Application Note
IRS20954S and IRS20957S Comparison
Table of Contents
Page
Introduction ..........................................................................................2
Block Diagram......................................................................................2
Electrical Characteristic Differences.....................................................3
VCLAMPH Differences.........................................................................5
Logic Status Differences ......................................................................5
Summary..............................................................................................6
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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 IRS20954S. This application note describes the differences between the
IRS20954S and IRS20957S.
Block Diagram
FLOATING INPUT CSH
UV
UV DETECT
VDD DETECT VB
UV
HIGH
Q
SIDE
INPUT CS
LOGIC HO
IN
15.3V
10.2V
HV
LEVEL VS
SHIFT HV HV
FLOATING HIGH SIDE
LEVEL LEVEL
VSS SHIFT SHIFT
5V REG VCC
UV
CHARGE/ DETECT
DISCHARGE
CSD
DEAD-TIME
LO
20.4V
SD DT
HV
LEVEL
COM
SHIFT
PROTECTION
CONTROL HV
LEVEL LOW SIDE CS OCSET
SHIFT
5.1V REFERENCE VREF
DT
The IRS20954S and the IRS20957S share the same functional structure. In normal
operating conditions, there are no functional changes between corresponding part
numbers.
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Electrical Characteristic Differences
All measurement conditions are the same for both the IRS20954S and IRS20957S.
Absolute Maximum Ratings
IRS20954S IRS20957S
Symbol Definition Min Typ Max Min Typ Max Units
High side floating
VB
supply voltage
-0.3 - 220 -0.3 - 215 V
High side floating VB VB
VS VB -20 - VB -15 - 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
IRS20954S IRS20957S
Symbol Definition Min Typ Max Min Typ Max Units
High side floating
VB supply absolute Vs+10 - Vs+18 Vs+10 - Vs+14 V
voltage
Low side fixed
VCC 10 - 18 10 - 15 V
supply voltage
10
IPW Input pulse width - - - - - ns
(Note)
Note: Output logic status may not respond correctly if input pulse width is smaller than the minimum pulse
width.
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Electrical Characteristics
IRS20954S IRS20957S
Symbol Definition Min Typ Max Min Typ Max Units
High and low side
turn-on
Ton_1 - 105 - - 95 - ns
propagation delay,
floating inputs
High and low side
turn-off
Toff_1 - 90 - - 80 - ns
propagation delay,
floating inputs
High and low side
turn-on
Ton_2 - 105 - - 95 - ns
propagation delay,
non-floating inputs
High and low side
turn-off
Toff_2 - 90 - - 80 - ns
propagation delay,
non-floating inputs
Deadtime: LO
turn-off to HO
turn-on (DTLO-
DT4 HO) & HO turn-off 25 45 60 50 80 110 ns
to LO turn-on
(DTHO-LO)VDT=
VDT4
Static Electrical Characteristics
IRS20954S IRS20957S
Symbol Definition Min Typ Max Min Typ Max Units
High side zener
VCLAMPH diode clamp 19.8 20.8 21.8 14.7 15.3 16.2 V
voltage
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Logic Status Differences
Narrow Pulse Behavior
In the IRS20954S, 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 IRS20954S.
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 IRS20954 with IRS20957
Current Design with IRS20954S Action Item for
Deadtime Vcc IRS20957S
>15V Reduce Vcc to 15V
DT1-3 or less.
Up to 15V Direct replacement.
>15V Reduce Vcc to 15V
or less.
DT4 Up to 15V Direct replacement
with wider
deadtime.
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Summary
The IRS20957S is an improved version of the IRS20954S 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 IRS20954S is no
longer recommended for new designs.
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