User manual

LTC4100
24
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b) I
THRM
current is due to SafetySignal (thermistor pin)
sampling that will vary with the presence of DC power
being on or off. DCDIV is detected every 32ms. RTHX
is the value of the safety signal resistance, which will
vary with temperature or battery confi guration.
b1) I
THRM(ON)
when DC is on:
I
THRM(ON)_OVERRANGE
= 1/16 • V
DD
/(54.9k + RTHX)
where RTHX > 100k
I
THRM(ON)_COLD
= 1/8 • V
DD
/(54.9k + RTHX) where
RTHX > 30k
I
THRM(ON)_NORMAL
= 1/8 • V
DD
/(54.9k + RTHX)
+ 1/16 • V
DD
/(1.13k + RTHX)
I
THRM(ON)_HOT
* = 1/8 • V
DD
/(54.9k + RTHX)
+ 1/8 • V
DD
/(1.13k + RTHX)
where RTHX < 3k
*= includes underrange
b2) I
THRM(OFF)
when DC is off, the thermistor monitoring
rate is reduced to every 250ms or less.
I
THRM(OFF)_OVERRANGE
= 1/50 • V
DD
/(54.9k + RTHX)
where RTHX > 100K
I
THRM(OFF)_COLD
= 1/50 • V
DD
/(54.9k + RTHX)
+ 1/1000 • V
DD
/(54.9k + RTHX)
where RTHX > 30K
I
THRM(OFF)_NORMAL
= 1/50 • V
DD
/(54.9k + RTHX) +
1/500 • V
DD
/(54.9k + RTHX) + 1/1000 • V
DD
/(1.13k
+ RTHX)
I
THRM(OFF)_HOT
* = 1/50 • V
DD
/(54.9k + RTHX) +
1/500 • V
DD
/(54.9k + RTHX) + 1/500 • V
DD
/(1.13k +
RTHX)
where RTHX < 3k
* includes underrange
APPLICATIONS INFORMATION
c) I
ACCEL
is the current used by the SMBus accelerators.
This directly depends on the SMBus frequency, duty
cycle of messages sent on the SMBus and how long
it takes to drive the SMBus to V
DD
.
I
ACCEL
= I
PULL-UP
• 2 • SMBus Frequency •
Message Duty Cycle •V
DD
/2.25V• Rise Time
Complete Examples
1) Battery thermistor = 400Ω, V
DD
= 5.0V
Battery mode (DC is off), SMBus activity is 10kHz
and a 2% SMBus duty cycle, which represents a
suspended or sleep condition of a notebook.
I
TOTAL
= I
RUN
+ I
THRM(OFF)
+ I
ACCEL
= 121.9µA
+ 5.26µA + 2.44µA = 130µA
Battery mode and a 10% SMBus duty cycle, which
represents an active notebook at idle.
I
TOTAL
= I
RUN
+ I
THRM(OFF)
+ I
ACCEL
= 189.5µA
+ 5.26µA + 12.2µA = 207µA
DCIN = ON and a 20% SMBus duty cycle which
represents an active notebook charging.
I
TOTAL
= I
RUN
+ I
THRM(ON)
+ I
ACCEL
= 274µA
+ 215.6µA + 24.4µA = 514µA
2) Battery thermistor = 10k, V
DD
= 5.0V
Battery mode (DC is off), SMBus activity is 10kHz
and a 2% SMBus duty cycle:
I
TOTAL
= I
RUN
+ I
THRM(OFF)
+ I
ACCEL
= 121.9µA
+ 2.14µA + 2.44µA = 126µA
Battery mode and a 10% SMBus duty cycle:
I
TOTAL
= I
RUN
+ I
THRM(OFF)
+ I
ACCEL
= 189.5µA
+ 2.14µA + 12.2µA = 204µA
DCIN = ON and a 20% SMBus duty cycle:
I
TOTAL
= I
RUN
+ I
THRM(OFF)
+ I
ACCEL
= 274µA
+ 37.7µA + 24.4µA = 336µA