2. Ratiometric. This mode configures the product to ramp its
output voltage at a rate that is a percentage of the voltage
applied to the VTRK pin. The default setting is 50%, but a
different tracking ratio may be set by an external resistive
voltage divider or through the PMBus interface.
Illustration of Ratiometric Voltage Tracking
The master device in a tracking group is defined as the device
that has the highest target output voltage within the group. This
master device will control the ramp rate of all tracking devices
and is not configured for tracking mode. All of the CTRL pins in
the tracking group must be connected and driven by a single
logic source. It should be noted that current sharing groups
that are also configured to track another voltage do not offer
pre-bias protection; a minimum load should therefore be
enforced to avoid the output voltage from being held up by an
outside force.
See application note AN310 for further information.
Voltage Margining Up/Down
The product can adjust its output higher or lower than its
nominal voltage setting in order to determine whether the load
device is capable of operating over its specified supply voltage
range. This provides a convenient method for dynamically
testing the operation of the load circuit over its supply margin
or range. It can also be used to verify the function of supply
voltage supervisors. Margin limits of the nominal output voltage
±5% are default, but the margin limits can be reconfigured
using the PMBus interface.
Pre-Bias Startup Capability
Pre-bias startup often occurs in complex digital systems when
current from another power source is fed back through a dual-
supply logic component, such as FPGAs or ASICs. The
product family incorporates synchronous rectifiers, but will not
sink current during startup, or turn off, or whenever a fault
shuts down the product in a pre-bias condition. Pre-bias
protection is not offered for current sharing groups that also
have voltage tracking enabled.
Group Communication Bus
The Group Communication Bus, GCB, is used to communicate
between products. This dedicated bus provides the
communication channel between devices for features such as
sequencing, fault spreading, and current sharing. The GCB
solves the PMBus data rate limitation. The GCB pin on all
devices in an application should be connected together. A pull-
up resistor is required on the common GCB in order to
guarantee the rise time as follows:
Eq. 5.
s
1
GCB
GCB
C
R
,
where
GCB
R
is the pull up resistor value and
GCB
C
is the bus
loading. The pull-up resistor should be tied to an external
supply voltage in range from 3.3 to 5 V, which should be
present prior to or during power-up.
If exploring untested compensation or deadtime configurations,
it is recommended that 27 Ω series resistors are placed
between the GCB pin of each product and the common GCB
connection. This will avoid propagation of faults between
products potentially caused by hazardous configuration
settings. When the configurations of the products are settled
the series resistors can be removed.
The GCB is an internal bus, such that it is only connected
across the modules and not the PMBus system host. GCB
addresses are assigned on a rail level, i.e. modules within the
same current sharing group share the same GCB address.
Addressing rails across the GCB is done with a 5 bit GCB ID,
yielding a theoretical total of 32 rails that can be shared with a
single GCB bus. See application note AN307 for further
information.
Fault spreading
The product can be configured to broadcast a fault event over
the GCB bus to the other devices in the group. When a non-
destructive fault occurs and the device is configured to shut
down on a fault, the device will shut down and broadcast the
fault event over the GCB bus. The other devices on the GCB
bus will shut down together if configured to do so, and will
attempt to re-start in their prescribed order if configured to do
so.
Over Temperature Protection (OTP)
The products are protected from thermal overload by an
internal over temperature shutdown function in the controller
circuit N1, located at position P2 (see section Thermal
Consideration). Some of the products that this specification
covers use the temperature at position P2 (T
P2
) as a reference
for specified OTP threshold and some use position P1 (T
P1
) as
a reference for specified OTP threshold. See the Over
Temperature Protection section in the electrical specification
for each product.
Products with P1 as reference for OTP:
When T
P1
as defined in thermal consideration section exceeds
approximately 120 °C the product will shut down. The specified
OTP threshold and hysteresis are valid for worst case
operation regarding cooling conditions, input voltage and
output voltage. The actually configured default value in the
BMR4
6
series
PoL Regulators
Input 4.5-14 V, Output up to 50 A / 165 W
1/28701-BMR 464 Rev.B
July 2019
© Flex
Technical Specification
BMR4
6
series
PoL Regulators
Input
4.5-14
V, Output up to
50
A
/
165
W
1/28701-BMR 464 Rev.B
July 2019
©
Flex
Technical Specification
56
