LTC3882_15 Datasheet, PDF (60/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

LTC3882
APPLICATIONS INFORMATION
IC Junction Temperature
The user must ensure that the maximum rated junction
temperature is not exceeded under all operating conditions.
The thermal resistance of the LTC3882 package (θ_JA) is
33°C/W, provided the exposed pad is in good thermal
contact with the PCB. The actual thermal resistance in
the application will depend on forced air cooling and other
heat sinking means, especially the amount of copper on
the PCB to which the LTC3882 is attached. The following
formula may be used to estimate the maximum average
power dissipation P_D (in watts) of the LTC3882 when V_CC
is supplied externally.
P_D = V_CC(0.024 + f_PWM • 1.6e-5 + I_EXT + I_RC25)
where:
I_EXT = total external load drawn from V_DD33, including
local pull-up resistors, in amps
I_RC25 = total current drawn from V_DD25 by LTC3882
configuration resistor dividers, in amps
and the _PWM frequency f_PWM is given in kHz
If an external source supplies V_DD33 directly, the following
formula may be used to estimate the maximum average
power dissipation P_D (in watts) of the LTC3882
P_D = V_DD33(0.024 + f_PWM • 1.6e-5 + I_RC25)
The maximum junction temperature of the LTC3882 in °C
may then be found from the following equation
T_J = T_A + 33 • P_D
with ambient temperature T_A expressed in °C
Derating EEPROM Retention at Temperature
EEPROM read operations between 85°C and 125°C will not
affect data storage. But retention will be degraded if the
EEPROM is written above 85°C or stored above 125°C. If
an occasional fault log is generated above 85°C, the slight
reduction in data retention in the EEPROM fault log area
will not affect the use of the function or other EEPROM
storage. See the Operation section for other high tem-
perature EEPROM functional details. Degradation in data
can be approximated by calculating the dimensionless
acceleration factor using the following equation.
AF
=
e


Ea 
k ^

•_
1
T_USE +273
−
1

T_STRESS+273 



Where:
AF = acceleration factor
Ea = activation energy = 1.4eV
k = 8.617 • 10^–5 eV/°K
T_USE = is the specified junction temperature
T_STRESS = actual junction temperature in °C
As an example, if the device is stored at 130°C for 10 hours,
T_STRESS = 130°C, and
AF
=

e ^{}
1.4 
8.617•10^{–5 }
•


1
398
−
1
403 ^



= 1.66
indicating the effect is the same as operating the device at
125°C for 10 • 1.66 = 16.6 hours, resulting in a retention
derating of 6.6 hours.
Configuring Open-Drain Pins
The LTC3882 has the following open-drain pins:
3.3V Pins
1. GPIOn
2. SYNC
3. SHARE_CLK
5V-Capable Pins
(These pins operate correctly when pulled to 3.3V.)
1. RUNn
2. ALERT
3. SCL
4. SDA
GPIO pins can be programmed as power good indicator
outputs, which is most useful on master phases. If valid
indication (pin low) is required at or immediately after
power-on, a Schottky diode should be added between the
3882f
60
For more information www.linear.com/LTC3882