AN29502.6 APPLICATIONS NOTEBOOK: CLARIFYING 2953/2954 REPLACEMENT

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AN29502.6 APPLICATIONS NOTEBOOK: CLARIFYING 2953/2954 REPLACEMENT

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PAOLO'S PERSPECTIVES POWER Paul Emerald
AN29502.6
APPLICATIONS NOTEBOOK: CLARIFYING 2953/2954 REPLACEMENT/SUBSTITUTION APPLICATIONS: EXISTING 2953/54 DESIGNS NECESSITATIONG CONVERSION NEWER
SYNOPSIS Earlier, UDN2953B UDN2954W were included product status change listing. These motor were discontinued year 1995; thus, numerous questions dialogues have ensued. objective this applications note clarification suitable alternative motor driver ICs, distinctions between fading replacements. interim solutions designers unable unwilling) redesign circuit boards A3951SB (supersedes 2953B) and/or A3951SW (replaces 2954W). However, despite having identical package connections, there nuances that should identified understood before directly substituting 2953B/2954W. Further, designs should "leapfrog" 3951 utilize complete capabilities A3952. A3952 different lead connections, plus number improvements that should recognized; however, emphasis here clarifying substitution perspective. straightforward technique distinguishing differences operation ratings will presented three motor (2953 2954 differences relate packaging). ABSOLUTE MAXIMUM RATINGS REFERENCE VOLTAGE RANGES Rather than list absolute maximums, only dissimilarities listed. three full-bridge motor specify identical continuous current maximum voltage (50V), logic supply power (7.0V); other basic distinctions involve: 2953/54 Output Current (Peak)* +3.5 3951/52 Output Current (tw<20 +3.5 Pulse width noted 3951/3952; sustained operation +3.5 damages destroys) these high-current motor control ICs. 2953/2954 3951 reference input dual function control, there other disparities between devices. Braking single, shared input both 2953/54 3951. Switching combined VREF/BRAKE input logic (<0.8 actuates dynamic braking 2953/54 3951. 3952 separate inputs Reference Braking; this allows broader range current control than 2953/54 3951 enumerated below). 2953/54 Flyback Voltage, 3951/52 Flyback Internal Connection connection changes should affected. Ground 2953/54 Min. Clamp Voltage, 3951/52 Clamping Internal Connection Normally, connection changes expected. 2953/54 Logic Input Voltage VPHASE VENABLE
3951/52 Logic Input Voltage Range -0.3 +0.3
Seldom this logic input voltage issue; however, both Phase Enable inputs limited range specified above. 2953/54 Reference Voltage (max) 3951 Reference Voltage (max) 3952 Reference Voltage (max)
2953/54 Reference Range >2.4 3951 Reference Range >2.4 3952 Reference Range VREF OTHER REFERENCE VOLTAGE CONCERNS 2953/54 design allowed operation without connecting reference input; these devices internally default voltage reference. neither 3951 3952 function this condition; suitable, stable voltage (VREF) must connected newer ICs. Converting 2953/54 designs lacking this VREF connection necessitates reference voltage (VCC), plus doubling sense resistor provide same current. With reference voltage applied, typically 2953/54 "defaults" (5.0 logic supply). output current based factors: VREF (10x) RSENSE; thus, 2953/54 internal default "half-supply" converts 3951/52 operation doubling conform formula below): VREF ITRIP (Normal PWM) RSENSE devices have continuous output rating hence, trip current should exceed this value. mentioned, operating above damage destroy these bridge circuits; also, dynamic braking induce (uncontrolled peak currents that 2953/54 cannot sustain. SAFE DYNAMIC BRAKING: Utilize 3952 Neither 2953 2954 integrate control (peak) current braking mode. Only 3951 3952 incorporate control output current during braking operation; safe, reliable dynamic braking often formidable design problem. Realistically, 3952 only suitable driver safe braking. 3951 severely restricted both reference voltage limit range.
