SA5777A Datasheet, PDF (8/12 Pages) NXP Semiconductors – Dual air-core gauge driver

Philips Semiconductors
Dual air-core gauge driver
Product specification
SA5777A
CS
S_CLK
DATA_IN
T_CSH
1
D19
FS_CLK
2
D18
20 S_CLK CYCLES
19
TS_CLKL
20
TS_CLKH
D1
TSU
80%
20%
THI
TC_SL
D0
DATA_OUT
D19*
D18*
D1*
D0*
TFO
TRO
GAUGE 2
GAUGE 1
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 D18 D19
LSB
*DO IS THE PREVIOUSLY LOADED DATA WORD
MSB LSB
Figure 6. Serial interface timing
Serial Interface
The SA5777A is controlled through a serial interface with the following control functions (reference Figure 6):
MSB
SL00465
S_CLK
CS
DATA_IN
DATA_OUT
Serial input clock. When CS is high, the rising edge of S_CLK shifts a new data bit into the SA5777A and the falling edge shifts
the data out of DATA_OUT.
Active high chip select. Enables the SA5777A to receive serial input data. The falling edge of CS loads a new 20-bit data word
into the internal DAC registers which updates the tangent coil output buffers (C1+, C1–, C2+, C2–).
Serial data input. The data at this pin is shifted into the internal shift register on the rising edge of S_CLK. Data is shifted in MSB
first, gauge 1 first.
Serial data output. This pin is the output of the internal shift register. The data output on this pin is the input data from DATA_IN
pin delayed by 20 clock cycles. This pin can be used to cascade several SA5777As with one CS line to load all of the
SA5777As concurrently.
Power Moding
The SA5777A has a power-on reset capability. On the rising edge
of V_CC, the internal latches and registers are set to zero and the coil
output buffers (C1+, C1–, C2+, C2–, COM) are disabled.
4. Due to excessive power dissipation (i.e., thermal shut-down).
The die temperature must go below 140°C before a falling edge
on the CS pin will clear this fault condition and allow the coil
outputs to go active.
Coil Output Buffer Control
The coil buffers (C1+, C1–, C2+, C2–, COM) are disabled:
1. With the rising edge of V_CC (power-on reset).
2. When OE is taken low or held low. The data registers for the
outputs can still be updated while OE is low. When OE is taken
high, the current output data value is displayed. A falling edge
on CS will be required to activate the outputs if a fault condition
has occurred prior to the OE going high.
3. Due to an overcurrent condition on either of the coil output
buffers. The coil output buffers will be enabled after the next CS
high-to-low transition; assuming OE is high. If the overcurrent
condition has not been removed, the outputs will immediately
return to their disabled condition. The ST pin will indicate status
of the coil outputs.
Application Notes
The air-core gauge is constructed of two coils would on a cavity at
90° to each other. Inside the cavity there is a disk which is
magnetized on its diameter. The currents through the coils generate
a resultant magnetic vector that causes the magnetic disc to move
until the magnetic fields are aligned. If the ratio of the currents in the
two coils follows the tangent function, then the transfer characteristic
relating the input data to output angle is linear.
Maximum current is when output is at zero and full scale degrees,
T_A = –40°C, and R_L = 180.
Copper wire has a typical temperature coefficient of 0.4%/C
1999 Sep 20
8