a5974ad STMicroelectronics, a5974ad Datasheet
a5974ad
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a5974ad Summary of contents
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... step-down switching regulator for automotive applications HSOP8 - exposed pad Description The A5974AD is a step-down monolithic power switching regulator with a minimum switch current limit of 2 therefore able to deliver current to the load depending on the application conditions. The output voltage can be set from 1 ...
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... PWM comparator and power stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.7 Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.8 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6 Additional features and protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.1 Feedback disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.2 Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.3 Zero load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7 Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7.1 Error amplifier and compensation network . . . . . . . . . . . . . . . . . . . . . . . . 20 7.2 LC filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.3 PWM comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 8 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2/49 Doc ID 018762 Rev 1 A5974AD ...
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... A5974AD 8.1 Component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8.2 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 8.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 8.3.1 8.3.2 8.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 8.5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 8.6 Positive buck-boost regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 8.7 Negative buck-boost regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 8.8 Floating boost current generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 8.9 Synchronization example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 8.10 Compensation network with MLCC at the output . . . . . . . . . . . . . . . . . . . 40 8.11 External soft-start network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 9 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 10 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 11 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 12 Revision history ...
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... Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Table 2. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Table 3. Thermal data Table 4. Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 5. Uncompensated error amplifier characteristics Table 6. List of ceramic capacitors for the A5974AD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 7. Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 8. Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Table 9. Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Table 10. HSOP8 mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Table 11. Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Table 12 ...
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... A5974AD List of figures Figure 1. Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Pin connection (top view Figure 3. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 4. Internal circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 5. Oscillator circuit block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Figure 6. Synchronization example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Figure 7. Current limitation circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 8. Driving circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 9. Block diagram of the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 10. Error amplifier equivalent circuit and compensation network . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 11 ...
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... When it is open, an internal pull-up disable the device. E/A output for frequency compensation. Feedback input. Connecting directly to this pin results in an output voltage of 1. external resistive divider is required for higher output voltages. 3 cap is requested for stability. REF REF Ground. Unregulated DC input voltage. CC Doc ID 018762 Rev 1 A5974AD Description ...
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... A5974AD 2 Electrical data 2.1 Maximum ratings Table 2. Absolute maximum ratings Symbol V Input voltage 8 OUT pin DC voltage V 1 OUT pin peak voltage at Δt = 0.1 µs I Maximum output current Analog pins INH 3 V SYNCH 2 P Power dissipation at T TOT T Operating junction temperature range ...
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... COMP Doc ID 018762 Rev 1 Min. Typ. Max 0.250 2.5 3.0 425 500 0 1.198 1.235 1.272 2.2 3 190 300 1 2.3 A5974AD Unit 36 V Ω 0.5 3.5 A 575 kHz 100 % 2.7 mA 100 µA 100 µA 0 0.4 V µ µ ...
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... A5974AD Table 4. Electrical characteristics (continued) Symbol High input voltage Low input voltage Slave synch current Master output amplitude Output pulse width Reference section Reference voltage Line regulation Load regulation Short-circuit current 1. Guaranteed by design. Parameter Test condition ...
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... T temperature. All the datasheet parameters can be guaranteed to a maximum junction temperature of +125 °C, to avoid triggering the thermal shutdown protection during the testing phase due to self heating. 10/49 Section 2.2). SHTDWN Doc ID 018762 Rev 1 A5974AD (+150 °C±10 °C) ...
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... A5974AD 5 Functional description The main internal blocks are shown in the device block diagram in ● A voltage regulator supplying the internal circuitry. From this regulator, a 3.3 V reference voltage is externally available. ● A voltage monitor circuit which checks the input and the internal voltages. A fully integrated sawtooth oscillator with a frequency of 500 kHz ± 15%, including also ● ...
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... Beating frequency noise is an issue when more than one voltage rail is on the same board. A simple way to avoid this issue is to operate all the regulators at the same switching frequency. The synchronization feature set of the A5974AD, is simply obtained by connecting together their SYNCH pins. The device with the highest switching frequency is the master, 12/49 ...
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... A5974AD which provides the synchronization signal to the others. Therefore the SYNCH is an I/O pin to deliver or recognize a frequency signal. The synchronization circuitry is powered by the internal reference (V V pin and the signal ground of the master device is recommended for its proper REF operation. However, when a set of synchronized devices populates a board not possible to know in advance the one working as master, so the filtering capacitor must be designed for a whole set of devices ...
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... Figure 6. Synchronization example 5.4 Current protection The A5974AD features two types of current limit protection; pulse-by-pulse and frequency foldback. The schematic of the current limitation circuitry for the pulse-by-pulse protection is shown in Figure 7. The output power PDMOS transistor is split into two parallel PDMOS transistors. ...
