LINEAR TECHNOLOGY LTC1760 Technical data
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Dual Smart Battery Charger Simplifies Battery Backup for Servers
Design Note 342
Mark Gurries
Introduction
Smart Batteries are an increasingly popular choice for
more than just traditional compact consumer electronic
devices. For example, Smart Batteries are being used as
battery backup for products such as blade servers, where
knowing battery status is very important.
PowerPathTM MUX
V
IN
6V TO 28V
SMBALERT
SCL
SDA
V
DDS
R5
1.21k
49.9k
0.012µF
0.1µF
R
CL
0.03Ω
R1
4.99k
R7
C11
1800pF
C3
V
R
PU
R
VLIMIT
10k
C1
DDS
R4
12.7k
R
PU
C1
0.1µF
36
41
16
37
47
48
46
45
13
40
24
25
29
18
22
20
33
32
26
I6
CB2
0.47µF
CLP
DC
3
BAT1
2
BAT2
DCDIV
COMP1
GCH2
SCH2
GCH1
SCH1
V
SET
V
CC
V
SS
V
CC2
SMBALERT
SCL
SDA
V
DDS
V
LIMIT
I
LIMIT
MODE
BAT2
D2
C8, 1µF
LTC1760
IN
R11
1k
CB1, 0.1µF
BAT1
I5
C13
0.1µF
LOPWR
D3
R10, 100Ω
C9, 0.1µF
V
PLUS
GDCI
GDCO
GB1I
GB1O
GB2I
GB2O
SCP
SCN
CSN
CSP
I
TH
I
SET
SW
BOOST
TGATE
BGATE
PGND
TH2A
TH2B
SCL2
SDA2
TH1A
TH1B
SCL1
SDA1
C6
4.7µF
100Ω
1
7
6
9
8
11
10
5
4
12
34
35
14
15
42
43
44
39
38
28
27
17
21
30
31
19
23
D4
C4, 0.22µF
R6
LTC1760 Dual Smart Battery Charger
Figure 1 shows a typical dual battery charger. This circuit
can charge batteries with up to 4A and switch continuously
down to zero load currents. This circuit takes advantage
of ceramic capacitors’ space saving features without pro-
, LTC and LT are registered trademarks of Linear Technology Corporation.
PowerPath is a trademark of Linear Technology Corporation.
*U.S. patent number 6,650,174 **U.S. patent number 5,723,970
C7
0.1µF
Q1
Q2
QTG
QBG
R9
3.3k
1000pF
C5
0.15µF
L1
10µH
C12
D1
R
SENSE
0.025Ω
Q6
Q5
CHARGE
MUX
R2
280k
R3
49.9k
R2A, 1.13k
R2B, 54.9k
R1A, 1.13k
R1B, 54.9k
C
IN
20µF
C
OUT
20µF
Q4
SAFETY 2
TH
SCL
SDA
SAFETY 1
TH
SCL
SDA
Q7
Q8
R
SC
0.02Ω
CL
20µF
LOAD
BAT2
BAT1
Q9
D1: MBR130T3
D2: IN4148 TYPE
Q1, Q2, Q5, Q6, Q7, Q8: Si4925DY
Q3, Q4, Q9, Q10, QTG, QBG: FDS6912A
10/04/342
Figure 1. 4A Dual Battery System
Q3
Q10
DN342 F01
duc
ing any audible noise. The high 300kHz switching fre-
quency allows the use of small low cost 10µH inductors.
The LTC1760 complies with the Smart Battery System
Manager (SBSM) specification V1.1. It has a very wide
input and charge output voltage range of 6V to 28V.
Current and voltage accuracies of 0.2% of the reported
values provide precision charge capability. Low dropout
is achieved with 99% maximum duty cycle while maintaining efficiency greater than 95%. The LTC1760 also
offers many unique features, including a special current
limit and voltage limit system that prevents SMBus data
corruption errors from generating false charge values,
which could harm the battery. An SMBus accelerator
increases data rates in high capacitance traces while
preventing bus noise from corrupting data*.
Other features include: an AC present signal with precision 3%-accurate user adjustable trip points; a safety
signal circuit that rejects false thermistor tripping due to
ground bounce caused by the sudden presence of high
charge currents, and an ultrafast overvoltage comparator
circuit that prevents voltage overshoots when the battery
is suddenly removed or disconnects itself during charge.
Last but not least is an input current limit sensing circuit
that limits charge current to prevent wall adapter overload
as the system power increases**.
LTC1760 Power Management
Dual battery systems are traditionally used to simply
extend system battery run time by allowing a sequential
battery drain—drain battery 1, then battery 2. New server
applications are also using batteries and demand drain
currents beyond the capability of a single battery.
The LTC1760 addresses this need by allowing the safe
parallel discharge of two batteries. Parallel discharge
offers more than just increased current capability. It
reduces I
2
R losses and improves voltage regulation under
extremely high load conditions, both of which can improve total discharge time over a sequential solution.
Figure 2 compares discharge times for equivalent parallel
and sequential solutions. In high current, rapid discharge
applications, quick recharging of the batteries is a priority.
Again the LTC1760 goes beyond the simple sequential
solution and offers
parallel charging
, which, depending
on the battery chemistry, can result in significant charge
time reductions over a sequential solution, as shown in
Figure 3.
Safely managing the charge and discharge states of
multiple batteries and the DC input power source presents
a significant power management issue that historically
has involved a host processor running custom written
application software. The LTC1760 simplifies this task by
operating in a standalone Level 3 Bus Master mode. It
autonomously controls simultaneous battery charging
and discharging, full dual battery conditioning support
and ideal diode PowerPath
teries and a wall adapter
processor
.
TM
switching between two bat-
without requiring any host
3500
3000
2500
2000
1500
1000
500
3500
3000
2500
2000
BATTERY CURRENT (mA)
1500
1000
500
BAT1
CURRENT
0
BAT1
CURRENT
0
0
BATTERY TYPE: 10.8V Li-Ion (MOLTECH NI2020)
REQUESTED CURRENT = 3A
REQUESTED VOLTAGE = 12.3V
MAX CHARGER CURRENT = 4.1A
100 150 200 250 300
50
BAT2
CURRENT
BAT2
CURRENT
TIME (MINUTES)
SEQUENTIAL
DUAL
100
MINUTES
DN342 F02
Figure 2. Dual Battery vs Sequential Battery Charge Time
Data Sheet Download
http://www.linear.com
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
12.0
11.0
10.0
9.0
8.0
12.0
11.0
BATTERY VOLTAGE (V)
10.0
9.0
8.0
0
BATTERY TYPE: 10.8V Li-Ion(MOLTECH NI2020)
LOAD CURRENT = 3A
BAT1
VOLTAGE
BAT2
VOLTAGE
BAT2
VOLTAGE
BAT1
VOLTAGE
20 180
60 80 100 140
40
TIME (MINUTES)
DUAL
SEQUENTIAL
11
MINUTES
120
160
DN342 F03
Figure 3. Dual Battery vs Sequential Battery
Discharge Time
For applications help,
call (408) 432-1900, Ext. 2593
dn342f LT/TP 1004 344K • PRINTED IN THE USA
© LINEAR TECHNOLOGY CORPORATION 2004
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