Linear Technology DC1978A, Руководство пользователя

Страница: 8 / 33

7
dc1978af
DEMO MANUAL DC1978A
COMMON DEMO BOARD OPERATIONS
SELECTING I
2
C ADDRESS
The I
2
C/SMBus address of the LTC2974 equals the base
a N, where N is a number from 0 to 8. N can be
configured by setting the ASEL0 and ASEL1 pins to V
DD33
,
GND or FLOAT. See Table 3. Using one base address and
the nine values of N, nine LTC2974s can be connected
together to control thirty six outputs. The base address
is stored in the MFR_I2C_BASE_ADDRESS register. The
base address can be written to any value, but generally
should not be changed unless the desired range of ad-
dresses overlap existing addresses. Watch that the address
range does not overlap with other I
2
C/SMBus device or
global addresses, including I
2
C/SMBus multiplexers and
bus buffers.
RESET THE LTC2974
To reset the LTC2974 and reload the EEPROM contents
into operating memory (RAM), press SW4 on DC1809A.
Table 3. Device Address Lookup Table
ADDRESS
DESCRIPTION
HEX DEVICE ADDRESS BINARY DEVICE ADDRESS BITS ADDRESS PINS
7-Bit 8-Bit 6 5 4 3 2 1 0 R/W ASEL1 ASEL0
ALERT RESPONSE 0C 19 0 0 0 1 1 0 0 1 X X
GLOBAL 5B B6 1 0 1 1 0 1 1 0 X X
N = 0 5C* B8 1 0 1 1 1 0 0 0 L L
N = 1 5D BA 1 0 1 1 1 0 1 0 L NC
N = 2 5E BC 1 0 1 1 1 1 0 0 L H
N = 3 5F BE 1 0 1 1 1 1 1 0 NC L
N = 4 60 C0 1 1 0 0 0 0 0 0 NC NC
N = 5 61 C2 1 1 0 0 0 0 1 0 NC H
N = 6 62 C4 1 1 0 0 0 1 0 0 H L
N = 7 63 C6 1 1 0 0 0 1 1 0 H NC
N = 8 64 C8 1 1 0 0 1 0 0 0 H H
H = Tie to V
DD33
, NC = No Connect = Open or Float, L = Tie to GND, X = Don’t Care
* MFR_I2C_BASE_ADDRESS = 7-Bit 0x5C (Factory Default)
DC1978A LEDS
The red LEDs on ALERTB, FAULTB0, FAULTB1 and AUX-
FAULTB (D3, D4, D5, D2) indicate a fault has occurred.
The green LED (D6) next to them is the LTC2974 PWRGD
signal. Each individual channel on DC1810A also has
its own green PWR GOOD LED (PG0, PG1, PG2, PG3).
When the USB to I
2
C/SMBus/PMBus controller power or
external power is applied, the green LED D1 will illuminate,
indicating that the LTC2974 is powered.
FAULTING AN OUTPUT
The outputs of the power supplies CH0 to CH3 may be
shorted indefinitely. This is a good way to induce UV faults.
Use a jumper wire or a coin to short any output.