L6902
Up to 1 A switching regulator with adjustable current limit
Features
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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
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
Package
SO-8
L6902D013TR
Tape and reel
Packaging
Tube
SO-8
Applications
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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
Order codes
L6902D
November 2010
Doc ID 7332 Rev 9
1/11
www.st.com
11
Content
L6902
Content
1
2
3
4
5
6
7
Test and application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2/11
Doc ID 7332 Rev 9
L6902
Test and application circuit
1
Test and application circuit
Figure 1.
Test and application circuit
2
Pin connection
Figure 2.
Pin connection
Table 2.
N°
1
2
3
4
Pin
OUT
CS+
CS-
Pin description
Function
Regular output
Current error amplifier input (current sense at higher voltage)
Current error amplifier input (current sense at lower voltage)
COMP E/A output to be used for frequency compensation
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:
V
out
=
V
FB
⋅ ⎛
1
+
R1
⎞
=
1.235V
⎛
1
+
R1
⎞
-------
-
-------
-
⎝
⎝
R2
⎠
R2
⎠
3.3 V VREF. No cap is need for stability.
Ground
Unregulated DC input voltage.
5
FB
6
7
8
VREF
GND
VCC
Doc ID 7332 Rev 9
3/11
Maximum ratings
L6902
3
Maximum ratings
Table 3.
Symbol
V
8
V
1
I
1
V
4
, V
5
V
2
, V
3
P
tot
T
j
T
stg
Input voltage
Output DC voltage output peak voltage at t = 0.1
μs
Maximum output current
Analog pins
Analog pins
Power dissipation at T
amb
≤
70 °C
Operating junction temperature range
Storage temperature range
Absolute maximum ratings
Parameter
Value
40
-1 to 40 -5 to 40
Internally limited
4
-0.3V to VCC
0.7
-40 to 150
-55 to 150
V
V
W
°C
°C
Unit
V
VV
Table 4.
Symbol
Rth j-amb
Thermal data
Parameter
Thermal Resistance Junction to Ambient Max.
Value
110
(1)
Unit
°C/W
1. Package mounted on board.
4/11
Doc ID 7332 Rev 9
L6902
Internal block diagram
4
Internal block diagram
Figure 3.
Block diagram
Doc ID 7332 Rev 9
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