L6902D

L6902 Up to 1 A switching regulator with adjustable current limit 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 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. 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 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. 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 November 2010 SO-8 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 Order codes Package L6902D Packaging Tube SO-8 L6902D013TR Doc ID 7332 Rev 9 Tape and reel 1/11 www.st.com 11 Content L6902 Content 1 Test and application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 Internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2/11 Doc ID 7332 Rev 9 L6902 1 Test and application circuit Test and application circuit Figure 1. Test and application circuit 9,1 9WR9 9&& 9 95()  &203 & M) 9 &(5$0,& & S) 287   56(16( ' 67368 P7    & Q)  5 . /M+ 9287 9 5 . )%  5 . *1' & M) 9 326&$3 ',1$ 2 Pin connection Figure 2. Table 2. Pin connection 287   9& & &6    *1' &6    95( ) &203   )% Pin description N° Pin 1 OUT Regular output 2 CS+ Current error amplifier input (current sense at higher voltage) 3 CS- Current error amplifier input (current sense at lower voltage) 4 Function COMP E/A output to be used for frequency compensation Stepdown feedback input. Connecting directly to this pin results in an output voltage of 1.235 V. An external resistive divider is required for higher output voltages. In this case: 5 FB 6 VREF 3.3 V VREF. No cap is need for stability. 7 GND Ground 8 VCC Unregulated DC input voltage. V out = V FB ⋅ ⎛ 1 + R1 --------⎞ = 1.235V ⎛ 1 + R1 --------⎞ ⎝ ⎝ R2⎠ R2⎠ Doc ID 7332 Rev 9 3/11 Maximum ratings 3 L6902 Maximum ratings Table 3. Absolute maximum ratings Symbol Parameter Unit 40 V VV V8 Input voltage V1 Output DC voltage output peak voltage at t = 0.1 μs -1 to 40 -5 to 40 I1 Maximum output current Internally limited V4, V5 Analog pins 4 V V2, V3 Analog pins -0.3V to VCC V 0.7 W Operating junction temperature range -40 to 150 °C Storage temperature range -55 to 150 °C Ptot Tj Tstg Table 4. Power dissipation at Tamb ≤ 70 °C Thermal data Symbol Parameter Value Unit Rth j-amb Thermal Resistance Junction to Ambient Max. 110 (1) °C/W 1. Package mounted on board. 4/11 Value Doc ID 7332 Rev 9 L6902 4 Internal block diagram Internal block diagram Figure 3. Block diagram 9FF 92/7$*(6 021,725 9 ,1+,%,7 &6 &6 9UHI &XUUHQWB($  7+(50$/ 6+87'2:1  75,00,1* &203 3($.723($. &855(17/,0,7,1* 9ROWDJHB($ 9)% 95() *22' 6833/< 9 9  ($   ' 3:0  &. 4 '5,9(5 26&,//$725 287 )5(48(1&< 6+,)7(5 *1' Doc ID 7332 Rev 9 5/11 Electrical characteristics 5 L6902 Electrical characteristics Tj = 25°C, VCC = 12V, unless otherwise specified. Table 5. Electrical characteristics Symbol Parameter Test condition VCC Operating input voltage range VO = 1.235V; IO = 1A Vd Dropout voltage VCC = 8V; IO = 1A IO Operating charging current Rsense = 0.1Ω Il Maximum limiting current Min. (1) VCC = 8V to 36V (1) Switching frequency d Duty cycle Max. Unit 36 V 0.25 0.5 V 1 1.05 A 1.08 A 8 0.95 fs Typ. 0.92 2 2.5 3.2 A 212 250 287 kHz 225 250 275 kHz 100 % 0 Dynamic characteristics 1.21 V5 Voltage feedback (FB) η Efficiency 8V < VCC < 36V, 20mA < IO < 1A (1) 1.235 1.259 V 1.198 1.235 1.272 V 90 % VO = 5V, VCC = 12V DC characteristics Iqop Iq Total operating quiescent current Quiescent current (1) 3 Duty cycle = 0; VFB = 1.5V 5 mA 3 mA Voltage error amplifier VOH High level output voltage VFB = 1V VOL Low level output voltage VFB = 1.5 Io source Source output current Io sink Sink output current Ib Source bias current gm Vcomp = 1.9V; VFB = 1V Vcomp = 1.9V; VFB = 1.5V 3.6 V 0.4 200 300 µA 1 1.5 mA 2.5 DC open loop gain RL = 0 Transconductance Icomp = -0.1 to 0.1mA, Vcomp = 1.9V V 50 4 μA 58 dB 2.3 mS Current error amplifier Voffs Input offset voltage VCS- = 1.8V; VCS+ = Vcomp ICS+ CS+ output current ICS- CS- output current 6/11 100 105 mV IO = 1A, Rsense = 100mΩ, Vout < VCC -2V 1.5 3 µA IO = 1A, Rsense = 100mΩ Vout < VCC -2V 1.5 3 µA Doc ID 7332 Rev 9 95 L6902 Table 5. Electrical characteristics Electrical characteristics (continued) Symbol Parameter Test condition Min. Typ. Max. Unit 3.234 3.3 3.366 V 3.2 3.3 3.399 V Reference section Reference voltage IREF = 0 to 5mA VCC = 8V to 36V (1) Line regulation IREF = 0mA, VCC = 8V to 36V 5 10 mV Load regulation IREF = 0 to 5 mA 8 15 mV Short circuit current 10 mA 1. Specification Referred to TJ from -40 to 125°C. Specification over the -40 to +125 TJ Temperature range are assured by design, characterization and statistical correlation Doc ID 7332 Rev 9 7/11 Package mechanical data 6 L6902 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. Table 1. SO-8 mechanical data mm. inch Dim. Min Typ Max Min Typ Max A 1.35 1.75 0.053 0.069 A1 0.10 0.25 0.004 0.010 A2 1.10 1.65 0.043 0.065 B 0.33 0.51 0.013 0.020 C 0.19 0.25 0.007 0.010 (1) D 4.80 5.00 0.189 0.197 E 3.80 4.00 0.15 0.157 e 1.27 0.050 H 5.80 6.20 0.228 0.244 h 0.25 0.50 0.010 0.020 L 0.40 1.27 0.016 0.050 k ddd 0° (min.), 8° (max.) 0.10 0.004 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). 8/11 Doc ID 7332 Rev 9 L6902 Package mechanical data Figure 4. Package dimensions Doc ID 7332 Rev 9 9/11 Revision history 7 L6902 Revision history Table 6. 10/11 Document revision history Date Revision Changes January 2004 7 Technical migration from ST-PRESS to EDOCS. October 2004 8 Changed style look and feel. 26-Nov-2010 9 Updated Note 1 on page 7 Doc ID 7332 Rev 9 L6902 Please Read Carefully: Information in this document is provided solely in connection with ST products. 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