ISL78693 Datasheet, PDF (11/18 Pages) Intersil Corporation – Reverse battery leakage 700nA

ISL78693
constant V_CH in the CV mode and the charge current starts to
reduce towards zero. After the charge current drops below I(EOC)
programmed to 1/10 of I_REF (see “End-of-Charge (EOC) Current”
on page 12 for more information), the ISL78693 indicates the
EOC with the STATUS pin. The charging actually does not
terminate until the internal timer completes its length of
TIMEOUT in order to bring the battery to its full capacity. Signals
in a charge cycle are illustrated in Figure 21 between points t₂ to
t₅.
V_IN
V2P8
POR THRESHOLD
CHARGE CYCLE
CHARGE CYCLE
STATUS
FAULT
VBAT
15 CYCLES TO
1/8 TIMEOUT
VCH
VTRICKLE
VRECHRG
15 CYCLES
ICHARGE
IEOC
t₀ t₁ t₂ t₃
t₄
t₅
t₆ t₇
t₈
FIGURE 21. OPERATION WAVEFORMS
The following events initiate a new charge cycle:
• POR
• A new battery being inserted (detected by TEMP pin)
• The battery voltage drops below a recharge threshold after
completing a charge cycle
• Recovery from a battery over-temperature fault
• The EN pin is toggled from GND to floating
• Further description of these events are given later in this
datasheet
Recharge
After a charge cycle completes, charging is prohibited until the
battery voltage drops to a recharge threshold, V_RECHRG of 3.3V
(TYP), (see “Electrical Specifications” on page 5”). Then a new
charge cycle starts at point t₆ and ends at point t₈, as shown in
Figure 21. The safety timer is reset at t₆.
Internal Oscillator
The internal oscillator establishes a timing reference. The
oscillation period is programmable with an external timing
capacitor, C_TIME, as shown in Figure 1. The oscillator charges the
timing capacitor to 1.5V and then discharges it to 0.5V in one
period, both with 10µA current. The period t_OSC is given by
Equation 3:
t_OSC = 0.2  10⁶  C_TIME
 seconds
(EQ. 3)
A 1nF capacitor results in a 0.2ms oscillation period. The
accuracy of the period is mainly dependent on the accuracy of
the capacitance and the internal current source.
Total Charge Time
The total charge time for the CC mode and CV mode is limited to
a length of TIMEOUT. A 22-stage binary counter increments each
oscillation period of the internal oscillator to set the TIMEOUT.
The TIMEOUT can be calculated in Equation 4:
TIMEOUT
=
2²²



t_{--O-----S----C-6----0-S----E----C----}
=
14  -^C---₁-^T---_n-^I--^M-_F---^E-- minutes
(EQ. 4)
A 1nF capacitor leads to 14 minutes of TIMEOUT. 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 charge and the FAULT pin goes low. There are two ways to
release such a latch-up: either recycle the input power or toggle
the EN pin to disable the charger and then enable it again.
The Trickle Charge mode has a time limit of 1/8 TIMEOUT. If the
battery voltage does not reach V_TRICKLE within this limit, a
TIMEOUT fault is issued and the charger latches off. The charger
stays in Trickle mode for at least 15 cycles of the internal
oscillator and, at most, 1/8 of TIMEOUT, as shown in Figure 21.
Charge Current Programming
The charge current is programmed by the IREF pin. There are
three ways to program the charge current:
1. Driving the IREF pin above 1.2V.
2. Driving the IREF pin below 0.4V.
3. Using the R_IREF as shown in “TYPICAL APPLICATION” on
page 1.
The voltage of I_REF is regulated to a 0.8V reference voltage when
not driven by any external source. The charging current during the
Constant Current mode is 100,000 times that of the current in
the R_IREF resistor. Therefore, depending on how IREF pin is used,
the charge current is given by Equation 5:


500 m A
I_REF=



-_R--⁰--_I-^.-_R-⁸---_E-^V---_F--  10⁵A


80 m A
V_IREF  1.2V
R_IREF
V_IREF  0.4V
(EQ. 5)
The internal reference voltage at the IREF pin is capable of sourcing
less than 100µA current. When pulling down the IREF pin with a
logic circuit, the logic circuit must be able to sink at least 100µA
current. For design purposes, a designer should assume a tolerance
of ±20% when computing the minimum and maximum charge
current from Equation 5.
When the adapter is current-limited, it is recommended that the
reference current be programmed to at least 30% higher than the
adapter current limit (which equals the charge current). In addition,
the charge current should be at least 350mA, which the voltage
difference between the VIN and the VBAT pins is higher than 100mV.
The 100mV is the offset voltage of the input/output voltage
comparator shown in “Block Diagram” on page 2.
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December 12, 2016