Datasheet

LTC3880/LTC3880-1
52
3880fc
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
To choose address 0x4E R
TOP
= 10.0k and
R
BOTTOM
= 15.8k
Table 15. ASEL
R
TOP
(k) R
BOTTOM
(k) SLAVE ADDRESS LSB HEX
0 or Open Open NVM
10 23.2 xyz_1111 F
10 15.8 xyz_1110 E
16.2 20.5 xyz_1101 D
16.2 17.4 xyz_1100 C
20 17.8 xyz_1011 B
20 15 xyz_1010 A
20 12.7 xyz_1001 9
20 11 xyz_1000 8
24.9 11.3 xyz_0111 7
24.9 9.09 xyz_0110 6
24.9 7.32 xyz_0101 5
24.9 5.76 xyz_0100 4
24.9 4.32 xyz_0011 3
30.1 3.57 xyz_0010 2
30.1 1.96 xyz_0001 1
Open 0 xyz_0000 0
EFFICIENCY CONSIDERATIONS
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can
be expressed as:
%Efficiency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percent
-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC3880 circuits: 1) IC V
IN
current, 2) INTV
CC
regulator current, 3) I
2
R losses, 4) Topside MOSFET
transition losses.
1. The V
IN
current is the DC supply current given in
the Electrical Characteristics table, which excludes
MOSFET driver and control currents. V
IN
current typi-
cally results in a small (<0.1%) loss.
2.
INTV
CC
current is the sum of the MOSFET driver and
control currents. The MOSFET driver current results
from switching the gate capacitance of the power
MOSFETs. Each time a MOSFET gate is switched from
low to high to low again, a packet of charge dQ moves
from INTV
CC
to ground. The resulting dQ/dt is a cur-
rent out of INTV
CC
that is typically much larger than the
control circuit current. In continuous mode, I
GATECHG
= f(Q
T
+ Q
B
), where Q
T
and Q
B
are the gate charges of
the topside and bottom side MOSFETs.
On the LTC3880-1, supplying EXTV
CC
from an output-
derived source will scale the V
IN
current required for
the driver and control circuits by a factor of:
V
EXTVCC
V
IN






1
Efficiency






For example, in a 20V to 5V application, 10mA of INTV
CC
current results in approximately 2.5mA of V
IN
current.
Table 15A
1
. LTC3880 MFR_ADDRESS Command Examples
Expressing Both 7- or 8-Bit Addressing
DESCRIPTION
HEX DEVICE
ADDRESS
BIT
7
BIT
6
BIT
5
BIT
4
BIT
3
BIT
2
BIT
1
BIT
0 R/W7 BIT 8 BIT
Rail
4
0x5A 0xB4 0 1 0 1 1 0 1 0 0
Global
4
0x5B 0xB6 0 1 0 1 1 0 1 1 0
Default 0x4F 0x9E 0 1 0 0 1 1 1 1 0
Example 1 0x60 0xC0 0 1 1 0 0 0 0 0 0
Example 2 0x61 0xC2 0 1 1 0 0 0 0 1 0
Disabled
2,3,5
1 0 0 0 0 0 0 0 0
Note 1: This table can be applied to the MFR_CHANNEL_ADDRESS,
and MFR_RAIL_ADDRESS commands as well as the MFR_ADDRESS
command.
Note 2: A disabled value in one command does not disable the device, nor
does it disable the Global address.
Note 3: A disabled value in one command does not inhibit the device from
responding to device addresses specified in other commands.
Note 4: It is not recommended to write the value 0x00, 0x0C (7 bit),
or 0x5A or 0x5B(7 bit) to the MFR_ADDRESS, MFR_CHANNEL_
ADDRESS or the MFR_RAIL_ADDRESS commands.
Note 5: To disable the address enter 0x80 in the MFR_ADDRESS
command. The 0x80 is greater than the 7-bit address field, disabling
the address.