Rainbow Electronics MAX8804Z - Manual (Page 11)

Soft-Start
The soft-start circuitry activates when entering fast-
charge mode. In the MAX8804Y, soft-start is entered
directly after being enabled, and the charging current
ramps up in 250µs from 0 to 500mA (95mA in USB
mode). This reduces the inrush current on the input
supply. Note that the MAX8804Z has a prequalification
state and the charging current ramps up when the pre-
qualification state is complete (V
BAT exceeds 2.5V).
Thermal Regulation Control
The thermal-regulation loop limits the MAX8804Y/
MAX8804Z die temperature to +105°C by reducing the
charge current as necessary. This feature not only pro-
tects the ICs from overheating, but also allows a higher
charge current at room temperature without risking
damage to the system.
Charging-Status Output (
CHG)
CHG is an open-drain output that indicates charger sta-
tus. CHG goes low during charge cycles where the
MAX8804Y/MAX8804Z are in prequalification or fast-
charge mode. CHG goes high impedance when the
charge current reaches the top-off threshold for more
than 4ms, indicating charging is done. The CHG status
is latched after the top-off threshold is reached. The
latch is reset by toggling the SET input, recycling input
power, or increasing the charging current to the top-off
threshold plus 57mA (typ).
When the MAX8804Y/MAX8804Z are used in conjunc-
tion with a microprocessor (µP), connect a pullup resis-
tor between CHG and the logic I/O voltage to indicate
charge status to the µP. Alternatively, CHG can sink up
to 5mA for an LED charge indicator.
MAX8804Y/MAX8804Z
High-Voltage, Dual-Input, USB/AC
Adapter Chargers in 2mm x 3mm TDFN
______________________________________________________________________________________ 11
> 2ms
1 2 3
95mA
380mA
475mA
80mA
95mA
USB
SET
0mA 0mA
USBPWR
POK
I
CHG
TOP-OFF
CURRENT
THRESHOLD
t
SOFTSTART
t
LOW
2ms
DELAY
Figure 4. USB Charging Current Programming