STBB1-AXX STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 24
Technical content
Datasheet sections
- 1 Block diagram
- 2 Absolute maximum ratings
- 3 Pin configuration
- 4 Typical application
- 5 Electrical characteristics
- 6 Detailed description
- 6.1 General description
- 6.2 Dual mode operation
- 6.3 External synchronization
- 6.4 Enable pin
- 6.5 Protection features
- 6.5.1 Soft-start and short-circuit
- 6.5.2 Undervoltage lockout
- 6.5.3 Overtemperature protection
- 7 Typical performance characteristics
- 8 Application information
- 8.1 Programming the output voltage
- 8.2 Inductor selection
- 8.3 Input and output capacitor selection
- 9 Recommended PCB layout
- 10 Package mechanical data
- 10.1 DFN10 (3X3 mm) mechanical data
- 11 Revision history
Features
Buck-boost DC-DC converter Operating input voltage range from 2.0 V to 5.5 V 2% DC feedback voltage tolerance Synchronous rectification Shutdown function 1.5 MHz switching frequency Power save mode at light load Typical efficiency: > 94% 1 A output current capability Shutdown current < 1 µA Available in DFN10 (3x3 mm)
Applications
Single cell Li-Ion and 3 cells alkaline, Ni-MH powered devices SD/MMC memory card supply Palmtop computers Cell phones Digital cameras
Description
The STBB1-AXX is a fixed frequency, high efficiency, buck-boost DC-DC converter able to provide output voltages ranging from 1.2 V to 5.5 V and input voltages from 2.0 V to 5.5 V. The device can operate with input voltages higher than, equal to, or lower than the output voltage making the product suitable for single lithium-Ion, multicell alkaline or NiMH applications where the output voltage is within the battery voltage range. The integrated low-RDS(on) N-channel and P-channel MOSFET switches contribute to its high efficiency. The mode pin allows the selection between auto mode and forced PWM mode thus taking benefit either of lower power consumption or better dynamic performance. The device also includes soft-start control, thermal shutdown and current limit. The STBB1-AXX is packaged in DFN10 (3x3 mm). Table 1: Device summary Order code Package Packing STBB1-APUR DFN10 (3x3 mm) Tape and reel
1 Block diagram
Figure 1: STBB1-AXX block diagram control G ate C urrent s ens or VR E F Os cillator control T emperature S W 1 S W 2 VO UT F B P G ND Modulator G ND MO DE /S Y NC V INA E N VIN Device control GIPG3107141209LM
2 Absolute maximum ratings
Table 2: Absolute maximum ratings Symbol Parameter Value Unit VINA, VIN Input voltage -0.3 to 7 V VOUT Output voltage -0.3 to 7 V SW1, SW DC voltage -0.3 to 7 V FB DC voltage -0.3 to 1.5 V MOD/SYNC, EN DC voltage -0.3 to 7 V TJ Maximum junction temperature 150 °C TSTG Storage temperature range -65 to +150 °C TJOP Operating junction temperature range -40 to +85 °C ESD Human body model 2 kV Absolute maximum ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not implied. Table 3: Thermal data Symbol Parameter Value Unit RTHJC Thermal resistance junction-case 2.96 °C/W RTHJA Thermal resistance junction-ambient 30.9 °C/W
STBB1-AXX Pin configuration
3 Pin configuration
Figure 2: Pin connection (top view) Table 4: Pin description Pin Symbol Name and function
1 VOUT Output voltage
2 SW2 Switch pin. Internal switches are connected to this pin. Connect inductor between SW1 to SW2
3 PGND Power ground
4 SW1 Switch pin. Internal switches are connected to this pin. Connect inductor between SW1 and SW2 5 VIN Power input voltage. Connect a ceramic bypass capacitor (10 µF minimum) between this pin and PGND 6 EN Enable pin. Connect this pin to GND or a voltage lower than 0.4 V to shut down the IC. A voltage higher than 1.2 V is required to enable the IC
7 MODE (SYNC)
