EUP8057
Selecting Input Capacitor
Charge Inhibit Function
In most applications, all that is needed is high-frequency
decoupling capacitor. A 0.1µF ceramic, placed in
proximity to VCC and VSS pins, works well. The
EUP8057 works with both regulated and unregulated
external dc supplies. If a non-regulated supply is chosen,
the supply unit should have enough capacitance to hold
up the supply voltage to the minimum required input
voltage at maximum load. If not, more capacitance must
be added to the input of the charger.
The TS pin can be used as charge-inhibit input. The user
can inhibit charge by connecting the TS pin to VCC or
VSS (or any level outside the V(TS1) to V(TS2) thresholds).
Applying a voltage between the V(TS1) and V(TS2)
thresholds to pin TS returns the charger to normal
operation.
Charge Status Indication
The EUP8057 reports the status of the charger on the
3-state STAT pin. The following table summarized the
operation of the STAT pin.
Selecting Output Capacitor
The EUP8057 does not require any output capacitor for
loop stability.
Condition
STAT pin
High
Battery conditioning and charging
Charge complete(done)
Temperature fault or sleep mode
In order to maintain good AC stability in the Constant
Voltage mode, a minimum capacitance of 10µF is
recommenced to bypass the VBAT pin to VSS. This
capacitance provides compensation when there is no
battery load. In addition, the battery and interconnections
appear inductive at high frequencies. These elements are
in the control feedback loop during Constant Voltage
mode. Therefore, the bypass capacitance may be
necessary to compensate for the inductive nature of the
battery pack.
Virtually any good quality output filter capacitor can be
used, independent of the capacitor’s minimum ESR
(Effective Series Resistance) value. The actual value of
the capacitor and its associated ESR depends on the
forward transconductance (gm) and capacitance of the
external pass transistor. A 10µF tantalum or aluminum
electrolytic capacitor at the output is usually sufficient to
ensure stability for up to a 1A output current.
Low
Hi-Z
The STAT pin can be used to drive a single LED
(Figure1), dual-chip LEDs (Figure2) or for interface to a
host or system processor (Figure11). When interfacing
the EUP8057 to a processor, the user can use an output
port, to recognize the high-Z state of the STAT pin. In
this configuration, the user needs to read the input pin,
toggle the output port and read the STAT pin again. In a
high-Z condition, the input port always matches the
signal level on the output port.
Selecting An External Pass-Device (PMOS or PNP)
The EUP8057 is designed to work with both P-channel
MOSFET or PNP transistor. The device should be chosen
to handle the required power dissipation, given the circuit
parameters, PCB layout and heat sink configuration. The
following examples illustrate the design process for
PMOS device:
Low-Power Sleep Mode
When the input supply is disconnected, the charger
automatically enters power-saving sleep mode.
This feature prevents draining the battery pack during the
absence of VCC.
DS8057 Ver 1.8 Nov. 2006
12
EUTECH [ EUTECH MICROELECTRONICS INC ]
