STOD13A
250 mA dual DC-DC converter
for powering AMOLED displays
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 250 mA output current
■
4.6 V fixed positive output voltage
■
Programmable negative voltage by SWIRE from
-2.4 V to -6.4 V at 100 mV steps
■
Typical efficiency 85%
■
Pulse skipping mode in light load condition
■
1.5 MHz PWM mode control switching
frequency
Description
■
TDMA noise high immunity
■
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 outputs discharge circuit after shutdown
■
Short-circuit protection
■
Package DFN12L (3 x 3) 0.6 mm height
The STOD13A is a dual DC-DC converter 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
low 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 single-wire protocol. Soft-start
with controlled inrush current limit, thermal
shutdown and short-circuit protection are
integrated functions of the device.
DFN12L (3 x 3 mm)
Applications
■
Active matrix AMOLED power supply in
portable devices
■
Cellular phones
■
Camcorders and digital still cameras
■
Multimedia players
Table 1.
Device summary
Order code
Positive voltage
Negative voltage
Package
Packaging
STOD13ATPUR
4.6V
-2.4V to -6.4V
DFN12L (3 x 3mm)
3000 parts per reel
December 2011
Doc ID 022599 Rev 1
1/24
www.st.com
24
Contents
STOD13A
Contents
1
Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5
Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6
Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1
6.2
7
7.2
2/24
SWIRE features and benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1.2
SWIRE protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1.3
SWIRE basic operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Negative output voltage levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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
9
6.1.1
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1
8
SWIRE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1.1
Multiple operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1.2
Enable pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.3
Soft-start and inrush current limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.4
Undervoltage lockout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.5
Overtemperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.6
Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1.7
Fast discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Doc ID 022599 Rev 1
STOD13A
10
Contents
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Doc ID 022599 Rev 1
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Schematic
1
STOD13A
Schematic
Figure 1.
Application schematic
L1
VBAT
CIN
VINP
LX1
VINA
VMID
S-Wire
CMID
Swire
STOD13A
EN
EN
VO2
CO2
FD
FD
VREF
CREF
PGND AGND
LX2
L2
AM10430v1
Table 2.
Typical external components
Comp. Manufacturer
Part number
Value
Size
Ratings
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
±20%, curr. 1.7A, res. 0.175Ω
±20%, curr. 1.1A, res. 0.156Ω
±20%, curr. 1.1A, res. 0.300Ω
±20%, curr. 0.85A, res. 0.33Ω
LPS4012-472ML
4.0 x 4.0 x 1.2
LQH3NPN4R7MJ0
4. 7µH 3.0 x 3.0 x 1.1
DFE252012C 1239AS-H-4R7N
2.5 x 2.0 x 1.2
±20%, curr. 1.7A, res. 0.175Ω
±20%, curr. 1.1A, res. 0.156Ω
±30%, curr. 1.2A, res. 0.252Ω
L1 (1)
CoilCraft
Murata
SEMCO
ABCO
L2 (2)
CoilCraft
Murata
TOKO
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
LPS4012-472ML
LQH3NPN4R7MJ0
CIG22B4R7MNE
LPF2810T-4R7M
1. A 250 mA load can be provided with inductor saturation current as a minimum of 0.9 A.
2. At -6.4 V, a 250 mA load can be provided with inductor saturation current as a minimum of 1.5 A. See Section 7.1.1.
Note:
4/24
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 STOD13A.
Doc ID 022599 Rev 1
STOD13A
Schematic
Figure 2.
Block schematic
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Pin configuration
2
STOD13A
Pin configuration
Figure 3.
Pin configuration (top view)
Table 3.
Pin description
Pin name
Pin number
Lx1
1
Boost converter switching node.
PGND
2
Power ground pin.
VMID
3
Boost converter output voltage.
FD
4
Fast discharge control pin. When pulled LOW the fast discharge after
shutdown is active. When pulled HIGH the fast discharge is OFF.
