ez80f91 ZiLOG Semiconductor, ez80f91 Datasheet - Page 278

• Manufacturer Part Number: ez80f91
• Description: Ez80 Acclaimplus!? Connectivity Assp Ez80f91 Assp
• Manufacturer: ZiLOG Semiconductor

eZ80F91 ASSP
Product Specification
270
Phase Frequency Detector
The Phase Frequency Detector (PFD) is a digital block. The two inputs are the reference
clock (XTAL oscillator; see
On-Chip Oscillators
on page 339) and the PLL divider output.
The two outputs drive the internal charge pump and represent the error (or difference)
between the falling edges of the PFD inputs.
Charge Pump
The Charge Pump is an analog block that is driven by two digital inputs from the PFD that
control its programmable current sources. The internal current source contains four
programmable values: 1.5 mA, 1 mA, 500 µA, and 100 µA. These values are selected by
PLL_CTRL1[7:6]. The selected current drive is sinked/sourced onto the loop-filter node
according to the error (or difference) between the falling edges of the PFD inputs. Ideally,
when the PLL is locked, there are no errors (error = 0) and no current is sourced/sinked
onto the loop-filter node.
Voltage Controlled Oscillator
The Voltage Controlled Oscillator (VCO) is an analog block that exhibits an output
frequency proportional to its input voltage. The VCO input is driven from the charge
pump and filtered via the off-chip loop filter.
Loop Filter
The Loop Filter comprises off-chip passive components (usually 1 resistor and 2
capacitors) that filter/integrate charge from the internal charge pump. The filtered node
also drives the VCO input, which creates a proportional frequency output. When PLL is
not used, the Loop Filter pin must not be connected.
Divider
The Divider is a digital, programmable downcounter. The divider input is driven by the
VCO. The divider output drives the PFD. The function of the Divider is to divide the
frequency of its input signal by a programmable factor N and supply the result in its
output.
MUX/CLK Sync
The MUX/CLK Sync is a digital, software-controllable multiplexer that selects between
PLL or the XTAL oscillator as the system clock (SCLK). A PLL source is selected only
after the PLL is locked (via the lock detect block) to allow glitch-free clock switching.
Lock Detect
The Lock Detect digital block analyzes the PFD output for a locked condition. The PLL
block of the eZ80F91 device is considered locked when the error (or difference) between
the reference clock and divided-down VCO is less than the minimum timing lock criteria
PS027001-0707
Phase-Locked Loop