FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
33800 will wait for the Short Fault Time period and then shut
down the output drive, setting the fault status bit to a 1 in the
Serial Output Response Register.
Table 11. PWM Short Fault Timer
Predriver 1
VDSNS1
PWM FLT Timer
Bits
V
PWR
210
543
876
Fault Timer Select
Gate Drive
Control &
Diagnostics
GD1
000
001
010
011
100
101
110
111
30µs
60µs
VSSNS123
Predriver 2
120µs
VDSNS2
V
PWR
240µs
Gate Drive
Control &
Diagnostics
GD2
480µs
960µs
VSSNS123
No Change
No Change
Differential
Amplifier
+
−
+
−
Notes: Tolerance on fault timer setting is ±10% with calibrated part.
LRFDBK
Example: Load Measurement Operation
To perform an accurate load resistance measurement the
33800 device uses an alternate channel to determine a
differential load voltage and forces a known load current.
With the differential load voltage and the forced current the
load resistance is calculated. As shown in Table 6, channel 2
is used as the battery reference for the load measurement of
channel 1. The current through the channel 1 load is set by
the external resistor. Setting the resistance to 25Ω forces a
current of 100mA. The measurement is sampled within
200µs and is held for 150ms on the Load Resistance
Feedback (LRFDBK) output. The differential amplifier has a
fixed gain of 2.5V. Hence for this example, a 10Ω load will
produce a 2.5V output. When a second pair is selected for
measurement, the sample and hold is reset and the
measurement is immediately directed to the new load
measurement. The previous pair immediately revert back to
normal operation.
+
−
VCAL
REXT
Figure 9. Example of Channel 1 Measurement
OCTAL OUTPUT DRIVER (OCTAL SERIAL
SWITCH; OSS)
The 33800 provides flexible control of 8 low side driver
outputs. Outputs 1 and 2 are specifically designed with higher
current limit to accommodate lamp inrush current. The device
allows for parallel control and/or SPI control through the use
of several input command words. This section describes the
logic operation and commands for the octal driver.
The 33800 Octal Output Driver message set consists of
eight commands, and one response as shown in Table 12.
Bits 11 through 15 determine the specific command and bits
0 through 10 determine how a specific output will operate.
The 33800 operates on the command word on the rising edge
of CS. The Most Significant Bit (MSB) is sent and received
first.
Note Upon Power-ON Reset all OSS bits are defined as
shown in Table 12.
33800
Analog Integrated Circuit Device Data
Freescale Semiconductor
24
FREESCALE [ Freescale ]
