SLUS249B − FEBRUARY 1997 − REVISED DECEMBER 2001
UCC3956
SWITCH MODE LITHIUM ION
BATTERY CHARGE CONTROLLER
pin descriptions
CA–:
The inverting input to the current-error amplifier.
CAO:
The output of the current-error amplifier and inverting input of the PWM comparator. This pin is driven high
during shutdown.
CS–, CS+:
The inverting and non-inverting inputs to the current-sense amplifier. This amplifier has a fixed-gain of
5.
CHG:
A rising-edge triggered-input pin that indicates charging. Once the internal 14-bit timer has timed out, the chip
enters its shutdown charge state. At this point, CHG is pulled low by an internal buffer. Another low-to-high transition
is required to reset the timer and restart charging.
CHGENB:
The input to a comparator that detects when the battery voltage is low and places the charger in trickle
charge. The charge-enable comparator forces the output of the voltage-error amplifier to a high-impedance state
while forcing a fixed 10-µA current into the CA– to set the trickle charge.
COSC:
The oscillator ramp pin which has a capacitor (COSC) to ground. The ramp oscillates between 0.8 V to 3.2 V
and the frequency is determined by:
Frequency
+
3.475
(COSC
)
20 pF)
RSET
(1)
A rising edge on CHG initiates the oscillator.
CTO:
The slow oscillator ramp pin, which is used to generate a clock signal for the 14-bit timer to program the
overcharge time. A capacitor (tied to ground) is charged and discharged with equal currents at a frequency
programmed between 0.75 Hz and 5 Hz. The ramp oscillates between 0.1 V and 3.0 V and the frequency is
determined by:
Frequency
+
0.06
(CTO RSET)
(2)
The oscillator operates only while in overcharge.
GND:
The reference point for the internal reference, all thresholds, and the return for the remainder of the device.
IBAT:
The output of the current-sense amplifier.
IMIN:
The minimum-charge-current programming pin is provided to program an optional-charge termination in
addition to the programmable timer.
OUT:
The output of the PWM driver.
REF:
The 4.1-V precision reference, which should be bypassed with a 0.1-µF capacitor.
RSET:
This pin programs the charge current for the oscillator ramp. The oscillator-charge current is determined by:
I
+
1.37 V
COSC
RSET
(3)
The trickle-control current (I
TRCK_CONTROL
) is determined by:
I
TCK_CONTROL
+
0.68 V
RSET
(4)
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