A quick review of the data sheet's first page revealed this... (I attached the data sheet for the ULN2891)
The suffix ‘A’ (all devices) indicates an 18-lead plastic dual in-line
package with copper lead frame for optimum power dissipation. Under
normal operating conditions, these devices will sustain 120 mA continuously
for each of the eight outputs at an ambient temperature of +50°C and a supply
of 15 V.
The 500 Ma limit is for one channel driven and is a Max current rating.
@ Crossroads, I stand corrected it was the current limit that I remembered... Not the average current for any one channel.
Unfortunately I didn't read the data sheet before I jumped the gun and posted bad information.
The TPIC6B595 is only good for 150 mA continuous current for all 8 outputs driven at the same time.