A6902D Up to 1 A step down switching regulator with adjustable current limit for automotive applications Features ■ Qualified following the AEC-Q100 requirements (temperature grade 3), see PPAP for more details. ■ Temperature range -40 °C to 85 °C ■ Up to 1 A DC output current ■ Operating input voltage from 8 V to 36 V ■ Output voltage adjustable from 1.235 V to 35 V ■ Precise 3.3 V (±2 %) reference voltage ■ 250 kHz Internally fixed frequency ■ Voltage feedforward ■ Zero load current operation ■ Internal current limiting ■ Protection against feedback disconnection ■ Thermal shutdown SO-8 Applications ■ Automotive applications ■ Adjustable current generator ■ Simple step-down converters with adjustable current limit Figure 1. Application schematic VIN=8V to 36V VCC OUT VREF VIN=8V to 36V COMP D1 L6902D C1 10µF C2 35V 22nF C3 220pF CS+ CS- STPS340U Rsense VOUT=3.3V 100mO R1 5.6kO C4 100µF FB 10V R3 R2 GND 5.1kO May 2008 L1 22µH 3.3kO Rev 3 1/12 www.st.com 1 A6902D Contents 1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 2.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2/12 Description 1 A6902D Description The A6902D 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 Cscompatible with GND too) a current limit programming is very simple and accurate. 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 250 kHz, and the SO-8 package pin allow to built an ultra compact DC/ DC converter with a minimum board space. 3/12 A6902D 2 Pin connection 2.1 Pin connection Figure 2. 2.2 Pin connection (top view) Pin description Table 1. Pin description N Pin Description 1 OUT Regulator output. 2 CS+ Current error amplifier input (current sense at higher voltage) 3 CS- Current error amplifier input (current sense at lower voltage) 4 COMP 5 FB 6 VREF 3.3 V reference voltage. No cap is need for stability. 7 GND Ground. 8 VCC Unregulated DC input voltage. E/A output for frequency compensation. Feedback input. Connecting directly to this pin results in an output voltage of 1.23 V. An extenal resistive divider is required for higher output voltages. 4/12 Electrical data A6902D 3 Electrical data 3.1 Maximum ratings Table 2. Absolute maximum ratings Symbol Unit 40 V V V Input voltage V1 OUT pin DC voltage OUT pin peak voltage at ∆t = 0.1µs -1 to 40 -5 to 40 I1 Maximum output current int. limit. V4 , V5 Analog pins 4 V V2, V3 Analog pins -0.3 to VCC V PTOT Power dissipation at TA ≤ 70 °C 0.7 W Operating junction temperature range -40 to 150 °C Storage temperature range -55 to 150 °C SO8 Unit 110 (1) °C/W TSTG Thermal data Table 3. Thermal data Symbol RthJA Parameter Maximum thermal resistance junction-ambient 1. Package mounted on board 5/12 Value V8 TJ 3.2 Parameter A6902D Electrical characteristics Table 4. Electrical characteristics (TJ = -40 to 125 °C, VCC = 12 V, unless otherwise specified) Symbol VCC RDS(on) IL fSW Parameter Operating input voltage range Test conditions V0 = 1.235 V; I0 = 2 A Min Max Unit Maximum limiting current VCC = 8.5 V Switching frequency Duty cycle Typ 36 V 0.250 0.5 Ω 1.8 2.5 3.2 A 212 250 280 kHz 100 % 1.272 V 8 Mosfet on resistance 0 Dynamic characteristics (see test circuit). V5 Voltage feedback 8 V < VCC < 36 V, 20 mA < I0 < 1 A η Efficiency V0 = 5 V, VCC = 12 V 1.198 1.235 90 % DC characteristics Iqop Total operating quiescent current Iq Quiescent current 3 Duty cycle=0; VFB=1.5 V 5 mA 2.7 mA Error amplifier VOH High level output voltage VFB=1 V VOL Low level output voltage VFB=1.5 V Source output current VCOMP = 1.9 V; VFB = 1 V 160 300 µA Io sink Sink output current VCOMP = 1.9 V; VFB = 1.5 V 1 1.5 mA Ib Source bias current Io source 3.6 V 0.4 2.5 DC open loop gain RL= gm Transconductance ICOMP = -0.1 mA to 0.1 mA; VCOMP = 1.9 V VOFFS Input offset voltage VCS- = 1.8 V; VCS+ = Vcomp ICS+ CS+ output current ICS- CS- output current 8 4 50 90 4 V µA 58 dB 2.3 mS 100 110 mV I0 =1 A; RSENSE =100 mΩ; VOUT < VCC-2 V 1.5 3 µA I0 =1A; RSENSE =100 mΩ; VOUT < VCC-2 V 1.5 3 µA 6/12 Electrical characteristics Table 4. Symbol A6902D Electrical characteristics (continued) (TJ = -40 to 125 °C, VCC = 12 V, unless otherwise specified) Parameter Test conditions Min Typ Max Unit 3.2 3.3 3.399 V Reference section Reference voltage IREF = 0 to 5 mA VCC = 8 V to 36 V Line regulation IREF = 0mA VCC = 8 V to 36 V 5 10 mV Load regulation IREF = 0 to 5 mA 8 15 mV 18 35 mA Short circuit current 7/12 5 A6902D 5 Package mechanical data In order to meet environmental requirements, ST offers these devices in ECOPACK® packages. These packages have a lead-free second level interconnect . The category of second level interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com 8/12 Package mechanical data Table 5. A6902D 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 D(1) 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. Dimension D does not include mold flash, protrusions or gate burrs. Mold flash, protrusions or gate burrs shall not exceed 0.15mm (0.006 inch) in total (both side). 9/12 A6902D 6 Order codes Table 6. Order codes Order codes Package A6902D Packaging Tube SO-8 A6902D13TR Tape and reel 10/12 Revision history 7 A6902D Revision history Table 7. 11/12 Document revision history Date Revision Changes 02-Oct-2007 1 Initial release 5-Nov-2007 2 Updated: Table 4 on page 6 2-May-2008 3 Updated: Table 4 on page 6 A6902D Please Read Carefully: Information in this document is provided solely in connection with ST products. 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