L6902D
UP TO 1A SWITCHING REGULATOR WITH
ADJUSTABLE CURRENT LIMIT
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FEATURES
UP TO 1A OUTPUT CURRENT
OPERATING INPUT VOLTAGE FROM 8V TO 36V
PRECISE 3.3V (±2%) REFERENCE VOLTAGE
5% OUTPUT CURRENT ACCURACY
OUTPUT VOLTAGE ADJUSTABLE FROM
1.235V TO 34V
250KHz INTERNALLY FIXED FREQUENCY
VOLTAGE FEEDFORWARD
ZERO LOAD CURRENT OPERATION
ADJUSTABLE CURRENT LIMIT
PROTECTION AGAINST FEEDBACK
DISCONNECTION
THERMAL SHUTDOWN
Figure 1. Package
SO-8
Table 1. Order Codes
Part Number
L6902D
L6902D013TR
Package
SO-8
SO-8 in Tape & Reel
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 250mΩ 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 (150°C with 20°C hysteresis), the
power stage is turned off.
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APPLICATIONS
CHARGERS FOR NiCd, NiMH BATTERIES
AND PREREGULATOR FOR LITHIUM-ION
BATTERIES
ADJUSTABLE CURRENT GENERATOR
SIMPLE STEP-DOWN CONVERTERS WITH
ADJUSTABLE CURRENT LIMIT
BATTERY EQUIPPED SYSTEMS
DISTRIBUTED POWER SUPPLY
MOBILE PC & SUBNOTEBOOK
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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-
Figure 2. Test And Application Circuit
V
IN
=8V to 36V
3.3V
C1
10µF
25V
CERAMIC
V
CC
VREF
COMP
C2
22nF
R3
5.1K
GND
8
6
4
2
3
7
5
1
OUT
L1 22µH
D1
STPS340U
R
SENSE
100mΩ
R1
5.6K
V
OUT
=3.3V
FB
R2
3.3K
C3
220pF
C4
100µF
10V
POSCAP
D01IN1306A
October 2004
Rev. 8
1/7
L6902D
3 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.
Figure 3. Pin Connection
OUT
CS+
CS-
COMP
1
2
3
4
8
7
6
5
VCC
GND
VREF
FB
Table 2. Pin Description
N°
1
2
3
4
5
Pin
OUT
CS+
CS-
COMP
FB
Regular Output
Current Error Amplifier input (current sense at higher voltage)
Current Error Amplifier input (current sense at lower voltage)
E/A output to be used for frequency compensation
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:
V
out
=
V
FB
⋅
1
+
R1
=
1.235V
1
+
R1
-------
-
-------
-
R2
R2
6
7
8
V
REF
GND
VCC
3.3V VREF. No cap is need for stability.
Ground
Unregulated DC input voltage.
Function
Table 3. Thermal Data
Symbol
R
th j-amb
(*) Package mounted on board.
Parameter
Thermal Resistance Junction to Ambient Max.
Value
110 (*)
Unit
°C/W
Table 4. Absolute Maximum Ratings
Symbol
V
8
V
1
I
1
V
4
, V
5
V
2
, V
3
P
tot
Tj
T
stg
Input Voltage
Output DC voltageOutput peak voltage at t = 0.1µs
Maximum output current
Analog pins
Analog pins
Power dissipation at T
amb
≤
70 °C
Operating junction temperature range
Storage temperature range
Parameter
Value
40
-1 to 40
-5 to 40
Internally limited
4
-0.3V to V
CC
0.7
-40 to 150
-55 to 150
V
V
W
°C
°C
Unit
V
V
V
2/7
L6902D
Figure 4. Internal Block Diagram
V
cc
VOLTAGES
MONITOR
3.8V
1.235V
CS+
Current_E/A
+
-
CS-
COMP
PEAK TO PEAK
CURRENT LIMITING
Voltage_E/A
VFB
1.235V
+
E/A
-
-
+
PWM
INHIBIT
SUPPLY
VREF
GOOD
V
ref
THERMAL
SHUTDOWN
TRIMMING
D
CK
Q
DRIVER
OSCILLATOR
OUT
FREQUENCY
SHIFTER
GND
Table 5. Electrical Characteristcs
(T
j
= 25°C, V
CC
= 12V, unless otherwise specified.) (•) Specification Referred to Tj from 0 to 125°C.
