LTC3882-1
23
Rev A
OPERATION
of the LTC3882-1 monitor ADC, they have an input range
of approximately ±128mV and a noise floor of 7μV
RMS
.
Peak-peak noise is approximately 46.5μV. The internal ADC
anti-aliasing filter and conversion rate produce an average
reading of the I
SENSE
differential voltage. The resulting value
is returned by the READ_IOUT PMBus command. Refer to
the Applications Information section for details on sensing
output current using inductor DCR or discrete resistors.
External and Internal Temperature Sense
External temperature can best be measured using a remote,
diode-connected PNP transistor such as the MMBT3906.
The emitter should be connected to a TSNS pin while the
base and collector terminals of the PNP transistor must be
shorted together and returned directly to the LTC3882-1
GND pin. Two different currents are applied to the diode
(nominally 2μA and 32μA) and the temperature is calcu-
lated from a ∆V
BE
measurement made with the internal
16-bit monitor ADC.
The LTC3882-1 also supports direct V
BE
based external
temperature measurements. In this case the diode or di-
ode network is trimmed to a specific voltage at a specific
current and temperature. In general this method does not
yield as accurate a result as the ∆V
BE
measurement. Refer
to MFR_PWM_MODE_LTC3882-1 in the PMBus Command
Details section for additional information on programming
the LTC3882-1 for these two external temperature sense
configurations.
The calculated temperature is returned by the PMBus
READ_TEMPERATURE_1 command. Refer to the Appli-
cations Information section for details on proper layout
of external temperature sense elements and PMBus
commands that can be used to improve the accuracy of
calculated temperatures.
The READ_TEMPERATURE_2 command returns the
internal junction temperature of the LTC3882-1 using an
on-chip diode with a ∆V
BE
measurement and calculation.
Resistor Configuration Pins
Six input pins can be used to configure key operating param-
eters with selected 1% resistors arranged between V
DD25
and GND as a divider to the pin(s). The pins are ASEL0,
ASEL1, V
OUT0_CFG
, V
OUT1_CFG
, FREQ_CFG, and PHAS_CFG.
If any of these pins are left open the value stored in the
corresponding EEPROM command is used. The resistor
configuration pins are only measured during power-up
and execution of RESTORE_USER_ALL or MFR_RESET
commands. If bit 6 of the MFR_CONFIG_ALL_LTC3882-1
command is set in EEPROM, all resistor inputs
except
ASEL
n
are ignored. Per the PMBus specification, all pin-
programmed parameters can be overridden at any time
by commands from the digital interface.
The ASEL
n
pin settings are described in application
Table 11. These pins can be used to select the entire
LTC3882-1 device address. ASEL0 always programs the
bottom four bits of the device address for the LTC3882-1
unless left open. ASEL1 can be used to program the three
most-significant bits. Either portion of the address can also
be retrieved from the MFR_ADDRESS value in EEPROM.
If both pins are left open, the full 7-bit MFR_ADDRESS
value stored in EEPROM is used to determine the device
address. The LTC3882-1 always responds to 7-bit global
addresses 0x5A and 0x5B. MFR_ADDRESS should not be
set to either of these values.
The V
OUT
n
_CFG
pin settings are described in application
Table 8. These pins select the output voltages for the
related channel.
The following parameters are also set as a percentage of
the programmed V
OUT
if resistor configuration pins are
used to determined output voltage:
• 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%
The FREQ_CFG pin settings are described in application
Table 9. This pin selects the switching frequency of the
internal oscillator and enables the SYNC output if not left
open, shorted to GND or ignored by EEPROM setting.
