EUP8054/8054X
Charge Current Soft-Start
2k pull-up resistor. To determine if there is a weak
pull-down current, the OUT pin should be forced to a
high impedance state. The weak current source will pull
The EUP8054 includes a soft-start circuit to minimize the
inrush current at the start of a charge cycle. When a
charge cycle is initiated, the charge current ramps from
zero to the full-scale current over a period of
approximately 100µs. This has the effect of minimizing
the transient current load on the power supply during
start-up.
the IN pin low through the 800k resistor; if CHRG is
high impedance, the IN pin will be pulled high,
indicating that the part is in a UVLO state.
Reverse Polarity Input Voltage Protection
In some applications, protection from reverse polarity
voltage on VCC is desired .If the supply voltage is high
enough, a series blocking diode can be used. In other
cases, where the voltage drop must be kept low a
P-channel MOSFET can be used (as shown in Figure
11.)
CHRG Status Output Pin
The CHRG pin can provide an indication that the input
voltage is greater than the undervoltage lockout threshold
level. A weak pull-down current of approximately 12µA
indicates that sufficient voltage is applied to VCC to begin
charging. When a discharged battery is connected to the
charger, the constant current portion of the charge cycle
begins and the CHRG pin pulls to ground. The
CHRG pin can sink up to 10mA to drive an LED that
indicates that a charge cycle is in progress.
When the battery is nearing full charge, the charger
enters the constant-voltage portion of the charge cycle
and the charge current begins to drop. When the charge
current drops below 1/10 of the programmed current, the
charge cycle ends and the strong pull-down is replaced
by the 12µA pull-down, indicating that the charge cycle
has ended. If the input voltage is removed or drops below
the undervoltage lockout threshold, the CHRG pin
becomes high impedance. Figure 10 shows that by using
two different value pull-up resistors, a microprocessor
can detect all three states from this pin.
Figure 11. Low Loss Input Reverse Polarity
Protection
USB and Wall Adapter Power
The EUP8054 allows charging from both a wall adapter
and a USB port. Figure 12 shows an example of how to
combine wall adapter and USB power inputs. A
P-channel MOSFET, MP1,is used to prevent back
conducting into the USB port when a wall adapter is
present and a Schottky diode, D1, is used to prevent USB
power loss through the 1k pull-down resistor.
Typically a wall adapter can supply more current than the
500mA-limited USB port. Therefore, an N-channel
MOSFET, MN1, and extra 10k program resistor are used
to increase the charge current to 600mA when the wall
adapter is present.
Figure 10. Using a Microprocessor to Determine
CHRG State
To detect when the EUP8054 is in charge mode, force the
digital output pin (OUT) high and measure the voltage at
the CHRG pin. The N-channel MOSFET will pull the
pin voltage low even with the 2k pull-up resistor. Once
the charge cycle terminates, the N-channel MOSFET is
turned off and a 12µA current source is connected to the
Figure 12. Combining Wall Adapter and USB Power
CHRG pin. The IN pin will then be pulled high by the
DS8054 Ver1.1 Jan. 2007
15
EUTECH [ EUTECH MICROELECTRONICS INC ]
