Intv Cc /Vbias Power; Output Current Sensing And Sub Milliohm Dcr Current Sensing; Input Current Sensing - Analog Devices LTM4683 Manual

OPERATION
INTV /V POWER
CC BIAS
Power for the internal top and bottom MOSFET drivers and
most other internal circuitry is derived from the INTV
pin. When the RUNP pin is shorted to GND and the V
is off, an internal 5.5V linear regulator INTV
power from SV . When enabling V
IN_nn
and SV exceeds 7.0V, an internal switch is turned on to
IN
source power from V
BIAS
Using the V allows the INTV
BIAS
from a high-efficiency internal source. V
power to the internal 3.3V linear regulators when SV
is present, which allows the LTM4683 controllers to be
initialized and programmed, even with channels off.
The INTV regulator is powered from the SV
CC_nn
the power through the IC is equal to SV
The gate charge current is dependent on the operating fre-
quency. The typical INTV
CC_nn
~50mA. A 12V input voltage would equate to a difference
of 7V per controller drop across the internal controller,
when multiplied by 50mA, equals a 350mW power loss.
This loss can be eliminated by utilizing the V
Do not connect INTV
CC_nn
supply because INTV
CC_nn
supply high and hit the current limit, significantly increas-
ing the die temperature.
For applications where V
INTV pins together to the 5V input through a 1Ω
CC_nn
resistor, as shown in Test Circuit 2.
OUTPUT CURRENT SENSING AND SUB MILLIOHM
DCR CURRENT SENSING
The LTM4683 uses a unique sub-milliohm inductor cur-
rent sensing technique that provides a high-level signal-
to-noise ratio while sensing very low signals in current
mode operation. This enables higher conversion efficien-
cies using the internal sub-milliohm inductors in heavy
load applications. The current limit threshold can be accu-
rately set with the MFR_PWM_MODE[7] for the High and
Low range (see the IOUT_OC_FAULT_LIMIT in the PMBus
Command Details section for the high and the low details.
supplies
CC
at 5.5V output
BIAS
instead of the INTV regulator.
CC
power to be derived
CC
can provide
BIAS
IN_nn
• I
IN_nn INTVCCnn
current for the LTM4683 is
regulator.
BIAS
on the LTM4683 to an external
will attempt to pull the external
is 5V, tie the SV
IN IN_nn
For more information
The internal direct current resistance (DCR) sensing net-
work, thus the current limit, is calculated based on the
DCR of the inductor at room temperature. The DCR of the
CC
inductor has a large temperature coefficient, approximately
BIAS
3900ppm/°C. The temperature coefficient of the inductor
is written to the MFR_IOUT_CAL_GAIN_TC register. The
external temperature is sensed near the inductor and used
to modify the internal current limit circuit to maintain an
essentially constant current limit with temperature. The
current sensed is then digitized by the LTM4683's telem-
etry ADC with an input range of ±128mV, a noise floor of
IN
7µV , and a peak-peak noise of approximately 46.5µV.
RMS
The LTM4683 computes the inductor current using the
DCR value stored in the IOUT_CAL_GAIN command
pin;
and the temperature coefficient stored in the command
.
MFR_IOUT_CAL_GAIN_TC. The resulting current value is
returned by the READ_IOUT command.

INPUT CURRENT SENSING

To sense the total input current consumed by the LTM4683's
power stages, a sense resistor is placed between the supply
voltage and the drain of the top N-channel MOSFET. The
+ –
I and I
IN_nn IN_nn
The filtered voltage is amplified by the internal high-side
current sense amplifier and digitized by the LTM4683's
telemetry ADC. The input current sense amplifier has three
and gain settings of 2×, 4×, and 8× set by the bit [6:5] of the
MFR_PWM_CONFIG command. The maximum input sense
voltage for the three gain settings is 50mV, 25mV, and
10mV, respectively. The LTM4683 computes the input
current using the internal R
CAL_GAIN command. The resulting measured power stage
current is returned by the READ_IIN command. I
–
I for controller 1 (Channels 0 and 1), and I
IN_01
–
I for controller 2 (Channels 2 and 3).
IN_23
The LTM4683 uses a 1Ω resistor to measure the SV
pin supply current being consumed by each LTM4683
internal controller. This value is returned by the MFR_
READ_ICHIP command. The chip current is calculated by
using the 1Ω value stored in the MFR_ICHIP_CAL_GAIN
command. See the Input Current Sense Amplifier subsec-
tion in the Applications Information section for further
details.
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LTM4683
pins are connected to the sense resistor.
value stored in the IIN_
SENSE
+
,
IN_01
+
,
IN_23
IN_nn
Rev. 0
33