EUP8092X
C
22
TIMEOUT = 2 × T
OSC
TIME
1nF
(minutes)(6)
= 14 ×
For example, a 15nF capacitor sets the TIMEOUT to be
3.5 hours. The charger has to reach the end-of-charge
condition before the TIMEOUT, otherwise, a TIMEOUT
fault is issued. The TIMEOUT fault latches up the
charger. There are two ways to release such a latch-up:
either to recycle the input power, or toggle the EN pin to
disable the charger and then enable it again.
The trickle mode charge has a time limit of 1/8
TIMEOUT. If the battery voltage does not reach VMIN
within this limit, a TIMEOUT fault is issued and the
charger latches up.
2.8V Bias Voltage
The EUP8092 provides a 2.8V voltage for biasing the
internal control and logic circuit. This voltage is also
available for external circuits such as the NTC thermistor
circuit. The maximum allowed external load is 2mA.
Figure 24. The Internal and External circuit for The
NTC Interface
NTC Thermistor
At the low temperature limit, the TEMP pin voltage is
1.4V, which is 1/2 of the 2.8V bias. Thus,
The EUP8092 uses two comparators (CP2 and CP3) to
form a window comparator, as shown in Figure 23.
When the TEMP pin voltage is “out of the window,”
determined by the VTMIN and VTMAX, the EUP8092 stops
charging and indicates a fault condition. When the
temperature returns to the set range, the charger re-starts
a charge cycle. The temperature window is shown in
Figure 23.
RCOLD
RCOLD + RU 2.8
1.4
1
2
(7)
=
=
⇒ RCOLD = RU
where RU is the pull-up resistor as shown in Figure 24.
On the other hand, at the high temperature limit the
TEMP pin voltage is 0.35V, 1/8 of the 2.8V bias.
Therefore,
RHOT
RHOT + RU
RU
7
0.35
2.8
1
8
(8)
=
=
⇒ RHOT
=
For applications that do not need to monitor the battery
temperature, the NTC thermistor can be replaced with a
regular resistor of a half value of the pull up resistor RU.
Another option is to connect the TEMP pin to the IREF
pin that has a 0.8V output. With such connection, the
IREF pin can no longer be programmed with logic
inputs.
Charge Status Outputs
The open-drain STATUS and FAULT outputs indicate
various charger operations as shown in the following
table. These status pins can be used to drive LEDs or
communicate to the host processor. Note that OFF
indicates the open-drain transistor is turned off.
Figure 23. Critical voltage Levels for Temp Pin
As the TEMP pin voltage rises from low and exceeds the
1.4V threshold, the under temperature signal rises and
does not clear until the TEMP pin voltage falls below the
1.2V falling threshold. Similarly, the over-temperature
signal is given when the TEMP pin voltage falls below
the 0.35V threshold and does not clear until the voltage
rises above 0.398V. The actual accuracy of the 2.8V is
not important because all the thresholds and the TEMP
pin voltage are ratios determined by the resistor dividers,
as shown in Figure 24.
Table 1 summarizes the other two pins.
Table 1. STATUS INDICATIONS
FAULT STATUS
INDICATION
Charge completed with no fault
(Inhibit) or Standby
High
High
High
Low
Low Charging in one of the three modes
High Fault
DS8092X Ver 0.1 May 2008
13
EUTECH [ EUTECH MICROELECTRONICS INC ]
