LTC4067 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4067' PDF : 20 Pages View PDF
LTC4067
APPLICATIO S I FOR ATIO
NTC thermistor, RCOLD, increases to 2.82 times the value
or RNOM. (For a Vishay NTHS0603N02N1002 thermistor
this value is 28.2k which corresponds to a temperature of
approximately 0°C). The hot and cold comparators each
have approximately 3°C of hysteresis to prevent oscillation
about the trip points.
Fault Conditions
The ⎯C⎯H⎯R⎯G pin is used to signal two distinct fault condi-
tions: NTC faults and bad battery faults. Both of these
conditions are signaled at the ⎯C⎯H⎯R⎯G pin with a series of
serrated open-drain pull-down pulses that are intended
to produce a visible “blinking” at an LED tied to this pin
as well as to produce a pulse train that is detectable to a
microprocessor input connected to this pin. The serrated
pulses are described with the aid of Figure 3, assuming
that the ⎯C⎯H⎯R⎯G pin is connected to a positive rail with a
resistive pull-up. When an NTC fault condition is detected
during a normal charge cycle, the ⎯C⎯H⎯R⎯G pin immediately
goes from a strong open-drain pull down to a high-im-
pedance state that pulses on for 1.4μs and then off at a
35kHz rate. This signal is further modulated by a 1.5Hz
blink frequency that reverses from pulsing high-to-low to
pulsing low-to-high.
V (CHRG)
PW = 27.7μs (NTC FAULT)
TS
26.3μs (BAD BAT)
Table 3 illustrates the four possible states of the ⎯C⎯H⎯R⎯G
pin when the battery charger is active.
Table 3. ⎯C⎯H⎯R⎯G Output Pin
STATUS
FREQUENCY
MODULATION
(BLINK)
FREQUENCY
DUTY CYCLE
Charging
0Hz
0Hz (Lo-Z)
100%
IBAT < ICC-CHG/10
NTC Fault
0Hz
35kHz
0Hz (Hi-Z)
0%
1.5Hz at 50% 4.7% to 95.3%
Bad Battery
35kHz
6.1Hz at 50% 9.4% to 90.6%
A bad battery fault has a 2.8μs pulse at the same rate that
is modulated by a 6Hz blink frequency. As the ⎯C⎯H⎯R⎯G pin
immediately changes state upon entering a failure mode, a
microprocessor observing this pin detects the fault condi-
tion within 29μs of the failure occurring, by measuring the
pulse width. Furthermore the blink frequency is visually
detected by hooking this signal up to an LED.
When connecting a microprocessor with a positive logic
suppy that is different than the LED anode, a diode must
be inserted in series with the microcontroller input so as
to aviod the condition where the LED may inadvertantly
power up the microcontroller. A circuit that allows visual
fault and/or charge status as well as providing a safe
microcontroller interface is shown in Figure 4.
OUT
VLOGIC
PW = 1.3μs OR
2.7μs
TS = 667ms/2 (NTC FAULT)
167ms/2 (BAD BAT)
NORMAL
CHARGING
FAULT
CONDITION
Figure 3
4067 F03
LTC4067
TO MICRO
4067 F04
CHRG
Figure 4. ⎯C⎯H⎯R⎯G Pin Connection to Drive a Microcontroller at the
Same Time as Providing a Visual Fault and/or Charge Status
4067f
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