STLED25 STMICROELECTRONICS | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 30
Technical content
Datasheet sections
- 1 Application schematic
- 2 Pin configuration
- 3 Maximum ratings
- 4 Electrical characteristics
- 5 Typical application performance
- 5.1 Quiescent current consumption
- 5.2 Switching frequency
- 5.3 Continuous output current
- 5.4 Efficiency at 100 mA I OUT
- 5.5 Efficiency at 75 mA I OUT
- 5.6 Efficiency at 50 mA I OUT
- 5.7 Absolute channel accuracy
- 5.8 Current matching between LED strings
- 5.10 PWM dimming linearity 10 - 100%
- 5.11 Inductor peak current
- 5.12 Maximum continues output current
- 6 Detailed description
- 6.1 Boost DC-DC converter operation
- 6.2 Current setting
- 6.3 EN13 and EN45
- 6.4 Modes of operation
- 6.5 Undervoltage lockout
- 6.6 Overtemperature protection
- 6.7 Open LED protection
- 6.8 Overvoltage protection
- 6.9 Short LED protection
Features
■ Operating input voltage range from 2.3 V to 5.5 V ■ ± 7.5% LED current accuracy ■ Two LEDs in series per channel ■ High side current source ■ Up to 125 mA of total LED current ■ 86% efficiency at 100 mA ■ PWM dimming with automatic shutdown time window ■ 2.5 MHz switching frequency
Applications
■ LCD backlight with up to 10 LEDs ■ Cellular phones ■ PDAs
Description
The STLED25 is a fixed frequency, high efficiency, boost DC-DC converter with five parallel high side current sources. It is capable of providing 125 mA of total current with a maximum voltage of 7.5 V on each channel. Each current source supports single or dual LED connection. The output voltage of the step-up converter is automatically set at 100 mV above the highest voltage required on any driver, to guarantee proper operation of the linear current sources. The device implements a self-test feature to detect failure of any of the LEDs and to disable the related channel. The failure status is reset as soon the IC is disabled. This mode of failure detection allows the device to continue operating driver channels that are functioning normally, while avoiding excessive power consumption or associated thermal issues. The control technique is able to maintain the efficiency close to 87% at medium load and higher than 85% at light or full load. The device also includes soft-start control, inrush current limit, thermal shutdown and inductor peak current limit. The STLED25 is packaged in a 12-bump CSP (1.4 x 1.8 mm, 0.5 mm height). Flip-Chip 12 bumps (1.4 x 1.8 mm.) Table 1. Device summary
1 Application schematic
Figure 1. STLED25 application schematic to the choice of these external components. Table 2. Typical external components
Figure 2. Functional block diagram
2 Pin configuration
Figure 3. Pin configuration (top view) Table 3. Pin description
3 Maximum ratings
Table 4. Absolute maximum ratings Table 5. Thermal data
- This parameter corresponds to a 4-laye r PCB board with 1 inch² of cooling area.
4 Electrical characteristics
TA = 25 °C, unless otherwise specified. Table 6. Electrical characteristics
- 10% value reduction at V IN = 2.3 V
- The PWM linearity is measured on the mean value of the output current in PWM mode in the 100 ms window. The
Table 6. Electrical characteristics (continued)
5 Typical application performance
5.1 Quiescent current consumption
Figure 4. Quiescent current at different ambient temperatures
5.2 Switching frequency
Figure 5. Switching frequency at different ambient temperatures
5.3 Continuous output current
Figure 6. Output current when V OUT = 8.5 V at different ambient temperatures
5.4 Efficiency at 100 mA I OUT
Figure 7. Efficiency when I OUT = 100 mA at different ambient temperatures
5.5 Efficiency at 75 mA I OUT
Figure 8. APPL efficiency when I OUT = 75 mA at TA = 25 °C
5.6 Efficiency at 50 mA I OUT
Figure 9. APPL efficiency when I OUT = 50 mA at TA = 25 °C
5.7 Absolute channel accuracy
Figure 10. Absolute channel accuracy - set string current to 20 mA
5.8 Current matching between LED strings
Figure 11. Current matching - set string current to 20 mA
Figure 12. PWM linearity 0.39 - 10% at T A = 25 °C
5.10 PWM dimming linearity 10 - 100%
Figure 13. PWM linearity 10 - 100% at T A = 25 °C
5.11 Inductor peak current
Figure 14. Inductor peak current at T A = 25 °C
5.12 Maximum continues output current
Figure 15. Maximum output current at T A = 25 °C
STLED25 Detailed description Doc ID 022323 Rev 3 17/30
6 Detailed description
The STLED25 is a high efficiency white LED power supply which integrates a step-up converter and 5 high-side current sources. The device is controlled by two enable inputs called EN13 and EN45 according to the labels of the LED channels. EN13 enables LED channels 1, 2, 3 and EN45 enables LED channels 4, 5. The device is protected against shorted LED channels by short LED protection and against open LED channels by open LED protection. The device is able to recognize which channel has failed, and switch off this channel to maintain correct operation of the remaining channels. The STLED25 device is 125 mA total output current capable and works over a battery voltage range of 2.3 V to 5.5 V. The typical output voltage during operation corresponds to the voltage level equal to V FLED + 125 mV. The STLED25 device has an optimized switching power bridge to reach a high level of application efficiency (86%) with the typical battery voltage of 3.7 V. The device is also able to work at high efficiency when not all the LED channels of the device are used.
