UZXYY ANALOGICTECH [Advanced Analogic Technologies], UZXYY Datasheet - Page 11

• Manufacturer Part Number: UZXYY
• Description: PCMCIA Current Limit Interface and Capacitor Charger
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

System Ready Hysteresis (RHYS) and
System Ready (RDY)
In internal comparator senses the output voltage
and delivers a ready signal to the external micro
controller when the output voltage reaches 98% of
the final value (V
programmed by a resistor from the RHYS pin to
ground. The RHYS voltage determines the hys-
teresis voltage and is equal to the RHYS source
current (1µA) times the RHYS resistance.
The system ready pin (RDY) is an open drain out-
put that switches low when the output voltage
reaches 98% of the input voltage. It requires an
external pull up resistor tied to the input voltage
with a typical value of 100kΩ.
Power Loop
The AAT4620 power loop limits the load current in
the event that the device power dissipation becomes
excessive. The AAT4620 power loop regulates the
die temperature to 100°C, decreasing the load cur-
rent in increments of 1/32 of the current limit set point
when the die temperature reaches 100°C. When the
4620.2007.04.1.1
Figure 1: Calculated Current Limit R
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.10
0.30
V
I
HYST
LOAD
CC
Characteristic.
0.50
). The comparator hysteresis is
R
SETU
= R
= 200kΩ · 1μA
= 0.2V
vs. R
0.70
and R
HYS
SETU
· 1μA
SETL
0.90
and R
(MΩ Ω )
1.10
SETL
1.30
SET
1.50
die temperature exceeds 100°C it decreases the
load current by 1/32 of the current limit set point. If
die temperature is less than 100°C, it increases the
load current in increments of 1/32 of the current limit
set point until the set current limit point is reached or
the die temperature exceeds 100°C.
The delay time between die temperature measure-
ments varies depending on the load current limit
set point. The delay ranges from 1ms for a 75mA
current limit set point to 8ms for a 1.5A current limit
set point.
For the condition where there is no current limit set
point (shorting R
start increments the current limit is 1/32 steps of
1.2A until the current reaches 1.2A, at which point
the power MOSFET turns on fully. At this point, the
current is limited by the R
FET and other series resistance. The Power Loop
and Over-Temperature Loop then takes control to
limit the current until the output voltage has fully
charged.
Over-Temperature Protection
If the die temperature rate of rise is fast enough to
exceed the power loop regulated temperature,
over-temperature shutdown disables the device.
The over-temperature threshold is 145°C. After
over-temperature shutdown, soft start is initiated
once the die temperature drops to 130°C.
Short Circuit Protection
The series pass power MOSFET turns off com-
pletely after the output has charged to within 18mV
of the input voltage. This protects the device in the
event of a short circuit applied to the output.
Applying a short circuit or heavy load to the output
initiates the digital soft start where the current
ramps from zero to the final programmed value. The
power loop will be activated once the digital soft
start begins.
Under-Voltage Shutdown
Under-voltage lockout enables the device at 2.7V
typical with 100mV of hysteresis. The maximum
UVLO level is 3.0V.
PCMCIA Current Limit Interface
and Capacitor Charger
SETU
or R
DS(ON)
SETL
to ground) the soft
of the power MOS-
AAT4620
11