ltc1760 Linear Technology Corporation, ltc1760 Datasheet - Page 29

• Manufacturer Part Number: ltc1760
• Description: Dual Smart Battery System Manager
• Manufacturer: Linear Technology Corporation

OPERATIO
6 MODE Pin Operation
The MODE pin is a multifunction pin that allows the
LTC1760 to: 1) display charging status in stand alone
operation; 2) activate hardware charge inhibit; 3) charge
when SCL and SDA are low and; 4) charge with an SMBus
Host.
Summary of SDA, SCL and SMBALERT Operation as a Function
of MODE and V
CONDITION
V
V
V
V
V
V
V
V
6.1 Stand Alone Charge Indication
When MODE is tied to GND and V
function of SDA, SMBALERT, and SCL are changed as
described below.
SDA is an output and is used to monitor charging status of
Battery 2.
Allowed valued are:
SMBALERT is used to monitor charging status of Bat-
tery1. Allowed valued are:
MODE
VDDS
MODE
VDDS
MODE
VDDS
MODE
VDDS
Low: Battery 2 is charging.
High: Battery 2 not charging (AC is not present or
battery is not present).
Blinking: Battery 2 charge complete (AC is present,
battery is present and not charging).
Low: Battery 1 is charging.
High: Battery 1 not charging (AC is not present or
battery is not present).
Blinking: Battery 1 charge complete (AC is present,
battery is present and not charging).
< V
> V
< V
> V
= V
= V
= V
= V
ILVDDS
ILVDDS
ILVDDS
ILVDDS
VSS
VSS
VSS
VSS
DDS
LTC1760 OPERATING MODE
SCL: Clock for Status Indicators
SDA: Battery 2 Status
SMBALERT: Battery 1 Status
SCL, SDA, SMBALERT: Normal Operation
LTC1760 Charging Inhibited
SCL, SDA Ignored and May Float Low
SMBALERT: Normal Operation
SCL1, SDA1, SCL2 and SDA2: Normal Operation and
Charging is Allowed
Normal Operation on all Pins, Charging is Allowed
Levels
U
VDDS
< V
IL_VDDS
, the
SCL is an input and is used to determine the blinking rate
of SDA and SMBALERT. Tie SCL high if blinking is not
desired. This will provide two different states to indicate
charging (output low) and not charging (output high).
6.2 Hardware Charge Inhibit
When MODE is tied to GND and V
is inhibited and BatterySystemStateCont(CHARGING_INHIBIT)
will report a logic high.
6.3 Charging When SCL And SDA Are Low
When MODE is tied to V
SCL are not used and will not interfere with LTC1760
battery communication. This feature allows the LTC1760
to autonomously charge when SCL and SDA are not
available. This scenario might occur when SMBus Host
has powered down and is no longer pulling up on SCL and
SDA.
6.4 Charging With an SMBus Host
When Mode is tied to V
SCL are used to communicate with the SMBus Host.
7 Battery Charger Controller
The LTC1760 charger controller uses a constant off-time,
current mode step-down architecture. During normal op-
eration, the top MOSFET is turned on each cycle when the
oscillator sets the SR latch and turned off when the main
current comparator I
MOSFET is off, the bottom MOSFET is turned on until
either the inductor current trips the current comparator
I
the equation.
to set the bottom MOSFET on time. The result is quasi-
constant frequency operation where the converter fre-
quency remains nearly constant over a wide range of
output voltages. This activity is diagrammed in Figure 4.
The peak inductor current, at which I
latch, is controlled by the voltage on I
controlled by several loops, depending upon the situation
REV
t
OFF
, or the beginning of the next cycle. The oscillator uses
= (V
DCIN
- V
BAT
CMP
CC2
)/(V
CC2
resets the SR latch. While the top
and V
DCIN
and V
• f
VDDS
VDDS
DDS
OSC
>V
< V
> V
)
CMP
IH_VDDS
LTC1760
TH
IL_VDDS
IL_VDDS
. I
resets the SR
TH
,charging
, SDA and
, SDA and
is in turn
29
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