status is maintained, avoiding current flowing
to the load. A new ENABLE transition is needed to restart the device. During startup the
short-circuit protection is active.
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Detailed description
8.1.10
STOD03AS
Fast discharge
When ENABLE turns from high to low level, the device goes into shutdown mode and LX1
and LX2 stop switching. Then, the discharge switch between VMID and VIN and the switch
between VO2 and GND turn on and discharge the positive output voltage and negative
output voltage. When the output voltages are discharged to 0 V, the switches turn off and
the outputs are high impedance.
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9
Package mechanical data
Package mechanical data
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.
Table 9. DFN 12L 3X3 mechanical data
mm
Dim.
Min.
Typ.
Max.
A
0.51
0.55
0.60
A1
0
0.02
0.05
A3
0.20
b
0.18
0.25
0.30
D
2.85
3
3.15
D2
1.87
2.02
2.12
E
2.85
3
3.15
E2
1.06
1.21
1.31
e
L
0.45
0.30
0.40
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STOD03AS
Figure 16. DFN 12L 3X3 drawing
8085116_B
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Package mechanical data
Figure 17. DFN 12L 3X3 footprint (a)
8085116_B
a. All dimensions are in millimeters
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Revision history
10
STOD03AS
Revision history
Table 10. Document revision history
Date
Revision
20-Dec-2011
1
Initial release.
28-Jul-2013
2
Updated Table 5: Thermal data on page 7, Table 6: Electrical characteristics
on page 8 and Section 9: Package mechanical data.
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