apex microtechnology corporation ? telephone (520) 690-8600 ? fax (520) 888-3329 ? orders (520) 690-8601 ? email prodlit@apexmicrotech.com 1 introduction the EK22 evaluation kit is designed to provide a convenient way to breadboard design ideas for the sa56 pwm amplifers. the eval25 evaluation board is pre-wired for all required and recommended external components. the eval25 also includes a breadboard area for constructing your application circuit including provisions for an output flter. please refer to applications note 32 in the apex catalog for guidance in flter component selection. the 1f ceramic capacitors supplied with the kit are for high frequency bypassing of the vs and vdd supplies (c1 C c3 on the eval25 board). an additional user supplied low esr capacitor of at least 10uf per amp of output current is required for adequate bypass of the vs supply (c4 on the eval25 board). please refer to applica - tions note 30 for help with power supply bypassing and other useful information. sa56 prototype beta samples this evaluation kit is supplied for evaluation of sa56 pro - totype beta samples. there are some limitations to the sa56 prototypes that must be noted. suggestions to minimize the effect of these limitations are included. the sa56 combines both high speed high power switching and low level analog signals on a single silicon chip. the dif - fculty in achieving clean noise free operation is much greater then that of discrete or hybrid microcircuit designs. though much care and attention has been given to these considerations in the design and layout of the sa56, there is still some work to be done and these prototypes do not switch as cleanly as necessary for completely trouble free operation. grounding for the sa56 is critical. the eval25 board has separate ground paths for signal ground (sgnd) and power ground (pgnd). the signal and power grounds are common at one point on the sa56. ground loops can be formed if these two grounds are tied together externally. these two grounds are not tied together on the eval25 board through trace rout - ing. when building your evaluation circuit, insure that each component referenced to ground is tied to the proper ground path. external components at the high speed, high current output of the sa56 must be returned to pgnd. analog mode operation of the sa56 prototype is affected by switching noise through non-linear operation towards the pwm duty cycle extremes. this limits the useable duty cycle range of the sa56 prototype. the use of external fyback diodes and the use of rc snubbers from each output to ground reduces switching noise, increasing the usable duty cycle range. however the duty cycle should be limited within the range of 5% to 95%. this kit is supplied with four schottky diodes, p/n sb5100, for use as external fyback diodes (d1 C d4). it is recom - mended that diodes d1 C d4 be used regardless of the mode of operation. in addition four 20 ohm, 5w resistors, and two 15nf, 100v capacitors are supplied for use as an rc snubber for each output (c9, r3a, r3b and c10, r4a, r4b). the snubbers are especially useful in reducing the noise generated by the high dv/dt during output switching. the power dissipated in the snubber components can be estimated by; ) 5 5 1 8 8 8 " 1 & 9 . * $ 3 0 5 & $ ) $ 0 . " 1 & 9 . * $ 3 0 5 & $ ) / 0 - 0 ( : & |