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... A5974AD Figure 7. Current limitation circuitry 5.5 Error amplifier The voltage error amplifier is the core of the loop regulation transconductance operational amplifier whose non inverting input is connected to the internal voltage reference (1.235 V), while the inverting input (FB) is connected to the external divider or directly to the output voltage. The output (COMP) is connected to the external compensation network ...
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... V against any cross conduction between the supply line and ground. Figure 8. Driving circuitry 16/49 Figure 8). The basic idea is to change the current levels used to turn GSmax Doc ID 018762 Rev 1 A5974AD . The on/off control block protects GS ...
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... A5974AD 5.7 Inhibit function The inhibit feature is used to put the device in standby mode. With the INH pin higher than 2.2 V, the device is disabled and the power consumption is reduced to less than 100 µA. With the INH pin lower than 0.8 V, the device is enabled. If the INH pin is left floating, an internal pull-up ensures that the voltage at the pin reaches the inhibit threshold and the device is disabled ...
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... Due to the fact that the internal power is a PDMOS, no bootstrap capacitor is required and so the device works properly even with no load at the output. In this case it works in burst mode, with a random burst repetition rate. 18/ ⋅ ⋅ ------------------- - 1.3 OVP Doc ID 018762 Rev 1 A5974AD (Figure 18), the OVP 2 ...
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... A5974AD 7 Closing the loop Figure 9. Block diagram of the loop Doc ID 018762 Rev 1 Closing the loop 19/49 ...
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... R ⋅ --------------------------------------------------- - P2 2 π R ⋅ ⋅ c Doc ID 018762 Rev 1 introduce a pole and a zero in the open C ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ A5974AD 1 + ...
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... A5974AD whereas the zero is defined as: Equation the low frequency which sets the bandwidth, while the zero F P1 the frequency of the double pole of the LC filter (see below). F frequency. 7.2 LC filter The transfer function of the LC filter is given by: Equation where R is defined as the ratio between V ...
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... ESR = 25 mΩ, the poles and zeroes of A OUT = 3.3 kΩ. 2 Doc ID 018762 Rev – V OSCMIN is the OSCMIN ⋅ const ⎞ ⋅ ⋅ ⎠ 150 pF, the poles and zeroes Figure 11 and Figure A5974AD . CC are: 0 become: 12. ...
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... A5974AD Figure 11. Module plot Figure 12. Phase plot The cut-off frequency and the phase margin are: Equation 38kHz Phase margin = 52° C Doc ID 018762 Rev 1 Closing the loop 23/49 ...
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... RMS O 2 η OUT ------------------------------------ - MAX V V – INMIN OUT ------------------------------------- - MIN V V – INMAX possible to determine the max. MIN MAX Doc ID 018762 Rev 1 A5974AD is the output DC O the voltage drop across the ...
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... However, they can occasionally burn if subjected to very high current during charge Therefore better to avoid this type of capacitor for the input filter of the device. They can, however, be subjected to high surge current when connected to the power supply Table 6. List of ceramic capacitors for the A5974AD Manufacturer TAIYO YUDEN MURATA ● ...
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... V and ΔI = 0.9 A, the inductor value is about 12 µH. The peak Series DO3316T MSS1260T WE-PD L Figure 13 below. Doc ID 018762 Rev 1 ΔI ---- - 2 Table 8, some inductor Inductor value (µH) Saturation current (A) 5 3.5 to 4 A5974AD ...
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... A5974AD Figure 13. Layout example 8.3 Thermal considerations 8.3.1 Thermal resistance the equivalent static thermal resistance junction-to-ambient of the device; it can be THJ-A calculated as the parallel of many paths of heat conduction from the junction to the ambient. For this device, the path through the exposed pad is the one conducting the largest amount of heat ...
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... thJA Doc ID 018762 Rev 1 Figure 14 the equivalent SW ⋅ ⋅ ⋅ ⋅ ⋅ OUT – 3 ⋅ ⋅ ⋅ ≅ 1.38W ⋅ P TOT A5974AD ...
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... A5974AD Equation 28 8.3.2 Thermal impedance Z The thermal impedance of the system, considered as the device in the HSO8 package soldered on the application board, takes on an important rule when the maximum output power is limited by the static thermal performance and not by the electrical performance of the device. Therefore, the embedded power elements could manage a higher current but the system is already taking away the maximum power generated by the internal losses ...
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... pulsed output power is requested from the load: Therefore, depending on the pulse duration and its frequency, the maximum output current can be delivered to the load. The characterization of the thermal impedance is strictly dependent on the layout of the board. In Figure 17 of the A5974AD is provided. 30/49 =12 V and main output rails ...
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... A5974AD Figure 17. Measurement of the thermal impedance of the demonstration board As can be seen, for example, for load pulses with a duration of 1 second, the actual thermal impedance is lower than 20 °C/W. This means that, for short pulses, the device can deliver a higher output current value. ...
