ST1S14 STMicroelectronics, ST1S14 Datasheet

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ST1S14

Manufacturer Part Number
ST1S14
Description
Up to 3 A step down switching regulator
Manufacturer
STMicroelectronics
Datasheet

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Features
Application
October 2010
Figure 1.
3 A DC output current
Operating input voltage from 5.5 V to 48 V
850 kHz internally fixed switching frequency
Internal soft start
Power good open collector output
Current mode architecture
Embedded compensation network
Zero load current operation
Internal current limiting
Inhibit for zero current consumption
2 mA maximum quiescent current over
temperature range
250 mΩ typical R
Thermal shutdown
Factory automation
Printers
DC-DC modules
High current LED drivers
Application schematic
DS(on)
VIN
VIN
GND
GND
10uF
10uF
C2
C2
100nF
100nF
C3
C3
1
7
5
3
U1
U1
BOOT
VIN
EN2
EN1
Up to 3 A step down switching regulator
Doc ID 17977 Rev 1
C1
C1
GND
6
PGOOD
100nF
100nF
ST1S14
ST1S14
SW
FB
Description
The ST1S14 is a step down monolithic power
switching regulator able to delivers up to 3 A DC
current to the load depending on the application
conditions. The high current level is also achieved
thanks to an HSOP8 package with exposed
frame, that allows to reduce the R
approximately 40 °C/W. The output voltage can
be set from 1.22 V. The device uses an internal N-
channel DMOS transistor (with a typical R
200 mΩ) as switching element to minimize the
size of the external components. The internal
oscillator fixes the switching frequency at 850
kHz. Power good open collector output validates
the regulated output voltage as soon as it reaches
the regulation. Pulse by pulse current limit offers
an effective constant current short circuit
protection. Current foldback decreases overstress
in persistent short circuit condition.
8
2
4
D1
D1
R2
R2
2.7K
2.7K
small signal
power plane
R3
R3
R1
R1
C4
C4
L1
L1
HSOP8 - exposed pad
8.5uH
8.5uH
47K
47K
4.7K
4.7K
PGOOD
PGOOD
C5
C5
100uF
100uF
VOUT
VOUT
GND
GND
ST1S14
th(JA)
down to
DS(on)
www.st.com
1/42
of
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ST1S14 Summary of contents

Page 1

... GND October 2010 step down switching regulator Description The ST1S14 is a step down monolithic power switching regulator able to delivers current to the load depending on the application conditions. The high current level is also achieved thanks to an HSOP8 package with exposed frame, that allows to reduce the R approximately 40 ° ...

Page 2

... Additional features and limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.1 Maximum duty cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.2 Minimum output voltage over V 6 Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.1 G (s) Control to output transfer function . . . . . . . . . . . . . . . . . . . . . . . . 15 CO 6.2 Error amplifier compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.3 Voltage divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.4 Total loop gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.1 Component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.1.1 2/42 range . . . . . . . . . . . . . . . . . . . . . . . . . . 13 IN Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Doc ID 17977 Rev 1 ST1S14 ...

Page 3

... ST1S14 7.1.2 7.1.3 7.2 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 7.4.1 7.4.2 7.5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 8 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 10 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 300 mV < V < 1. < 300 Doc ID 17977 Rev 1 Contents 3/42 ...

Page 4

... BOOT pin to SW Power good Enable pin active low Feedback voltage Enable pin active high Ground pin Input supply pin IN Switching node Exposed pad must be connected to GND EN2 Doc ID 17977 Rev 1 Description Device status INH INH INH ON ST1S14 ...

Page 5

... ST1S14 2 Electrical data 2.1 Maximum ratings Table 3. Absolute maximum ratings Symbol V Power supply input voltage IN V Enable 1 voltage EN1 V Enable 2 voltage EN2 PG Power good BOOT Bootstrap pin SW Switching node V Feedback voltage FB T Operating junction temperature range J T Storage temperature range STG T Lead temperature (soldering 10 sec.) LEAD 2 ...

Page 6

... LOAD I = LOAD V = =2V, V =48V FB IN DEVICE OFF (see Table 2 V falling edge 6mA SINK Doc ID 17977 Rev 1 ST1S14 =0 V unless otherwise EN2 Min Typ Max Unit 5 Ω 0.2 0.4 3.7 4.5 5 600 850 1000 kHz (1) 90 ...

Page 7

Table 6. Electrical characteristics (continued) Symbol Parameter Inhibit V Enable 1 levels EN1 Enable 1 biasing I EN1 current V Enable 2 levels EN2 Enable 2 biasing I EN2 current Thermal shutdown Thermal shutdown T SHDWN temperature Thermal shutdown T ...

Page 8

... Functional description 4 Functional description The ST1S14 is based on a “peak current mode”, constant frequency control consequence the intersection between the error amplifier output and the sensed inductor current generates the control signal to drive the power switch. The main internal blocks shown in the block diagram in ● ...

Page 9

... ST1S14 4.1 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) ...

