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L6902D
UP TO 1A SWITCHING REGULATOR WITH ADJUSTABLE CURRENT LIMIT
1

FEATURES
UP TO 1A OUTPUT CURRENT OPERATING INPUT VOLTAGE FROM 8V TO 36V PRECISE 3.3V (2%) REFERENCE VOLTAGE 5% OUTPUT CURRENT ACCURACY OUTPUT VOLTAGE ADJUSTABLE FROM 1.235V TO 34V 250KHz INTERNALLY FIXED FREQUENCY VOLTAGE FEEDFORWARD ZERO LOAD CURRENT OPERATION ADJUSTABLE CURRENT LIMIT PROTECTION AGAINST FEEDBACK DISCONNECTION THERMAL SHUTDOWN
Figure 1. Package
SO-8
Table 1. Order Codes
Part Number L6902D L6902D013TR Package SO-8 SO-8 in Tape & Reel
rent 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 250m assures high efficiency and a minimum dropout even at high output current level. The internal limiting current (latched function) of typical value of 2.5A 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 (150C with 20C hysteresis), the power stage is turned off.
2
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 & SUBNOTEBOOK

3
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 curFigure 2. Test And Application Circuit
VIN=8V to 36V 3.3V C1 10F 25V CERAMIC VCC VREF COMP C2 22nF R3 5.1K GND 8 6 4 2 3 7 5 1
OUT
L1 22H D1 STPS340U
RSENSE 100m R1 5.6K
VOUT=3.3V
FB R2 3.3K
C3 220pF
C4 100F 10V POSCAP
D01IN1306A
October 2004
Rev. 8 1/7
L6902D
3 DESCRIPTION (continued)
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. Figure 3. Pin Connection
OUT CS+ CSCOMP
1 2 3 4
8 7 6 5
VCC GND VREF FB
Table 2. Pin Description
N 1 2 3 4 5 Pin OUT CS+ CSCOMP FB Regular Output Current Error Amplifier input (current sense at higher voltage) Current Error Amplifier input (current sense at lower voltage) E/A output to be used for frequency compensation Stepdown feedback input. Connecting directly to this pin results in an output voltage of 1.235V. An external resistive divider is required for higher output voltages. In this case: V out = V FB 1 + R1 = 1.235V 1 + R1 ------------ R2 R2 6 7 8 VREF GND VCC 3.3V VREF. No cap is need for stability. Ground Unregulated DC input voltage. Function
Table 3. Thermal Data
Symbol Rth j-amb
(*) Package mounted on board.
Parameter Thermal Resistance Junction to Ambient Max.
Value 110 (*)
Unit C/W
Table 4. Absolute Maximum Ratings
Symbol V8 V1 I1 V4, V5 V2, V3 Ptot Tj Tstg Input Voltage Output DC voltageOutput peak voltage at t = 0.1s Maximum output current Analog pins Analog pins Power dissipation at Tamb 70 C Operating junction temperature range Storage temperature range Parameter Value 40 -1 to 40 -5 to 40 Internally limited 4 -0.3V to VCC 0.7 -40 to 150 -55 to 150 V V W C C Unit V V V
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L6902D
Figure 4. Internal Block Diagram
Vcc VOLTAGES MONITOR 3.8V 1.235V CS+ Current_E/A + CSCOMP PEAK TO PEAK CURRENT LIMITING Voltage_E/A VFB 1.235V + E/A +
PWM
INHIBIT
SUPPLY
VREF GOOD
Vref
THERMAL SHUTDOWN TRIMMING
D CK
Q DRIVER
OSCILLATOR
OUT FREQUENCY SHIFTER GND
Table 5. Electrical Characteristcs (Tj = 25C, VCC = 12V, unless otherwise specified.) (*) Specification Referred to Tj from 0 to 125C.
Symbol VCC Vd IO Parameter Operating input voltage range Dropout voltage Operating charging current Test Condition VO = 1.235V; IO = 1A VCC = 8V; IO = 1A Rsense = 0.1 * Il fs Maximum limiting current Switching frequency VCC = 8V to 36V * * * * 0.95 0.92 2 212 225 d Duty cycle 0 2.5 250 250 Min. 8 0.25 1 Typ. Max. 36 0.5 1.05 1.08 3.2 287 275 100 Unit V V A A A kHz kHz %
DYNAMIC CHARACTERISTICS V5 Voltage feedback (FB) 8V < VCC < 36V, 20mA < IO < 1A VO = 5V, VCC = 12V 1.21 * 1.198 1.235 1.235 90 1.259 1.272 V V %
Efficiency
DC CHARACTERISTICS Iqop Iq Total operating quiescent current Quiescent current Duty cycle = 0; VFB = 1.5V * 3 5 3 mA mA
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L6902D
Table 5. Electrical Characteristcs (continued) (Tj = 25C, VCC = 12V, unless otherwise specified.) (*) Specification Referred to Tj from 0 to 125C.
Symbol Parameter Test Condition Min. Typ. Max. Unit
VOLTAGE ERROR AMPLIFIER VOH VOL Io source Io sink Ib High level output voltage Low level output voltage Source output current Sink output current Source bias current DC open loop gain gm Transconductance RL = 0 Icomp = -0.1 to 0.1mA Vcomp = 1.9V 50 VFB = 1V VFB = 1.5 Vcomp = 1.9V; VFB = 1V Vcomp = 1.9V; VFB = 1.5V 200 1 300 1.5 2.5 58 2.3 4 3.6 0.4 V V A mA A dB mS
CURRENT ERROR AMPLIFIER Voffs ICS+ ICSInput offset voltage CS+ Output Current VCS- = 1.8V; VCS+ = Vcomp IO = 1A, Rsense = 100m Vout < VCC -2V IO = 1A, Rsense = 100m Vout < VCC -2V 95 100 1.5 105 3 mV A A
CS- Output Current
1.5
3
REFERENCE SECTION Reference Voltage IREF = 0 to 5mA VCC = 8V to 36V Line Regulation IREF = 0mA VCC = 8V to 36V IREF = 0 to 5mA 10 * 3.234 3.2 3.3 3.3 3.366 3.399 V V
5
10
mV
Load Regulation Short Circuit Current
8
15
mV mA
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L6902D
Figure 5. SO-8 Mechanical Data & Package Dimensions
mm DIM. MIN. A A1 A2 B C D (1) E e H h L k ddd 5.80 0.25 0.40 1.35 0.10 1.10 0.33 0.19 4.80 3.80 1.27 6.20 0.50 1.27 0.228 0.010 0.016 TYP. MAX. 1.75 0.25 1.65 0.51 0.25 5.00 4.00 MIN. 0.053 0.004 0.043 0.013 0.007 0.189 0.15 0.050 0.244 0.020 0.050 TYP. MAX. 0.069 0.010 0.065 0.020 0.010 0.197 0.157 inch
OUTLINE AND MECHANICAL DATA
0 (min.), 8 (max.) 0.10 0.004
Note: (1) 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).
SO-8
0016023 C
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L6902D
Table 6. Revision History
Date January 2004 October 2004 Revision 7 8 Description of Changes Technical Migration from ST-PRESS to EDOCS. Changed Style Look & Feel. Changed Iq value in Table 5 page 3/7 from 2.7mA max. to 3.0mA max.
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L6902D
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners (c) 2004 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com
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