AGND
5
Signal ground pin. This pin must be connected to the power ground
layer.
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. high = converter on; low = converter in shutdown
mode.
VO2
9
Inverting converter output voltage.
Lx2
10
Inverting converter switching node.
VIN A
11
Analogic input supply voltage.
VIN P
12
Power input supply voltage.
Exposed
Pad
6/24
Description
Internally connected to AGND. Exposed pad must be connected to
ground layers in the PCB layout in order to guarantee proper operation
of the device.
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STOD13A
3
Maximum ratings
Maximum ratings
Table 4.
Absolute maximum ratings
Symbol
Parameter
Value
Unit
- 0.3 to 6
V
VINA, VINP
DC supply voltage
EN, SWIRE
Logic input pins
- 0.3 to 4.6
V
FD
Logic input pin
- 0.3 to VINA+0.3
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 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’s switching current
Internally limited
A
VREF
Reference voltage
- 0.3 to 3
V
PD
Power dissipation
Internally limited
mW
TST
Storage temperature range
- 65 to 150
°C
Maximum junction temperature
+150
°C
Human body model protection
±2
kV
Machine body model protection
± 200
V
TJ
ESD
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.
Symbol
RthJA
RthJC
Thermal data
Parameter
Thermal resistance junction-ambient
Thermal resistance junction-case (FR-4 PCB)
(1)
Value
Unit
33
°C/W
2.12
°C/W
1. The package is mounted on a 4-layer (2S2P) JEDEC board as per JESD51-7.
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Electrical characteristics
4
STOD13A
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
2.5
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
VINA=2.5V to 4.5V,
TJ=-40°C to +85°C
VEN L
Enable low threshold
IEN
Enable input current
VEN=VINA=4.5V;
TJ=-40°C to +85°C
VFD H
Fast discharge high threshold
VINA=2.5V to 4.5V,
TJ=-40°C to +85°C
VFD L
Fast discharge low threshold
I_VI
fs
1.9
2.18
1.7
V
2.1
mA
1
µA
1.2
V
0.4
1
1.2
µA
V
0.4
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
78
%
IMID,O2=30 to 150mA, VMID=4.6V,
VO2=-4.9V
85
IMID,O2=150 to 250mA,
VMID=4.6V, VO2=-4.9V
82
Total system efficiency
VREF
Reference voltage
IREF=10µA
IREF
Reference current capability
At 98.5% of no load
reference voltage
1.35
1.208
1.5
1.220
1.65
1.232
100
MHz
V
µA
Step-up converter section
Positive output voltage
VMID
ΔVMID LT
8/24
4.6
Positive output voltage total
variation
VINA=VINP=2.9V to 4.5V;
IMID=5mA to 250mA, IO2 no load
TJ = -40°C to +85°C
Line transient
VINA,P=3.4V to 2.9V, IMID=100mA;
TR=TF=10µs
Doc ID 022599 Rev 1
-0.8
V
0.8
-10
%
mV
STOD13A
Table 6.
Electrical characteristics
Electrical characteristics (continued)
Symbol
ΔVMID T
Parameter
Load transient response
Test conditions
Min.
Max.
Unit
IMID=3 to 30mA and IMID=30 to
3mA, TR=TF=150µs
±20
mV
IMID=10 to 100mA and IMID=100
to 10mA, TR=TF=150µs
±25
mV
Undershoot/overshoot
TDMA Noise Static variation between low
and high VIN level
Typ.
