STOD03AS 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 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 ■ 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 Applications ■ Active matrix AMOLED power supply ■ Cellular phones ■ Camcorders and digital still cameras ■ Multimedia players Table 1. DFN12L (3 x 3 mm) Description 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. 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 December 2011 Doc ID 022614 Rev 1 1/24 www.st.com 24 Contents STOD03AS 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 SWIRE features and benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1.2 SWIRE protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1.3 SWIRE basic operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Negative output voltage levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 External passive components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.1.1 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.1.2 Input and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Recommended PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1 2/24 6.1.1 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.1 8 SWIRE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1.1 Multiple operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1.2 Pulse skipping operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1.3 Discontinuous conduction mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1.4 Continuous conduction mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1.5 Enable pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1.6 Soft-start and inrush current limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1.7 Undervoltage lockout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1.8 Overtemperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1.9 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Doc ID 022614 Rev 1 STOD03AS Contents 8.1.10 Fast discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Doc ID 022614 Rev 1 3/24 Schematic 1 STOD03AS Schematic Figure 1. Application schematic 6"!4 , #). 6).0 , 8 6-)$ 6).! #-)$ 37)2% 37IRE 34/$!3 6/ %. %. 62%& #2%& #/ 0'.$ !'.$ , 8 , !-V 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: 4/24 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 STOD03AS. Doc ID 022614 Rev 1 STOD03AS Schematic Figure 2. Block schematic 6).0 ,8 $-$ 6).! 56,/ 2).' +),,%2 6-)$ 0! 0" . 34%050 #/.42/, %. &!34 $)3#(!2'% ,/')##/.42/, /40 37)2% 3 7)2% /3# $-$ 6).0 6/ . 0 62%& 3WIRE CONTROL 62%& ).6%24).' !'.$ 62%& #/.42/, &!34 $)3#(!2'% 0'.$ ,8 Doc ID 022614 Rev 1 !-V 5/24 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 6/24 Doc ID 022614 Rev 1 STOD03AS Maximum ratings 3 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 Storage temperature range Maximum junction temperature ESD protection HBM 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 RthJA RthJC 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. Doc ID 022614 Rev 1 7/24 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 η 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 1.7 V 2.1 mA 1 µA 1.2 V 0.4 1.2 1.216 1.5 1.228 1 µA 1.7 MHz 1.240 100 V µA Step-up converter section VMID ΔVMID LT 8/24 VINA=VINP=2.5V to 4.5V; Positive voltage total variation IMID=5mA to 150mA, IO2 no load, TJ=25°C 4.55 4.6 4.65 V Temperature accuracy VINA=VINP=3.7V; IMID=5mA; IO2 no load; TJ=-40°C to +85°C ±0.5 % Line transient VINA,P=3.5V to 3.0V, IMID=100mA; TR=TF=50µs -12 mV Doc ID 022614 Rev 1 STOD03AS Table 6. Symbol ΔVMIDT Electrical characteristics Electrical characteristics (continued) Parameter Load transient regulation Test conditions Min. Typ. Max. Unit 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 Ω 0.4 1.0 Ω -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 RDSONP2 P-channel static drain-source ON resistance VINA,P=3.7V, ISW=100mA 0.42 Ω RDSONN2 N-channel static drain-source ON resistance VINA,P=3.7V, ISW=100mA 0.43 Ω VO2 ΔVO2 LT ΔVO2T I-L2MAX Doc ID 022614 Rev 1 -4.97 -4.9 mA -0.9 A 9/24 Electrical characteristics Table 6. STOD03AS Electrical characteristics (continued) Symbol Parameter Test conditions Min. Typ. Max. Unit Thermal shutdown OTP Overtemperature protection 140 °C OTPHYST Overtemperature protection hysteresis 15 °C 400 Ω 8 ms Discharge resistor RDIS Resistor value No load TDIS Discharge time No load, VMID-VO2 at 10% of nominal value 10/24 Doc ID 022614 Rev 1 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] 40 60 80 100 120 140 160 180 200 IOUT [mA] Input current vs. VIN no load Figure 7. IOUT [mA] Figure 6. 20 Max. power output vs. VIN, TA = 25 °C 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 Doc ID 022614 Rev 1 11/24 Typical performance characteristics STOD03AS Figure 10. Step-up CCM operation Figure 11. Inverting CCM operation VEN = VINA = VINP = 3.7 V, IMID = 100 mA, TA = 25 °C VEN = VINA = VINP = 3.7 V, IO2 = 100 mA, TA = 25 °C Figure 12. Line transient 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 12/24 Doc ID 022614 Rev 1 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. Doc ID 022614 Rev 1 13/24 Detailed description STOD03AS 6.2 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 6 (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 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. 14/24 Doc ID 022614 Rev 1 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 = (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 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. Doc ID 022614 Rev 1 15/24 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) 16/24 Doc ID 022614 Rev 1 STOD03AS Application information Figure 15. Bottom layer and silk-screen (top view, not to scale) Doc ID 022614 Rev 1 17/24 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. 18/24 Doc ID 022614 Rev 1 STOD03AS 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. 8.1.10 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. Doc ID 022614 Rev 1 19/24 Package mechanical data 9 STOD03AS 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. 20/24 Doc ID 022614 Rev 1 STOD03AS Package mechanical data Table 9. DFN12L (3 x 3) mechanical data mm. inch. Dim. Min. Typ. Max. Min. Typ. Typ. 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 Figure 16. DFN12L (3 x 3) drawing 8085116-A Doc ID 022614 Rev 1 21/24 Package mechanical data STOD03AS Figure 17. DFN12L (3 x 3 mm) footprint recommended data 22/24 Doc ID 022614 Rev 1 STOD03AS Revision history 10 Revision history Table 10. Document revision history Date Revision 20-Dec-2011 1 Changes Initial release. Doc ID 022614 Rev 1 23/24 STOD03AS Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. 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