Application Note AN-1141 IRS20955S and IRS20957S Comparison Table of Contents Page Introduction ..........................................................................................2 Block Diagram......................................................................................2 Electrical Characteristic Differences.....................................................3 VCLAMPH Differences.........................................................................5 Logic Status Differences ......................................................................5 Summary..............................................................................................5 www.irf.com AN-1141 1 Introduction The IRS20957S is a high voltage, high speed MOSFET driver with a floating PWM input designed for Class D audio amplifier applications. The IRS20957S is an improved version of the IRS20955S. This application note describes the differences between the IRS20955S and IRS20957S. Block Diagram FLOATING INPUT VDD VB UV HIGH SIDE CS INPUT LOGIC Q HO 15.3V IN CSH UV DETECT UV DETECT 10.2V HV LEVEL SHIFT VSS HV LEVEL SHIFT FLOATING HIGH SIDE VS HV LEVEL SHIFT 5V REG VCC UV DETECT CHARGE/ DISCHARGE CSD DT 20.4V DEAD-TIME SD HV LEVEL SHIFT PROTECTION CONTROL LO COM HV LEVEL SHIFT LOW SIDE CS 5.1V REFERENCE OCSET VREF DT The IRS20955S and the IRS20957S share the same functional structure. In normal operating conditions, there are no functional changes between corresponding part numbers. www.irf.com AN-1141 2 Electrical Characteristic Differences All measurement conditions are the same for both the IRS20955S and IRS20957S. Absolute Maximum Ratings Symbol Definition Min IRS20955S Typ Max Min IRS20957S Typ Max Units High side floating 215 VB -0.3 220 -0.3 V supply voltage VB VB High side floating VB -15 VS VB -20 V supply voltage (†) +0.3 +0.3 † VDD - VSS, VCC -COM and VB - VS contain internal shunt zener diodes. Please note that the voltage ratings of these can be limited by the clamping current. Recommended Operating Conditions Symbol VB VCC Definition High side floating supply absolute voltage Low side fixed supply voltage Min IRS20955S Typ Max Min IRS20957S Typ Max Units Vs+10 - Vs+18 Vs+10 - Vs+14 V 10 - 18 10 - 15 V 10 ns (Note) Note: Output logic status may not respond correctly if input pulse width is smaller than the minimum pulse width. IPW www.irf.com Input pulse width AN-1141 3 Electrical Characteristics Symbol Ton_1 Toff_1 Ton_2 Toff_2 DT4 Definition High and low side turn-on propagation delay, floating inputs High and low side turn-off propagation delay, floating inputs High and low side turn-on propagation delay, non-floating inputs High and low side turn-off propagation delay, non-floating inputs Deadtime: LO turn-off to HO turn-on (DTLOHO) & HO turn-off to LO turn-on (DTHO-LO)VDT= VDT4 IRS20955S Min Typ Max IRS20957S Min Typ Max Units - 105 - - 95 - ns - 90 - - 80 - ns - 105 - - 95 - ns - 90 - - 80 - ns 25 45 60 50 80 110 ns Static Electrical Characteristics Symbol Definition Min VCLAMPH High side zener diode clamp voltage 19.6 www.irf.com IRS20955S Typ Max 20.4 AN-1141 21.6 Min 14.7 IRS20957S Typ Max 15.3 16.2 Units V 4 Logic Status Differences Narrow Pulse Behavior In the IRS20955S, a narrow input pulse below 10 ns, such as spikes from switching stage, may flip the logic states of LO and HO opposite to the input. Next transition in input PWM fixes the inverted logic in the output. However, this wrong logic status is harmful in self-oscillating type topologies because it makes the system latch up and stop operation. With natural PWM topologies, pulse width can be as narrow as 1ns that leads the wrong logic status with IRS20955S. The IRS20957S ignores narrow input pulses. The logic states of HO and LO does not respond to the input of the IC if pulse width is less than 50ns, providing more noise immunity to systems using self-oscillating type topologies. VCLAMPH Differences Pre-charging with VBS Zener Diode During start up sequence, pre-charging bootstrap power supply through positive bus voltage might be necessary to start self oscillating PWM. It would be convenient to integrate 15V zener diode to clamp the high side power supply, VBS, for applications with MOSFETs that have rated gate voltage of 20V. Upgrading IRS20955 with IRS20957 Current Design with IRS20955S Deadtime Vcc >15V DT1-3 Up to 15V >15V DT4 www.irf.com Up to 15V AN-1141 Action Item for IRS20957S Reduce Vcc to 15V or less. Direct replacement. Reduce Vcc to 15V or less. Direct replacement with wider deadtime. 5 Summary The IRS20957S is an improved version of the IRS20955S with shorter propagation delay. The longer deadtime window of IRS20957S enables use of MOSFET with larger gate charge. Applications using a natural PWM topology should use the IRS20957S. The IRS20957S has more immunity to incoming noise in IN pin. The IRS20955S is no longer recommended for new designs. www.irf.com AN-1141 6