
Phase Adding and Shedding fo r Parallel Operation
During periods of light load ing, it may be beneficial to disable
one or more phases (modules) in order to el iminate the current
drain and switching losses associated with those phases,
resulting in higher efficiency. The product offers the ability to
add and drop phases (modules) using a PMBus command in
response to an observed load current chan ge. All phases
(modules) in a current share rail ar e considered active prior to
the current sharing rail ramp to power-good. Phases can be
dropped after power-good is reached. An y member of the
current sharing rail can be dropped. If the reference module is
dropped, the remaining active module with the lowest member
position will become the ne w referenc e. Additionally, any
change to the number of members of a current sharing rail will
precipitate autonomous phase distribution within the rail where
all active phases realign their phase position based on their
order within the number of active members. If the members of
a current sharing rail are forced to shut down due to an
observed fault, all members of the rail will attempt to re-start
simultaneously after the fault has cleared.
Adaptive Diode Emulation
Most power converters use synchronous rectification to
optimize efficiency over a wide range of input and output
conditions. However, at light loads the synchronous MOSFET
will typically sink current and introduce additional energy
losses associated with higher peak inductor currents, resulting
in reduced efficiency. Adaptive diode emulation mode turns off
the low-side FET gate drive at low load currents to prevent the
inductor current from going negative, reduci ng the energy
losses and increasing overall efficiency. Diode emul ation is not
available for current sharing groups. Note: the overall
bandwidth of the product may be reduced when in diode
emulation mode. It is recommended that diode emulation is
disabled prior to applying significant load steps. The diode
emulation mode can be configured using the PMBus interface.
Adaptive Frequency and Pulse Skip Control
Since switching losses contribute to the efficiency of the power
converter, reducing the switching frequency will reduce the
switching losses and incr ease efficiency. The product includes
an Adaptive Frequency C ontrol mode, which effectively
reduces the observed s witchi ng frequency as the load
decreases. Adaptive frequency mode is only available while
the device is operating within Adaptive Diode Emulation Mode.
As the load current is decreased, diode emulation mode
decreases the Synch-FET on-time to prevent negative inductor
current from flowing. As the load is decreased further, the
Switch-FET pulse width will be gin to decrease while
maintaining the programmed frequ ency, fPROG (set by the
FREQ_SWITCH command). Once the Switch-FET pulse width
(D) reaches 50% of the nominal duty cycle, DNOM (determined
by VI and VO), the switching frequency will start to decrease
according to the following equation:
Eq. 5.
MIN
NOM
MINPROG
sw f
Dff
Df
2.
Disabling a minimum Sync h-FET makes the product also pulse
skip which reduces the power loss further.
It should be noted that adaptive frequency mode is not
available for current sharing groups and is not allowed when
the device is placed in auto-detect mode and a clock source is
present on the SYNC pin, or if the device is outputting a clock
signal on its SYNC pin. The adaptive frequency an d pulse skip
modes can be configured usin g the PMBus interface.
Efficiency Optimized Dead Time Control
The product utilizes a closed l oop algorithm to optimize the
dead-time applied between the gate drive signals for the switch
and synch FETs. The algorithm constantly adjusts the
deadtime non-overlap to minimize the duty cycle, thus
maximizing efficiency. This algorithm will null out deadtime
differences due to component variation, temperature and
loading effects. The algorithm can be configured via the
PMBus interface.
Over Current Protection (OCP)
The product includes current limiting circuitry for protection at
continuous overload. The following OCP response options ar e
available:
1. Initiate a shutdown and attempt to restart an infinite number
of times with a preset delay period between attempts.
2. Initiate a shutdown and attempt to restart a preset number
of times with a preset delay period
3. Continue operating for a given delay period, followed by
shutdown if the fault still exists.
4. Continue operating thro ugh the fault (this could result in
permanent damage to the product).
5. Initiate an immediate shutdown.
The default response from an over current fault is an
immediate shutdo wn of the device. The device will
continuously check for the presence of the fault condition, and
if the fault condition no longer exists the device will be re-
enabled.The load distribution should be designed for the
maximum output short circuit current specified. The OCP limit
and response of the product can be reconfigured using the
PMBus interface.
Note for BMR464.
When the ratio VO/VI is below 0.07 (e.g. VI = 12 V and VO= 0.6
V), and the default configuration file is used, the OCP limit
threshold may be below specified minimum value. If the
specified maximum output current is reached under such ope-
rating conditions, it is recommended to incr ease the OCP limit.
Start-up Procedure
The product follows a specific internal start-up procedure after
power is applied to the VIN pin:
1. Status of the address and output voltage pin-strap pins are
checked and values associated with the pin settings are
loaded.
E
BMR 464 series POL Regulators
Input 4.5-14 V, Output up to 40 A / 132 W EN/LZT 146 435 R2A July 2011
© Ericsson AB
Technical Specification
E
BMR 464 series POL Regulators
Input 4.5-14 V, Output up to 40 A / 132 W EN/LZT 146 435 R2B August 2011
© Ericsson AB
Technical Specification