ST1S14 Up to 3 A step-down switching regulator Datasheet - production data Applications • Factory automation • Printers • DC-DC modules +623 H[SRVHG SDG HSOP8 - exposed pad • High current LED drivers Features Description • 3 A DC output current The ST1S14 is a step-down monolithic power switching regulator able to deliver up to 3 A DC current to the load depending on the application conditions.
Contents ST1S14 Contents 1 2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3 Enable inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Electrical data . . .
ST1S14 Contents 7.1.2 Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.1.3 Inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.2 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 7.4 Short-circuit protection . . . . . . . . .
List of figure ST1S14 List of figure Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Figure 36. Figure 37. Figure 38. Figure 39. Figure 40. Figure 41. Figure 42. Figure 43.
ST1S14 Figure 46. Figure 47. Figure 48. Figure 49. Figure 50. Figure 51. List of figure Zoom - 1 A to 3 A rising edge load transient (VIN 24 V) . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Zoom - 1 A to 3 A falling edge load transient (VIN 24 V). . . . . . . . . . . . . . . . . . . . . . . . . . . 41 1 A to 3 A load transient (VIN 32 V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Zoom - 1 A to 3 A rising edge load transient (VIN 32 V) . . . . . . . . .
Pin settings ST1S14 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) %80/3%$ 0!$ 4/ '.$ $0 9 1.2 Pin description Table 1. Pin description 1.3 N Pin Description 1 BOOT Bootstrap capacitor for N-channel gate driver. Connects 100 nF low ESR capacitor from BOOT pin to SW 2 PG Power good 3 EN1 Enable pin active low 4 FB 5 EN2 Enable pin active high 6 GND Ground pin 7 VIN Input supply pin 8 SW Switching node E.p.
ST1S14 Electrical data 2 Electrical data 2.1 Maximum ratings Table 3. Absolute maximum ratings Symbol Value Unit Power supply input voltage -0.3 to 52 V VEN1 Enable 1 voltage -0.3 to 7 V VEN2 Enable 2 voltage -0.3 to (VIN+0.3) V PG Power good -0.3 to (VIN+0.3) V BOOT Bootstrap pin -0.3 to 55 V -1 to (VIN+0.3) V -0.3 to 3 V Operating junction temperature range -40 to 150 °C TSTG Storage temperature range -65 to 150 °C TLEAD Lead temperature (soldering 10 sec.
Electrical characteristics 3 ST1S14 Electrical characteristics All the population tested at TJ = 25 °C, VCC =12 V, VEN1 = 0 V, VEN2 = VCC unless otherwise specified. The specification is guaranteed from (-40 to +125 °C) TJ temperature range by design, characterization, and statistical correlation. Table 6. Electrical characteristics Symbol VIN RDS(on) ISW Parameter Test condition Min Operating input voltage range MOSFET on resistance Max Unit 48 V 0.2 0.4 Ω 4.5 5.2 A 5.
ST1S14 Electrical characteristics Table 6. Electrical characteristics (continued) Symbol VEN1 IEN1 VEN2 IEN2 Parameter Enable 1 levels Enable 1 biasing current Enable 2 levels Test condition Min Typ Device ON VIN=5.5 V to 48 V Device OFF VIN=5.5 V to 48 V 1.5 VEN1=5 V 0.7 Device ON VIN=5.5 V to 48 V 1.5 Unit 0.5 V V 1.6 3.5 μA V Device OFF VIN=5.5 V to 48 V Enable 2 biasing current Max 0.5 V VEN1=0 V; VEN2=0 V -1 -2.4 -4.5 μA VEN1=0 V; VEN2=12 V 2.7 5.
Function description 4 ST1S14 Function description The ST1S14 is based on a “peak current mode”, constant frequency control. As a consequence the intersection between the error amplifier output and the sensed inductor current generates the control signal to drive the power switch.
ST1S14 4.1 Function description Power supply and voltage reference The internal regulator circuit consists of a start-up circuit, an internal voltage pre-regulator, the bandgap voltage reference, and the bias block that provides current to all the blocks. The starter supplies the start-up current to the entire device when the input voltage goes high and the device is enabled (inhibit pin connected to ground).