Safe braking current, plus regulation, 3952s involve: VREF 0.75 VSENSE This combination meets limit during operation under default braking conditions. However, 3951s cannot satisfy both braking limits together; with VREF ITRIP 0.25 With these conditions, default braking current (i.e. 1.5V 0.25 value that greatly exceeds safe limits. DEVICE TRUTH TABLES Although 2953/54 3951 terminology sequence respective truth tables differ, function identically. Further, A3951 truth table includes description column indicating mode operation. Truth Table: UDN2953B UDN2954W
Output Enable High
irrelevant
Phase High
VREF/ BRAKE >2.4 >2.4 >2.4 <0.8
OUTA High Open High
OUTB High Open High
Truth Table: A3951SB A3951SW
BRAKE ENABLE PHASE OUTA OUTB
DESCRIPTION Outputs Disabled Forward Reverse Brake, Note
Irrelevant High Impedance (source sink both OFF) NOTE: Includes internal default VSENSE level over-current protection.
A3952 incorporates additional logic input (MODE) that expands motor function offering drive methods (i.e. "sleep", standby, fourquadrant operation). adding MODE input 3952 truth table enlarged; with safe, dynamic braking effective microstepping added (fastdecay) options complete truth table.
Truth Table: A3952SB/SEB/SLB/SW
BRAKE ENABLE PHASE MODE OUTA OUTB DESCRIPT Sleep Mode Standby, Note Forward, Fast-Decay Mode Forward, SlowDecay Mode Reverse, Fast-Decay Mode Reverse, SlowDecay Mode Brake, Fast-Decay Mode Brake, Current Control, Note
CURRENT CONTROL OPTIONS Only 2953/2954 specifications include table listing current control techniques. comprehensive table which encompasses three fullbridge motor distinguishes differences between operating methods (where applicable) component values. Although this information included specifications, this table summarizes simplifies comparison alleviates device substitution process. SUMMARY Existing designs using either UDN2953B and/or UDN2954W must converted newer ICs. cited, "leapfrogging" beyond A3951 A3952 (very strongly) recommended. This involves redesign; provides better long-range solution. Further, A3952 offers superior benefits protective functions (especially reliable, safe, current controlled braking). Note: network capacitor value must increased (per table below). Also, minimum resistor value decreases. Please provide this applications material known 2953/54 customers. Refer other pertinent concerns questions Allegro Applications: Paul Emerald 508/854-5267 John Pyle 508/854-5333.
Irrelevant High Impedance (source sink both OFF) NOTES: Includes active pull-offs power outputs Includes internal default VSENSE level over-current protection.
CURRENT CONTROL ALTERNATIVES Circuit Package Connections
CONTROL OPTION MODE) VREF INPUT INPUT (TIMING) VSENSE ENABLE >2.0k! GROUND GROUND 2953 HIGH OPEN GND) GROUND 3951 HIGH OPEN GND) GROUND 3952 HIGH 2953 HIGH Rsense INTERNAL TIMING CIRCUITRY; NETWORK REQUIRED (INTERNAL TIMING) 3951 INTERNAL TIMING CIRCUITRY; NETWORK REQUIRED 3952 20-100k!/200-500pF Rsense 2953* 2.4V-15V* 3951 2.4V Vcc* 12-100k!/0.82-1.5nF Rsense (EXTERNAL TIMING) !0V-15V* 12-100k!/0.82-1.5nF 3952 Rsense TOGGLE** 2953* HIGH >20k! GROUND Rsense EXTERNAL TOGGLE*** 12-100k!/0.82-1.2nF >2.4V-5V* 3951 TOGGLE*** 12-100k!/0.82-1.2nF >0V-15V* 3952 NOTES: Applies both UDN2953B UDN2954W; Variable, programmable reference (ex: converter) Default (Peak) ITRIP protection; Closed-loop speed/position control applications Default (Peak) ITRIP protection; Closed-loop speed/position control applications; Also, 3951/3952 allow utilizing both 2-quadrant 4-quadrant current control.

AN29502.6 APPLICATIONS NOTEBOOK: CLARIFYING 2953/2954 REPLACEMENT

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