7
FN8154.0
Principles of Operation
Power Sequencing Control (PSC)
The Intersil X80200 supports a variety of sequencing
applications. The sequencing can be voltage-based or time-
based. Some examples are shown in Figure , Figure , and
Figure in the Applications section. The X80200 allows for
designs that can control the power sequencing of up to three
voltage supplies. For systems with more than three supplies,
the X80200 may be cascaded.
Basic Functions
VDDH is the primary voltage for the X80200. Once VDDH
rises above the primary undervoltage lockout level (UVLO
H
)
for time t
PURST
, the READY output goes HIGH indicating
that the supply power is good. By connecting READY
directly to GATEH_EN, the GATE_H output goes high
immediately, turning on the power FET connected in series
with VDDH. The system primary voltage may be delayed by
using an external RC circuit between READY and
GATEH_EN.
VDDH must be stable before VDDM and VDDL supplies are
monitored and power sequencing begins.
The second supply voltage (I/O supply) is monitored by the
VDDM pin. VDDM must be greater than the I/O supply
undervoltage lockout level (UVLO
M
) prior to any activation of
the GATE_M output. The VDDM voltage is used to turn on
the charge pump that drives the GATE_M output.
The third supply (core supply) is monitored by the VDDL pin.
VDDL must be greater than the core supply undervoltage
lockout level (UVLO
L
) prior to any activation of the GATE_L
output. The VDDL voltage is used to turn on the charge
pump that drives the GATE_M output.
Power Sequencing Functions
X80200 provides two options for power sequencing. In time
based sequencing, the ENS (Enable Sequence) input
signals that the core and I/O voltages are to turn on with a
fixed time relationship. In voltage based sequencing, the
SETV (Set Voltage) initiates turn-on of the core voltage. The
I/O voltage remains off until the core voltage reaches a set
threshold.
In both cases the X80200 uses a core-voltage first and core
voltage-last power up/down algorithm.
TIME-BASED POWER SEQUENCING
A rising edge (LOW to HIGH) transition of the ENS pin turns
on the charge pump that drives the GATE_L output.
A falling edge (HIGH to LOW) transition of the ENS signal
turns off the charge pump that drives the GATE_M output.
This technique provides a “forced” core-voltage-first power
up and core-voltage-last power down algorithm. The ENS
signal does not control the ramp up/down rates of the
GATE_M or GATE_L outputs.
In the absence of an externally provided ENS signal, the
ENS pin can be connected in a number of different ways.
• ENS can connect to the VDDH pin. In this case, the
GATE_H and GATE_L outputs are enabled at the same
time. GATE_H could be delayed by using an external RC
timer between READY and GATEH_EN to provide a
sequence where VDDL is the first supply voltage applied
to the system.
• ENS can connect to a delayed READY signal, so that the
VDDL voltage follows the VDDH voltage by a fixed time.
• ENS can connect to the system side of the VDDH FET, so
the VDDL voltage will follow immediately after the primary
supply is applied to the system.
See "Functional Description" on page 7 for details on timing
and ramp-up.
VOLTAGE-BASED POWER SEQUENCING
In this configuration, the drain of the “L” MOSFET is
connected to the VFB input of the X80200, the ENS pin is
tied to ground and a resistor divider provides a reference
voltage to the REF pin.
A LOW to HIGH transition of the SETV pin turns on the
GATE_L output. This turns on the “L” MOSFET. Once the
drain of this FET reaches the REF level, GATE_M turns on.
Since the trigger for the GATE_M output is selected by a
threshold level, the user has the ability to specify relative
core and I/O voltage sequencing.
System Monitoring and Remote Shutdown
The X80200 Status Register contains fault detection bits that
indicate the status of the GATE_H, GATE_M, and GATE_L
pins. These bits are Stat_GATEH, Stat_GATEM, and
Stat_GATEL. The status register can be read via 2-wire bus.
This feature allows for system monitoring of the power
sequencing of supplies.
The system can turn off the FETs by writing to the Remote
Shutdown Register through the 2-wire interface. There are
three turn-off selections. See "Remote Shutdown Register
(RSR) (Volatile)" on page 10 for more details.
Functional Description
Voltage Inputs. The X80200 has three voltage monitors for
power sequencing: the VDDH (primary voltage), VDDM (I/O
voltage), and VDDL (core voltage). These voltage monitors
operate independently of each other.
PRIMARY VOLTAGE VDDH
This voltage is the primary voltage for the device and is
required before X80200 can power sequence VDDM and
VDDL. As VDDH powers up, it is compared to an internal
UVLO
H
reference. This undervoltage lockout level is preset
at the factory. For information on this setting, see Ordering
Information. For custom programmed levels, contact Intersil.
X80200, X80201, X80202, X80203, X80204
