L6902 STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 11
Technical content
Features
■ Up to 1 A output current ■ Operating input voltage from 8 V to 36 V ■ Precise 3.3 V (±2%) reference voltage ■ 5 % output current accuracy ■ Output voltage adjustable from 1.235 V to 34 V ■ 250 kHz internally fixed frequency ■ Voltage feedforward ■ Zero load current operation ■ Adjustable current limit ■ Protection against feedback Disconnection ■ Thermal shutdown
Applications
■ Chargers for NiCd, NiMH batteries and preregulator for lithium-ion batteries ■ Adjustable current generator ■ Simple step-down converters with adjustable current limit ■ Battery equipped systems ■ Distributed power supply ■ Mobile PC and subnotebook
Description
The L6902D is a complete and simple step down switching regulator with adjustable current limit. Based on a voltage mode structure it integrates a current error amplifier to have a constant voltage and constant current control. By means of an on board current sense resistor and the availability of the current sense pins (both compatible to Vcc and for Cs- compatible with GND too) a current limit programming is very simple and accurate (±5%). Moreover constant current control can be used to charge NiMH and NiCd batteries. The device can be used as a standard DC/DC converter with adjustable current limit (set by using the external sense resistor). The internal robust P-channel DMOS transistor with a typical of 250 mΩ assures high efficiency and a minimum dropout even at high output current level. The internal limiting current (latched function) of typical value of 2.5 A protects the device from accidental output short circuit avoiding dangerous loads damage. If the temperature of the chip goes higher than a fixed internal threshold (150°C with 20°C hysteresis), the power stage is turned off. Other protections beside thermal shutdown complete the device for a safe and reliable application: overvoltage protection, frequency folback overcurrent protection and protection vs. feedback disconnection. The internal fixed switching frequency of 250KHz, and the SO-8 package pin allow to built an ultra compact DC/ DC converter with a minimum board space. Table 1. Device summary
1 Test and application circuit
Figure 1. Test and application circuit
2 Pin connection
Figure 2. Pin connection Table 2. Pin description
1 OUT Regular output
2 CS+ Current error amplifier input (current sense at higher voltage)
3 CS- Current error amplifier input (c urrent sense at lower voltage)
4 COMP E/A output to be used for frequency compensation
6 VREF 3.3 V VREF . No cap is need for stability.
7 GND Ground
8 VCC Unregulated DC input voltage.
3 Maximum ratings
Table 3. Absolute maximum ratings Table 4. Thermal data
- Package mounted on board.
4 Internal block diagram
Figure 3. Block diagram
5 Electrical characteristics
Tj = 25°C, VCC = 12V, unless otherwise specified. Table 5. Electrical characteristics
- Specification Referred to TJ from -40 to 125°C. Specification over the -40 to +125 TJ Temperature range are assured by
Table 5. Electrical characteristics (continued)
6 Package mechanical data
specifications, grade definitions and product status are available at: www.st.com. Table 1. SO-8 mechanical data
- Dimensions D does not include mold flash, protrusions or gate burrs. Mold flash, potrusions or gate burrs
shall not exceed 0.15mm (.006inch) in total (both side).
Figure 4. Package dimensions
7 Revision history
Table 6. Document revision history January 2004 7 Technical migration from ST -PRESS to EDOCS. October 2004 8 Changed style look and feel.