Function description ST1S14 Figure 5. Soft-start phases $0 9 During normal operation a new soft start cycle takes place in case of: • HICCUP mode current protection • thermal shutdown event • UVLO event • the device is driven in INH mode Figure 6.
ST1S14 4.4 Function description Error amplifier The voltage error amplifier is the core of the loop regulation. It is a transconductance operational amplifier whose non inverting input is connected to the internal voltage reference (1.222 V), while the inverting input (FB) is connected to the external divider or directly to the output voltage. The error amplifier is internally compensated to minimize the size of the final application. Table 7.
Additional features and limitations ST1S14 5 Additional features and limitations 5.1 Maximum duty cycle The bootstrap circuitry charges, cycle-by-cycle, the external bootstrap capacitor to generate a voltage higher than VIN necessary to drive the internal N-channel power element. An internal linear regulator charges the CBOOT during the conduction time of the external freewheeling diode during the switching activity. The internal logic implements a minimum OFF time of the high side switch (90 nsec typ.
ST1S14 5.2 Additional features and limitations Minimum output voltage over VIN range The minimum regulated output voltage at a given input voltage is limited by the minimum conduction time of the power element, that is 90 nsec typ. for the ST1S14: Equation 1 T ON_MIN 90ns V O_MIN ( V IN ) = V IN ⋅ D MIN = V IN ⋅ ---------------------- = V IN ⋅ -----------------T SW 1.18μs which is plotted in Figure 14. The reference of the embedded error amplifier (1.22 V) sets the minimum VO_SET at low VIN. Figure 8.
Closing the loop 6 ST1S14 Closing the loop Figure 9. Block diagram of the loop 07- CONTROL #URRENT SENSE 6).
ST1S14 6.1 Closing the loop GCO(s) control to output transfer function The accurate control to output transfer function for a buck peak current mode converter can be written as: Equation 2 s-⎞ ⎛ 1 + ---⎝ ωz⎠ R0 1 G CO ( s ) = ------- ⋅ ------------------------------------------------------------------------------------------------- ⋅ --------------------- ⋅ F H ( s ) R 0 ⋅ T SW Ri s⎞ ⎛ 1 + -------------------------- ⋅ [ m C ⋅ ( 1 – D ) – 0.
Closing the loop ST1S14 Equation 7 1 Q P = --------------------------------------------------------------π ⋅ [ m C ⋅ ( 1 – D ) – 0.5 ] 6.2 Error amplifier compensation network The ST1S14 embeds the error amplifier (see Figure 10) and a pre-defined compensation network which is effective in stabilizing the system in most of the application conditions. Figure 10.
ST1S14 Closing the loop Equation 10 1 f P HF = ----------------------------------------------------------2 ⋅ π ⋅ Rc ⋅ ( C0 + Cp ) whereas the zero is defined as: Equation 11 1 F Z = ----------------------------------------2 ⋅ π ⋅ Rc ⋅ Cc The embedded compensation network is RC=200 K, CP=24 pF, CC=211 pF and CO can be considered negligible, so the singularities are: Equation 12 f Z = 3, 77 kHz 6.
Closing the loop ST1S14 ( 1 + s ⋅ R 1 ⋅ C R1 ) R2 G DIV ( s ) = -------------------- ⋅ ----------------------------------------------------------------R1 ⋅ R2 R1 + R2 ⎛ 1 + s ⋅ --------------------- ⋅ C R1⎞ ⎝ ⎠ R1 + R2 where: 1 f Z = ---------------------------------------------2 ⋅ π ⋅ R 1 ⋅ C R1 1 f P = -----------------------------------------------------------R1 ⋅ R2 2 ⋅ π ⋅ --------------------- ⋅ C R1 R1 + R2 fZ < fP 6.
ST1S14 Closing the loop Figure 13.
Application information ST1S14 7 Application information 7.1 Component selection 7.1.1 Input capacitor The input capacitor must be able to support the maximum input operating voltage and the maximum RMS input current. Since step-down converters draw current from the input in pulses, the input current is squared and the height of each pulse is equal to the output current.
ST1S14 Application information Ceramic capacitors: If available for the required value and voltage rating, these capacitors usually have a higher RMS current rating for a given physical dimension (due to very low ESR). The drawback is the considerably high cost. Tantalum capacitors: Small tantalum capacitors with very low ESR are becoming more available. However, they can occasionally burn if subjected to very high current during charge.
