Philips Semiconductors
Product specification
Timer for NiCd and NiMH chargers
74LV4799
PIN DESCRIPTION
PIN NO.
SYMBOL
NAME AND FUNCTION
1
2
LED
EN
LED driver output pin (active LOW)
Enable output (active HIGH)
Enable output (active LOW)
External power input
3
EN
4
V
in
5
PWRS
Power sense input
6
MOLLI/SCO
SEL
More-or-less-low-indication output (active LOW)/scan test output
LED mode select input
7
8
GND
Ground (0 V)
9
DIS
Discharge input (active LOW)
10
11
12
13
14
15
16
R
R
R
External resistor pin 3-State oscillator output (charge)
External resistor pin 3-State output (discharge)
External resistor pin 3-State output (self-discharge)
Oscillator input
C
D
S
I
OSC
SCAN
SCI
Scan test mode select input (active HIGH)
Scan test input
V
CC
Positive supply voltage
Power On Reset.
reaches its maximum value and the EN and EN outputs switch over
from the continuous charge to the trickle charge mode.
An automatic Power On Reset initiates the IC when the battery is
discharged and power is connected to the circuit. The initial
condition is the charge mode in which the counter is reset and
counts from zero up to maximum. At start up, the battery therefore
always receives a full charge cycle. When a partially charged battery
is inserted, it may be over-charged during the first cycle. To guard
Trickle charge mode.
At the maximum counter value, it is assumed that the battery is fully
charged. The counter stops and remains on this maximum value.
The EN and EN outputs switch over from the continues charge to
the trickle charge mode. In the trickle charge mode, the average
charge current is reduced to only compensate the self-discharge of
the battery by using the dedicated duty cycle control. The control is
dedicated because it adjusts the duty cycle in inverse proportion to
the load current, resulting in a fixed charger current irrespective of
the kind of charger (e.g. 4-hour or 16-hour charger). In the trickle
charge mode, the oscillator circuitry alternately generates 4 periods
against this, simply replace the resistor at the R pin with an NTC
C
type which is in good thermal contact with the battery. If the
temperature of the battery increases, the frequency of the oscillator
also increases to quickly reach a counter full indication and
switch-over to trickle charge. With a battery that is almost
completely discharged, the POR input can also be activated during
discharge or self-discharge. The counter will then be reset to zero.
This is a correct action while returning to the initial condition.
of R -C1 time-constant, and 3 periods of the R -C1 time-constant
C
S
(See Figure 1).
Power-on sensing.
Because this IC supports virtually all battery chargers, the PWRS input
has a broad input frequency spectrum (active HIGH to 100 kHz). A
pull-down circuit at the PWRS input allows detection of the open state
which corresponds to an inactive charger. A HIGH level on the PWRS
input, or an AC signal up to 100 kHz, enables the charge mode.
Discharge mode.
The discharge input (DIS) is used to detect the discharge of the
battery. If DIS is LOW, the counter counts down. The clock
frequency is determined by the external capacitor and resistor at the
R
output. If PWRS is inactive (LOW or open), the EN output is
D
LOW, and the EN output is in the high impedance OFF-state (no
charge of the battery). This is called the discharge mode. If PWRS is
active, the circuit is in the charge/discharge mode.
Start-up with low battery voltage.
Good start-up, even with an un-charged battery, is assured by using
the V input. The voltage on the V input biases the external
IN
IN
bipolar transistors at the EN or EN output, even if the IC is not yet
functioning. After the battery has received sufficient charge, the
internal control logic takes over control of the EN and EN outputs.
Charge/Discharge mode.
If DIS is LOW and PWRS is active (HIGH or pulsed), the circuit is in
the charge/discharge mode. The counter counts down. The clock
frequency is determined by the external capacitor and resistor tied
Charge mode.
at the R output. The EN output is HIGH, and the EN output is LOW
D
This mode is selected when PWRS is active (HIGH or pulsed) and
the discharge input DIS is HIGH. The EN output is HIGH, and the
EN output is LOW initiating continuous charge of the battery. The
counter then counts from the zero state up to the maximum value.
The clock frequency is determined by the external capacitor and
initiating continuous charge of the battery. The battery is therefore
charged and discharged at the same instant, thereby maintaining a
better load condition of the battery.
resistor connected to the R output. The counter stops when it
C
4
1998 Apr 20
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