LTC3882_15 Datasheet, PDF (57/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

LTC3882
APPLICATIONS INFORMATION
0.6
1-PHASE
0.5
0.4
0.3
2-PHASE
0.2
0.1
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
DUTY FACTOR (V_OUT/V_IN)
3882 F41
Figure 41. Normalized RMS Input Ripple Current
1.0
0.9
0.8
1-PHASE
0.7
0.6
0.5
0.4
0.3
2-PHASE
0.2
0.1
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
DUTY FACTOR (V_OUT/V_IN)
3882 F42
Figure 42. Normalized Output Ripple Current
[I_RMS ~ 0.3(DI_C(PP))]
such as the MMBT3906 as shown in Figure 43 with bit 5
of MFR_PWM_MODE_LTC3882 set to 0 (ΔV_BE method).
The BJT should be placed in contact with or immediately
adjacent to the power stage inductor. Its emitter should be
connected to the TSNSn pin while the base and collector
terminals of the PNP transistor must be returned to the
LTC3882 GND paddle using a Kelvin connection. For best
noise immunity, the connections should be routed differ-
entially and a 10nF capacitor should be placed in parallel
with the diode-connected PNP.
The LTC3882 also supports direct junction voltage mea-
surements when bit 5 of MFR_PWM_MODE_LTC3882 is
set to one. The factory defaults support a resistor-trimmed
dual diode network as shown in Figure 44. However, this
measurement method can be applied to simple single-diode
TSNS
LTC3882
GND
10nF
MMBT3906
GND
3882 F43
Figure 43. External ΔV_BE Temperature Sense
TSNS
LTC3882
GND
495µA
1nF
1.35V AT 25°C
GND
3882 F44
Figure 44. 2D+R Temperature Sense
circuits of the type shown in Figure 43 with parameter
adjustments as described below. This second measure-
ment method is not generally as accurate as the first, but
it supports legacy power blocks or may prove necessary if
high noise environments prevent use of the ΔV_BE approach
with its lower signal levels.
For either method, the slope of the external temperature
sensor can be modified with the coefficient stored in
MFR_TEMP_1_GAIN. With the ΔV_BE approach, typical
PNPs require temperature slope adjustments slightly
less than 1. The MMBT3906 has a recommended value
in this command of approximately MFR_TEMP_1_GAIN =
0.991 based on the ideality factor of 1.01. Simply invert
the ideality factor to calculate the MFR_TEMP_1_GAIN.
Different manufacturers and different lots may have dif-
ferent ideality factors. Consult with the manufacturer to
set this value. Bench characterization over temperature is
recommended when adjusting MFR_TEMP_1_GAIN for
the direct p-n junction measurement.
The offset of the external temperature sense can be ad-
justed by MFR_TEMP_1_OFFSET. For the ΔV_BE method a
value of 0 in this register sets the temperature offset to
–273.15°C. For a direct p-n junction measurement, this
parameter adjusts the nominal circuit voltage at 25°C away
from that shown in Figure 44.
To ensure proper use of these temperature adjustment
parameters, refer to the specific formulas given for the two
methods by the MFR_PWM_MODE_LTC3882 command
For more information www.linear.com/LTC3882
3882f
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