MC33567
http://onsemi.com
4
OPERATING DESCRIPTION
Introduction
The MC33567 series is a family of Dual Linear FET
Controllers designed for Power Management applications
where high current, voltage regulation is needed. Some
computer applications include:
• 1.2 V − Power Supply
• 1.515 V − AGP (Advanced Graphic Port) and GTL+
(Gunning Transistor Logic − Intel’s electrical bus
technology)
• 1.818 V − I/O planes on motherboards
• 2.3 V − Power Supply
• 2.525 V − Clock and memory
The MC33567 provides tight output voltage regulation,
(V
out
), and incorporates individual SHDN controls for each
FET controller and voltage protection by sensing the output
voltage.
Output:
The MC33567 provides tight output voltage regulation
from one or two supply voltages using 2 external N−Channel
MOSFETs. Each controller operates independently and
regulates the output voltage to a predetermined level (1.2 V,
1.515 V 1.818 V, 2.3 V or 2.525 V). In addition, regulator 2
of the MC33567−1 incorporates a V
in
bypass mode on which
the external FET is fully enhanced.
Shutdown:
The regulated outputs of the MC33567 can be disabled
with the use of the SHDN pin. It also determines the output
voltage level. SHDN
can be controlled externally from
board signals like the AGP or GTL+ as shown in Figure 3.
Figure 3. 1.5 V/3.3 V AGP Card Detection
*V
in
while on bypass mode (MC33567−1 only)
1
2
3
4
8
7
6
5
MC33567
DRV2
SENSE2
3.3 V
AGP
Card Type
Detection
AGP
Card
Voltage
V
out
or V
in
*
12 V (V
CC
)
3.3 V (V
in
)
SHDN2
10 k
Listed below are the SHDN threshold voltage levels and
the corresponding regulator output voltages:
1. If the SHDN pin is left open, the output voltage is set
to its regulated value.
2. If a voltage less than 0.8 V is applied to the SHDN
pin,
the output voltage is set to 0 V.
3. If a voltage greater than 1.3 V and less than 4.1 V is
applied to the SHDN pin, the output voltage is set to its
regulated voltage.
4. If the SHDN
voltage is pulled above 4.1 V, the
MC33567 enters a V
in
bypass mode. In this mode, the
MOSFET is fully enhanced and the output voltage is
the MOSFET drain voltage (V
in
) minus the MOSFET
drain−source on voltage V
DS(on)
. This feature is only
available on REGULATOR 2 of the MC33567−1.
Table 1 summarizes the output voltage options and its
relationship with V
SHDN
.
Table 1. Logic Table for SHDN Pin
Device V
SHDN
(V) V
out
(V)
MC33567−1
REGULATOR 1
No Connect
0.8 V
1.3 V
1.818 V
0 V
1.818 V
REGULATOR 2 No Connect
0.8 V
1.3 V V
SHDN
4.1 V
4.1 V
1.515 V
0 V
1.515 V
V
in
−V
DS(on)
(Bypass
Mode)
MC33567−2
REGULATOR 1 &
REGULATOR 2
No Connect
0.8 V
1.3 V
2.525 V
0 V
2.525 V
MC33567−3
REGULATOR 1
No Connect
0.8 V
1.3 V
2.3 V
0 V
2.3 V
REGULATOR 2 No Connect
0.8 V
1.3 V
1.2 V
0 V
1.2 V
Undervoltage Detection:
If V
out
drops below 75% of the regulated threshold for
greater than 250 µs or a short circuit condition is present, that
output will go into short circuit or Hiccup Mode. While in
Hiccup mode, the output is turned ON for 1.0 ms and OFF
for 40 ms for a duty cycle of 1:41 as shown in Figure 4. This
mode will continue as long as the fault is present. Once the
fault is removed, the regulator will resume normal
operation.
40 ms
1 ms
Figure 4. Hiccup Mode Duty Cycle
