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February 2011 Doc ID 18476 Rev 1 1/29

STLDC08

Step-up controller for LED supply

Features

■ Input voltage range from 0.8 V to 3.6 V

■ Overvoltage protection

■ Drives N-channel MOSFET or NPN bipolar

transistor

■ No control loop compensation required

■ FET driver for very precise PWM dimming

Applications

■ Single/dual cell NiMH, NiCd, or alkaline

batteries

■ Small appliances LED lighting

■ Portable lighting

Description

The STLDC08 LED driver step-up controller is

optimized to operate from one or two NiCd/NiMH

or alkaline cells. The IC is able to drive an

external MOSFET (N-channel) enabling it for use

with wide power levels. Hysteretic control

eliminates the need for small signal control loop

compensation. The IC integrates an FET driver for

a precise PWM dimming. STLDC08 comes in a

DFN10 (3 x 3 mm) package.

DFN10 (3 x 3 mm)

Table 1. Device summary

Order code Marking Package

STLDC08PUR STLDC08 DFN10 (3 x 3 mm.)

www.st.com

Summary of content (29 pages)

PAGE 1
STLDC08 Step-up controller for LED supply Features ■ Input voltage range from 0.8 V to 3.
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Contents STLDC08 Contents 1 Application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 Typical performance characteristics . . . . . . . . . .
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STLDC08 12 Contents Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Application diagram STLDC08 1 Application diagram Figure 1. Electric schematic optimized for 2 LEDs and ILED = 200 mA L1 D1 RF BATTERY C1 C2 D3 M1 C3 Rs U1 4 7 EN/PWM 3 VCC DRV EN/PWM SENSE VOUT 2VCC PWMOUT C4 10 V5 FB GND EXP 8 11 C5 D2 9 6 C6 1 M2 2 5 Rfb AM07845v1 Table 2. List of components Reference Manufacturer Part number Value Size C1 Murata GRM21BR60J475 4.7 µF, 6.
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STLDC08 Application diagram Figure 2. Electric schematic optimized for 4 LEDs and ILED = 300 mA L1 D1 RF BATTERY C1 C2 D4 D5 D2 D3 M1 C3 Rs U1 4 7 EN/PWM 3 VCC DRV EN/PWM SENSE VOUT 2VCC PWMOUT C4 10 V5 FB GND C5 8 9 6 C6 1 2 M2 5 EXP 11 Rfb AM07892v1 Table 3. List of components Part reference Manufacturer Part number Value Size C1 Murata GRM21BR60J106KE19 10 µF, 6.3 V 0805 C2 Murata GRM31CR61C226K 22 µF, 16 V 1206 C4 Murata GRM188R70J103KA01B 10 nF, 6.
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Absolute maximum ratings STLDC08 2 Absolute maximum ratings Table 4. Absolute maximum ratings Symbol Parameter VCC Supply voltage Value Unit - 0.3 to 4.6 V EN/PWM Analog input - 0.3 to 7 V FB Analog input - 0.3 to 2 V SENSE Analog input - 0.3 to 20 V 2VCC Analog outputs 0 to 4 V V5 Analog outputs - 0.3 to 7 V DRV, PWMOUT Analog outputs VCC - 1.2 to 7 V VOUT Output voltage - 0.3 to 20 V ESD Human body model (all pins) ±2 kV PD DFN10L 3x3 TA = 25 °C 2.
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STLDC08 Pin configuration 3 Pin configuration Figure 3. Pin connections (top through view) Bottom view Table 6.
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Electrical characteristics 4 STLDC08 Electrical characteristics TA = -40 to 85; CIN = 22 µF; COUT =10 µF; PWMOUT = 3300 pF; DVR = 3300 pF; 2VCC =10 nF; V5 =1 µF; VCC = 1.5V; VOUT = 3 V; FB = GND; SENSE = GND; EN/PWM = VCC; unless otherwise specified. Table 7. Electrical characteristics Symbol Parameter Test conditions Min. Typ. Max. Unit 3.6 V General section VCC IVCC OVP IVOUT 2VCC Supply voltage range VOUT = GND 0.
