
TPS3513
PC POWER SUPPLY SUPERVISORS
SLVS313 – FEBRUARY 2001
7
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
detailed description (continued)
overcurrent protection
In bridge or forward type, off-line switching power supplies, usually designed for medium to large power, the
overload protection design needs to be very precise. Most of these types of power supplies are sensing the
output current for an overload condition. The trigger-point needs to be set higher than the maximum load in order
to prevent false turnon.
The TPS3513 provides overcurrent protection (OCP) for the 3.3-V, 5-V, and 12-V rails. When an over current
condition appears at the OCP comparator input pins for more than 73
μ
s
, the
FPO output goes high and PGO
goes low. Also, this fault condition will be latched until PSON is toggled from low-to-high or VDD is removed.
The resistor connected between the RI pin and the GND pin will introduce an accurate I
(ref)
for the OCP function.
Of course, a more accurate resistor tolerance will be better. The formula for choosing the RI resistor is V
(RI)
/I
(ref)
.
The I
(ref)
range is from 12.5
μ
A to 62.5 mA. Three OCP comparators and the I
(ref)
section are supplied by VS12.
Current drawn from the VS12 pin is less than 1 mA.
Following is an example on calculating OCP for the 12-V rail:
RI = V
(RI)
/I
(ref)
= 1.15 V/20
μ
A
= 56 K
I
(ref)
x C x R
(IS12)
= R
(sense)
x I
(OCP_Trip)
I
(OCP_Trip)
= 20
μ
A
x 8 x 560
/0.01
= 9.2 A
C = Current ratio (see recommended operating conditions)
overvoltage protection
The overvoltage protection (OVP) of the TPS3513 monitors 3.3 V, 5 V, and 12 V. When an overvoltage condition
appears at one of the 3.3-V, 5-V, or 12-V input pins for more than 73
μ
s, the FPO output goes high and PGO
goes low. Also, this fault condition will be latched until PSON is toggled from low-to-high or VDD is removed.
During fault conditions, most power supplies have the potential to deliver higher output voltages than those
normally specified or required. In unprotected equipment, it is possible for output voltages to be high enough
to cause internal or external damage of the system. To protect the system under these abnormal conditions,
it is common practice to provide overvoltage protection within the power supply.
absolute maximum ratings over operating free-air temperature (unless otherwise noted)
Supply voltage, V
DD
(see Note1)
Input voltage, V
I
(PSON, IS5, IS33, PGI) (see Note1)
Input voltage, V
I
(VS33, VS5)
Output voltage: V
O
(FPO)
V
O
(PGO)
All other pins (see Note 1)
Continuous total power dissipation
Operating free-air temperature range, T
A
Storage temperature range, T
stg
Soldering temperature
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16 V
8 V
16 V
16 V
8 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
–0.3 V to 16 V
See Dissipation Rating Table
–40
°
C to 85
°
C
–65
°
C to 150
°
C
260
°
C
Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
NOTE 1: All voltage values are with respect to GND.