STOD14 STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 22
Technical content
Datasheet sections
- 1 Schematic
- 2 Pin configuration
- 3 Maximum ratings
- 4 Electrical characteristics
- 5 Typical performance characteristics
- 6 Application Information
- 6.1 Inductor selection
- 6.2 Input and output capacitor selection
- 6.3 Recommended PCB layout
- 7 Detailed description
- 7.1 Mode of operation
- 7.2 Enable pin
- 7.3 Soft-start and inrush current limiting
- 7.4 Startup sequence
- 7.5 Fast discharge
- 7.6 Undervoltage lockout
- 7.7 Overtemperature protection
- 7.8 Short-circuit startup detection (SSD)
- 7.9 Overload protection (OLP)
- 7.10 Short-circuit protection (SCP)
- 7.11 S-WIRE protocol description
- 7.12 Enable and S-WIRE operation
- 7.13 Programming negative output voltage
- 8 Package mechanical data
- 9 Revision history
Features
■ Step-down and inverter converters ■ Operating input voltage range from 6 V to 13 V ■ Synchronous rectification for both converters ■ 700 mA output current ■ Fixed positive voltage 4.6 V ■ Programmable negative voltage by SWIRE from - 2.4 V to - 6.0 V ■ Typical efficiency 85% ■ PWM mode controller @ 1.6 MHz switching frequency ■ Enable pin for shutdown mode ■ Low quiescent current in shutdown mode ■ Soft-start with inrush current protection ■ Short-circuit protection on positive output ■ Overtemperature protection ■ Temperature range - 40 °C to 85 °C ■ True shutdown mode ■ Fast output discharge after shutdown ■ Package DFN 4x4 mm 12 leads 0.75 mm height, 0.5 mm pitch
Applications
■ Digital photo frames ■ Ultra mobile PCs ■ Mobile Internet devices ■ Digital still cameras / camcorders ■ Portable media players / DVD players
Description
The STOD14 is a dual channel DC-DC converter driver for medium-sized AMOLED display panels. It integrates a step-down and an inverting converter in a compact IC design. The excellent efficiency makes it particularly suitable for battery operated products. The high frequency operation allows the value and size of external components to be reduced. The positive output voltage is fixed at 4.6 V with very high current capability and is generated using a buck converter. The negative output is programmable by an external MCU through a dedicated pin which implements single-wire protocol, with values from - 2.4 to - 6.0 V . Soft-start with controlled inrush current limit, load disconnect and thermal shutdown are integrated functions of the device. DFN12L (4 x 4 mm) Table 1. Device summary
1 Schematic
Figure 1. Application schematic Note: 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. Table 2. Typical external components
- Doubled C INP useful at low temperatures.
Figure 2. Block schematic
2 Pin configuration
Figure 3. Pin configuration (top view) Table 3. Pin description layout in order to guarantee proper operation of the device.
3 Maximum ratings
Note: Absolute maximum ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not implied. Table 4. Absolute maximum ratings Table 5. Thermal data
- The package is mounted on a 4-layer (2S2 P) JEDEC board as per JESD51-7 and JESD51-5.
4 Electrical characteristics
Table 6. Electrical characteristics
Table 6. Electrical characteristics (continued)
5 Typical performance characteristics
Figure 4. Total system efficiency @ 25 °C, (L1 = L2 = LPS4012-472MLB) Figure 5. Startup and inrush current Figure 6. Fast discharge Figure 7. Line transient (t R = 10 µs) Figure 8. Line transient (t F = 10 µs)
6 Application Information
6.1 Inductor selection
The inductor is the key passive component for switching converters. For the step-down converter an inductance between 3.3 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 a proper inductor according to the maximum current the inductor can handle in order to avoid saturation. The peak current for the step-down and the inverting can be calculated with the following formulas: Equation 1 Equation 2 where V O1 is step-down output voltage VO2 is inverting output voltage including sign IO is output current for both DC-DC converters VIN is input voltage; use minimum of operating voltage fs is switching frequency; use the minimum value of 1.44 MHz for worst case η2 is inverter efficiency; typ. 85% L1 is buck inductor value; including tolerance L2 is inverter inductor value; including tolerance.
6.2 Input and output capacitor selection
It is recommended to use ceramic capacitors with low ESR as input and output capacitors in order to filter any disturbance present in the input line and to get stable operation for the switching converters.
6.3 Recommended PCB layout
The STOD14 is a high frequency power switching device so it requires a proper PCB layout in order to obtain the necessary stability and optimize line/load regulation and output voltage ripple. Analog input (V INA) 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. To minimize the ground noise, a common ground node for power ground and a different one for analog ground must be used. The exposed pad is connected to AGND through vias. O IN1O1OBUCK_PEAK ILf2 V/V1VI +⋅⋅ −⋅= IN2 2OINO IN2O2s 2OININV_PEAK V VVI VVLf2 VVI ⋅η −+−⋅⋅
STOD14 Detailed description Doc ID 023562 Rev 1 13/22
7 Detailed description
The STOD14 is a high efficiency dual DC-DC converter which integrates a step-down 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 both the 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 inductor saturation. The STOD14 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.