±20
IMID=10 to 100mA; IO2 no load
IMID MAX
Maximum output current
I-L1MAX
Step-up inductor peak current VMID 10% below nominal value
(1)
mV
4
VINA,P=2.9V to 4.5V
250
mA
1.08
1.32
A
RDSONP1
P-channel static drain-source
ON resistance
VINA=VINP=3.7V, ISW-P1=100mA
1.0
2.0
Ω
RDSONN1
N-channel static drain-source
ON resistance
VINA=VINP=3.7V, ISW-N1=100mA
0.4
1.0
Ω
-2.4
V
Inverting converter section
Negative output voltage range
VO2
ΔVO2 LT
ΔVO2 T
41 different values set by the
SWIRE pin (see Section 6.1.2)
-6.4
Negative output voltage
-4.9
V
Negative output voltage total
variation
VINA=VINP=2.9V to 4.5V;
IO2=5mA to 250mA, IMID no load
TJ=-40°C to +85°C
Line transient
VINA,P=3.4V to 2.9V, IO2=100mA,
TR=TF=10µs
+10
mV
IO2=3 to 30mA and IO2=30 to
3mA, TR=TF=150µs
± 20
mV
IO2=10 to 100mA and IO2=100 to
10mA, TR=TF=150µs
± 25
mV
± 20
mV
Load transient response
-1.7
Undershoot/overshoot
TDMA Noise Static variation between low
and high VIN level
IO2=10 to 100mA; IMID no load
1.7
%
(1)
5
IO2 MAX
Maximum output current
VINA,P=2.9V to 4.5V
-250
I-L2MAX
Inverting peak current
VO2 below 10% nominal value
-1.43
RDSONP2
P-channel static drain-source
ON resistance
VINA=VINP=3.7V, ISW-P2=100mA
RDSONN2
N-channel Static Drain-source
VINA=VINP=3.7V, ISW-N2=100mA
ON resistance
mA
-1.17
A
0.42
0.8
Ω
0.43
0.8
Ω
Thermal shutdown
OTP
Overtemperature protection
140
°C
OTPHYST
Overtemperature protection
hysteresis
15
°C
Doc ID 022599 Rev 1
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Electrical characteristics
Table 6.
STOD13A
Electrical characteristics (continued)
Symbol
Parameter
Test conditions
Min.
Typ.
Max.
Unit
Discharge resistor
RDIS
Resistor value
No load, EN=SW=FD=Low
400
Ω
TDIS
Discharge time
No load, EN=SW=FD=Low, VMIDVO2 at 10% of nominal value
10
ms
1. VINA,P = 4.2 to 3.7 V, 3.7 to 3.2 V, 3.4 to 2.9 V, f = 200 Hz; tON = 3.65 ms; tOFF = 1.25 ms; TR = TF = 10 µs, pulse signal.
10/24
Doc ID 022599 Rev 1
STOD13A
5
Typical performance characteristics
Typical performance characteristics
VINA = VINP = 3.7 V, VO2 = - 4.9 V, TJ = 25°C; see Table 1 for external components used in
the tests below.
Figure 4.
Maximum power output vs. input
voltage (VINA = VINP = 2.9 to 4.2 V)
Figure 5.
Efficiency vs. output current
VINA = VINP = 3.3 to 4.2 V, IMID,O2 = 10 to 250 mA
Figure 6.
Efficiency vs. inductor
Figure 7.
Soft-start and inrush current (no
load)
Figure 9.
Switching and output waveforms
IMID,O2 = 10 to 250 mA, L1 = L2
Figure 8.
Fast discharge
No load, EN = SW = FD = Low
VINA = VINP = 2.9 V, IMID,O2 = 250 mA, TJ = 85 °C
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Typical performance characteristics
STOD13A
Figure 10. Step-up CCM operation
Figure 11. Inverting CCM operation
IMID = 100 mA
IO2 = 100 mA
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STOD13A
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 STOD13A 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 both
rising and 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 (STOD13A) 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.
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Detailed description
STOD13A
6.2
Negative output voltage levels
Table 7.
