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L6902D
June 2002
s
UP TO 1A OUTPUT CURRENT
s
OPERATING INPUT VOLTAGE FROM 8V TO 36V
s
PRECISE 3.3V (2%) REFERENCE VOLTAGE
s
5% OUTPUT CURRENT ACCURACY
s
OUTPUT VOLTAGE ADJUSTABLE FROM
1.235V TO 34V
s
250KHz INTERNALLY FIXED FREQUENCY
s
VOLTAGE FEEDFORWARD
s
ZERO LOAD CURRENT OPERATION
s
ADJUSTABLE CURRENT LIMIT
s
PROTECTION AGAINST FEEDBACK
DISCONNECTION
s
THERMAL SHUTDOWN
APPLICATIONS
s
CHARGERS FOR NiCd, NiMH BATTERIES
AND PREREGULATOR FOR LITHIUM-ION
BATTERIES
s
ADJUSTABLE CURRENT GENERATOR
s
SIMPLE STEP-DOWN CONVERTERS WITH
ADJUSTABLE CURRENT LIMIT
s
BATTERY EQUIPPED SYSTEMS
s
DISTRIBUTED POWER SUPPLY
s
MOBILE PC & SUBNOTEBOOK
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 cur-
rent error amplifier to have a constant voltage and con-
stant current control.
By means of an on board current sense resistor and
the availability of the current sense pins (both com-
patible to Vcc and for Cs- compatible with GND too)
a current limit programming is very simple and accu-
rate (5%). Moreover constant current control can be
used to charge NiMH and NiCd batteries.
The device can be used as a standard DC/DC con-
verter with adjustable current limit (set by using the
external sense resistor).
The internal robust P-Channel DMOS transistor with a
typical of 250m
assures high efficiency and a mini-
mum dropout even at high output current level. The in-
ternal limiting current (latched function) of typical value
of 2.5A 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 (150C with 20C hysteresis), the
power stage is turned off.
SO8
ORDERING NUMBERS: L6902D
L6902D013TR (Tape & Reel)
UP TO 1A SWITCHING REGULATOR WITH
ADJUSTABLE CURRENT LIMIT
TEST AND APPLICATION CIRCUIT
L1 22
H
OUT
C1
10
F
25V
CERAMIC
C3
220pF
C2
22nF
D1
STPS340U
R3
5.1K
C4
100
F
10V
POSCAP
R1
5.6K
R
SENSE
100m
R2
3.3K
V
IN
=8V to 36V
3.3V
V
OUT
=3.3V
V
CC
COMP
VREF
GND
FB
D01IN1306A
8
6
4
2
3
5
1
7
L6902D
2/6
DESCRIPTION (Continued)
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 250KHz, and the SO-8 package pin allow to built an ultra compact DC/
DC converter with a minimum board space.
PIN CONNECTION
PIN DESCRIPTION
THERMAL DATA
(*) Package mounted on board.
ABSOLUTE MAXIMUM RATINGS
N
Pin
Function
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
COMP
E/A output to be used for frequency compensation
5
FB
Stepdown feedback input. Connecting directly to this pin results in an output voltage of 1.235V.
An external resistive divider is required for higher output voltages. In this case:
6
V
REF
3.3V VREF. No cap is need for stability.
7
GND
Ground
8
VCC
Unregulated DC input voltage.
Symbol
Parameter
Value
Unit
R
th j-amb
Thermal Resistance Junction to Ambient Max.
110 (*)
C/W
Symbol
Parameter
Value
Unit
V
8
Input Voltage
40
V
V
1
Output DC voltageOutput peak voltage at t = 0.1
s
-1 to 40
-5 to 40
V
V
I
1
Maximum output current
Internally limited
V
4
, V
5
Analog pins
4
V
V
2
, V
3
Analog pins
-0.3V to V
CC
V
P
tot
Power dissipation at T
amb
70 C
0.7
W
Tj
Operating junction temperature range
-40 to 150
C
T
stg
Storage temperature range
-55 to 150
C
8
6
4
7
3
2
5
1
O U T
C S +
C S -
C O M P
V C C
G N D
V R E F
F B
V
out
V
F B
1
R1
R2
--------
+
1.235V 1
R 1
R 2
--------
+
=
=
3/6
L6902D
INTERNAL BLOCK DIAGRAM
ELECTRICAL CHARACTERISTCS
(T
j
= 25C, V
CC
= 12V, unless otherwise specified.) () Specification Referred to Tj from 0 to 125C.