Page 10

... HICCUP mode current protection ● thermal shutdown event ● UVLO event ● the device is driven in INH mode Figure 6. Soft-start block diagram 10/42 PHASE 2 2816 clks S2 VREF Ctrl S1 VREF_OUT 64clks VFB 300mV VFB Doc ID 17977 Rev 1 PHASE 3 Vsaw Vsense Logic EA 400mV Iclamp Vsense SHORT ST1S14 ...

Page 11

... ST1S14 4.4 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 (1.222 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. ...

Page 12

... The internal logic implements a minimum OFF time of the high side switch (90 nsec typical) to prevent the bootstrap discharge at high duty cycle consequence the ST1S14 can operate at a maximum duty cycle around 90% typical. The ST1S14 embeds the diode V Figure 7 ...

Page 13

... ST1S14 5.2 Minimum output voltage over V The minimum regulated output voltage at a given input voltage is limited by the minimum conduction time of the power element, that is 90nsec typical for the ST1S14: Equation 1 which is plotted in minimum V O_SET Figure 8. V O_MIN Figure 8 shows the minimum output voltage over input voltage range to have constant switching activity and a predictable output voltage ripple ...

Page 14

... Closing the loop 6 Closing the loop Figure 9. Block diagram of the loop PWM control Current sense - - + + PWM comparator 14/ switch L C compensation network Doc ID 17977 Rev 1 ST1S14 LC filter resistor divider OUT REF + R 2 Error amplifier ...

Page 15

... ST1S14 6.1 G (s) Control to output transfer function CO The accurate control to output transfer function for a buck peak current mode converter can be written as: Equation where R represents the load resistance sense circuitry, ω ESR of the output capacitor. F (s) accounts the sampling effect performed by the PWM comparator on the output of the H error amplifier that introduces a double pole at one half of the switching frequency ...

Page 16

... Closing the loop 6.2 Error amplifier compensation network The ST1S14 embeds (see network which is effective to stabilize the system in most of the application conditions Figure 10. Transconductance embedded error amplifier and C introduce a pole and a zero in the open loop gain system stability but it is useful to reduce the noise at the output of the error amplifier. ...

Page 17

... ST1S14 Equation 9 Equation 10 whereas the zero is defined as: Equation 11 The embedded compensation network is R considered negligible, so the singularities are: Equation 12 6.3 Voltage divider The contribution of a simple voltage divider is: Equation 13 Figure 11. Leading network example f = --------------------------------- - 2 π R ⋅ ⋅ --------------------------------------------------- - 2 π R ⋅ ⋅ ...

Page 18

... ESR = 75 mΩ, the gain and phase bode OUT Figure 12 and =3A) OUT Doc ID 17977 Rev 1 Figure 11.) of the voltage ⋅ ⋅ ⋅ R ⎞ ⋅ ⎠ ⋅ R1 ⋅ =510 kHz). P Figure 13 over input voltage range ST1S14 ...

Page 19

... ST1S14 Figure 12. Module plot Figure 13. Phase plot The cut-off frequency and the phase margin are: Equation kHz = = 12V f 71 kHz = = 48V kHz IN C Doc ID 17977 Rev 1 Closing the loop pm 49° 62° 78° 19/42 ...

Page 20

... The maximum and minimum duty cycles OUT ------------------------------------ - MAX V – V INMIN OUT ------------------------------------- - MIN V V – INMAX possible to determine the max MIN MAX Doc ID 17977 Rev 1 ST1S14 is the output DC O the voltage drop across the ...

Page 21

... Therefore suggested to avoid this type of capacitor for the input filter of the device as they could be stressed by an high surge current when connected to the power supply. Table 8. List of ceramic capacitors for the ST1S14 Manufacturer TAIYO YUDEN MURATA In case the selected capacitor is ceramic (so neglecting the ESR contribution), the input ...

Page 22

... XPL 7030 Doc ID 17977 Rev < < -------- - BW 5 Table 9.: Output capacitor (1) ESR (mΩ) 1 ------------------------------------------------- - π ESR COUT ⋅ ⋅ ⋅ which is 0.6 - 1.2 A with omax ) ⋅ ON ΔI ---- - 2 Table 10.: Inductor Inductor value (µH) Saturation current ( 4 4 4.0 2 7.2 ST1S14 (1) < BW ...

Page 23

... ST1S14 7.2 Layout considerations The layout of switching DC-DC converters is very important to minimize noise and interference. Power-generating portions of the layout are the main cause of noise and so 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 ...

Page 24

... OUT SW 2 represent the switching times of the power element that cause the FALL ⋅ Doc ID 17977 Rev 1 , which are equal to: DSON 2 ) ⋅ D OUT ⋅ ⋅ ⋅ OUT SW_EQ SW Figure 15 the equivalent ST1S14 ...

Page 25

... This is the pulse by pulse current limitation to implement constant current protection feature. For the ST1S14, the operation of the pulse by pulse current limitation depends on the FB voltage: ● ...

