RT9722 RICHTEK [Richtek Technology Corporation], RT9722 Datasheet - Page 9

• Manufacturer Part Number: RT9722
• Description: 145m?, 1.5A Power Switch with Programmable Current Limit
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Application Information
The RT9722 is a high-side power switch with programmable
current limit function. The RT9722 provides active-high
(RT9722A) and active-low (RT9722B) enable input and full
protection functions make it optimized to replace complex
discrete on/off control circuitry.
Current Limit Setting
The current limit value I
resistor between SET and GND. Figure 3 shows the typical
current limit value under various setting resistance, R
The accuracy of current limit set point may vary with
operating temperature and supply voltage, see “Typical
Operating Characteristics” graph for further details.
A few standard resistor values of the R
current limit set point with ±25% tolerance are listed in
Table 1.
Input and Output
V
circuitry and the source of the MOSFET. V
the drain of the MOSFET. In a typical application, current
flows through the switch from V
If V
V
RT9722 is designed to control current flowing from V
V
on V
device.
DS9722-00 August 2011
IN
OUT
IN
OUT
(input) is the power source connected to the internal
since the MOSFET is bidirectional when on. The
IN
. If a voltage applied to V
1600
1400
1200
1000
800
600
400
200
, large currents may flow and cause damage to the
Figure 3. Current Limit vs. R
is greater than V
0
0
10
Current Limit vs. R
20
IN
LIM
, current will flow from V
, can be set by an external
OUT
R
30
SET
IN
is greater than the voltage
to V
(kΩ)
(kΩ)
SET
40
OUT
Resistance
SET
toward the load.
50
SET
OUT
and its typical
(output) is
60
OUT
IN
SET
70
to
to
.
Chip Enable Input
The switch will be disabled when the EN/EN pin is in a
logic low/high condition. During this condition, the internal
circuitry and MOSFET are turned off, reducing the supply
current to 0.1μA typically. The maximum guaranteed
voltage for a logic low at the EN pin is 0.6V. A minimum
guaranteed voltage of 1.4V at the EN pin will turn on the
RT9722 again. Floating the input may cause unpredictable
operation. EN should not be allowed to go negative with
respect to GND. The EN pin can be directly tied to V
keep the part on.
Soft-Start for Hot Plug-In Applications
In order to eliminate the upstream voltage droop caused
by the large inrush current during hot-plug events, the
“soft-start” feature effectively isolates the power source
from extremely large capacitive loads.
Fault Flag
The RT9722 provides a FLG signal pin which is an
N-Channel open drain MOSFET output. This open drain
output goes low when current limit V
die temperature exceeds 150°C approximately. The FLG
R
Table 1. Current Limit vs. R
SET
5.49
7.32
8.66
10.5
22.6
34.8
4.7
6.8
13
16
18
20
30
47
(kΩ)
1125.0
937.5
750.0
675.0
600.0
525.0
450.0
375.0
337.5
300.0
262.5
225.0
187.5
150.0
Design Current Limit (mA)
Min
1500
1250
1000
Typ
900
800
700
600
500
450
400
350
300
250
200
SET
OUT
Resistance
RT9722
< V
www.richtek.com
IN
1875.0
1562.5
1250.0
1125.0
1000.0
875.0
750.0
625.0
562.5
500.0
437.5
375.0
312.5
250.0
− 1V, or the
Max
IN
to
9