LT7184S datasheet(29/52 Pages) AD

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Data Sheet

LT7184S

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Rev. 0

29 of 52

If the PWM_CFG pin is connected to a 5.6kΩ ±10% resistor to select PolyPhase operation (See Table 9), then the

VOUT1_CFG configuration resistor controls PWM settings, including frequency and phase (See Table 10).

Output voltage set point is controlled by VOUT_COMMAND.

VOUT Range Mode selection is controlled by MFR_PWM_MODE_LT7184S bit 1. A value of 1 selects high-performance

Low VOUT Mode, when this bit is set the output voltage cannot be programmed above 1.375V.

The PMBus ON_OFF_CONFIG command selects whether the RUN pin and/or OPERATION command enables the

regulator.

If the VOUTN_CFG pin is open or tied to VDD18, the VOUT_COMMAND is loaded from EEPROM to determine the output

voltage. The default EEPROM setting is to initialize with the regulator disabled unless the voltage configuration

resistors are installed. The commands listed below are initialized based on a percentage of VOUT_COMMAND if the

resistor configuration pins are used to initialize the output voltage.

Table 8. Command Initialization Defaults when Resistor Configuration Pins are used

COMMAND

DEFAULT % of VOUT_COMMAND

VOUT_OV_FAULT_LIMIT

+10%

VOUT_OV_WARN_LIMIT

+7.5%

VOUT_MAX

+7.5%

VOUT_MARGIN_HIGH

+5%

VOUT_MARGIN_LOW

-5%

VOUT_UV_WARN_LIMIT

-6.5%

VOUT_UV_FAULT_LIMIT

-7%

Switching Frequency and Phase

The PWM switching frequency can be established using the internal oscillator or applying an external clock on the

SYNC pin. An internal phase-locked loop (PLL) synchronizes PWM control to this timing reference, whether the

clock is provided internally or externally. The internal oscillator frequency is set by the FREQUENCY_SWITCH

command. The MFR_PWM_PHASE_LT7184S command configures the phase of each channel.

The SYNC pin is a flexible multipurpose input/output pin, which can be used as a clock input or output. The

LT7184S synchronizes PWM switching to an external clock input on SYNC unless the LT7184S has been configured

as an output driver or has been programmed to ignore the input clock. The LT7184S continues PWM operation

using its own internal oscillator if the external clock signal is lost. If an external clock is to be used, it is

recommended to program the FREQUENCY_SWITCH command or to use a configuration resistor to set the internal

oscillator frequency to a similar value as the external clock frequency. This ensures that the PWM switching

frequency remains reasonable if the external clock is lost. The LT7184S can be programmed to ignore an external

clock by writing a 1-to-Bit 1 of MFR_SYNC_CONFIG_LT7184S.

For an input clock frequency below 625kHz, it is recommended to use a configuration resistor that selects a PWM

frequency of 500kHz. For an input clock frequency between 625kHz and 1.25MHz, it is recommended to use a

configuration resistor that selects a PWM frequency of 1MHz. For an input clock frequency between 1.25MHz and

2.5MHz, it is recommended to use a configuration resistor that selects a PWM frequency of 2MHz. For an input clock

frequency greater than 2.5MHz, it is recommended to use a configuration resistor that selects a PWM frequency of

4MHz.

The LT7184S can be configured to provide a synchronizing clock output on the SYNC pin to other devices by setting

bit 0 of MFR_SYNC_CONFIG_LT7184S to 1. If the SYNC output clock is enabled, the LT7184S drives the SYNC pin as a

square wave from 0V to 1.88V (typical) at the frequency programmed in FREQUENCY_SWITCH, leads the phase of

LT7184S Datasheet(PDF) 29 Page - Analog Devices

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