LTC3738 Datasheet, PDF (20/32 Pages) Linear Technology – 3-Phase Buck Controller for Intel VRM9/VRM10 with Active Voltage Positioning

LTC3738
APPLICATIO S I FOR ATIO
Table 1. VRM9 VID Table
PROCESSOR PINS (0 = L0W, 1 = HIGH)
VID4
VID3
VID2 VID1
VID0
1
1
1
1
1
1
1
1
1
0
1
1
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
0
1
1
0
0
1
1
1
0
0
0
1
0
1
1
1
1
0
1
1
0
1
0
1
0
1
1
0
1
0
0
1
0
0
1
1
1
0
0
1
0
1
0
0
0
1
1
0
0
0
0
0
1
1
1
1
0
1
1
1
0
0
1
1
0
1
0
1
1
0
0
0
1
0
1
1
0
1
0
1
0
0
1
0
0
1
0
1
0
0
0
0
0
1
1
1
0
0
1
1
0
0
0
1
0
1
0
0
1
0
0
0
0
0
1
1
0
0
0
1
0
0
0
0
0
1
0
0
0
0
0
V_CC(CORE)
(V_DC)
Output Off
1.100
1.125
1.150
1.175
1.200
1.225
1.250
1.275
1.300
1.325
1.350
1.375
1.400
1.425
1.450
1.475
1.500
1.525
1.550
1.575
1.600
1.625
1.650
1.675
1.700
1.725
1.750
1.775
1.800
1.825
1.850
Thermal Control
When external thermal detection is enabled, the TSNS pin
serves as the input to an accurate comparator which is
referenced to V_CC/3 and has a hysteresis of V_CC/24.
VR_HOTB is pulled low when the voltage at TSNS is less
than V_CC/3. In this case, the input of TSNS is an analog
signal. If necessary, lowpass filter the signal before feed-
ing it into the pin to avoid a false thermal trip.
When VR_HOTB is reported, the operation of LTC3738 will
not be affected, although there is another thermal sensor
inside the IC for self protection. When the temperature of
the IC is around 140°C, the LTC3738 will shut down and
not start-up again until this overtemperature situation has
been removed. This self shutdown feature is not tested but
is guaranteed by design.
ON/OFF Control
The OUTEN pin provides simple ON/OFF control for the
LTC3738. Driving the OUTEN pin above 0.8V permits the
controller to start operating. Pulling OUTEN below 0.4V
puts the LTC3738 into low current shutdown (I_Q ≈ 50µA).
Soft-Start Function
The SS pin provides two functions: 1) soft-start and 2) a
defeatable short-circuit latch off timer. Soft-start reduces
the input power sources’ surge currents by gradually
increasing the controller’s current limit (proportional to an
internal buffered and clamped V_ITH). The latchoff timer
prevents very short, extreme load transients from tripping
the overcurrent latch. A small pull-up current (>5µA)
supplied to the SS pin will prevent the overcurrent latch
from operating. The following explanation describes how
this function operates.
An internal 1.5µA current source charges up the C_SS
capacitor. As the voltage on SS increases from 0V to 2.4V,
3738f
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