General features
■ 0.8V start up input voltage
■ Up to 5.5V operating input voltage
■ Internal synchronous rectifier
■ Adjustable output voltage from 1.8V
■ 3.3V and 5V fixed output voltages
■ Low battery voltage detection
■ Reverse battery protection
■ 750mA input current limit
■ Switching frequency up to 1MHz
■ 1.23V reference voltage available
Applications
■ Conversion from 1 to 3 alkaline,
■ NiMH, NiCd battery cells or 1 lithium ION
■ PDA and handheld instruments
■ Digital cameras
■ Cellular phones
■ GPS
■ Distributed power
L6920DB
Synchronous rectifier step up converter
MSOP8
Description
The L6920DB is a high efficiency monolithic step
up switching converter IC especially designed for
battery powered application.
Package is MSOP8 in order to minimize PCB
space. It requires only three external components
to realize the conversion from the battery voltage
to the selected output voltage.
The minimum output voltage is 1.8V: suitable to
supply the most advanced ASIC and µP.
High switching frequency allows for a low profile,
small sized inductor and output capacitor to be
used.
Reference voltage, low battery detection and
Shutdown are provided together with over current.
Application circuit
L6920DB
October 2006 Rev 5 1/16
3.3V
www.st.com
16
Contents L6920DB
Contents
1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Typical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1 Principle of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2 Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.3 Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4 Low battery detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.5 Low battery input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.6 Reverse polarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.7 Output voltage selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2/16
L6920DB Pin settings
1 Pin settings
1.1 Pin connection
Figure 1. Pin connection (top view)
1.2 Pin description
Table 1. Pin description
N° Type Description
1 FB Output voltage selector. Connect FB to GND for Vout=5V or to OUT for
Vout=3.3V. Connect FB to an external resistor divider for adjustable
output voltage
2 LBI Battery low voltage detector input. The internal threshold is set to 1.23V.
A resistor divider is needed to adjust the desired low battery threshold.
3LBO
4 REF 1.23V reference voltage. Bypass this output to GND with a 100nF
5 SHDN
6 GND Ground pin
7 LX Step-up inductor connection
8 OUT Power OUTPUT pin
Battery low voltage detector output. If the voltage at the LBI pin drops
below the internal threshold typ. 1.23V, LBO goes low.
The LBO is an open drain output and so a pull-up resistor (about
200KΩ) has to be added for correct output setting .
capacitor for filtering high frequency noise. No capacitor is required for
stability
Shutdown pin. When pin 5 is below 0.2V the device is in shutdown,
when pin 5 is above 0.6V the device is operating.
3/16
Electrical data L6920DB
2 Electrical data
2.1 Maximum ratings
Table 2. Absolute maximum ratings
Symbol Parameter Value Unit
V
ccmax
Vcc to GND 6 V
LBI, SHDN
, FB to GND 6 V
V
out max
Vout to GND 6 V
2.2 Thermal data
Table 3. Thermal data
Symbol Parameter Value Unit
R
thJA
T
Maximum thermal resistance junction-ambient 180 ° C/W
Maximum junction temperature 150 °C
J
4/16
L6920DB Electrical characteristics
3 Electrical characteristics
Table 4. Electrical characteristcs
(V
= 2V, FB = GND, TJ = 25°C unless otherwise specified)
IN
Symbol Parameter Test condition Min Typ Max Unit
V
Section
CC
V
Minimum Start Up Input
IN
Voltage
I
Quiescent Current
q
= 3.3V
V
out
= 0 mA, FB = 1.4V, V
I
l
LBI = SHDN = 2V
Il = 0 mA, FB = 1.4V, V
LBI = SHDN = 2V
= 3.3V
out
out
= 5V
0.8 V
912µA
11 15 µA
I
Shut Down Current
sd
Irev Reverse battery current
Power section
R
R
Active switch ON resistance 300 mΩ
on-N
Synchronous switch ON
on-P
resistance
Control section
V
ou
t
Output voltage
Output voltage range External divider 1.8 5.2 V
V
V
T
onmax
T
offmin
SHDN
LBI threshold
LBI
LBO logic LOW
LBO
I
LX switch current limit
lim
Maximum on time
Minimum off time
SHDN logic LOW 0.2 V
= 5V, Il = 0 mA
V
V
in
= -4V
in
0.1 1 µA
0.1 1 µA
300 mΩ
FB = OUT, I
FB = GND, I
= 0 mA 3.2 3.3 3.4
l
= 0 mA 4.955.1
l
1.23
= 1mA 0.2 0.4
I
sink
0.7 0.8 0.9
V
= 3.3V 3.75 5 6.25
out
= 3.3V 0.75 1 1.25
V
out
V
V
V
V
A
µs
µs
SHDN logic HIGH 0.6 V
V
Reference Voltage
ref
1.18 1.23 1.27
V
5/16
Typical performance L6920DB
0
0
4 Typical performance
Figure 2. Efficiency vs output current @ V
95
Vin=2. 4V
90
85
80
Vin=1. 2V
75
70
65
60
55
50
45
40
0.1 1 10 100 100
Figure 3. Efficiency vs output current @ V
100
Vin=3. 6V
90
80
70
60
50
40
30
20
10
0
0.1 1 10 100 100
Vi n=1 . 2 V
OUT
OUT
= 3.3V
L6920DB
Vout=3. 3V
L=10µ H
Cout=47 µF
Ci n=10µF
= 5V
Vin=2. 4V
L6920DB
Vout=5V
L=10µH
Cout=47µF
Cin=10µF
Figure 4. Start up voltage vs output current @ V
VStar t up vs . out put cur rent
1600
1500
1400
1300
1200
1100
1000
VStar t u p (mV)
6/16
Vout=5V
900
800
700
600
0.1 1 10 100 1000
Out put cu rr ent (mA)
= 5V & V
out
VStar t up v s. ou tput cur rent
1600
Vout =3.3V
1500
1400
1300
1200
1100
1000
VStart up (mV)
900
800
700
600
0.1 1 10 100 1000
= 3.3V
out
Output cur rent (mA)
L6920DB Detailed description
5 Detailed description
The L6920DB is a high efficiency, low voltage step-up DC/DC converter particularly suitable
for 1 to 3 cells (Li-Ion/ polymer, NiMH respectively) battery up conversion.
