OKDL-T Datasheet, PDF (19/31 Pages) Murata Power Solutions Inc. – 12A Digital PoL DC-DC Converter Series

OKDL-T/12-W12-xxx-C
12A Digital PoL DC-DC Converter Series
By default, PG is deasserted if the output voltage falls below 85% of
the nominal voltage. These limits may be changed using the PMBus™
commands POWER_GOOD_ON and POWER_GOOD_OFF.
The PG output is not defined during ramp up of the input voltage
due to the initialization of the product.
Over Current Protection (OCP)
The product includes robust current limiting circuitry for protection
at continuous overload. After ramp-up is complete the product can
detect an output overload/short condition. The following OCP response
options are available:
1. Continue operating without interruption (this could result in perma-
nent damage to the product).
2. Immediate and definite shutdown of output voltage until the fault is
cleared by PMBus™ or the output voltage is re-enabled.
3. Immediate shutdown of output voltage followed by continous
restart attempts of the output voltage with a preset interval
(“hiccup” mode).
The default response from an over current fault is 3. Note that
delayed shutdown is not supported. The load distribution should be
designed for the maximum output short circuit current specified. The
OCP limit and response can be reconfigured using the PMBus™ com-
mands IOUT_OC_FAULT_LIMIT and IOUT_OC_FAULT_RESPONSE.
If option 2 above is to be used, the TON_MAX_FAULT_RESPONSE
setting should match the setting of IOUT_OC_FAULT_RESPONSE in
order to make sure that no restart attempts occur.
Switching Frequency
The default switching frequency yields optimal performance. The
switching frequency can be re-configured in a certain range using the
PMBus™ command FREQUENCY_SWITCH. Refer to Electrical Specifi-
cation for default switching frequency and range.
If changing the switching frequency more than +/-10% from the
default value, the following should be considered to maintain reliable
operation:
The default FLC value in COMP_MODEL should be adjusted, see section
Compensation Implementation.
Adjustment of the fixedDTR and fixedDTF values in DEADTIME_GCTRL may
be required, for higher switching frequencies in particular.
Changing the switching frequency will affect efficiency/power dis-
sipation, load transient response and output ripple.
Synchronization
The product may be synchronized with an external clock to eliminate
beat noise on the input and output voltage lines by connecting the
clock source to the SYNC pin. Synchronization can also be utilized for
phase spreading, described in section Phase Spreading.
The clock frequency of the external clock source must be stable
prior to enabling the output voltage. Further, the PMBus™ command
FREQUENCY_SWITCH must be set to a value close to the frequency of
the external clock prior to enabling the output voltage, in order to set
the internal controller in proper operational mode.
The product automatically checks for a clock signal on the SYNC
pin when input power is applied and when the output is enabled. If
no incoming clock signal is present, the product will use the internal
oscillator at the configued switching frequency.
In the event of a loss of the external clock signal during normal
operation, the product will automatically switch to the internal
oscillator and switch at a frequency close to the original SYNC input
frequency.
Phase Spreading
When multiple products share a common DC input supply, spreading
of the switching clock phase between the products can be utilized.
This dramatically reduces input capacitance requirements and effi-
ciency losses, since the peak current drawn from the input supply is
effectively spread out over the whole switch period. This requires that
the products are synchronized.
The phase offset is measured from the rising edge of the applied
external clock to the center of the PWM pulse as illustrated below.
SYNC
clock
Phase offset = 120°
PWM pulse
(VO/VI = 0.33)
Illustration of phase offset.
By default the phase offset is controlled by the defined PMBus™
address (see section PMBus™ Interface) according to the table below.
This provides a way to configure phase spreading with up to eight dif-
ferent phase positions without using a PMBus™ command.
Set PMBus address
xxxx000b
xxxx001b
xxxx010b
xxxx011b
xxxx100b
xxxx101b
xxxx110b
xxxx111b
Phase offset
0°
60°
120°
180°
240°
300°
90°
270°
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