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This is information on a product in full production.

June 2013 DocID18279 Rev 5 1/37

ST1CC40

3 A monolithic step-down current source with synchronous

rectification

Datasheet - production data

Features

 3.0 V to 18 V operating input voltage range

 850 kHz fixed switching frequency

 100 mV typ. current sense voltage drop

 6 A standby current in inhibit mode



7% output current accuracy

 Synchronous rectification

 95 mHS / 69 m LS typical R

DS(on)

 Peak current mode architecture

 Embedded compensation network

 Internal current limiting

 Ceramic output capacitor compliant

 Thermal shutdown

Applications

 Battery charger

 Signage

 Emergency lighting

 High brightness LED driving

 General lighting

Description

The ST1CC40 device is an 850 kHz fixed

switching frequency monolithic step-down DC-DC

converter designed to operate as precise

constant current source with an adjustable current

capability up to 3 A DC. The regulated output

current is set connecting a sensing resistor to the

feedback pin. The embedded synchronous

rectification and the 100 mV typical R

SENSE

voltage drop enhance the efficiency performance.

The size of the overall application is minimized

thanks to the high switching frequency and

ceramic output capacitor compatibility. The device

is fully protected against thermal overheating,

overcurrent and output short-circuit. Inhibit mode

minimizes the current consumption in standby.

The ST1CC40 is available in VFQFPN8 4 mm x 4

mm 8-lead, and standard SO8 package.

VFQFPN8 4x4

Figure 1. Typical application circuit

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Summary of content (37 pages)