Page 26

... ON I ⋅ DCR OFF is the series resistance of the inductor TOFF and the higher is V OUT FW the voltage applied the inductor general the worst case scenario is R ⎛ ⎞ ⋅ ------ - ⎝ ⎠ O_SET 1.22 ST1S14 . IN of the free ...

Page 27

... ST1S14 Equation 34 The Equation 29 Equation 35 considering T ON Equation 36 ( – Δ I --------------------------------------------------------------------- - TOFF where T =1 The voltage divider introduces a gain factor K between the V effectiveness of the current protection. The worst case scenario is the minimum K, that is the minimum output voltage, over the input voltage over V range) ...

Page 28

... In most of the application condition the pulse by pulse current limitation is effective to limit the inductor current. 28/42 for effective pulse by pulse protection over VIN FB ) could not be effective to limit the inductor current to the OSET Δ I could be higher than L TON Doc ID 17977 Rev 1 ST1S14 < 1.22V. FB Δ I and so the inductor L TOFF Equation current level higher = 48V) IN ...

Page 29

... ST1S14 Whenever the current escalates, a second level current protection called “hiccup mode” is enabled. In case the hiccup current level (6.2A typical) is triggered the switching activity is prevented for 16ms and then a new soft start phase takes place (see 7.4.2 V < 300 mV FB The device reduces the switching frequency five time than the nominal value when V < ...

Page 30

... T ⎛ 1. ----------------------------------- ---------- - – ⎝ ⋅ ON_MIN Equation 40 considering the foldback current limitation threshold for effective pulse by pulse protection over VIN FB Doc ID 17977 Rev 1 Equation 37 ⎞ ⋅ ⋅ DCR ⎠ Figure 14). ST1S14 is: ...

Page 31

... ST1S14 Figure 20. Short-circuit current V Figure 21 shows the operation of the constant current protection when a short circuit is applied at the output at the maximum input voltage. Accordingly to inductor current escalates over the foldback current limitation. Figure 21. Short-circuit current V = 24V ( L_PK FOLD = 43V (I > ...

Page 32

... Nippon Chemicon (size 8 x 11.5 mm) NOT MOUNTED 4.7 KΩ (size 0603) 2.7 KΩ (size 0603) 47 KΩ (size 0603) 3A 60V STMicroelectronics (size SMB) 8.5μH =4.5A, I =4A Wurth SAT RMS ST1S14 PGOOD PGOOD TP7 TP7 VOUT VOUT TP4 TP4 C10 C10 C11 C11 GND GND TP6 TP6 ...

Page 33

... ST1S14 Figure 23. PCB layout (component side) Figure 24. PCB layout (bottom side) Doc ID 17977 Rev 1 Application information 33/42 ...

Page 34

... Typical characteristics 8 Typical characteristics Figure 25. Line regulation Figure 27 temperature (V DSon Figure 29 temperature SW 34/42 Figure 26. Load regulation = 12 V) Figure 28 Figure 30. Quiescent current vs temperature Doc ID 17977 Rev 1 ST1S14 vs temperature ( ...

Page 35

... ST1S14 Figure 31. Shutdown current vs temperature Figure 33. Efficiency vs I OUT Figure 35. Efficiency vs I OUT Figure 32. Duty cycle max vs temperature ( Figure 34 Figure 36 Doc ID 17977 Rev 1 Typical characteristics OUT OUT IN 35/42 ...

Page 36

... Figure 39 load transient (V Figure 41. Zoom - rising edge load transient ( 36/ Figure 38 Figure 40. Zoom - load transient (V IN Figure 42 falling edge load Doc ID 17977 Rev OUT transient ( ST1S14 IN ...

Page 37

... ST1S14 Figure 43. Zoom - rising edge load transient ( Figure 45 load transient (V Figure 47. Zoom - falling edge load transient ( Figure 44. Zoom - falling edge load transient ( Figure 46. Zoom - rising edge load ...

Page 38

... Package mechanical data 9 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. 38/42 Doc ID 17977 Rev 1 ST1S14 ® ...

Page 39

... ST1S14 Table 12. HSOP8 mechanical data Dim. Min ccc Figure 48. Package dimensions 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 17977 Rev 1 Package mechanical data inch Min. Typ. Max. 0.0669 0.00 0.0039 0.0492 0.0122 0.0201 0.0067 ...

Page 40

... Order code 10 Order code Table 13. Ordering information 40/42 Order code ST1S14PHR Doc ID 17977 Rev 1 ST1S14 Package HSOP8 - exposed pad ...

Page 41

... ST1S14 11 Revision history Table 14. Document revision history Date 27-Oct-2010 Revision 1 Initial release Doc ID 17977 Rev 1 Revision history Changes 41/42 ...

Page 42

... Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Philippines - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America 42/42 Please Read Carefully: © 2010 STMicroelectronics - All rights reserved STMicroelectronics group of companies www.st.com Doc ID 17977 Rev 1 ST1S14 ...

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