sg6521 Fairchild Semiconductor, sg6521 Datasheet - Page 7

• Manufacturer Part Number: sg6521
• Description: Sg6521 ? Pc Power Supply Supervisors
• Manufacturer: Fairchild Semiconductor

© 2007 Fairchild Semiconductor Corporation
SG6521 • Rev. 1.0.0
Functional Description
The SG6521 is designed to provide the supply voltage,
current supervisor, remote on/off (PSON), power-good
(PGO) indicator, and fault protection (FPO) functions for
switching power systems.
For supervisory functions, it provides the over-voltage
protection (OVP) for 3.3V, 5V, and two 12V; over-
current protection (OCP) for 3.3V, 5V, and two 12V;
under-voltage protection (UVP) for 3.3V, 5V, and two
12V. When 3.3V, 5V, or 12V voltage decreases to 2.3V,
3.5V, and 9V, respectively, the under-voltage protection
function is enabled. FPO is set HIGH to turn off the
PWM controller IC. The voltage difference across
external current shunt is used for OCP functions. An
external resistor can be used to adjust protection
threshold. An additional protection input pin provides
the flexibility for designing protection circuits.
The power supply is turned on after a 48ms delay when
PSON signal is set from HIGH to LOW. To turn off the
power supply, the PSON signal is set from LOW to
HIGH with a delay of 48ms. The PGI circuitry provides a
power-down warning signal for PGO. When PGI input is
lower than the internal 1.25V reference voltage, PGO
signal is pulled LOW.
The SG6521 provides over-current protection for the
3.3V, 5V, and two 12V rails. Whenever an OCP
condition occurs at any of the voltage rails, PGO is
LOW and FPO is open. The internal OCP comparators
7
have a very small offset voltage ( ± 3mV). The sink
currents of IS33, IS5, and IS12 are eight times the
current at the RI pin. The current at the RI pin is V
Here is an example demonstrating how to set the over
current protection. If I
R
then the R
where C is bypass noise, suggested value is between
1µF ~ 2.2µF
R
1
=5mΩ, R
2
=
I
I
1
RI
×
×
R
8
2
1
resistor is:
I
=
=30KΩ, and the OCP active level is 35A,
525
Figure 4. OCP Setup
Ω
1
×R
1
> I
RI
×R2, OCP is active. If
www.fairchildsemi.com
RI
(1)
/R
I
.