ST A6902D User Manual

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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

A6902D

SO-8

Applications

■ Automotive applications

■ Adjustable current generator

■ Simple step-down converters with adjustable

current limit

Figure 1. Application schematic

=8V to 36V

10µF

35V

220pF

22nF

REF

COMP

5.1kO

L6902D

GND

OUT

CS+

CS-

L1 22µH

STPS340U

Rsense

100mO

OUT

5.6kO

3.3kO

=3.3V

100µF

10V

April 2009 Doc ID 13959 Rev 5 1/12

www.st.com

Contents A6902D

Contents

1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 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 Doc ID 13959 Rev 5

A6902D 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 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.

Doc ID 13959 Rev 5 3/12

Pin connection A6902D

2 Pin connection

2.1 Pin connection

Figure 2. Pin connection (top view)

2.2 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 E/A output for frequency compensation.

Feedback input. Connecting directly to this pin results in an output

5FB

voltage of 1.23 V. An extenal resistive divider is required for higher output voltages.

REF

3.3 V reference voltage. No cap is need for stability.

7 GND Ground.

8 VCC Unregulated DC input voltage.

4/12 Doc ID 13959 Rev 5

A6902D Electrical data

3 Electrical data

3.1 Maximum ratings

Table 2. Absolute maximum ratings

Symbol Parameter Value Unit

, V

TOT

STG

Input voltage 40 V

OUT pin DC voltage OUT pin peak voltage at Δt = 0.1 μs

Maximum output current int. limit.

Analog pins 4 V

Analog pins -0.3 to V

Power dissipation at T

Operating junction temperature range -40 to 150 °C

Storage temperature range -55 to 150 °C

3.2 Thermal data

Table 3. Thermal data

Symbol Parameter SO8 Unit

thJA

1. Package mounted on board

Maximum thermal resistance junction-ambient 110

-1 to 40

-5 to 40

≤ 70 °C 0.7 W

(1)

V V

°C/W

Doc ID 13959 Rev 5 5/12

Electrical characteristics A6902D

4 Electrical characteristics

TJ = -40 to 125 °C, V

= 12 V, unless otherwise specified

Table 4. Electrical characteristics

Symbol Parameter Test conditions Min. Typ. Max. Unit

DS(on)

Dynamic characteristics (see test circuit)

η Efficiency V

DC characteristics

qop

Error amplifier

Operating input voltage range

MOSFET on resistance

Maximum limiting

current

(1)

= 1.235 V; I0 = 2 A 8 36 V

0.250 0.5 Ω

= 8.5 V 1.8 2.5 3.2

= 8.5 V, TJ = 25 °C 2 2.5 3.2

Switching frequency 212 250 280 kHz

Duty cycle 0 100 %

Voltage feedback

8 V < V 20 mA < I0 < 1 A

Total operating quiescent current

Quiescent current Duty cycle = 0; V

= 5 V, V

< 36 V,

= 12 V 90 %

1.198 1.235 1.272 V

35mA

= 1.5 V 2.7 mA

o source

o sink

gm Transconductance

OFFS

CS+

CS-

High level output voltage

Low level output voltage

Source output current

Sink output current

Source bias current 2.5 4 μA

DC open loop gain R

Input offset voltage

CS+ output current

CS- output current

COMP

L= 50 58 dB

COMP

CS-

CS+

=1 A; R

OUT

=1A; R

OUT

6/12 Doc ID 13959 Rev 5

=1 V 3.6 V

=1.5 V 0.4 V

= 1.9 V;

= 1 V

= 1.9 V;

= 1.5 V

160 300 μA

11.5 mA

= -0.1 mA to 0.1 mA;

= 1.9 V

= 1.8 V;

= V

comp

=100 mΩ;

SENSE

< VCC-2 V

=100 mΩ;

SENSE

< VCC-2 V

90 100 110 mV

2.3 mS

1.5 3 μA

A6902D Electrical characteristics

Table 4. Electrical characteristics (continued)

Symbol Parameter Test conditions Min. Typ. Max. Unit

Reference section

= 0 to 5 mA

Reference voltage

Line regulation

Load regulation I

Short circuit current 5 18 35 mA

REF

= 8 V to 36 V

= 0mA

REF

= 8 V to 36 V

= 0 to 5 mA 8 15 mV

REF

3.2 3.3 3.399 V

510mV

1. With TJ = 85 °C, I

= 2 A, assured by design, characterization and statistical correlation.

lim_min

Doc ID 13959 Rev 5 7/12

Package mechanical data A6902D

5 Package mechanical data

In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK specifications, grade definitions and product status are available at: www.st.com. ECOPACK

packages, depending on their level of environmental compliance. ECOPACK®

is an ST trademark.

8/12 Doc ID 13959 Rev 5

A6902D Package mechanical data

Table 5. 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)

E 3.80 4.00 0.15 0.157

e1.27 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

k0° (min), 8° (max)

ddd 0.10 0.004

4.80 5.00 0.189 0.197

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

Doc ID 13959 Rev 5 9/12

Order codes A6902D

6 Order codes

Table 6. Ordering information

Order codes Package Packaging

A6902D

Tu b e

SO-8

A6902D13TR Tape and reel

10/12 Doc ID 13959 Rev 5

A6902D Revision history

7 Revision history

Table 7. 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

28-Aug-2008 4 Updated: Coverpage and Table 4 on page 6

23-Apr-2009 5 Updated first feature in coverpage

Doc ID 13959 Rev 5 11/12

A6902D

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12/12 Doc ID 13959 Rev 5

ST A6902D User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Figure 1. Application schematic

1 Description

2 Pin connection

2.1 Pin connection

Figure 2. Pin connection (top view)

2.2 Pin description

Table 1. Pin description

3 Electrical data

3.1 Maximum ratings

Table 2. Absolute maximum ratings

3.2 Thermal data

Table 3. Thermal data

4 Electrical characteristics

Table 4. Electrical characteristics

5 Package mechanical data

Table 5. SO-8 mechanical data

Figure 3. Package dimensions

6 Order codes

Table 6. Ordering information

7 Revision history

Table 7. Document revision history