6.1 Boost DC-DC converter operation
The step-up bridge with current mode control of the regulation regulates the output voltage level according to the LED channel with the highest V FLED, in order to maintain sufficient voltage headroom for the related current sources. The typical headroom of the current sources is in the range of 135 mV. The STLED25 contains a current limiter, with a typical value 600 mA, and soft-start control to limit the supply current from the battery. The method of regulation during startup and normal operation is explained in Section 6.4.
6.2 Current setting
Each LED channel regulates to the same current. The value of the LED current is set by choosing the R SET resistor. The current flowing through this resistor is mirrored in order to obtain the LED current. The multiplication factor is 390. The LED current is calculated with the following formula: Equation 1 where: VSET = 1.28 V typical
6.3 EN13 and EN45
EN13 and EN45 play the dual role of enable pin and PWM dimming. EN13 drives strings D1, D2, D3 while EN45 drives D4 and D5. Both EN13 and EN45 are pulled down internally by 100 k resistors. The EN pins accept a signal between 100 Hz and 800 Hz, at duty cycles from 0.39% to 100%. The output average current maximum error is 10% at 0.39%, PWM duty cycle at 300 Hz. 390R VI SET SETLED ×=
6.4 Modes of operation
soon as EN13 or EN45 are pulled high. reaches 7 V; this phase takes around 1.2 ms. sources and continue in PWM_normal mode. current sources in regulation. When both EN pins are low, the drivers are turned off and the RUN_HOLD timer starts. Figure 19. Modes of operation
STLED25 Detailed description Doc ID 022323 Rev 3 19/30
6.5 Undervoltage lockout
The undervoltage lockout function prevents improper operation of the STLED25 when the input voltage is not high enough. When the input voltage is below the UVLO threshold, the device is in shutdown mode. The hysteresis of 100 mV prevents unstable operation when the input voltage is close to the UVLO threshold.
6.6 Overtemperature protection
An internal temperature sensor continuously monitors the IC junction temperature. If the IC temperature exceeds 150 °C (typical), the device stops operating. As soon as the temperature falls below 135 °C (typical), normal operation is restored.
6.7 Open LED protection
The device is able to detect an “Open LED” failure in each LED channel independently. When this failure appears, the DC-DC increases the output voltage to maintain the current source headroom voltage until the OVP threshold is reached; the device detects which LED channel is the root cause and switches off this LED channel. This state is maintained until the STLED25 goes into shutdown mode.
6.8 Overvoltage protection
The device has overvoltage protection on the VOUT pin to protect the device and external components against the high voltage coming from the DC-DC, in case of a disconnected load. When the output voltage level reaches the OVP threshold (9.3 V typical), the DC-DC is turned off until the output voltage level goes below the OVP threshold. The hysteresis of the OVP threshold is approximately 250 mV.
6.9 Short LED protection
The device is able to detect a shorted LED in each LED channel independently; when the protection detects a failure on any of the LED channels, it switches off this channel until the STLED25 enters shutdown mode.
7 Application information
7.1 External passive components
7.1.1 Inductor selection
The inductor is the key passive component for switching converters.
7.1.2 Input and output capacitor selection
and 4.2 µF COUT in all conditions. Table 7. List of recommended inductors
7.2 Recommended PCB layout
voltage ripple. Input and output capacitors must be as close as possible to their relative pins. Figure 20. Top layer Table 8. Input and output capacitor
Figure 25. Photo of the application board
8 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.
Dim. mm. Min. Typ. Max. A 0.45 0.50 0.55 A1 0.17 0.20 0.2 3 A2 0.2 8 0.300 . 32 b 0.22 0.26 0. 30 D1 . 815 1. 845 1. 875 D1 1.20 E1 . 358 1.388 1.418 E1 0. 80 e0 . 36 0.40 0.44 fD 0. 313 0.323 0.333 fE 0.2 84 0.2 940 . 304 ccc 0.05 Flip-chip 12 mechanical data 8116384-D
Dim. mm. inch. A1 80 7.0 87 C 12. 8 13.2 0.504 0.520 D 20.2 0.7 95 N6 0 2 . 362 T 14.4 0.567 Po 3.9 4.1 0.154 0.161 P 3.9 4.1 0.154 0.161 Tape & reel Flip-Chip 12 mechanical data
Figure 26. Footprint recommended data (mm.)
9 Revision history
Table 9. Document revision history 10-Oct-2011 1 Initial release. 11-May-2012 3 Document status promoted from preliminary data to production data.