These performances are achieved via a strong reduction of quiescent current (10µA only)
and adopting a synchronous rectification that implies also a reduced cost in the application
(no external diode required).
Operation is based on maximum ON time - minimum OFF time control, tailored by a current
limit set to 800mA. A simplified block diagram is shown here below.
Figure 5. Simplified block diagram
V
REF
SHDN
LBO
-
+
VBG
FB Y
V
OUT
A
GND
B
R
C
-
+
Y
VBG
1,R2
-
+
Toff min
1µsec
VBG
OPAMP
(CR)
LBI
A
B
C
5.1 Principle of operation
In L6920DB the control is based on a comparator that continuously checks the status of
output voltage.
ZERO CROSSING
RQS
Ton max
5µsec
-
+
- +
CURRENT LIMIT
OUT
VOUT
LX
-
+
GND
FB
D99IN1041
V
OUT
V
IN
If the output voltage is lower than the expected value, the control function of the L6920DB
directs the energy stored in the inductor to be transferred to the load. This is accomplished
by alternating between two basic steps:
● T
phase: the energy is transferred from the battery to the inductor by shorting LX
ON
node to ground via the N-channel power switch. The switch is turned off if the current
flowing in the inductor reaches 750mA or after a maximum on time set to 5µs.
● T
phase: the energy stored in the inductor is transferred to the load through the
OFF
synchronous switch for at least a minimum off time equal to 1µs. After this, the
synchronous switch is turned off as soon as the output voltage goes lower than the
regulated voltage or the current flowing in the inductor goes down to zero.
7/16
Detailed description L6920DB
So, in case of light load, the device works in PFM mode, as shown in Figure 8:
Figure 6. PFM mode condition: V
Current
= 5V; V
out
=1.5V ; C2 = V
batt
; C3 = Inductor
out
Figure 7 shows how the device works in case of heavy load.
Figure 7. Heavy load conditions C2 = V
V
=1.5V
batt
; C3 = Inductor Current; V
out
= 5V;
out
8/16
L6920DB Detailed description
Considering that current in the inductor is limited to 800mA, the maximum load current is
defined by the following relationship:
Equation 1
I
LOAD_LIM
Where η is the efficiency and I
Of course, if I
is greater than I
LOAD
LIM
Figure 8. No regulation C2 = V
V
in
⎛⎞
---------- -
V
I
LIMTOFF_MIN
⎝⎠
out
V
outVin
-------------------------
⋅–
2L⋅
–
η⋅⋅=
= 750mA
LOAD_LIM
; C3 = Inductor Current
out
the regulation is lost (Figure 8).
5.2 Start-up
One of the key features of L6920DB is the startup at supply voltage down to 0.8V (please
see the diagram in Figure 4).
The device leaves the startup mode of operation as soon as Vout goes over 1.4V. During
startup, the synchronous switch is off and the energy is transferred to the load through its
intrinsic body diode.
The N-channel switches with a very low R
bias the power MOS gate. Because of this modified behavior, T
lengthened. Current limit and zero crossing detection are still available.
thanks to an internal charge pump used to
DS(on)
ON/TOFF
9/16
times are
Detailed description L6920DB
5.3 Shutdown
In shutdown mode (SHDN pulled low) all internal circuitries are turned off, minimizing the
current provided by the battery (I
Both switches are turned off, and the low battery comparator output is forced in high
impedance state.
The synchronous switch body diode causes a parasitic path between power supply and
output that can't be avoided also in shutdown.
< 100 nA, in typical case).
SHDN
5.4 Low battery detection
The L6920DB includes a low battery detector comparator.
