November 2010 Doc ID 7332 Rev 9 1/11
11
L6902
Up to 1 A switching regulator with adjustable current limit
Features
■Up to 1 A output current
■Operating input voltage from 8 V to 36 V
■Precise 3.3 V (±2%) reference voltage
■5 % output current accuracy
■Output voltage adjustable from 1.235 V to 34 V
■250 kHz internally fixed frequency
■Voltage feedforward
■Zero load current operation
■Adjustable current limit
■Protection against feedback Disconnection
■Thermal shutdown
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 and 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
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 Cs- compatible with
GND too) a current limit programming is very
simple and accurate (±5%). 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 250KHz,
and the SO-8 package pin allow to built an ultra
compact DC/ DC converter with a minimum board
space.
Table 1. Device summary
Order codes Package Packaging
L6902D SO-8 Tube
L6902D013TR Tape and reel
SO-8
www.st.com
Content L6902
2/11 Doc ID 7332 Rev 9
Content
1 Test and application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
L6902 Test and application circuit
Doc ID 7332 Rev 9 3/11
1 Test and application circuit
Figure 1. Test and application circuit
2 Pin connection
Figure 2. Pin connection
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Table 2. Pin description
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
5FB
Stepdown feedback input. Connecting directly to this pin results in an output voltage of
1.235 V. An external resistive divider is required for higher output voltages. In this case:
6 VREF 3.3 V VREF. No cap is need for stability.
7 GND Ground
8 VCC Unregulated DC input voltage.
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Maximum ratings L6902
4/11 Doc ID 7332 Rev 9
3 Maximum ratings
Table 3. Absolute maximum ratings
Symbol Parameter Value Unit
V8 Input voltage 40 V
V1 Output DC voltage output peak voltage at t = 0.1 μs -1 to 40 -5 to 40 V V
I1 Maximum output current Internally limited
V4, V5 Analog pins 4 V
V2, V3 Analog pins -0.3V to VCC V
Ptot Power dissipation at Tamb ≤ 70 °C 0.7 W
Tj Operating junction temperature range -40 to 150 °C
Tstg Storage temperature range -55 to 150 °C
Table 4. Thermal data
Symbol Parameter Value Unit
Rth j-amb Thermal Resistance Junction to Ambient Max. 110 (1)
1. Package mounted on board.
°C/W
L6902 Internal block diagram
Doc ID 7332 Rev 9 5/11
4 Internal block diagram
Figure 3. Block diagram
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Electrical characteristics L6902
6/11 Doc ID 7332 Rev 9
5 Electrical characteristics
Tj = 25°C, VCC = 12V, unless otherwise specified.
Table 5. Electrical characteristics
Symbol Parameter Test condition Min. Typ. Max. Unit
VCC Operating input voltage range VO = 1.235V; IO = 1A 8 36 V
Vd Dropout voltage VCC = 8V; IO = 1A 0.25 0.5 V
IO Operating charging current Rsense = 0.1Ω 0.95 1 1.05 A
(1) 0.92 1.08 A
Il Maximum limiting current VCC = 8V to 36V 2 2.5 3.2 A
fs Switching frequency
(1) 212 250 287 kHz
225 250 275 kHz
d Duty cycle 0 100 %
Dynamic characteristics
V5 Voltage feedback (FB) 8V < VCC < 36V, 20mA < IO < 1A 1.21 1.235 1.259 V
(1) 1.198 1.235 1.272 V
ηEfficiency VO = 5V, VCC = 12V 90 %
DC characteristics
Iqop Total operating quiescent
current
(1) 3 5 mA
Iq Quiescent current Duty cycle = 0; VFB = 1.5V 3 mA
Voltage error amplifier
VOH High level output voltage VFB = 1V 3.6 V
VOL Low level output voltage VFB = 1.5 0.4 V
Io source Source output current Vcomp = 1.9V; VFB = 1V 200 300 µA
Io sink Sink output current Vcomp = 1.9V; VFB = 1.5V 1 1.5 mA
Ib Source bias current 2.5 4 μA
DC open loop gain RL = 0 50 58 dB
gm Transconductance Icomp = -0.1 to 0.1mA, Vcomp = 1.9V 2.3 mS
Current error amplifier
Voffs Input offset voltage VCS- = 1.8V; VCS+ = Vcomp 95 100 105 mV
ICS+ CS+ output current IO = 1A, Rsense = 100mΩ,
Vout < VCC -2V 1.5 3 µA
ICS- CS- output current IO = 1A, Rsense = 100mΩ
Vout < VCC -2V 1.5 3 µA
L6902 Electrical characteristics
Doc ID 7332 Rev 9 7/11
Symbol Parameter Test condition Min. Typ. Max. Unit
Reference section
Reference voltage 3.234 3.3 3.366 V
IREF = 0 to 5mA VCC = 8V to 36V (1) 3.2 3.3 3.399 V
Line regulation IREF = 0mA, VCC = 8V to 36V 5 10 mV
Load regulation IREF = 0 to 5 mA 8 15 mV
Short circuit current 10 mA
1. Specification Referred to TJ from -40 to 125°C. Specification over the -40 to +125 TJ Temperature range are assured by
design, characterization and statistical correlation
Table 5. Electrical characteristics (continued)
Package mechanical data L6902
8/11 Doc ID 7332 Rev 9
6 Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK is an ST trademark.
Table 1. SO-8 mechanical data
Dim.
mm. inch
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)
1. Dimensions D does not include mold flash, protrusions or gate burrs. Mold flash, potrusions or gate burrs
shall not exceed 0.15mm (.006inch) in total (both side).
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 0° (min.), 8° (max.)
ddd 0.10 0.004
L6902 Package mechanical data
Doc ID 7332 Rev 9 9/11
Figure 4. Package dimensions
Revision history L6902
10/11 Doc ID 7332 Rev 9
7 Revision history
Table 6. Document revision history
Date Revision Changes
January 2004 7 Technical migration from ST-PRESS to EDOCS.
October 2004 8 Changed style look and feel.
26-Nov-2010 9 Updated Note 1 on page 7
L6902
Doc ID 7332 Rev 9 11/11
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