AAT4621_12 Datasheet, PDF (12/17 Pages) Skyworks Solutions Inc. – PC Card Current Limit Interface and Capacitor Charger

DATA SHEET
AAT4621
PC Card Current Limit Interface and Capacitor Charger
Application Information
ISETU and ISETL Current Limit Set
The AAT4621/AAT621-1 current limit is set at two differ-
ent levels. Resistors from ISETL and ISETU set the lower
and upper current limit levels respectively.
The ISETL and ISETU nodes operate within a window of
0.75V to 1.5V for resistor values ranging from 93.75 to
1.5M. Resistor values outside this range are not recom-
mended. The ISETL and ISETU source current varies with
the resistor value used according to Table 1. To determine
the resulting current limit multiply the R_SETU or R_SETL node
voltage times the gain in Table 1. Note that the voltage at
the node varies from 0.75V to 1.5V and the current limit
gain varies depending on the resistor value used.
V_ISET = R_SET · I_ISET = 0.75V to 1.5V
If the set pin is open circuit or allowed to exceed 2V, all
power devices are disabled and the input is disconnected
from the output. Shorting the set pin to GND enables all
power devices and shorts the V_CC to the output pin with
no current limit.
To activate the upper current level (R_SETU) pull EN IU low.
To activate the lower current level (R_SETL) pull EN IL low.
If both EN IU and EN IL are pulled low the EN IU current
limit level (R_SETU) will be selected.
The AAT4621 has a current limit range from 75mA to
1200mA; the AAT4621-1 has a current limit range from
150mA to 2400mA.
3000
2500
2000
AAT4621-1
1500
1000
500
AAT4621
0
100
300
500
700
900
1100 1300 1500
R_SETU and R_SETL (Ω)
Figure 1: Calculated Current Limit R_SET
Characteristic.
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_CC). The comparator hysteresis is programmed by a
resistor from the RHYS pin to ground. The RHYS voltage
determines the hysteresis voltage and is equal to the
RHYS source current (1μA) times the RHYS resistance.
V_HYST = R_HYS · 1µA
= 200kΩ · 1µA
= 0.2V
The system ready pin (RDY) is an open drain output 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 100k.
R_SET Range
(Ω)
1.5Meg -750K
750K -375K
375K -187.5K
187.5K-93.75K
I_ISET (μA)
1
2
4
8
I_LIM/V_ISET (A/V)
AAT4621
AAT4621_1
0.8
1.6
0.4
0.8
0.2
0.4
0.1
0.2
Current Limit Range (A)
AAT4621
1.2-0.6
0.6-0.3
0.3-0.15
0.15-0.075
AAT4621_1
2.4 - 1.2
1.2 - 0.6
0.6 -0.3
0.3 - 0.15
Table 1: R_SET Table.
Current Limit (A)
AAT4621
R_SET*1*0.8
R_SET*2*0.4
R_SET*4*0.2
R_SET*8*0.1
AAT4621_1
R_SET*1*1.6
R_SET*2*0.8
R_SET*4*0.4
R_SET*8*0.2
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
12
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012