LTC3882_15 Datasheet, PDF (21/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

LTC3882
OPERATION
Output Current Sensing and Monitoring
Both channels allow differential sensing of the inductor
current using either the inductor DCR or a resistor in series
with the inductor across the I_SENSE pins. When the I_SENSE
pins for a channel are multiplexed to the differential inputs
of the LTC3882 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 returned to the LTC3882 GND pin using a Kelvin con-
nection. Two different currents are applied to the diode
(nominally 2μA and 32μA) and the temperature is calcu-
lated from a ΔV_BE measurement made with the internal
16-bit monitor ADC.
The LTC3882 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 ΔV_BE measurement. Refer
to MFR_PWM_MODE_LTC3882 in the PMBus Command
Details section for additional information on programming
the LTC3882 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 inter-
nal junction temperature of the LTC3882 using an on-chip
diode with a ΔV_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
command is set in EEPROM, all resistor inputs except
ASELn are ignored. Per the PMBus specification, all pin-
programmed parameters can be overridden at any time
by commands from the digital interface.
The ASELn pin settings are described in application
Table 11. These pins can be used to select the entire
LTC3882 device address. ASEL0 always programs the
bottom four bits of the device address for the LTC3882
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 always responds to 7-bit global
addresses 0x5A and 0x5B. MFR_ADDRESS should not
be set to either of these values.
The V_{OUTn_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%
For more information www.linear.com/LTC3882
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