Datasheet

LTC3880/LTC3880-1
50
3880fc
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
Refer to Tables 12 and 13 to set the output voltage using
RCONFIG pins VOUTn_CFG and VTRIMn_CFG. RTOP is
connected between VDD25 and the pin and RBOTTOM is
connected between the pin and SGND. 1% resistors must
be used to assure proper operation.
The output voltage set point is equal to:
V
SETPOINT
= VOUTn_CFG + VTRIMn_CFG
For example, if the VOUTn_CFG pin has R
TOP
equal to 24.9k
and R
BOTTOM
equal to 4.32k, and VTRIMn_CFG is set with
R
TOP
not inserted and R
BOTTOM
equal to0Ω:
V
SETPOINT
= 1.1V – 0.099V or 1.001V
If odd values of output voltage are required from 0.5V
to 3.3V, use only the VOUTn_CFG resistor divider, the
V
TRIM
pin can be open or shorted to V
DD25
. If the output
set point is 5V, the VOUTn_CFG must have R
TOP
equal to
10k and R
BOTTOM
equal to 23.2k and VTRIMn_CFG must
have R
TOP
equal to 20k and R
BOTTOM
equal to 11k. If VOUT
is 2.5 volts or lower, low range is used. The maximum
voltage command on channel 0 is 4.096 volts including
VOUT_OV_FAULT, VOUT_OV_WARN, VOUT_MARGIN_HI
and VOUT.
Table 12. VOUTn_CFG
R
TOP
(k) R
BOTTOM
(k) V
OUT
(V)
0 or Open Open NVM
10 23.2 See VTRIM
10 15.8 3.3
16.2 20.5 3.1
16.2 17.4 2.9
20 17.8 2.7
20 15 2.5
20 12.7 2.3
20 11 2.1
24.9 11.3 1.9
24.9 9.09 1.7
24.9 7.32 1.5
24.9 5.76 1.3
24.9 4.32 1.1
30.1 3.57 0.9
30.1 1.96 0.7
Open 0 0.5
Table 13. VTRIMn_CFG
R
TOP
(k) R
BOTTOM
(k)
V
TRIM
(mV)
CHANGE TO
V
SET
VOLTAGE
V
OUT
(V)
IF V
OUT
HAS
10k/23.3k
0 or Open Open 0
10 23.2 99
10 15.8 86.625
16.2 20.5 74.25
16.2 17.4 61.875
20 17.8 49.5
20 15 37.125 5.5
20 12.7 24.75 5.25
20 11 12.375 5
24.9 11.3 –12.375 4.75
24.9 9.09 –24.75 4.5
24.9 7.32 –37.125 4.25
24.9 5.76 –49.5 4
24.9 4.32 –61.875 3.75
30.1 3.57 –74.25 3.63
30.1 1.96 –86.625 3.5
Open 0 –99 3.46
Frequency and Phase Selection Using RCONFIG
The frequency and phase commands are linked if they
are set using the RCONFIG pins. If PMBus commands
are used the two parameters are independent. The SYNC
pins must be shared in PolyPhase configurations where
multiple LTC3880s are used to produce the output. If the
configuration is not PolyPhase the SYNC pins do not
have to be shared. If the SYNC pins are shared between
LTC3880s only one SYNC pin can be set as a frequency
output, all other SYNC pins must be set to External Clock.
For example in a 4-phase configuration clocked at 425kHz,
one of the LTC3880s must be set to the desired frequency
and phase and the other LTC3880 must be set to External