Threshold is V
the threshold slowly. The LBO
proper use.
voltage and a hysteresis is added to avoid oscillations when input crosses
REF
5.5 Low battery input
It is possible to fix, using an external resistor divider, the LBO threshold, in order to adapt
the LBO
Equation 2
Where V
detection at the correct input source, by the following equation:
is the battery voltage at which the internal comparetor is triggered.
batt-th
5.6 Reverse polarity
A protection circuit has been implemented to avoid that L6920DB and the battery are
destroyed in case of wrong battery insertion.
In addition, this circuit has been designed so that the current required by the battery is zero
also in reverse polarity.
is an open drain output so a pull up resistor is required for a
R1
V
batt-th
1.23V= 1
⎛⎞
------- -+
⋅
⎝⎠
R2
If a battery can be inserted in reverse direction, a non polarized capacitor should be
installed in location of C2.
5.7 Output voltage selection
Output voltage must be selected acting on FB pin.
Three choices are available: fixed 3.3V, 5V or adjustable output set via an external resistor
divider.
10/16
L6920DB Detailed description
V
V
V
V
Table 5. Output voltage connection
V
out
V
out
1.8V < V
= 3.3V
= 5V
< 5.5V
out
FB pin connected to OUT (see application circuit)
FB pin connected to GND
FB pin connected to a resistive divider
V
out
1.23V 1
R4
⎛⎞
------- -+
⋅=
⎝⎠
R5
Figure 9. Test circuit
R2
R2
_____
_____
2
2
SHDN
SHDN
5
5
V
V
OUT
OUT
8
8
C1
C1
47µF
R3
___
___
LBO
LBO
3
3
FB
FB
1
1
R3
200KΩ
200KΩ
R5
R5
200KΩ
200KΩ
R4
R4
47µF
=2.5
=2.5
V
V
OUT
OUT
BATT
BATT
=1.5V
=1.5V
C2
C2
47µF
47µF
L1 10µH
L1 10µH
C4
C4
100nF
100nF
R1
R1
LBI
LBI
V
V
BATT
BATT
7
7
L6920DB
L6920DB
GND
GND
4
4
L6920DB
6
6
V
V
REF
REF
11/16
Package mechanical data L6920DB
6 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
12/16
L6920DB Package mechanical data
Table 6. MSOP8 Mechanical data
Dim.
Min Typ Max Min Typ Max
A 1.10 0.043
A1 0.050 0.150 0.002 0.006
A2 0.750 0.850 0.950 0.03 0.033 0.037
b 0.250 0.400 0.010 0.016
c 0.130 0.230 0.005 0.009
D
(1)
2.900 3.000 3.100 0.114 0.118 0.122
E 4.650 4.900 5.150 0.183 0.193 0.20
E1
(1)
2.900 3.000 3.100 0.114 0.118 0.122
e 0.650 0.026
L 0.400 0.550 0.700 0.016 0.022 0.028
L1 0.950 0.037
k 0° (min.) 6° (max.)
aaa 0.100 0.004
mm. inch
1. D and F does not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm
(.006inch) per side.
Figure 10. Package dimensions
13/16
Order code L6920DB
7 Order code
Table 7. Order code
Part number Package Packaging
L6920DB MSOP8 Tube
L6920DBTR MSOP8 Tape and reel
14/16
L6920DB Revision history
8 Revision history
Table 8. Revision history
Date Revision Changes
18-Mar-2005 1 First issue
Changed from “Preliminary Data” to “Datasheet”.
03-Aug-2005 2
01-Jun-2006 3 New template, modified application circuit and Figure 9.
13-Oct-2006 4 Cover page description updated.
30-Oct-2006 5 Typo in Figure 7 on page 8
Modified Section 1 and Table 5.
Added Figg. 3, 6 and new Section 3.
15/16
L6920DB
Please Read Carefully:
Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the
right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any
time, without notice.
All ST products are sold pursuant to ST’s terms and conditions of sale.
Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no
liability whatsoever relating to the choice, selection or use of the ST products and services described herein.
No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this
document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products
or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such
third party products or services or any intellectual property contained therein.
UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED
WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS
OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT.
UNLESS EXPRESSLY APPROVED IN WRITING BY AN AUTHORIZED ST REPRESENTATIVE, ST PRODUCTS ARE NOT
RECOMMENDED, AUTHORIZED OR WARRANTED FOR USE IN MILITARY, AIR CRAFT, SPACE, LIFE SAVING, OR LIFE SUSTAINING
APPLICATIONS, NOR IN PRODUCTS OR SYSTEMS WHERE FAILURE OR MALFUNCTION MAY RESULT IN PERSONAL INJURY,
DEATH, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE. ST PRODUCTS WHICH ARE NOT SPECIFIED AS "AUTOMOTIVE
GRADE" MAY ONLY BE USED IN AUTOMOTIVE APPLICATIONS AT USER’S OWN RISK.
Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void
any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any
liability of ST.
ST and the ST logo are trademarks or registered trademarks of ST in various countries.
Information in this document supersedes and replaces all information previously supplied.
The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners.
© 2006 STMicroelectronics - All rights reserved
STMicroelectronics group of companies
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -
Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
www.st.com
16/16
Loading...