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STLDC08 Table 7. Electrical characteristics Electrical characteristics (continued) Symbol Parameter Test conditions Min. Typ. Max. Unit 70 100 130 mV 10 20 µA SENSE VSENSE MAX ISENSE Maximum current sense threshold Bias current VSENSE = 20 V EN/PWM section VIL Low level threshold VCC = 0.8 V 0.3 V VIL Low level threshold VCC = 3.6 V 0.4 V VIH High level threshold VCC = 0.8 V 0.8 V VIH High level threshold VCC = 3.6 V 1.2 V IEN/PWM EN/PWM pin current EN/PWM = 3.
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Typical performance characteristics STLDC08 5 Typical performance characteristics Figure 4. VFB vs. temperature Figure 5. !- V Maximum VSENSE vs. temperature !- V 63%.3% ;M6= 6&" ;M6= 6 /54 6 6 /54 6 Figure 6. IOUT vs. temperature FB = 0.5 V Figure 7. !- V IOUT vs.
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STLDC08 Typical performance characteristics Figure 10. Startup timing and dimming ILED vs. time, 2 LEDs Figure 11. Dimming EN/PWM = 200 Hz, 2 LEDs VCC = 1.5 V; ILED = 200 mA 2LEDs VCC = 1.5 V; ILED = 200 mA 2LEDs Figure 12. Startup timing and dimming ILED vs. time, 4 LEDs Figure 13. Dimming EN/PWM = 200 Hz, 4 LEDs VCC = 3.6 V; ILED = 300 mA 4LEDs VCC = 3.6 V; ILED = 300 mA 4LEDs Figure 14. VCC = 1.5 V; ILED = 200 mA, 2LEDs Figure 15. VCC = 3.
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Block diagram 6 STLDC08 Block diagram Figure 16.
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STLDC08 Detailed description 7 Detailed description 7.1 Main control loop The STLDC08 is an LED driver step-up controller dedicated to handheld equipment, having a typical voltage ranging from 0.8 V to 1.5 V. The controller drives an N-channel Power MOSFET and implements a hysteretic current mode control with constant OFF time. Hysteretic operation eliminates the need for small signal control loop compensation.
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Detailed description STLDC08 Figure 17. Timing diagram VCC 1.7 V 2VCC 1.9 V VOUT DRV VOUT >1.9 V STLDC08 is supplied by VOUT ICC VOUT > VLED, the current starts flowing through the LEDs ILED Follows EN/PWM input Soft start cycle ended, PWMOUT is realeased PWMOUT Charge Pump active 7.3 STLDC08 supplied by VOUT AM07847v1 Over voltage protection (OVP) As with any current source, the output voltage rises when the output gets high impedance or is disconnected.
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STLDC08 7.5 Detailed description Dimming When PWMOUT goes to zero, the LED current immediately goes to zero and the energy stored in the coil is discharged on the output capacitor, causing an increase in the output voltage. As soon as the PWM goes back to high value, there is a big spike current on the LED. This could damage the LED itself.
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Application information STLDC08 8 Application information 8.1 LED current programming The LED current is set by an external resistor connected between the FB pin and GND. The following equation can be used to calculate the value of the RFB resistor which guarantees the desired output current: Equation 1 RFB = 0.1 ILED The feedback signal VFB is compared with the internal precision 100 mV voltage reference by the error amplifier. The internal reference has a guaranteed tolerance of 10 %.
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STLDC08 Application information As a first approximation we choose the inductor ripple current, IL, equal to approximately 40 % of the output current. Higher ripple current allows for smaller inductors, but it also increases the output capacitance for a given LED current ripple requirement. Conversely, lower ripple current can be obtained increasing the value of the inductance, and this enables a reduction of the output capacitor value.
