MCP37231 datasheet(91/144 Pages) MICROCHIP

91 / 144 page

MCP37231/21-200 AND MCP37D31/21-200

DS20005322D-page 91

 2014-2016 Microchip Technology Inc.

ADDRESS 0X56 – PLL PRESCALER (LSB)

R/W-0

R/W-1

R/W-0

PLL_PRE<7:0>

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7-0

PLL_PRE<7:0>: PLL prescaler selection(1)

1111-1111

= VCO clock divided by 255 (if PLL_PRE<11:8> = 0000)

• • •

0111-1000

= VCO clock divided by 120 (if PLL_PRE<11:8> = 0000) (Default)

• • •

0000-0010

= VCO clock divided by 2 (if PLL_PRE<11:8> = 0000)

0000-0001

= VCO clock divided by 1 (if PLL_PRE<11:8> = 0000)

0000-0000

= VCO clock not divided (if PLL_PRE<11:8> = 0000)

Note

PLL_PRE is a 12-bit-wide setting. The upper four bits (PLL_PRE<11:8>) are defined in Address 0x57. See Table 5-5 for the

PLL_PRE<11:0> settings. The PLL Prescaler is used to divide down the VCO output clock in the PLL phase-frequency detector

loop circuit.

ADDRESS 0X57 – PLL PRESCALER (MSB)

R/W-0

R/W-1

R/W-0

FCB<3:0>

PLL_PRE<11:8>

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7-4

FCB<3:0>: Factory-Controlled Bits. This is not for the user. Do not change default settings.

bit 3-0

PLL_PRE<11:8>: PLL prescaler selection(1)

1111

= 212 - 1 (max), if PLL_PRE<7:0> = 0xFF

• • •

0000

= Default)

Note

PLL_PRE is a 12-bit-wide setting. See the lower eight bit settings (PLL_PRE<7:0>) in Address 0x56 (Register 5-11). See

Table 5-5 for the PLL_PRE<11:0> settings for PLL feedback frequency.

TABLE 5-5:

Example: PLL Prescaler Bit Settings and PLL Feedback Frequency

PLL_PRE<11:0>

PLL Feedback Frequency

1111-1111-1111

VCO clock divided by 4095 (212 - 1)

1111-1111-1110

VCO clock divided by 4094 (212 - 2)

──

0000-0000-0011

VCO clock divided by 3

0000-0000-0010

VCO clock divided by 2

0000-0000-0001

VCO clock divided by 1

0000-0000-0000

VCO clock divided by 1

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