Download ATA6836C/ATA6838C Open Load Detection

APPLICATION NOTE
ATA6836C/ATA6838C Open Load Detection
ATAN0013
References
● Atmel ATA6836C Datasheet
● Atmel ATA6838C Datasheet
Description
The Atmel® ATA6836C/ATA6838C high-voltage drivers employ internal protection circuitry
to protect against short-circuit, overtemperature, undervoltage and open-load. The openload detection feature will be discussed in this application note.
9251E-AUTO-04/15
1.
Open-Load Detection
1.1
Circuit Overview
Open-load monitoring of the high-voltage driver IC is controlled by the OLD (open-load detection) bit, bit 13, of the input data
register. The open-load monitoring circuit for each output driver is defined in Figure 1-1.
Figure 1-1. Atmel ATA6836 Output Driver Open-load Detection Circuit
ATA6836C
VS
Output Bit
Open Load Lx
detected
VS-2V
ISOURCE = 1.5mA
Input Bit OLD
Input Bit HSx
Output Stage
HSx
OUTx
Input Bit OLD
Input Bit LSx
Output Stage
LSx
ISINK = ISOURCE*1.2
Output Bit
Open Load Hx
detected
1.5V
GND
When the OLD bit is set LOW, open-load detection is enabled. In this mode of operation, a pull-up current (Isource) for each
high-side switch (IHSx) and a pull-down current (Isink) for each low-side switch (ILSx) will be activated simultaneously. The
low-side open-load current is set to a level 25% greater than that of the high-side current in order to establish the
high-side/low-side open-load thresholds. An open-load condition is detected when the difference between the supply voltage
(VS) and the high-side voltage (VHSx) or the low-side voltage (VLSx) is lower than the open-load detection threshold for the
output stage:
VHS_th = VVS – VHSx
VLS_th = VLSx
Note:
Please refer to the specific device datasheet for the high-side/low-side open-load threshold levels VHS_th and
VLS_th.
When an open-load has been detected, the corresponding output bit (LSx or HSx) in the output data register will be set
HIGH.
Note:
2
Switching on an output stage with OLD bit set to HIGH disables the open-load function for this output.
ATAN0013 [APPLICATION NOTE]
9251E–AUTO–04/15
1.2
SPI Data Timing
Data transfer on the SPI begins with each falling edge of the CS (chip select) signal. Given the case where an open-load
condition begins and ends between two falling CS edge cycles, as represented by the first open-load event in Figure 1-2, the
open-load will not be reported and the corresponding DO bit will not be set. Only when the open-load event is present during
the falling CS edge will open-load be reported (see Figure 1-2, second open-load event). Once the open-load is removed,
the corresponding DO bit will be cleared, indicating the end of the open-load event.
Figure 1-2. SPI Reporting of Open-load Events
Open load event not reported since the event is
not present during the falling edge CS transition
Open load
reported
Open load end,
but not reported
Open load
removed
Open Load at
Output Switch OUTx
INH
CLK
16 clocks
16 clocks
16 clocks
16 clocks
DI
OLD=0
OLD=0
OLD=0
OLD=0
DO
OUTx=0
OUTx=0
OUTx=1
OUTx=0
CS
DI OLD = 0 (Bit 13)
activates Open load Detection
Output DO Bit not set,
no Open load detected
Output DO Bit set,
Open load detected
Output DO Bit cleared,
Open load removed
Notes:
1. When OLD = 1, the HSx/LSx DO bits report the Switch Status of the outputs
2. When OLD = 0, the HSx/LSx DO bits report the Open Load Status of the outputs
3. OUTx refers to the HSx/LSx bits in the Data Output Register
ATAN0013 [APPLICATION NOTE]
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3
1.3
Examples
1.3.1
Single-ended High-side Open-load
A high-side load as shown in Figure 1-3 can be directly monitored for an open-load condition. In this case, if the connected
load is open, activating open-load detection (OLD = 0) will indicate a high-side open-load at the dedicated low-side output
register (LSx) for the associated output (OUTx).
Figure 1-3. High-side Load Configuration
VS
VS
HSx
OUTx
LSx
GND
If LSx = 1, then the high-side load is open. Conversely, if LSx = 0, then the high-side load is properly connected.
1.3.2
Single-ended Low-side Open-load
A low-side load as shown in Figure 1-4 cannot be monitored for an open-load condition. In this case, regardless of the state
of the load, open or closed, the result will be the same when activating open-load detection (OLD = 0). The corresponding
HSx = 1 for the associated output (OUTx) in both instances.
Figure 1-4. Low-side Load Configuration
VS
HSx
OUTx
LSx
GND
4
ATAN0013 [APPLICATION NOTE]
9251E–AUTO–04/15
1.3.3
Low-side Open-load: H-bridge Configuration
A low-side load configured in an H-bridge as shown in Figure 1-5 can be directly monitored for an open-load condition.
Testing for the open-load is a two step process. First, switch off all high-side (HSx/HSy) and low-side (LSx/LSy) drivers. The
voltage at both clamps in this condition will be pulled-down (as shown in Figure 1-1 on page 2) due to the higher low-side
open-load detection current sources. Next, with both low-side drivers off, switch on one high-side driver (HSx or HSy). Since
the DC motor has a relatively low internal resistance, the voltage of the inactive high-side output should be at the same level
as the activated high-side output. In the case of an open-load, the inactive high-side output register will report a “0” if the
active high-side output is “1”. Conversely, if the load is connected, the inactive high-side output will report a “1”.
Figure 1-5. H-bridge Load Configuration
VS
HSx
HSy
OUTx
OUTy
LSx
M
LSy
GND
The register configuration to perform open-load test of the H-bridge is as follows:
1. Step #1, program all drivers OFF
a.
Input register command
i.
OLD = 0, HSx = 0, LSx = 0, HSy = 0, LSy = 0
b. Output register result
2.
i.
LSx = 1, LSy = 1 indicates “Open-load” at LSx/LSy, which is expected
Step #2, program HSy ON:
a.
Input register command
i.
OLD = 0, HSx = 0, LSx = 0, HSy = 1, LSy = 0
b. Check output register result
i.
ii.
HSy = 1, HSx = 1 indicates “Motor connected”
HSy = 1, HSx = 0 indicates “Motor disconnected”
ATAN0013 [APPLICATION NOTE]
9251E–AUTO–04/15
5
2.
Revision History
Please note that the following page numbers referred to in this section refer to the specific revision mentioned, not to this
document.
Revision No.
History
9251E-AUTO-04/15
Put document in the latest template
Type ATA6836 updated in ATA6836C
9251D-AUTO-02/14
Type ATA6837 removed
Type ATA6838 updated in ATA6838C
Section “References” on page 1 updated
9251C-AUTO-11/12
Section “Description” on page 1 updated
Figure 1-1 “Atmel ATA6836 Output Driver Open-load Detection Circuit” on page 2 updated
6
ATAN0013 [APPLICATION NOTE]
9251E–AUTO–04/15
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