Datasheet

LTC6802-1
33
68021fa
APPLICATIONS INFORMATION
Figure 19. Providing an Isolated High-Speed Data Interface
LTC6802-1
68021 F19
CSBI
V
−
V
REG
SDO
SDI
SCKI
LTC1693-2
ACSL-6410
IN1
GND1
IN2
GND2
V
CC1
OUT1
V
CC2
OUT2
3.57k
3.57k 3.57k
330
+5V_HOST
CSBI
SDI
SCKI
SDO
GND_HOST
4.99k
33nF
1
3
6
4
1µF
BAT54S
ISOLATED V
LOGIC
PE68386
BAT54S
••
470pF
100nF
1µF
20k
10k
330
100k
TP0610K
330
TP0610K
100k
TP0610K
100k
249
PROVIDING HIGH-SPEED OPTO-ISOLATION
OF THE SPI DATA-PORT
Isolation techniques that are capable of supporting the
1Mbps data rate of the LTC6802-1 require more power
on the isolated (battery) side than can be furnished by
the V
REG
output of the LTC6802-1. To keep battery drain
minimal, this means that a DC/DC function must be imple-
mented along with a suitable data isolation circuit, such as
shown in Figure 19. Here an optimal Avago 4-channel (3/1
bidirectional) opto-coupler is used, with a simple isolated
supply generated by an LTC1693-2 configured as a 200kHz
oscillator. The DC/DC function provides an unregulated
logic voltage (~4V) to the opto-coupler isolated side,
from energy provided by host-furnished 5V. This circuit
provides totally galvanic isolation between the batteries
and the host processor, with an insulation rating of 560V
continuous, 2500V transient.