Operation mode selection. If MODE pin is low, the STBB1-AXX automatically switches between pulse skipping and fixed frequency PWM according to the load level. If MODE pin is pulled high, the STBB1-AXX works in PWM mode. When a square waveform is applied, this pin provides the clock signal for oscillator synchronization
8 VINA Supply voltage for control stage
9 GND Signal ground
10 FB Feedback voltage
Typical application STBB1-AXX
4 Typical application
Figure 3: Application circuit (adjustable output version) Table 5: List of external components Component Manufacturer Part number Value Size CIN Murata GRM21BR71A106KE51 L 10 µF 0805 COUT Murata GRM21BR60J226ME39 L 22 µF 0805 L TDK VLCF4020T-2R2N1R7 2.2 µH 4x4x2 Coilcraft XFL4020-222ME 4x4x2 R1(1) 560 kΩ (VO = 3.3 V) See below note 0402 R2(1) 100 kΩ 0402 Notes: (1)R1 and R2 are calculated according to the following formula: R1 = R2 x (VOUT/VFB - 1). Suggested value for R2 is 100 kΩ. In order to reduce the quiescent current a maximum value of 500 kΩ is possible. The above listed components refer to a typical application. The STBB1-AXX operation is not limited to the choice of these components.
5 Electrical characteristics
VIN = VINA = VEN = 3.6 V, CIN = 10 µF, COUT = 10 µF, L = 2.2 µH, TJ = - 40 to 85 °C (unless otherwise specified; typical values are referred to TA = 25 °C). Table 6: Electrical characteristics Symbol Parameter Test conditions Min. Typ. Max. Unit VIN Input voltage range 2.0 5.5 V VUVLO Undervoltage lockout threshold VINA rising 1.70 1.80 V VINA falling 1.50 1.60 VFB Feedback voltage 485 500 515 mV TJ = 25 °C 490 500 510 mV VOUT Output voltage range 1.2 5.5 V ZFB FB input impedance MΩ IQ No switching quiescent current (VIN+VINA) (see Figure 3: "Application circuit (adjustable output version)", ) FB = 0.7 V, VMODE = 0 V 160 250 µA FB = 0.7 V, VMODE = VIN 600 750 IQ Operating quiescent current (VIN+VINA) IOUT = 0 A, VOUT = 3.3 V, VMODE = 0 V 200 µA IOUT = 0 A, VOUT = 3.3 V, VMODE = VIN 3.4 5.0 mA IQSHDN Shutdown quiescent current VEN = 0 V, VIN = 3.6 V 0.1 1 µA freq Oscillator frequency TA = 25 °C 1300 1500 1750 kHz Frequency range for synchronization 1300 2000 VEN Enable input logic low VIN = 2.2 V to 5.5 V 0.4 V Enable input logic high VIN = 2.2 V to 5.5 V 1.2 IEN Enable pin current VEN = 5.5 V 0.01 1 µA VMODE/SYNC MODE/SYNC input logic low VIN = 2.2 V to 5.5 V 0.4 V MODE/SYNC input logic high VIN = 2.2 V to 5.5 V 1.2 IMODE/SYNC MODE/SYNC pin current VMODE/SYNC = 5.5 V 0.01 1 µA %VOUT Line regulation 2.2 V < VIN < 5.5 V; IOUT = 1 mA 0.5 %VOUT Load regulation 10 mA < IOUT < 1000 mA ISWL Switch current limitation VIN = 3.3 V 1.6 2.3 2.6 A
Symbol Parameter Test conditions Min. Typ. Max. Unit ILKN NMOS leakage current VIN = 5.5 V 0.01 1 µA ILKP PMOS leakage current 0.01 1 µA RDS(on)-N NMOS switch on resistance 0.13 0.35 Ω RDS(on)-P PMOS switch on resistance 0.13 0.35 Ω n Efficiency, VIN = 3.6 V, VOUT = 3.3 V IOUT = 10 mA; VMODE = 0 % IOUT = 10 mA; VMODE = VIN IOUT = 100 mA; VMODE = VIN TSHDN Thermal shutdown 140 THYS Thermal shutdown hysteresis
STBB1-AXX Detailed description
6 Detailed description
6.1 General description
The STBB1-AXX is a high efficiency dual mode buck-boost switch mode converter. Thanks to the 4 internal switches, 2 P-channel and 2 N-channel, and its unique control mechanisms the device can deliver a well-regulated output voltage using a variable input voltage which can be higher than, equal to or lower than the desired output voltage. This solves most of the power supply problems that circuit designers face when dealing with battery-powered equipment. The controller uses an average current mode technique to obtain good stability in all possible conditions of input voltage, output voltage and output current. In addition, the peak inductor current is monitored to avoid saturation of the coil. The STBB1-AXX can work in two different modes: PWM mode or power save mode. The former operates with a fixed oscillator