PAGE 1
ST1CC40 3 A monolithic step-down current source with synchronous rectification Datasheet - production data Applications  Battery charger  Signage  Emergency lighting  High brightness LED driving VFQFPN8 4x4  General lighting Features Description  3.0 V to 18 V operating input voltage range The ST1CC40 device is an 850 kHz fixed switching frequency monolithic step-down DC-DC converter designed to operate as precise constant current source with an adjustable current capability up to 3 A DC.
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Table of contents ST1CC40 Table of contents 1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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ST1CC40 Table of contents 7.2 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 7.5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 8 Typical characteristics . . . . . . .
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List of tables ST1CC40 List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. 4/37 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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ST1CC40 List of figures List of figures 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. Typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Pin connection (top view) . . . . . .
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Pin settings ST1CC40 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) 6: 3*1' ,1+ 9,16: *1' $*1' 9,1$ 1& ,1+ )% 62 %: 9)4)31 $0 Y 1.2 Pin description Table 1. Pin description No. Type 6/37 Description VFQFPN8 S08-BW 1 3 VINA Analog circuitry power supply connection 2 4 INH Inhibit input pin. Low signal level disables the device. Leave this pin floating if not used 3 5 FB Feedback input.
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ST1CC40 2 Maximum ratings Maximum ratings Table 2. Absolute maximum ratings Symbol Value Power input voltage -0.3 to 20 VINA Input voltage -0.3 to 20 VINH Inhibit voltage -0.3 to VINA VSW Output switching voltage VPG Power Good -0.3 to VIN VFB Feedback voltage -0.3 to 2.
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Electrical characteristics 4 ST1CC40 Electrical characteristics TJ= 25 °C, VCC = 12 V, unless otherwise specified. Table 4. Electrical characteristics Value Symbol Parameter Test conditions Unit Min. Operating input voltage range VIN See(1) Typ. 3 Max. 18 Device ON level 2.6 2.75 2.9 Device OFF level 2.4 2.55 2.
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ST1CC40 5 Functional description Functional description The ST1CC40 device is based on a “peak current mode” architecture with fixed 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.
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Functional description 5.1 ST1CC40 Power supply and voltage reference The internal regulator circuit consists of a startup 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 startup current to the entire device when the input voltage goes high and the device is enabled (INHIBIT pin connected to ground).
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ST1CC40 Functional description Table 5. Uncompensated error amplifier characteristics Description Value Transconductance 250 µS Low frequency gain 96 dB CC 195 pF RC 70 K The error amplifier output is compared with the inductor current sense information to perform PWM control. 5.5 Inhibit The inhibit block disables most of the circuitry when the INH input signal is low. The current drawn from the input voltage is 6 µA typical in inhibit mode. 5.
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Application notes ST1CC40 6 Application notes 6.1 Closing the loop Figure 5. Block diagram of the loop 9,1 3:0 FRQWURO *&2 V &XUUHQW VHQVH +6 VZLWFK / 9287 /& ILOWHU /6 VZLWFK 3:0 FRPSDUDWRU & 287 HUURU DPSOLILHU 9 &21752/ )% 5& && 95() 56 FRPSHQVDWLRQ QHWZRUN Į /(' $2 V $0 Y 6.
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ST1CC40 Application notes Equation 2 1  Z = ------------------------------ESR  C OUT Equation 3 m C   1 – D  – 0,5 1  P = -------------------------------------- + --------------------------------------------L  C OUT  f SW R LOAD  C OUT where: Equation 4 Se   m C = 1 + -----Sn  S = V  f pp SW  e  V IN – V OUT  S = -----------------------------  Ri  n L Sn represents the slope of the sensed inductor current, Se the slope of the external ramp (VPP peak-to-peak amplitude) that implements
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Application notes ST1CC40 Figure 6. Transconductance embedded error amplifier ( $ &203 )% 5& &3 && 9 5 G9 & 5& &3 && *P G9 $0 Y RC and CC introduce a pole and a zero in the open loop gain. CP does not significantly affect system stability but it is useful to reduce the noise at the output of the error amplifier.
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ST1CC40 Application notes The embedded compensation network is RC = 70 K, CC = 195 pF while CP and CO can be considered as negligible. The error amplifier output resistance is 240 Mso the relevant singularities are: Equation 12 f Z = 11 6 kHz 6.4 f P LF = 3 4 Hz LED small signal model Once the system reaches the working condition the LEDs composing the row are biased and their equivalent circuit can be considered as a resistor for frequencies << 1 MHz.
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Application notes ST1CC40 Figure 8 shows the equivalent circuit of the LED constant current generator. Figure 8. Load equivalent circuit / / 'OHG 9,1 ' 'OHG &287 5V / / 5G 9,1 ' &287 5G 5V $0 Y As a consequence, the LED equivalent circuit gives the LED(s) term correlating the output voltage with the high impedance FB input: Equation 13 R SENSE  LED  n LED  = ---------------------------------------------------------n LED  r LED + R SENSE 6.
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ST1CC40 Application notes Accordingly, with Section 7.1.1 the sensing resistor value is: Equation 15 100 mV R S = ---------------------  140 m 700 mA Equation 16 R SENSE 140 m  LED  n LED  = ---------------------------------------------------------- = ------------------------------------------------- = 0,06 n LED  r LED + R SENSE 2  1,1 + 140 m The gain and phase margin Bode diagrams are plotted respectively in Figure 9 and Figure 10. Figure 9.
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Application notes ST1CC40 Figure 10. Phase plot (;7(51$/ /223 *$,1 3+$6( 3KDVH *V )UHTXHQF\ >+]@ $0 Y The cutoff frequency and the phase margin are: Equation 17 f C = 100 kHz 6.6 pm = 47 eDesign studio software The ST1CC40 device is supported by the eDesign software which can be seen online on the STMicroelectronics® home page (www.st.com).
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ST1CC40 Application notes Figure 11. eDesign studio screenshot The software easily supports the component sizing according to the technical information given in this datasheet (see Section 6). The final user is requested to fill in the requested information such as the input voltage range, the selected LED parameters and the number of LEDs composing the row. The software calculates external components according to the internal database.
