STLD40D_V01 STMICROELECTRONICS | Alldatasheet

Document overview

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  • PDF pages: 16

Technical content

Datasheet sections

  • 1 Block diagram
  • 2 Pin configuration
  • 3 Maximum ratings
  • 4 Electrical characteristics
  • 5 Functional description
  • 5.1 Boost controller
  • 5.2 Adjustable peak inductor current limit
  • 5.3 Enable
  • 5.4 OVP
  • 6 Typical application
  • 7 Typical performance characteristics
  • 8 Package mechanical data
  • 9 Revision history

Features

■ Inductor switches boost controller ■ PFM mode control ■ High efficiency over wide range of input voltage from 3.0 V to 5.5 V ■ Over voltage protection with automatic restart ■ Adjustable peak current limit ■ Enable pin with possibility of PWM dimming control ■ Low shutdown current < 1 µA ■ Small external component ■ Good load and line regulation ■ QFN8 3 x 3 mm

Applications

■ White LED supply for LCD backlight ■ Mobile phone ■ PDA and organizers ■ Any handsets powered form 3.0 V to 5.5 V

Description

STLD40D is a boost converter that operates from 3.0 V to 5.5 V. It can provide an output voltage as high as 37 V and can drive up to 10 white LEDs in series. The converter is a PFM (pulse frequency modulation) inductor switch that can work in discontinuous (DCM) mode operation. A minimum OFF time of the embedded boost switch T SW is fixed internally and allows limiting the switching frequency. The output current capability is 20 mA with an output voltage of 37 V. The regulation is done by sensing the LED current through the resistor R LED. The device can be turned ON/OFF through the logic enable signal pin EN. By applying a low frequency PWM signal the LEDs can be dimmed. The maximum peak inductor current can be programmed by connected a resistor R SET to the pin RSET. QFN8 (3 x 3 mm) Table 1. Device summary

1 Block diagram

Figure 1. Block diagram

2 Pin configuration

Figure 2. Pin connections (top through view) Table 2. Pin description

3 GND Analog ground

4 FB Feedback for the LED current regulation

7 EN IC enable signal

8 SW Boost switch drain

3 Maximum ratings

Table 3. Absolute maximum ratings Table 4. Thermal data

4 Electrical characteristics

VO = 32 V, typ. values @ 25 °C, unless otherwise specified. Table 5. Electrical characteristics

STLD40D Functional description Doc ID 12203 Rev 7 7/16

5 Functional description

5.1 Boost controller

The STLD40D is a boost converter operating in PFM (pulsed frequency modulation) mode. The converter monitors the LED current through the resistor RLED and when the feedback voltage falls below the reference voltage REF2, the boost switch TSW turns ON and the current ramps up. The inductor current is measured by sensing the temperature compensated drain voltage of the boost MOSFET. The boost turns off when its drain voltage reaches the internally reference REF1, the main switch remains off until the minimum off time (250 ns typical) has passed and the feedback voltage is below the reference again. A maximum ON time of 4 µs typical prevents the switch T SW to stay ON during a too long period of time.

5.2 Adjustable peak inductor current limit

The peak inductor current is monitored by sensing the drain voltage of the switch TSW. Since it exceeds the temperature compensated and supply voltage compensated reference REF1, the RS flip flop is reset and T SW is turned OFF . By connecting a resistance to the pin RSET the peak current limit can be adjusted from 200 mA to 1 A. When RSET resistor value is about 12 kΩ is connected directly to GND, the default value is 1 A.

5.3 Enable

The ENABLE pin is a high logic input signal and allows turning on/off the controller without cutting the input voltage from the boost regulator circuit. The pin ENABLE can be used to dim the LED by applying a low frequency PWM signal.

5.4 OVP

If the regulation loop is cut, there is no signal at the feedback pin, the PFM controller will then continue to switch without control and generate an output voltage at the SW, and VO pin exceeding the breakdown value VBSW, and VBO. The over voltage protection (OVP) senses the voltage at the VO pin. When the voltage exceed 38 V min. the controller is automatically turned OFF . A hysteresis control allows the device restarting automatically since the output voltage drops down of 1.5 V.

6 Typical application

operation of STLD40D is not limited with the use of components included in this list. Figure 3. Application circuit Table 6. External component proposal (see Figure 3)

7 Typical performance characteristics

load (VO = 32 V) typ. values @ 25 °C, unless otherwise specified. Figure 4. I LED vs. RLED Figure 5. I LED vs. VI Figure 6. I Q vs. temperature Figure 7. I SD vs. VI Figure 8. R DSON vs.VI Figure 9. I LIMIT vs. RSET

8 Package mechanical data

specifications, grade definitions and product status are available at: www.st.com. ECOPACK® is an ST trademark. Table 7. QFN8 (3 x 3 mm) mechanical data

Figure 15. Drawing dimension QFN8 (3 x 3 mm)

Dim. mm. inch. A1 80 7.0 87 C 12. 8 13.2 0.504 0.51 9 D 20.2 0.7 95 N6 0 2 . 362 T 14.4 0.567 Ao 3.3 0.130 Bo 3.3 0.130 Ko 1.1 0.04 3 Po 4 0.157 P 8 0.315 Tape & reel QFNxx/DFNxx (3x3) mechanical data

Figure 16. QFN8 (3x3) footprint recommended data

9 Revision history

Table 8. Document revision history 20-Mar-2006 1 Initial release. 04-Apr-2006 2 Add R SET in table 4 and fig 2 has been updated. 27-Feb-2009 3 Modified mechanical data. 03-Mar-2009 4 Modified packaging T a b l e1 o n p a g e1. 11-Mar-2009 5 Modified: Figure 2 on page 4 and added Figure 16 on page 14. 01-Jul-2010 6 Modified: Table 7 on page 11, Figure 15 on page 12 and Figure 16 on page 14. 31-May-2011 7 Modified: Table 6 on page 8.