LTC3733_15 Datasheet, PDF (19/32 Pages) Linear Technology – 3-Phase, Buck Controllers for AMD CPUs

LTC3733/LTC3733-1
APPLICATIO S I FOR ATIO
Output Voltage
Table 1. VID Output Voltage Programming
The IC includes a digitally controlled 5-bit attenuator
producing output voltages as defined in Table 1. Output
voltages with 25mV increments are produced from 0.8V to
1.55V.
Each VID digital input is pulled up to a logical high with an
internal 150k resistor. The input logic threshold is ap-
proximately 1.2V but the input circuit can withstand an
input voltage of up to 7V.
VID4
VID3
VID2
VID1
VID0
V_OUT
0
0
0
0
0
1.550
0
0
0
0
1
1.525
0
0
0
1
0
1.500
0
0
0
1
1
1.475
0
0
1
0
0
1.450
0
0
1
0
1
1.425
0
0
1
1
0
1.400
0
0
1
1
1
1.375
ON/OFF Control
0
1
0
0
0
1.350
0
1
0
0
1
1.325
The RUN pin provides simple ON/OFF control for the
0
1
0
1
0
1.300
LTC3733. Driving the RUN pin above 1.5V permits the
0
1
0
1
1
1.275
controller to start operating. Pulling RUN below 0.8V puts
0
1
1
0
0
1.250
the LTC3733 into low current shutdown (I_Q ≈ 20µA).
0
1
1
0
1
1.225
Soft-Start Function
0
1
1
1
0
1.200
0
1
1
1
1
1.175
The SS pin provides two functions: 1) soft-start and 2) a
1
0
0
0
0
1.150
defeatable short-circuit latch off timer. Soft-start reduces
1
0
0
0
1
1.125
the input power sources’ surge currents by gradually
1
0
0
1
0
1.100
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
1
1
0
0
0
1
1
0
1
1.075
0
1.050
the overcurrent latch. A small pull-up current (>5µA)
1
0
1
0
1
1.025
supplied to the SS pin will prevent the overcurrent latch
1
0
1
1
0
1.000
from operating. The following explanation describes how
1
0
1
1
1
0.975
this function operates.
1
1
0
0
0
0.950
1
1
0
0
1
0.925
An internal 1.5µA current source charges up the C_SS
1
1
0
1
0
0.900
capacitor. As the voltage on SS increases from 0V to 2.4V,
1
1
0
1
1
0.875
the internal current limit is increased from 0V/R_SENSE to
1
1
1
0
0
0.850
75mV/R_SENSE. The output current limit ramps up slowly,
taking 1.6s/µF to reach full current. The output current
1
1
1
0
1
0.825
thus ramps up slowly, eliminating the starting surge
1
1
1
1
0
0.800
current required from the input power supply.
1
1
1
1
1 Shutdown
( ) ^t_IRAMP
=
2.4V – 0V
1.5µA
C_SS
=
1.6s/µF
C_SS
The SS pin has an internal 6V zener clamp (see the
Functional Diagram).
3733f
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