LM9833 datasheet(35/42 Pages) NSC

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12.3 Steps to Reverse Register Increased

To improve performance with some mechanical designs, the

number of bits in register 50 was increased from 6 to 8 bits. This

allows the scanner to reverse up to 255 steps when pausing due

to a buffer full condition.

12.4 - Acceleration Profile Modified

The highest setting of the Acceleration Profile (bits 2-7 of register

51) has been modified to give the motor more time during the

acceleration/deceleration phases. In the LM9831, a setting of 3

for the “stopped” time, “25%” time, and “50%” time caused the

state machine to spend 3 full steps in that state. In the LM9833, a

setting of 3 will cause the state machine to spend 8 full steps in

that state.

12.5 1 Channel Color Mode

When using the LM9831 in 1 Channel Color Mode with the hold

current timeout set to 0, the LM9831 would sometimes skip a line

during a pause/resume cycle. This problem has been fixed in the

LM9833.

12.6 DRAM Control Signals

The RD, WR, CAS, and RAS pins are now tri-stated when the

LM9833 is in Suspend Mode. In a USB bus-powered application

where the DRAM is powered down in suspend mode but the

LM9833’s VDRAM supply still has power, this change prevents

the RD, WR, CAS, and RAS pins from potentially forward biasing

the input protection diodes of the external DRAM which could

cause the current drawn from the USB’s power source to exceed

the 2.5mA maximum allowable current draw when in suspend

mode.

12.7 Start of Scan Reset

In the LM9831, the value in register 01 is not reset (and therefore

not accurate) until the first line of the image has been scanned.

The LM9833 resets this counter as soon as a scan is initiated, so

the value in register 01 is always valid.

12.8 Power-On Reset (POR)

The LM9831 has a power-on reset circuit that causes the chip to

be reset during power-up when the analog power supply (VA)

passes 2V. If VA ramped very slowly (2V/ms), this could cause

the LM9831 to be reset and start trying to load data from the

external EEPROM before the external was EEPROM became

active, which could cause the LM9831 to think there was no

external EEPROM attached.

The LM9833 has a power-on reset threshold to 3V, to reduce the

chance of this occurring. Additionally, the input to the POR comes

from VD, not VA. This allows the VA supply to be switched off

when in Suspend mode, allowing more flexibility in USB bus-pow-

ered designs.

12.9 Remote Wakeup

The LM9833 supports enabling and disabling remote wakeup

through the LM9833 minidriver software.

12.10 Reduced Current Consumption

The LM9833 includes 4 current settings (100%, 80%, 70%, and

50%) to control the current consumed by the analog supply (VA).

The LM9833 is tested and guaranteed at the 100% setting, which

is the same as the LM9831’s analog section. For USB bus-pow-

ered settings, To reduce the current consumption (for bus-pow-

ered applications) set this register to one of the 3 other settings.

The performance of the analog section (INL, DNL, and noise) will

degrade at the lower settings, but this may not be noticeable in

the final image, particularly with CIS sensors where the noise and

non-linearities of the sensor may be far greater than that of the

LM9833’s analog front end.

12.11 Motor Phase Swap

Bit 5 has been added to register 45 to “swap” the A and B stepper

motor phases. This will reverse the stepper motor’s direction of

movement. This can be used to make the scanner scan in the

opposite (or both) directions, provides an alternative means of

sensing the home position by scanning towards home until a pat-

tern on the calibration strip (instead of an optical sensor) is

detected, and also provides a software fix for a motor that hap-

pens to be wired backwards. Note that this only works in fullstep

mode.

12.12 ITA Output on LAMPB

The LM9833 adds 1 bit (register 29 bit 2) that, when set, will out-

put the ITA (Integration Time Adjust) phase on the LAMPB output

pin. This signal can potentially be used to turn off the illumination

source during the ITA’s long integration time period.

12.13 Faster Fullstep Movement

In Fullstep Mode, the LM9831 and LM9833 normally move the

motor with the motor winding current set to 0.35V/RSENSE

(0.5V/RSENSE during the Kickstart period at the start of move-

ment). The problem is that the ideal RSENSE value for microstep-

ping was too small for fullstepping, and vice-versa. So if the

scanner needed to use both modes (fullstepping for high speed

movement and low resolution scans, microstepping for high reso-

lution scans), there wasn’t a sense resistor value that worked well

for both.

The LM9833 improves this situation by adding this function: if the

Kickstart Steps value (register 55 bits 0-2) is set to 0, the LM9833

will set the winding current to 0.5V/RSENSE for all fullstep move-

ment. This provides more current to the stepper motor in fullstep

mode, while allowing the sense resistor to be at a value optimized

for microstepping.

12.14 Fullstepping Fastfeed, Microstepping Scan

The LM9833 adds 1 bit (register 45 bit 6) that, when set, makes

the scanner automatically use fullstep mode for fastfeeding at the

start of scan, then switch to microstepping when scan begins.

12.15 Device and Vendor IDs for USB Interface

The LM9833’s internal (default) ROM is programmed for a Ven-

dor ID of 0x0400 and Device ID of 0x1002. The Vendor String is

“National Semiconductor” and the Device String is “LM9833 48

Bit Scanner”.

Applications Information (Continued)

LM9833 Datasheet(PDF) 35 Page - National Semiconductor (TI)

LM9833 Datasheet(HTML) 35 Page - National Semiconductor (TI)

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