Application information ST1S14 A list of some tantalum capacitor manufacturers is provided in Table 9. Table 9. Output capacitor selection Rated voltage (V) Cap value (µF)(1) Manufacturer Series Nippon Chemicon KZE 6.3 to 50 TAE 4 to 16 THB/C/E 4 to 16 TPS 4 to 35 (2) Sanyo POSCAP AVX ESR (mΩ)(1) 1 f Z = ---------------------------------------------------------- < BW 2 ⋅ π ⋅ ESR ⋅ COUT 1. see Section 6: Closing the loop for the selection of the output capacitor 2.
ST1S14 Application information high switching current loop areas should be kept as small as possible and lead lengths as short as possible. High impedance paths (in particular the feedback connections) are susceptible to interference, so they should be as far as possible from the high current paths. A layout example is provided in Figure 14 below. The input and output loops are minimized to avoid radiation and high frequency resonance problems.
Application information 7.3 ST1S14 Thermal considerations The dissipated power of the device is tied to three different sources: • Conduction losses due to the not insignificant RDSON, which are equal to: Equation 24 2 P ON = R DSON ⋅ ( I OUT ) ⋅ D where D is the duty cycle of the application. Note that the duty cycle is theoretically given by the ratio between VOUT and VIN, but in practice it is substantially higher than this value to compensate for the losses in the overall application.
ST1S14 Application information Example: – VIN = 24 V – VOUT = 5 V – IOUT = 3 A RDS(on) has a typical value of 0.2 Ω @ 25 °C and increases to a maximum value of 0.4 Ω @ 125 °C. We can consider a value of 0.3 Ω. TSW_EQ is approximately 12 ns. IQ has a typical value of 2 mA @ VIN = 24 V. The overall losses are: Equation 27 2 P TOT = R DSON ⋅ ( I OUT ) ⋅ D + V IN ⋅ I OUT ⋅ T SW ⋅ F SW + V IN ⋅ I Q = "" 2 = 0.3 ⋅ ( 3 ) ⋅ 0.137 + 24 ⋅ 3 ⋅ 12 ⋅ 10 –9 ⋅ 850 ⋅ 10 –3 + 24 ⋅ 2 ⋅ 10 –3 ≅ 1.
Application information ST1S14 reduced and, in most applications, this is enough to limit the switch current to the active current threshold, nominal or foldback depending on the FB voltage.
ST1S14 Application information so the output voltage is: Equation 34 V O_SET R V O = V FB ⋅ ⎛⎝ 1 + ------1-⎞⎠ = V FB ⋅ ------------------1.22 R2 Equation 29 and 30, in overcurrent conditions, can be simplified to: Equation 35 V IN – ( DCR L + R DSON ) ⋅ I V IN ΔI L TON = ------------------------------------------------------------------- ( T ON MIN ) ≅ --------- ( 90ns ) L L considering TON which has already been reduced to its minimum.
Application information ST1S14 Figure 16. Minimum VFB for effective pulse-by-pulse protection over VIN $0 9 As a consequence of VIN > 12 V the pulse-by-pulse current protection (in the worst case scenario which is the minimum VOSET) may not be effective to limit the inductor current to the peak current limitation over the entire FB range 300 mV < VFB < 1.22 V. In fact, at higher input voltage, ΔIL TON may be higher than ΔIL TOFF and so the inductor current could escalate.
ST1S14 Application information prevented for 16 ms and then a new soft-start phase takes place (see Figure 17). 7.4.2 VFB < 300 mV The device reduces the switching frequency by five times the nominal value when VFB<300 mV. The frequency foldback makes the pulse-by-pulse current protection effective to keep the current limited when the output voltage is shorted and VOUT negligible.
Application information ST1S14 Equation 40 1.22 ⋅ T SW V FB ( V IN ) = 1.22 ----------- – ⎛ -------------------------------------- ⋅ ( V D + ( I L ⋅ DCR ) )⎞ ⎝ ⎠ V IN ⋅ T ON_MIN 5 The Figure 19 plots the Equation 40 considering the foldback current limitation threshold (1.45A) given in Table 6: Electrical characteristics which is active out of the soft start time.
