STMICROELECTRONICS A6902D

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
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