LTC6915
13
6915fb
operaTion
DOUT is always active in serial mode (never tri-stated).
This simplifies the daisy chaining of the multiple devices.
DOUTcannotbe“wire-or”tootherSPIoutputs.Inaddition,
DOUT does not return to zero at the end of transmission,
i.e. when CS is pulled high.
A LTC6915 may be daisy-chained with other LTC6915s
or other devices having serial interfaces by connecting
the DOUT to the DIN of the next chip while CLK and CS
remain common to all chips in the daisy chain. The serial
data is clocked to all the chips then the CS signal is pulled
high to update all of them simultaneously. Figure 4
shows an example of two LTC6915s in a daisy chained SPI
configuration.
Figure 1. PGA in the Parallel Control Mode
Figure 2. Bidirectional Nature of DOUT/D3 Pin
Figure 3. Diagram of Serial Interface (MSB First Out)
4-BIT GAIN
CONTROL CODE
4-BIT
LATCH
Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7
8-BIT
SHIFT-REGISTER
DOUT
(D3)
CLK
DIN
CS
6915 F03
V–
V+
DGND
DOUT(D3)
6915 F02
(INTERNAL
NODE)
SHDN
IN–
IN+
V–
HOLD_THRU
CS(D0)
DIN(D1)
CLK(D2)
V+
OUT
SENSE
REF
NC
P/S
DGND
DOUT(D3)
LTC6915
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VOUT
VIN
0.1F
PARALLEL GAIN CONTROL CODE = 1010
VOUT = 29 VIN = 512VIN
SHDN
IN–
IN+
V–
HOLD_THRU
CS(D0)
DIN(D1)
CLK(D2)
V+
OUT
SENSE
REF
NC
P/S
DGND
DOUT(D3)
LTC6915
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VOUT
VIN
0.1F
GAIN IS SET BY MICROPROCESSOR. A 10k RESISTOR
ON DOUT(D3) PROTECT THE DEVICE WHEN VD3 > V+
P
5V
D0
D1
D2
D3
10k
6915 F01