frequency in all line/load conditions. This is the best condition to obtain the maximum dynamic performance. The latter operates in burst mode allowing a drastic reduction of power consumption. Top-class line and load transients are achieved thanks to feed-forward technique and due to the innovative control method specifically designed to optimize the performance in the buck-boost region where input voltage is very close to the output voltage. The STBB1-AXX is self-protected from short-circuit and overtemperature. Undervoltage lockout and soft-start guarantee proper operation during the startup. Input voltage and ground connections are split into power and signal pins. This allows reduction of internal disturbances when the 4 internal switches are being work ed. The switch bridge is connected between VIN and PGND pins while all logic blocks are connected between VINA and GND.
6.2 Dual mode operation
The STBB1-AXX works in PWM or in power save (PS) mode according to the different operating conditions. If MODE pin is pulled high, the device works in PWM mode only even at light or no load. In this condition the STBB1-AXX provides the best dynamic performance. If the MODE pin is logic low, the STBB1-AXX operation changes according to the average input current handled by the device. At low average current the STBB1-AXX enters PS mode allowing very low power consumption and thus obtaining very good efficiency at light load. When the average current increases, the device automatically switches to PWM mode to deliver the power needed by the load. In PS mode the STBB1-AXX implements a burst mode operation. If the output voltage increases above its nominal value the device stops switching. As soon as VOUT falls below the nominal value the device starts switching again with a programmed average current higher than the one needed by the load. not found in not found shows PS mode operation areas vs. output current in typical application conditions.
Detailed description STBB1-AXX
6.3 External synchronization
The STBB1-AXX implements the external synchronization pin. If an external clock signal is applied to the MODE (SYN) pin with a frequency between 1.35 MHz and 2.0 MHz and with proper low/high levels, the device automatically goes to PWM mode and the external clock is used as switching oscillator.
6.4 Enable pin
The device operates when EN pin is set high. If EN pin is set low the device stops switching, all the internal blocks are turned off. In this condition, the current drawn from VIN/VINA is below 1 µA in the whole temperature range. In addition, the internal switches are in off-state so the load is electrically disconnected from the input, by avoiding unwanted current leakage from the input to the load.
6.5 Protection features
The STBB1-AXX implements different types of protection features.
6.5.1 Soft-start and short-circuit
After EN pin is pulled high, or after a suitable voltage is applied to VIN, VINA and EN, the device initiates the start-up phase. The average current limit is set to 400 mA at the beginning and gradually rises while the output voltage increase is being tracked. As soon the output voltage reaches 1.0 V the average current limit is set to its nominal value. This method allows a current limit proportional to the output voltage. If there is a short in the VOUT pin, the output current doesn’t exceed 400 mA. This process is not handled by a timer so the device is also able to start even with large capacitive loads.
6.5.2 Undervoltage lockout
The undervoltage lockout function prevents improper operation of the STBB1-AXX when the input voltage is not high enough. When the input voltage is below VUVLO threshold the device is in shutdown mode. The hysteresis of 100 mV prevents unstable operation when the input voltage is close to UVLO threshold.
