SS6781B Datasheet, PDF (11/20 Pages) Silicon Standard Corp. – Battery Charge Controller

SS6781B
determined by PEAK pin voltage, the fast charge
action is terminated.
∆T/∆t Cutoff
The ∆T/∆t detection of the SS6781B is performed
by sensing the decrease of VTS pin voltage in a
specific timer interval dictated by the safety timer.
The fast charging terminates when the decrease of
VTS pin voltage in 56 seconds exceeds the
predetermined value set by ADJ pin input. This time
interval of 56 seconds is based on the assumption
that voltage of VTS pin is sampled once for every 8
seconds, which is also determined by safety timer.
Functioning of -∆V detection and peak voltage timer
(0∆V ) can be disabled if the MODE pin is biased to
GND. Functioning of ∆T/∆t detection can be
disabled if the voltage of ADJ pin is higher than V_CC
- 0.3V.
Maximum Safety Timer Cutoff
The maximum fast charge period is determined by
the safety timer, which is set by a resistor
connected from TMR pin to GND. Safety timer, -∆V
sampling rate, and ∆T/∆t sampling rate will be
longer if the resistor value is larger. When the value
of the resistor is 5.1KΩ, the safety timer period
equals 80 minutes. This can be verified by biasing
MODE pin to V_CC and the measured frequency on
DSW pin should be around 32.8 KHz. After the
safety timer period is finished, the fast charge
action is terminated.
Maximum Voltage and Temperature Cutoff
The SS6781B guards against the maximum limits
for battery voltage and temperature during fast
charging. If either of these limits is exceeded, fast
charge action is terminated.
Trickle Charge
There are five different selectable duty cycles for
trickle charge after the fast charge to prevent the
loss of charge due to battery self-discharging. The
duty cycle is controlled by the setting of SEL1 and
SEL2 pins.
The functions and charging states control
mentioned above are illustrated in the function flow
chart of SS6781B (Fig. 16)
DESIGN GUIDE
Selecting Peak Voltage Timer (0∆V)
The voltage of PEAK pin along with safety timer
determines the period of peak voltage timer. It can
be selected according to the following table:
TABLE 1
PEAK PIN
V_CC
Floating
GND
PEAK VOLTAGE TIMER
1.5% of safety timer
3.7% of safety timer
6% of safety timer
Battery Voltage Measurement
The SS6781B measures the battery voltage
through VBT pin, which is connected to battery
positive terminal through a resistor-divider network,
as shown in Fig. 17. The input voltage of SEL3 pin
determines the acceptable limit of divided battery
voltage.
V_BAT
RA
R5
2
VBT
+ ^100K
RB
C5
C6
AIC1781B
Fig. 17 Battery Voltage Divider
01/31/2008 Rev.1.00
www.SiliconStandard.com
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