Symbol
V
CC
V
d
I
O
Parameter
Operating input voltage range
Dropout voltage
Operating charging current
Test Condition
V
O
= 1.235V; I
O
= 1A
V
CC
= 8V; I
O
= 1A
R
sense
= 0.1Ω
•
I
l
fs
Maximum limiting current
Switching frequency
V
CC
= 8V to 36V
•
•
•
•
0.95
0.92
2
212
225
d
Duty cycle
0
2.5
250
250
Min.
8
0.25
1
Typ.
Max.
36
0.5
1.05
1.08
3.2
287
275
100
Unit
V
V
A
A
A
kHz
kHz
%
DYNAMIC CHARACTERISTICS
V
5
Voltage feedback (FB)
8V < V
CC
< 36V,
20mA < I
O
< 1A
V
O
= 5V, V
CC
= 12V
1.21
•
1.198
1.235
1.235
90
1.259
1.272
V
V
%
η
Efficiency
DC CHARACTERISTICS
I
qop
I
q
Total operating quiescent
current
Quiescent current
Duty cycle = 0; VFB = 1.5V
•
3
5
3
mA
mA
3/7
L6902D
Table 5. Electrical Characteristcs
(continued)
(T
j
= 25°C, V
CC
= 12V, unless otherwise specified.) (•) Specification Referred to Tj from 0 to 125°C.
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
VOLTAGE ERROR AMPLIFIER
V
OH
V
OL
I
o source
I
o sink
I
b
High level output voltage
Low level output voltage
Source output current
Sink output current
Source bias current
DC open loop gain
g
m
Transconductance
R
L
= 0
I
comp
= -0.1 to 0.1mA
V
comp
= 1.9V
50
V
FB
= 1V
V
FB
= 1.5
V
comp
= 1.9V; V
FB
= 1V
V
comp
= 1.9V; V
FB
= 1.5V
200
1
300
1.5
2.5
58
2.3
4
3.6
0.4
V
V
µA
mA
µA
dB
mS
CURRENT ERROR AMPLIFIER
V
offs
I
CS+
I
CS-
Input offset voltage
CS+ Output Current
V
CS-
= 1.8V; V
CS+
= V
comp
I
O
= 1A, R
sense
= 100mΩ
V
out
< V
CC
-2V
I
O
= 1A, R
sense
= 100mΩ
V
out
< V
CC
-2V
95
100
1.5
105
3
mV
µA
µA
CS- Output Current
1.5
3
REFERENCE SECTION
Reference Voltage
I
REF
= 0 to 5mA
V
CC
= 8V to 36V
Line Regulation
I
REF
= 0mA
V
CC
= 8V to 36V
I
REF
= 0 to 5mA
10
•
3.234
3.2
3.3
3.3
3.366
3.399
V
V
5
10
mV
Load Regulation
Short Circuit Current
8
15
mV
mA
4/7
L6902D
Figure 5. SO-8 Mechanical Data & Package Dimensions
mm
DIM.
MIN.
A
A1
A2
B
C
D
(1)
E
e
H
h
L
k
ddd
5.80
0.25
0.40
1.35
0.10
1.10
0.33
0.19
4.80
3.80
1.27
6.20
0.50
1.27
0.228
0.010
0.016
TYP.
MAX.
1.75
0.25
1.65
0.51
0.25
5.00
4.00
MIN.
0.053
0.004
0.043
0.013
0.007
0.189
0.15
0.050
0.244
0.020
0.050
TYP.
MAX.
0.069
0.010
0.065
0.020
0.010
0.197
0.157
inch
OUTLINE AND
MECHANICAL DATA
0˚ (min.), 8˚ (max.)
0.10
0.004
Note: (1) Dimensions D does not include mold flash, protru-
sions or gate burrs.
Mold flash, potrusions or gate burrs shall not exceed
0.15mm (.006inch) in total (both side).
SO-8
0016023 C
5/7