ST1S14 Application information Figure 20. Short-circuit current VIN = 24 V (IL_PK = IFOLD) $0 9 Figure 21 shows the operation of the constant current protection when a short-circuit is applied at the output at the maximum input voltage. According to Figure 20, the maximum inductor current escalates over the foldback current limitation. Figure 21. Short-circuit current VIN = 43 V (IL_PK > IFOLD) $0 9 7.4.
Application information ST1S14 Figure 22. Start up in short circuit condition $0 9 As soon as the current escalates to the current protection threshold (OCP1) the switching frequency is foldback 5 times the nomimal value.The OCP1 threshold is not foldback even if the VFB v< 300 mV ( see Chapter 7.4.2) becuase the device is operating in soft start time. Figure 23.
ST1S14 Application information Figure 24. Over current protection triggers the current and frequency foldback $0 9 Application circuit Figure 25. Demonstration board application circuit & Q) 3*22' 73 67 6 / & & X) 9 & Q) 9 & Q) 9 9,1 6: 5 3*22 ' (1 (1 (; 3$' 73 . 5 )% *1' 9287 X+ . & & ' S) *1' & & & X) -3 6736 / 8 X) 9 & %227 5 . VPDOO VLJQDO .
Application information ST1S14 Table 11. Component list (continued) Reference Part number Description 150 pF 50 V (size 0603) C7 C8 EKZE500ESS101MHB5D 100 μF 50 V (size 8 x 11.5 mm) C1, C9, C10, C11 Not Mounted R1 4.7 KΩ (size 0603) R2 2.7 KΩ (size 0603) R3 47 KΩ (size 0603) D1 L1 Manufacturer Nippon Chemicon STPS3L60U 3 A 60 V (size SMB) ST 744314850 8.5 μH ISAT=4.5 A, IRMS=4 A (size 7 x 6.9 x 4.8 mm) Wurth Figure 26.
ST1S14 Application information Figure 27.
Typical characteristics 8 ST1S14 Typical characteristics Figure 28. Line regulation Figure 29. Load regulation $0 9 Figure 30. RDSon vs. temperature (VIN = 12 V) $0 9 Figure 31. VFB vs. temperature (VIN = 12 V) $0 9 Figure 32. fSW vs. temperature $0 9 Figure 33. Quiescent current vs.
ST1S14 Typical characteristics Figure 34. Shutdown current vs. temperature Figure 35. Duty cycle max vs. temperature $0 9 Figure 36. Efficiency vs. IOUT (VIN 12 V) $0 9 Figure 38. Efficiency vs. IOUT (VIN 24 V) $0 9 DocID17977 Rev 2 $0 9 Figure 37. TJ vs. IOUT (VIN 12 V) $0 9 Figure 39. TJ vs.
Typical characteristics ST1S14 Figure 40. Efficiency vs. IOUT (VIN 32 V) Figure 41. TJ vs. IOUT (VIN 32 V) $0 9 Figure 42. 1 A to 3 A load transient (VIN 12 V) $0 9 Figure 43. Zoom - 1 A to 3 A load transient (VIN 12 V) $0 9 Figure 44. Zoom - 1 A to 3 A rising edge load transient (VIN 12 V) $0 9 Figure 45.
ST1S14 Typical characteristics Figure 46. Zoom - 1 A to 3 A rising edge load transient (VIN 24 V) Figure 47. Zoom - 1 A to 3 A falling edge load transient (VIN 24 V) $0 9 $0 9 Figure 48. 1 A to 3 A load transient (VIN 32 V) Figure 49. Zoom - 1 A to 3 A rising edge load transient (VIN 32 V) $0 9 $0 9 Figure 50.
Package mechanical data 9 ST1S14 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. Table 12. HSOP8 mechanical data mm Dim. Min. Max. A 1.75 A1 0.15 A2 1.25 b 0.38 0.51 c 0.17 0.25 D 4.80 4.90 5.00 D1 3.10 3.30 3.50 E 5.80 6.
ST1S14 Package mechanical data Figure 51.
Order code 10 ST1S14 Order code Table 13.
ST1S14 11 Revision history Revision history Table 14. Document revision history Date Revision Changes 12-Nov-2010 1 Initial release 04-Mar-2013 2 Updated IEN2 current limit. Updated Section 4.3: Soft-start and Section 7.4: Short-circuit protection.
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