LTC3819 Datasheet, PDF (18/32 Pages) Linear Technology – 2-Phase, High Efficiency, Step-Down Controller for Sun Server CPUs

LTC3819
APPLICATIO S I FOR ATIO
Output Voltage
Table 1. VID Output Voltage Programming
The LTC3819 has a true remote voltage sense capablity.
The sensing connections should be returned from the load
back to the differential amplifier’s inputs through a com-
mon, tightly coupled pair of PC traces. The differential
amplifier corrects for DC drops in both the power and
ground paths. The differential amplifier output signal is
divided down and compared with the internal precision
0.6V voltage reference by the error amplifier.
CODE VID4 VID3 VID2 VID1 VID0 OUTPUT
00000 GND GND GND GND GND 1.4125V
00001 GND GND GND GND Float 1.4000V
00010 GND GND GND Float GND 1.3875V
00011 GND GND GND Float Float 1.3750V
00100 GND GND Float GND GND 1.3625V
00101 GND GND Float GND Float 1.3500V
00110 GND GND Float Float GND 1.3375V
Output Voltage Programming
The output voltage is digitally programmed as defined in
Table 1 using the VID0 to VID4 logic input pins. The VID
logic inputs program a precision, 0.25% internal feedback
resistive divider. The LTC3819 has an output voltage range
of 1.025V to 1.4125V in 12.5mV steps.
00111 GND GND Float Float Float 1.3250V
01000 GND Float GND GND GND 1.3125V
01001 GND Float GND GND Float 1.3000V
01010 GND Float GND Float GND 1.2875V
01011 GND Float GND Float Float 1.2750V
01100 GND Float Float GND GND 1.2625V
01101 GND Float Float GND Float 1.2500V
Between the ATTENOUT pin and ground is a variable
resistor, R1, whose value is controlled by the five VID input
pins (VID0 to VID4). Another resistor, R2, between the
ATTENIN and the ATTENOUT pins completes the resistive
divider. The output voltage is thus set by the ratio of
(R1 + R2) to R1.
01110 GND Float Float Float GND 1.2375V
01111 GND Float Float Float Float 1.2250V
10000 Float GND GND GND GND 1.2125V
10001 Float GND GND GND Float 1.2000V
10010 Float GND GND Float GND 1.1875V
10011 Float GND GND Float Float 1.1750V
Each VID digital input is pulled up by a 40k resistor in series
with a diode from V_BIAS. Therefore, it must be grounded to
get a digital low input, and can be either floated or con-
nected to V_BIAS to get a digital high input. The series diode
is used to prevent the digital inputs from being damaged
or clamped if they are driven higher than V_BIAS. The digital
inputs accept CMOS voltage levels.
V_BIAS is the supply voltage for the VID section. It is
normally connected to INTV_CC but can be driven from
other sources. If it is driven from another source, that
source must be in the range of 2.7V to 5.5V and must be
alive prior to enabling the LTC3819.
10100 Float GND Float GND GND 1.1625V
10101 Float GND Float GND Float 1.1500V
10110 Float GND Float Float GND 1.1375V
10111 Float GND Float Float Float 1.1250V
11000 Float Float GND GND GND 1.1125V
11001 Float Float GND GND Float 1.1000V
11010 Float Float GND Float GND 1.0875V
11011 Float Float GND Float Float 1.0750V
11100 Float Float Float GND GND 1.0625V
11101 Float Float Float GND Float 1.0500V
11110 Float Float Float Float GND 1.0375V
11111 Float Float Float Float Float 1.0250V
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