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
V
CC
Operating input voltage range
V
O
= 1.235V; I
O
= 1A
8
36
V
V
d
Dropout voltage
V
CC
= 8V; I
O
= 1A
0.25
0.5
V
I
O
Operating charging current
R
sense
= 0.1
0.95
1
1.05
A
0.92
1.08
A
I
l
Maximum limiting current
V
CC
= 8V to 36V
2
2.5
3.2
A
fs
Switching frequency
212
250
287
kHz
225
250
275
kHz
d
Duty cycle
0
100
%
DYNAMIC CHARACTERISTICS
V
5
Voltage feedback (FB)
8V < V
CC
< 36V,
20mA < I
O
< 1A
1.21
1.235
1.259
V
1.198
1.235
1.272
V
Efficiency
V
O
= 5V, V
CC
= 12V
90
%
DC CHARACTERISTICS
I
qop
Total operating quiescent
current
3
5
mA
I
q
Quiescent current
Duty cycle = 0; VFB = 1.5V
2.7
mA
VREF
GOOD
3.8V
COMP
VFB
DRIVER
INHIBIT
+
-
1.235V
E/A
1.235V
THERMAL
SHUTDOWN
-
+
PWM
OSCILLATOR
OUT
V
cc
GND
V
ref
SUPPLY
TRIMMING
FREQUENCY
SHIFTER
VOLTAGES
MONITOR
D
Q
CK
CURRENT LIMITING
PEAK TO PEAK
+
-
Current_E/A
Voltage_E/A
CS-
CS+
L6902D
4/6
VOLTAGE ERROR AMPLIFIER
V
OH
High level output voltage
V
FB
= 1V
3.6
V
V
OL
Low level output voltage
V
FB
= 1.5
0.4
V
I
o source
Source output current
V
comp
= 1.9V; V
FB
= 1V
200
300
A
I
o sink
Sink output current
V
comp
= 1.9V; V
FB
= 1.5V
1
1.5
mA
I
b
Source bias current
2.5
4
A
DC open loop gain
R
L
= 0
50
58
dB
g
m
Transconductance
I
comp
= -0.1 to 0.1mA
V
comp
= 1.9V
2.3
mS
CURRENT ERROR AMPLIFIER
V
offs
Input offset voltage
V
CS-
= 1.8V; V
CS+
= V
comp
90
100
110
mV
I
CS+
CS+ Output Current
I
O
= 1A, R
sense
= 100m
V
out
< V
CC
-2V
1.5
3
A
I
CS-
CS- Output Current
I
O
= 1A, R
sense
= 100m
V
out
< V
CC
-2V
1.5
3
A
REFERENCE SECTION
Reference Voltage
3.234
3.3
3.366
V
I
REF
= 0 to 5mA
V
CC
= 8V to 36V
3.2
3.3
3.399
V
Line Regulation
I
REF
= 0mA
V
CC
= 8V to 36V
5
10
mV
Load Regulation
I
REF
= 0 to 5mA
8
15
mV
Short Circuit Current
10
mA
ELECTRICAL CHARACTERISTCS (continued)
(T
j
= 25C, V
CC
= 12V, unless otherwise specified.) () Specification Referred to Tj from 0 to 125C.
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
5/6
L6902D
DIM.
mm
inch
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
A
1.75
0.069
a1
0.1
0.25
0.004
0.010
a2
1.65
0.065
a3
0.65
0.85
0.026
0.033
b
0.35
0.48
0.014
0.019
b1
0.19
0.25
0.007
0.010
C
0.25
0.5
0.010
0.020
c1
45
(typ.)
D (1)
4.8
5.0
0.189
0.197
E
5.8
6.2
0.228
0.244
e
1.27
0.050
e3
3.81
0.150
F (1)
3.8
4.0
0.15
0.157
L
0.4
1.27
0.016
0.050
M
0.6
0.024
S
8
(max.)
(1) D and F do not include mold flash or protrusions. Mold flash or
potrusions shall not exceed 0.15mm (.006inch).
SO8
OUTLINE AND
MECHANICAL DATA
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of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted
by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
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L6902D
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