Application Report
SLOA092 – October 2001
PWM Power Driver Modulation Schemes
Richard Palmer
High Performance Linear
ABSTRACT
This application report describes the modulation schemes implemented in the DRV59x
family of PWM power drivers to facilitate user design efforts. Texas Instruments offers
three modulation options with the introduction of the DRV590 and DRV591 PWM power
drivers and the DRV592 H-bridge.
1
Introduction
This report contains four sections that describe the DRV59x family modulation techniques:
•
DRV590 Modulation Scheme
•
DRV591 Modulation Scheme
•
Comparison of the DRV590 and DRV591
•
DRV592 Operation: User-Defined Modulation
The DRV590 and DRV591 sections each contain block diagrams showing typical connections
and figures showing the output waveforms for various input voltages. The DRV592 section
contains only the block diagram, because it does not generate its own PWM output waveform.
1
SLOA092
2
DRV590 Modulation Scheme
The DRV590 PWM power driver integrates a PWM generator, gate drive circuitry, and power
transistors into a single, surface-mount package. Figure 1 is a block diagram of the DRV590.
The device converts an analog input (typically a dc voltage) into a PWM output that is averaged
by an LC output filter. The modulation scheme, shown in Figure 2, allows for very little load
current when there is no input, reducing the ripple voltage and current in the load.
DC
Input
Figure 1.
VDD
2
0V
OUT
Load
DRV590
5V
VOUT
0V
5V
VOUT
0V
VDIFF
0V
0V
VDIFF
0V
0V
5V
1A
IOUT
0V
5V
5V
5V
0V
5V
VOUT
5V
5V
VDIFF
IN
LC
Output
Filter
5V
VOUT
5V
VOUT
OUT
Block Diagram of the DRV590, Biased for Bidirectional Current
5V
VOUT
IN
1A
0A
IOUT
IOUT
0A
1A
0A
1A
No Input Voltage
Positive Input Voltage
Negative Input Voltage
NOTE: The voltage waveforms shown are unfiltered.
Figure 2.
2
DRV590 PWM Power Driver Modulation Scheme, VDD = 5 V, RL = 2 Ω
PWM Power Driver Modulation Schemes
SLOA092
3
DRV591 Modulation Scheme
The DRV591 is similar to the DRV590 as it also integrates the PWM generator, gate drive
circuitry, and power transistors into a single, surface-mount package. Figure 3 is a block
diagram of the DRV591. It takes an analog input (typically a dc voltage) and converts it into a
PWM output that is averaged by an LC output filter. The modulation scheme, shown in Figure 4,
has very little switching when there is no input, reducing EMI during quiescent conditions as well
as ripple voltage and current in the load.
VDD
2
DC
Input
Figure 3.
0V
OUT
Load
DRV591
5V
VOUT
0V
5V
VOUT
0V
VDIFF
0V
0V
VDIFF
0V
0V
5V
3A
IOUT
0V
5V
5V
5V
0V
5V
VOUT
5V
5V
VDIFF
IN
LC
Output
Filter
5V
VOUT
5V
VOUT
OUT
Block Diagram of the DRV591, Bidirectional Current
5V
VOUT
IN
3A
0A
IOUT
IOUT
0A
3A
0A
3A
Positive Input Voltage
No Input Voltage
Negative Input Voltage
NOTE: The voltage waveforms shown are unfiltered.
Figure 4.
4
DRV591 PWM Power Driver Modulation Scheme, VDD = 5 V, RL = 1.5 Ω
Comparison of the DRV590 and DRV591
Both devices generate the same differential voltage across the load for a given input. The
difference is how each device generates this voltage. The DRV590 outputs are both constantly
switching during operation regardless of the input signal. The waveforms from each output
create a differential voltage across the load that is twice the frequency of the internal oscillator.
The DRV591, however, has only one output switching when an input signal is applied. The
oscillator frequency is doubled internally so the output looks the same as that of the DRV590
under similar input conditions.
PWM Power Driver Modulation Schemes
3
SLOA092
5
DRV592 Operation: User-Defined Modulation Scheme
The DRV592 is an H-bridge with gate drive circuitry integrated into a small, surface-mount
package. Figure 5 is a block diagram of the DRV592. It takes a TTL-compatible logic level PWM
input and provides current gain. An LC output filter then averages the PWM output. The input
signal can range in frequency from dc to 1 MHz. The designer determines the modulation
scheme.
User-Defined
PWM Input
(0 Hz - 1 MHz)
OUT
IN
OUT
LC
Output
Filter
Load
DRV592
Figure 5.
6
IN
DRV592 Block Diagram
Summary
The DRV591 and DRV590 devices have the following similarities:
•
Integrate a PWM generator, gate drive circuitry, and power transistors into a single, surface
mount package
•
Convert an analog input (typically a dc voltage) into a PWM output
•
Produce little ripple current when there is no input
The primary difference is in their modulation scheme as shown below:
•
The DRV590 outputs both switch continuously, regardless of the input signal.
•
The DRV591 has only one output switching when an input signal is applied.
The DRV592 has the following characteristics:
4
•
Integrates an H-bridge and gate drive circuitry into a single surface mount package
•
Accepts a user-defined PWM input that must be TTL logic-level compatible from dc to 1
MHz
PWM Power Driver Modulation Schemes
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