6.5.3 Overtemperature protection
An internal temperature sensor continuously monitors the IC junction temperature. If the IC temperature exceeds 140 °C typically the device stops operating. As soon as the temperature falls below 120 °C typically normal operation is restored.
STBB1-AXX Typical performance characteristics
7 Typical performance characteristics
L = 2.2 µH, VO = 3.3 V, all measurements are fulfilled with circuit shown in Figure 3: "Application circuit (adjustable output version)" and external components listed in Table 5. Figure 4: Efficiency vs. IOUT in auto mode Figure 5: Efficiency vs. IOUT in PWM mode Figure 6: Efficiency vs. VIN, IOUT = 500 mA Figure 7: PS to PWM transition
8 Application information
8.1 Programming the output voltage
The STBB1-AXX is available in two versions: fixed output voltage (STBB1-APURXX) and adjustable output voltage (STBB1-APUR). The former integrates the resistor divider needed to set the correct output voltage. This allows 2 external components to be sav ed. The FB pin must be connected directly to VOUT. Regarding to the adjustable version, the resistor divider must be connected between VOUT and GND and the middle point of the divider has to be connected to FB as shown in Figure 3: "Application circuit (adjustable output version)" Equation 1 A suggested value for R2 is 100 kΩ. To reduce the power consumption a maximum value of 500 kΩ can be used.
8.2 Inductor selection
The inductor is the key passive component for switching converters. With a buck -boost device, the inductor selection must take into consideration the boundary conditions in which the converter works, as buck at the maximum input voltage and as a boost at the minimum input voltage. Two critical inductance values are then obtained according to the following formulas: equation 2 equation 3 where: fs: minimum switching frequency DIL = the peak-to-peak inductor ripple current. As a rule of thumb, the peak-to-peak ripple can be set at 10% - 20% of the output current. The minimum inductor value for the application is the highest between the above equations. Furthermore, the maximum current the inductor can handle must be calculated in order to avoid saturation. equation 4 R1 = R2 VFB –1-- V LMIN –BUCK VINMAX fs IL VOUT VIN –VOUT LMIN –BOOST VOUT fs IL VIN VOUT – VIN
where h is the estimated efficiency of the STBB1-AXX. The maximum of the two values above must be considered when the inductor is selected.
8.3 Input and output capacitor selection
Ceramic capacitors should be with low ESR in order to filter any disturbance present in the input line and to obtain stable operation. Minimum values of 10 µF for both capacitors are needed to achieve good behavior of the device. The input capacitor has to be placed as closer as possible to the device. IIPEAK –BUCK OUT/ fs L= VIN –(V IN MAX VOUT I IPEAK –BOOST VINMIN
2 VOUT
VOUT – VIN
Recommended PCB layout STBB1-AXX
9 Recommended PCB layout
Figure 16: Component placement Figure 17: Top layer routing
STBB1-AXX Recommended PCB layout Figure 18: Bottom layer routing
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.
10.1 DFN10 (3X3 mm) mechanical data
Figure 19: DFN10 (3X3 mm) drawings
Table 7: DFN10 (3x3 mm) mechanical data Dim. mm Typ. Min. Max. A 0.90 0.80 1.00 A1 (1) 0.02 00.5 A2 0.70 A3(1) 0.20 b 0.23 0.18 0.30 D 3.00 2.85 3.15 D2 2.38 2.23 2.50 E 3.00 2.85 3.15 E2 1.64 1.49 1.75 E3 0.230 0.365 E4 e 0.50 L 0.40 0.30 0.50 ddd 0.08 Notes: (1)The size is related to all leads, including exposed pad terminals.
Figure 20: DFN10 (3X3 mm) recommended footprint
Table 8: Document revision history Date Revision Changes 07-Sep-2011 1 Initial release. 04-Oct-2011 2 Added condition TA= 25 °C for the oscillator frequency parameter in table 6. 04-Aug-2014 3 Changed mechanical data. 29-Oct-2014 4 Updated mechanical data. Inserted the device summary table. Deleted the "application circuit (fixed output version)" figure.