enCoRe™ V CY7C643xx, enCoRe™ V LV CY7C604xx TRM, Document No. 001-32519 Rev *H
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Regulated I/O
12.1.1
Bias Generator
The bias generator generates gate bias to all pass transis-
tors. This block mainly contains a charge pump an opamp
along with a NMOS diode in a forward biased condition.
12.1.2
Charge Pump
The Charge Pump gets clock information from the internal
main oscillator and pumps the charge to forward bias the
NMOS diode. The NMOS diode is always in a slightly for-
ward biased condition. There are control bits that control the
current pumped into the charge pump for different frequen-
cies of the charge pump clock input.
12.1.3
Comparator
The comparator expects an input of 1.2V reference and is
used in negative feedback to generate a regulation voltage
at the output. he NMOS replica structure is an NMOS diode
configuration and is stacked over the output of the opamp.
Because of the charge pump forward bias in the NMOS
diode, the drain voltage is always the sum of the comparator
output voltage and the transistor threshold voltage. This
voltage is given as bias voltage to the gates of all pass tran-
sistors.
12.1.4
Replica Structure
The Replica Structure has a NMOS in series with the resis-
tive divider structure. The resistive divider network provides
feedback to the comparator in such a way that the source of
the replica NMOS is always set to 3V.
12.1.5
Pass Transistors
The Pass Transistors are NMOS pass transistors that sit
with the I/O driver. These transistors ensure that the I/O out-
put voltage does not exceed the regulated voltage and
support5 mA drive strength. In order to have acceptable
control of the I/O output voltage, the NMOS pass transistors
provide the same operating conditions as that of the replica
structure. This is archived by connecting a resistance of one
fourth of the replica resistor to the source of the NMOS pass
transistor. This is a common resistor for all four I/O.
12.2
Application Overview
The I/O voltage regulator regulates the output of the I/O to
3.0, 2.5, 1.8 volts. The pass transistor of the regulator sits
with the driver of the I/O. Bias for the pass transistor is
routed along the supply ring.