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A6902D
Up to 1 A step down switching regulator with adjustable current limit for automotive applications
Features

Qualified following the AEC-Q100 requirements (see PPAP for more details) 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.
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Application schematic
VCC VREF OUT L1 22H D1 Rsense 100mO R1 5.6kO C4 100F 10V R3 5.1kO GND R2 3.3kO VOUT=3.3V
VIN=8V to 36V
VIN=8V to 36V C1 10F 35V C3 220pF C2 22nF
COMP
L6902D
CS+ CSFB
STPS340U
April 2009
Doc ID 13959 Rev 5
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www.st.com 12
Contents
A6902D
Contents
1 2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 2.2 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 3.2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 5 6 7
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
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Description
1
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 m 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.
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Pin connection
A6902D
2
2.1
Pin connection
Pin connection
Figure 2. Pin connection (top view)
2.2
Pin description
Table 1.
N 1 2 3 4 5 6 7 8
Pin description
Pin OUT CS+ CSCOMP FB VREF GND VCC Regulator output. Current error amplifier input (current sense at higher voltage) Current error amplifier input (current sense at lower 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. 3.3 V reference voltage. No cap is need for stability. Ground. Unregulated DC input voltage. Description
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Electrical data
3
3.1
Electrical data
Maximum ratings
Table 2.
Symbol V8 V1 I1 V4 , V5 V2, V3 PTOT TJ TSTG Input voltage OUT pin DC voltage OUT pin peak voltage at t = 0.1 s Maximum output current Analog pins Analog pins Power dissipation at TA 70 C Operating junction temperature range Storage temperature range
Absolute maximum ratings
Parameter Value 40 -1 to 40 -5 to 40 int. limit. 4 -0.3 to VCC 0.7 -40 to 150 -55 to 150 V V W C C Unit V V V
3.2
Thermal data
Table 3.
Symbol RthJA
Thermal data
Parameter Maximum thermal resistance junction-ambient SO8 110 (1) Unit C/W
1. Package mounted on board
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Electrical characteristics
A6902D
4
Electrical characteristics
TJ = -40 to 125 C, VCC = 12 V, unless otherwise specified Table 4.
Symbol VCC RDS(on) IL fSW
Electrical characteristics
Parameter Operating input voltage range MOSFET on resistance Maximum limiting current (1) Switching frequency Duty cycle VCC = 8.5 V VCC = 8.5 V, TJ = 25 C 1.8 2 212 0 Test conditions V0 = 1.235 V; I0 = 2 A Min. 8 0.250 2.5 2.5 250 Typ. Max. 36 0.5 3.2 A 3.2 280 100 kHz % Unit V
Dynamic characteristics (see test circuit) V5 Voltage feedback Efficiency 8 V < VCC < 36 V, 20 mA < I0 < 1 A V0 = 5 V, VCC = 12 V 1.198 1.235 90 1.272 V %
DC characteristics Iqop Iq Total operating quiescent current Quiescent current Duty cycle = 0; VFB = 1.5 V 3 5 2.7 mA mA
Error amplifier VOH VOL Io source
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High level output voltage Low level output voltage Source output current Sink output current Source bias current DC open loop gain
VFB=1 V VFB=1.5 V VCOMP = 1.9 V; VFB = 1 V VCOMP = 1.9 V; VFB = 1.5 V
3.6 0.4 160 1 300 1.5 2.5 4
V V A mA A dB mS 110 3 3 mV A A
Io sink Ib
RL=
50
58 2.3
gm VOFFS ICS+ ICS-
Transconductance Input offset voltage CS+ output current CS- output current
ICOMP = -0.1 mA to 0.1 mA; VCOMP = 1.9 V VCS- = 1.8 V; VCS+ = Vcomp I0 =1 A; RSENSE =100 m; VOUT < VCC-2 V I0 =1A; RSENSE =100 m; VOUT < VCC-2 V 90
8
100 1.5 1.5
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A6902D Table 4.
Symbol
Electrical characteristics Electrical characteristics (continued)
Parameter Test conditions Min. Typ. Max. Unit
Reference section Reference voltage Line regulation Load regulation Short circuit current IREF = 0 to 5 mA VCC = 8 V to 36 V IREF = 0mA VCC = 8 V to 36 V IREF = 0 to 5 mA 5 3.2 3.3 5 8 18 3.399 10 15 35 V mV mV mA
1. With TJ = 85 C, Ilim_min = 2 A, assured by design, characterization and statistical correlation.
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Package mechanical data
A6902D
5
Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK(R) packages, depending on their level of environmental compliance. ECOPACK(R) specifications, grade definitions and product status are available at: www.st.com. ECOPACK(R) is an ST trademark.
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Package mechanical data
Table 5.
Dim
SO-8 mechanical data
mm Min. Typ. Max. 1.75 0.25 1.65 0.51 0.25 5.00 4.00 1.27 5.80 0.25 0.40 6.20 0.50 1.27 0.228 0.010 0.016 Min. 0.053 0.004 0.043 0.013 0.007 0.189 0.15 0.050 0.244 0.020 0.050 inch Typ. Max. 0.069 0.010 0.065 0.020 0.010 0.197 0.157
A A1 A2 B C D(1) E e H h L k ddd
1.35 0.10 1.10 0.33 0.19 4.80 3.80
0 (min), 8 (max) 0.10 0.004
1. 1. Dimension D does not include mold flash, protrusions or gate burrs. Mold flash, protrusions or gate burrs shall not exceed 0.15 mm (0.006 inch) in total (both side).
Figure 3.
Package dimensions
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Order codes
A6902D
6
Order codes
Table 6. Ordering information
Order codes A6902D SO-8 A6902D13TR Tape and reel Package Packaging Tube
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Revision history
7
Revision history
Table 7.
Date 02-Oct-2007 5-Nov-2007 2-May-2008 28-Aug-2008 23-Apr-2009
Document revision history
Revision 1 2 3 4 5 Initial release Updated: Table 4 on page 6 Updated: Table 4 on page 6 Updated: Coverpage and Table 4 on page 6 Updated first feature in coverpage Changes
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A6902D
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