Negative output voltage levels
Pulse
VO2
Pulse
VO2
Pulse
VO2
Pulse
VO2
1
-6.4
11
-5.4
21
-4.4
31
-3.4
2
-6.3
12
-5.3
22
-4.3
32
-3.3
3
-6.2
13
-5.2
23
-4.2
33
-3.2
4
-6.1
14
-5.1
24
-4.1
34
-3.1
5
-6.0
15
-5.0
25
-4.0
35
-3.0
6
-5.9
16 (1)
-4.9
26
-3.9
36
-2.9
7
-5.8
17
-4.8
27
-3.8
37
-2.8
8
-5.7
18
-4.7
28
-3.7
38
-2.7
9
-5.6
19
-4.6
29
-3.6
39
-2.6
10
-5.5
20
-4.5
30
-3.5
40
-2.5
41
-2.4
1. Default value.
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.
Table 9.
Fast Discharge operation table
FD pin
Action
Low
Fast discharge active after IC shutdown
High
No fast discharge function
The FD function is only controlled by the FD pin. It is not related to the enable block.
14/24
Doc ID 022599 Rev 1
STOD13A
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 =
(VINMIN - VO2MIN ) x I OUT
VINMIN x VO 2 MIN
+
η 2 x VINMIN
2 x (VO 2MIN - VINMIN ) x fs xL2
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 STOD03A;
fs: switching frequency. Use the minimum value of 1.35 MHz for the worst case;
η1: efficiency of step-up converter. Typical value is 0.70;
η2: efficiency of inverting converter. Typical value is 0.60.
The negative output voltage can be set via SWIRE at - 6.4 V. Accordingly, the inductor peak
current, at the maximum load condition, increases. A proper inductor, with a saturation
current as a minimum of 1.5 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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15/24
Application information
7.2
STOD13A
Recommended PCB layout
The STOD13A 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 12. Top layer and silk-screen (top view, not to scale)
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Application information
Figure 13. Bottom layer (top view, not to scale)
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Detailed description
STOD13A
8
Detailed description
8.1
General description
The STOD13A 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 STOD13A 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 STOD13A 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 STOD13A operate in three different modes:
pulse skipping (PSM), 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.
Pulse skipping operation:
The STOD13A works in pulse skipping mode when the load current is below a few 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.
Discontinuous conduction mode:
When the load increases above some tens of mA, the STOD13A 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.
Continuous conduction mode:
At medium/high output loads, the STOD13A enters in full CCM at constant switching
frequency mode for each of the two DC-DC converters.
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8.1.2
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.
8.1.3
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, 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 6ms after the EN pin is asserted high.
8.1.4
Undervoltage lockout
The undervoltage lockout function avoids improper operation of the STOD13A 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 50 mV avoids unstable operation when the
input voltage is close to the UVLO threshold.
8.1.5
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.
8.1.6
Short-circuit protection
When short-circuit occurs, the device is able to detect the voltage difference between VIN
and VOUT. Overshoots 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 shortcircuit protection is active.
8.1.7
Fast discharge
When ENABLE turns from high to low level and the FD pin is low, 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. When the FD pin is high, the fast
discharge after shutdown is off.
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Package mechanical data
9
STOD13A
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 registered trademark.
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Package mechanical data
DFN12L (3 x 3 x 0.6 mm) mechanical data
mm.
inch.
Dim.
Min.
Typ.
Max.
Min.
Typ.
Max.
A
0.51
0.55
0.60
0.020
0.022
0.024
A1
0
0.02
0.05
0
0.001
0.002
A3
0.20
0.008
b
0.18
0.25
0.30
0.007
0.010
0.012
D
2.85
3
3.15
0.112
0.118
0.124
D2
1.87
2.02
2.12
0.074
0.080
0.083
E
2.85
3
3.15
0.112
0.118
0.124
E2
1.06
1.21
1.31
0.042
0.048
0.052
e
L
0.45
0.30
0.40
0.018
0.50
0.012
0.016
0.020
8085116/A
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Package mechanical data
STOD13A
Figure 14. DFN12L (3 x 3 mm) footprint recommended data
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Revision history
10
Revision history
Table 10.
Document revision history
Date
Revision
14-Dec-2011
1
Changes
Initial release.
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STOD13A
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