7.1 Mode of operation
To guarantee the minimal output voltage ripple, the device works just in continuous conduction mode (CCM). In this mode, reverse current pulses flowing back to the power supply can appear, especially at low load.
7.2 Enable pin
The device operates when the Enable pin is set high. If the Enable pin is set low, the device stops switching, and all the internal blocks are turned off. 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 P1 switch is turned on for 100 µs. In normal operation, during this time, apart of a small drop due to parasitic resistance, V O1 reaches VIN. After 100 µs, if VO1 stays below VIN, the P1 is turned off and stays off until a new pulse is applied to EN. This mechanism avoids the device starting if a short-circuit is present on VO1.
7.3 Soft-start and inrush current limiting
As a first step, the CO1 capacitor is charged, the P1 switch implements a current limiting technique in order to keep the charge current below 400 mA. This avoids battery overloading during startup. After VO1 reaches VINP voltage level, the P1 switch is fully turned on and the soft-start procedure for the step-down is started. After around 2 ms the soft-start for the inverting is started. The positive and negative voltage is under regulation around 6 ms after the Enable pin is asserted high.
7.4 Startup sequence
After the Enable pin is pulled high, or after a suitable voltage is applied to VINP, VINA and the Enable pin, the device begins the startup phase. The positive and negative voltages are
Detailed description STOD14 14/22 Doc ID 023562 Rev 1 under regulation about 10 ms after the Enable pin is asserted high. The short-circuit protection is designed to prevent overload, performing a dynamic current limitation on both output pins. At light load condition (up to 150 mA), the load can be connected during the startup phase. At medium/high load condition (above 150 mA), the proper sequence needs the startup phase to be entirely completed before connecting a load.
7.5 Fast discharge
When the device goes into shutdown mode and LX1 and LX2 stop switching, the discharge switch between V O1 and VIN and the switch between VO2 and GND turn on and discharge the positive and the negative output voltages. After output voltages are discharged to zero, the switches turn off and the outputs stay in high impedance state.
7.6 Undervoltage lockout
The undervoltage lockout function avoids improper operation of the device 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 avoids unstable operation at input voltage levels close to the UVLO threshold.
7.7 Overtemperature protection
An internal temperature sensor continuously monitors the IC junction temperature. If the temperature exceeds the specified value (see Table 5) the device stops operating. As soon as the temperature falls below the threshold (including hysteresis), normal operation is restored.
7.8 Short-circuit startup detection (SSD)
During device soft-start on positive output, an internal comparator checks load condition to detect eventual panel damage. In such case soft-start is stopped and the device is parked in power-off. To reset the normal functionality (assuming that the anomalous load condition was removed), it is necessary to restart the converter by an enable transient. If no damage is detected during soft-start on the positive output, the startup procedure follows with negative output soft-start to reach, at the end, normal outputs functionality and voltages.
7.9 Overload protection (OLP)
Output current is internally limited. An overload condition, as a short-circuit between the two outputs or between each output and GND, produces the device power-off. To reset normal functionality (assuming that the short condition was removed), it is necessary to restart the converter by an enable transient.
7.10 Short-circuit protection (SCP)
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
7.11 S- WIRE protocol description
Protocol to digitally communicate over a single cable with single-wire components.
- 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
- Simple design with an interface protocol that supplies control and signaling over a single-wire connection to set the output voltages. S-WIRE protocol
- Single-wire protocol uses conventional CMOS/TTL logic levels (maximum 0.6 V for logic “zero” and a minimum 1.2 V for the logic “one”) with operation specified over a supply voltage range of 2.5 V to 4.5 V
- Both master (MCU) and slave (this device) 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 asserted valid within a frequency range of 250 kHz (maximum). S-WIRE basic operations The negative output voltage levels are selectable within a wide range (steps of 100 mV). The device can be enabled / disabled via S- WIRE in combination with the Enable pin.
7.12 Enable and S- WIRE operation
functionality for all combinations. Table 8. EN and S- WIRE operation table
Note: Enable pin must be set to AGND while using the S- WIRE function.
7.13 Programming negative output voltage
according to the following table. Table 9. Negative output voltage programming levels
8 Package mechanical data
Table 10. DFN12L (4 x 4) mechanical data
Figure 14. DFN12L (3 x 3) drawing
Dim. mm. inch. A 330 12. 992 C 12. 8 13.2 0.504 0.51 9 D 20.2 0.7 95 N 99 101 3.898 3 .976 T 14.4 0.567 Ao 4. 35 0.171 Bo 4. 35 0.171 Ko 1.1 0.04 3 Po 4 0.157 P 8 0.315 Tape & reel QFNxx/DFNxx (4x4) mechanical data
Figure 15. DFN12L footprint recommended data (dimensions in millimeters)
9 Revision history
Table 11. Document revision history 16-Aug-2012 1 Initial release.