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Application information STLDC08 Equation 6 ΔIL = 40% × IL( AVG) = 40% × ILED 1 − DMAX Where DMAX is given by: Equation 7 DMAX = 1 − VIN(MIN) VOUT + VD The value of the peak current on the inductor is given by the following equation: Equation 8 IL(PK ) = IL( AVG) + ΔIL 2 The minimum required saturation current of the inductor must be greater than IL(PK) and can be expressed as follows: Equation 9 IL(SAT ) > IL(PK ) = IOUT ΔI + L 1 − DMAX 2 The saturation current rating for the inductor should b
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STLDC08 Application information Equation 11 IIN(MAX) = 2 × IL(PK ) Equation 12 IL(PK ) = ΔI ILED + L 1 − DMAX 2 Equation 13 RSENSE = 0.1 2 × IL(PK ) If the RDS (ON) of the main Power MOSFET is used to sense the current on the inductor the following procedure must be performed to choose the Power MOSFET. During ON time, the SENSE comparator limits the voltage across the Power MOSFET to a nominal 100 mV.
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Application information STLDC08 Figure 19. Current diagram ON state L1 VBAT LX D1 COUT CIN LED DVR SENSE Rsense STLDC08 VOUT FB ON state RFB AM07849v1 Figure 20. Current diagram OFF state LX L1 VBAT D1 CIN COUT LED DVR SENSE Rsense STLDC08 VOUT FB OFF state RFB AM07850v1 Another important parameter is the drain source breakdown voltage.
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STLDC08 8.6 Application information Schottky diode selection Schottky diodes, with their low forward voltage and fast recovery time, are the ideal choice to maximize efficiency. The output diode in a boost converter conducts current only when the power switch is OFF. The average current is equal to the output current and the peak current is equal to the peak inductor current. Ensure that the diode's average and peak current ratings exceed the average and peak inductor current, respectively.
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Demonstration board 9 STLDC08 Demonstration board Figure 21. Electrical schematic TP1 VIN J1 TP2 SW L1 1 TP3 VOUT D1 1 J3 1 1 2 1 2 RF POWER IN C1 TP5 LED C2 1 J2 TP4 1 2 DRV C3 M1 1 SENSE GND Rs U1 J4 4 1 2 3 7 3 EN/PWM VCC DRV EN/PWM SENSE VOUT 2VCC PWMOUT C4 10 V5 C5 GND 8 EXP FB 9 6 C6 1 2 M2 5 11 Rfb AM07900v1 Table 8.
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STLDC08 10 Layout suggestion Layout suggestion Figure 22. Assembly layer Figure 23.
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Layout suggestion STLDC08 Figure 24.
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STLDC08 11 Package mechanical data 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.
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Package mechanical data STLDC08 DFN10 (3x3 mm) mechanical data mm. mils. Dim. A Min. Typ. Max. Min. Typ. Max. 0.80 0.90 1.00 31.5 35.4 39.4 0.02 0.05 0.8 2.0 0.65 0.80 25.6 31.5 A1 A2 0.55 A3 21.7 0.20 7.9 b 0.18 0.25 0.30 7.1 9.8 11.8 D 2.85 3.00 3.15 112.2 118.1 124.0 D2 2.20 E 2.85 118.1 124.0 E2 1.40 e L ddd 86.6 3.00 3.15 112.2 1.75 55.1 0.50 0.30 0.40 68.9 19.7 0.50 0.08 11.8 15.7 19.7 3.
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STLDC08 Package mechanical data Tape & reel QFNxx/DFNxx (3x3) mechanical data mm. inch. Dim. Min. Typ. A Max. Min. Typ. 180 13.2 7.087 C 12.8 D 20.2 0.795 N 60 2.362 T 0.504 0.519 14.4 0.567 Ao 3.3 0.130 Bo 3.3 0.130 Ko 1.1 0.043 Po 4 0.157 P 8 0.315 Doc ID 18476 Rev 1 Max.
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Revision history STLDC08 12 Revision history Table 9. Document revision history Date Revision 22-Feb-2011 1 28/29 Changes First release.
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STLDC08 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.