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Application information ST1CC40 7 Application information 7.1 Component selection 7.1.1 Sensing resistor In closed loop operation the ST1CC40 feedback pin voltage is 100 mV so the sensing resistor calculation is expressed as: Equation 18 100 mV R S = -------------------I LED Since the main loop (see Section 6.1) regulates the sensing resistor voltage drop, the average current is regulated into the LEDs.
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ST1CC40 Application information The LED ripple current can be calculated as the inductor ripple current ratio flowing into the output impedance using the Laplace transform (see Figure 11): Equation 19 8 -----2-  I L   1 + s  ESR  C OUT   I RIPPLE  s  = ----------------------------------------------------------------------------------------------------------1 + s   R S + ESR + n LED  R LED   C OUT where the term 8/2 represents the main harmonic of the inductor current ripple (which has a t
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Application information ST1CC40 Table 6. Inductor selection Manufacturer Würth Elektronik Coilcraft 7.1.3 Series Inductor value (µH) Saturation current (A) WE-HCI 7040 1 to 4.7 20 to 7 WE-HCI 7050 4.9 to 10 20 to 4.0 XPL 7030 2.2 to 10 29 to 7.2 Input capacitor The input capacitor must be able to support the maximum input operating voltage and the maximum RMS input current.
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ST1CC40 Application information where VF is the freewheeling diode forward voltage and VSW the voltage drop across the internal PDMOS. Considering the range DMIN to DMAX, it is possible to determine the max. IRMS going through the input capacitor. Capacitors that can be considered are: Electrolytic capacitors: These are widely used due to their low price and their availability in a wide range of RMS current ratings.
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Application information ST1CC40 To increase the design noise immunity, different signal and power ground should be implemented in the layout (see Section 7.5: Application circuit). The signal ground serves the small signal components, the device analog ground pin, the exposed pad and a small filtering capacitor connected to the VINA pin. The power ground serves the device ground pin and the input filter. The different grounds are connected underneath the output capacitor.
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ST1CC40 Application information  Switching losses due to turning ON and OFF. These are derived using Equation 29: Equation 29  T RISE + T FALL  P SW = V IN  I OUT  -----------------------------------------  F SW = V IN  I OUT  T SW_EQ  F SW 2 where TRISE and TFALL represent the switching times of the power element that causes the switching losses when driving an inductive load (see Figure 14). TSW is the equivalent switching time. Figure 14.
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Application information ST1CC40 The overall losses are: Equation 32 2 2 P TOT = R DS(on)_HS   I OUT   D + R DS(on)_LS   I OUT    1 – D  + V IN  I OUT  f SW  T SW + V IN  I Q Equation 33 2 2 P TOT = 0,14  0,7  0,6 + 0,1  0,7  0,4 + 12  0,7  12  10 –9 3  850  10 + 12  1,5  10 –3  205mW The junction temperature of the device is: Equation 34 T J = T A + Rth J – A  P TOT where TA is the ambient temperature and RthJ-A is the thermal resistance junction-toambient.
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ST1CC40 Application information The pulse-by-pulse current limitation is effective in implementing constant current protection when: Equation 38 I L TON = I L TOFF From Equation 36 and Equation 37 we can gather that the implementation of the constant current protection becomes more critical the lower the VOUT is and the higher VIN is.
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Application information ST1CC40 Figure 15. Constant current protection triggering hiccup mode AM12814v1 7.5 Application circuit Figure 16. Demonstration board application circuit 67 && ',0 ',0 )% 3*1' (3 $*1' 9,1 9,1B6: 9,1B$ & X 9 5 5 -3 10 .
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ST1CC40 Application information Table 8. Component list Reference Part number Description Manufacturer 100 nF 50 V (size 0805) C1 C2 GRM31CR61E106KA12L 10 µF 25 V (size 1206) Murata C3 GRM21BR71E225KA73L 2.2 µF 25 V (size 0805) Murata R1 4.7 K5% (size 0603) R2 Not mounted Rs ERJ14BSFR15U 0.151% (size 1206) Panasonic L1 XAL6060-223ME 22 µH ISAT = 5.6 A (30% drop) IRMS = 6.9 A (40 C rise) (size 6.36 x 6.56 x 6.1 mm) Coilcraft Figure 17.
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Application information ST1CC40 Figure 18. PCB layout (bottom side) VFQFPN8 package Figure 19. PCB layout (component side) SO8 package It is strongly recommended that the input capacitors are to be put as close as possible to the relative pins, see C1 and C2.
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ST1CC40 Application information Figure 20.
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Typical characteristics 8 ST1CC40 Typical characteristics Figure 21. Soft-start Figure 22. Inhibit operation AM12818v1 AM12819v1 Figure 23. Thermal shutdown protection Figure 24. Hiccup current protection AM12820v1 Figure 25. OCP blanking time AM12821v1 Figure 26. Current regulation Vin 12V Vled 7V 130 ns typ.
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ST1CC40 9 Package information Package information 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. Figure 27. VFQFPN8 (4 x 4 x 1.08 mm) package outline Table 9. VFQFPN8 (4 x 4 x 1.08 mm) package mechanical data Dimensions (mm) Symbol Min. Typ. Max. 0.80 0.90 1.
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Package information ST1CC40 Figure 28. SO8-BW package outline Table 10. SO8-BW package mechanical data Dimensions (mm) Symbol Min. Typ. Max. A 135 1.75 A1 0.10 0.25 A2 1.10 1.65 B 0.33 0.51 C 0.19 0.25 D(1) 4.80 5.00 E 3.80 4.00 e 1.27 H 5.80 6.20 h 0.25 0.50 L 0.40 1.27 k 0° (min.), 8° (max.) ddd 0.10 1. Dimension D does not include mold flash, protrusions or gate burrs. Mold flash, protrusions or gate burrs shouldn’t exceed 0.15 mm (.
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ST1CC40 10 Ordering information Ordering information Table 11.
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Revision history 11 ST1CC40 Revision history Table 12. Document revision history Date Revision 04-Mar-2011 1 Initial release. 21-Jun-2011 2 Updated coverpage 18-Oct-2012 3 Pin 2 operation has been updated: Figure 1 and Table 1 have been updated accordingly. Figure 19 and Figure 20 have been added. Minor text changes to improve the readability. Status promoted from preliminary to production data. 04-Mar-2013 4 Updated Table 9: VFQFPN8 (4 x 4 x 1.08 mm) package mechanical data and Section 7.1.
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ST1CC40 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.