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... I ⋅ ) – DCR D out L ) ≅ ( ------------------------------------------------------------- - 12μ the inductor current is IN 18). When the application must sustain the (Equation OFF (Equation 31). Figure 20 ON Δ Δ where > IL TON IL TOFF and 32 occurs at a current slightly A5974AD ) 32) shows an so the ...
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... A5974AD Figure 19. Short-circuit current V Figure 20. Short-circuit current Doc ID 018762 Rev 1 Application information 33/49 ...
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... V 68 nF, 5%, 0603 150 pF, 5%, 0603 22 nF, 5%, 0603 POSCAP 6TVB330ML 330 µF, 25 mΩ 5.6 kΩ, 1%, 0.1 W 0603 3.3 kΩ, 1%, 0.1 W 0603 4.7 kΩ, 1%, 0.1 W 0603 STPS3L40U MSS1246T-123ML 12 µH, I Doc ID 018762 Rev 1 A5974AD Manufacturer Taiyo Yuden Sanyo STMicroelectronics 20° Coilcraft RMS ...
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... A5974AD Figure 22. PCB layout (component side) Figure 23. PCB layout (bottom side) Figure 24. PCB layout (front side) Doc ID 018762 Rev 1 Application information 35/49 ...
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... – – I LOAD I = -------------- - – for details) while the average current must be lower than the rated ≅ ⋅ OUT MAX SW MAX Doc ID 018762 Rev 1 A5974AD ⋅ ---------- - --------- + ⋅ – ...
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... Equation 40 Equation 41 An important point to take into account is that the ground pin of the device is connected to the negative output voltage. Therefore, the device is subjected to a voltage equal to V which must be lower than 36 V (the maximum operating input voltage). A5974AD – OUT IN – ...
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... Floating boost current generator The A5974AD does not support a nominal boost conversion as this topology requires a low side switch, however, a floating boost can be useful in applications where the load can be floating. A typical example is a current generator for LEDs driving, as the LED does not require a connection to the ground ...
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... A5974AD Figure 28. 350 mA LED boost current source The device is powered from the output voltage so the maximum voltage drop across the LEDs and resistor sense The output voltage is given by: Equation 42 where the ideal duty cycle D for the boost converter is: Equation 43 As for positive and inverting buck-boost (see real duty cycle must be used to calculate the switch current level ...
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... Figure 29. Synchronization example 8.10 Compensation network with MLCC at the output The A5974AD standard compensation network (please refer to introduces a single zero and a low frequency pole in the system bandwidth high ESR output capacitor must be selected to compensate the 180-degree phase shift given by the LC double pole. ...
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... A5974AD MLCCs (multiple layer ceramic capacitor) with values in the range of 10 µF-22 µF and rated voltages in the range of 10 V-25 V are available today at relatively low cost from many manufacturers. These capacitors have very low ESR values (a few mΩ) and are therefore occasionally used for the output filter in order to reduce the voltage ripple and the overall size of the application ...
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... Application information Figure 31. Soft-start network example 42/49 Doc ID 018762 Rev 1 A5974AD ...
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... A5974AD 9 Typical characteristics Figure 32. Line regulator Figure 34. Output voltage vs. junction temperature Figure 36. Junction temperature vs. output current (V Figure 33. Shutdown current vs. junction temperature Figure 35. Junction temperature vs. output current (V Figure 37. Efficiency vs. output current = Doc ID 018762 Rev 1 Typical characteristics = 43/49 ...
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... Typical characteristics Figure 38. Efficiency vs. output current (V 44/ Doc ID 018762 Rev 1 A5974AD ...
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... A5974AD 10 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 trademark. Doc ID 018762 Rev 1 Package mechanical data ...
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... Figure 39. Package dimensions 46/49 mm Typ. Max. 1.70 0.00 0.10 1.25 0.31 0.51 0.17 0.25 4.80 4.90 5.00 3 3.1 3.2 5.80 6.00 6.20 3.80 3.90 4.00 2.31 2.41 2.51 1.27 0.25 0.50 0.40 1.27 0° (min), 8° (max) 0.10 Doc ID 018762 Rev 1 A5974AD inch Min. Typ. Max. 0.0669 0.00 0.0039 0.0492 0.0122 0.0201 0.0067 0.0098 0.1890 0.1929 0.1969 0.118 0.122 0.126 0.2283 0.2441 0.1496 0.1575 0.091 0.095 0.099 0.0098 0.0197 0.0157 0.0500 0.0039 ...
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... A5974AD 11 Ordering information Table 11. Ordering information Order codes A5974AD A5974ADTR Package HSOP8 Doc ID 018762 Rev 1 Ordering information Packaging Tube Tape and reel 47/49 ...
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... Revision history 12 Revision history Table 12. Document revision history Date 19-Apr-2011 48/49 Revision 1 Initial release Doc ID 018762 Rev 1 A5974AD Changes ...
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... A5974AD 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. ...