CIRRUS MP400FC_09

MP400FC
MP400
P r oMP400
d u c t IInnnnoovvaa t i o n FFr roomm
Power Operational Amplifiers
Features
General Description
The MP400FC combines a high voltage, high speed
precision power op amp with a supply voltage boost
function in an integrated thermally conductive module. The voltage boost function uses a switch mode
power supply (SMPS) to boost the input power supply
voltage. This allows the user the benefits of using his
standard 12 V or 24 V buss without the need to design a high voltage supply to power the op amp. The
SMPS voltage is adjustable from 50-350 V, allowing for
op amp output voltages up to 340 V. External phase
compensation provides the user with the flexibility to
tailor gain, slew rate and bandwidth for a specific application. The unique design of this amplifier provides
extremely high slew rates in pulse applications while
maintaining low quiescent current. The output stage is
well protected with a user defined current limit. Safe
Operating Area (SOA) must be observed for reliable
operation.
♦ Low Cost
♦ Wide Common Mode Range
♦ Standard Supply Voltage
♦ Single Supply: 10 V to 50 V
♦ Output Current - 150 mA Continuous
♦ Output Voltage 50-350 V
♦ 350 V/µS Slew Rate
♦ 200 kHz Power Bandwidth
Applications
♦ Piezoelectric positioning and Actuation
♦ Electrostatic Deflection
♦ Deformable Mirror Actuators
♦ Chemical and Biological Stimulators
Equivalent Circuit Diagram
21
Vin (10V to 50V)
15 14 13 12
22
23
25
Vbias 24
L1
D1
SMPS
CONTROLLER
Q2
8 Vboost
L2
R8
R7
6 LFin
R17
4 +Vs
37 Cr+
36 Cc+
R14
1 Out
R15
C6
AMP
2 Ilim
C8
34
Rset
MP400U
http://www.cirrus.com
R19
42 Cc38 Cr-
26 27 28 29 30 31 32 33
35
40 39 41
Analog -IN +IN -Vs
Power GND
GND
Copyright © Cirrus Logic, Inc. 2009
(All Rights Reserved)
AUG 20091
APEX − MP400UREVE
MP400
P r o d u c t I n n o v a t i o nF r o m
1. Characteristics and Specifications
ABsolute Maximum Ratings
Parameter
Symbol
Min
Max
Units
SUPPLY VOLTAGE, +VCC to GND
50
V
OUTPUT CURRENT, peak within SOA
200
mA
POWER DISSIPATION, internal, DC, Amplifier
14.2
W
OUTPUT POWER, SMPS
67
W
INPUT VOLTAGE, Differential
-16
16
V
INPUT VOLTAGE, Common Mode
-16
16
V
225
°C
150
°C
TEMPERATURE, pin solder, 10s
TEMPERATURE, junction
(Note 2)
TEMPERATURE RANGE, storage
−40
105
°C
OPERATING TEMPERATURE, case
−40
85
°C
Specifications
Parameter
Test Conditions
Min
Typ
Max
Units
8
40
mV
AMPLIFIER INPUT
OFFSET VOLTAGE
OFFSET VOLTAGE vs. temperature
0 to 85°C (Case)
-63
OFFSET VOLTAGE vs. supply
µV/°C
32
µV/V
8.5
200
pA
OFFSET CURRENT, initial
12
400
pA
INPUT RESISTANCE, DC
106
Ω
COMMON MODE VOLTAGE RANGE, pos.
+VS - 2
V
COMMON MODE VOLTAGE RANGE, neg.
-VS + 5.5
V
118
dB
418
µV RMS
120
dB
1
MHz
50
°
BIAS CURRENT, initial
(Note 3)
COMMON MODE REJECTION, DC
NOISE
90
700KHz bandwidth
AMPLIFIER GAIN
OPEN LOOP @ 15 Hz
89
GAIN BANDWIDTH PRODUCT @ 1 MHz
PHASE MARGIN
Full temperature range
AMPLIFIER OUTPUT
VOLTAGE SWING
IO = 10 mA
|VS| - 2
VOLTAGE SWING
IO = 100 mA
|VS| - 8.6
VOLTAGE SWING
IO = 150 mA
V
|VS| - 12
|VS| - 10
CURRENT, continuous, DC
150
SLEW RATE
100
V
V
mA
350
V/µS
SETTLING TIME, to 0.1%
2 V Step
1
µS
RESISTANCE, No load
RLIM = 6.2 Ω
44
Ω
POWER BANDWIDTH, 300 VP-P
+VS = 160 V, −VS = -160 V
200
kHz
CURRENT, quiescent, amplifier only
2
0.2
0.7
2.5
mA
MP400U
MP400
P r o d u c t I n n o v a t i o nF r o m
Specifications, (cont).
Parameter
Test Conditions
Min
Typ
Max
Units
SMPS
INPUT VOLTAGE, VIN
SMPS OUTPUT VOLTAGE, VB
SMPS OUTPUT CURRENT, IS
VB = 10x VIN
OUTPUT VOLTAGE TOLERANCE
VB ≤ 10x VIN, IS ≤ 150 mA,
RSET = 1%
10
50
V
46.75
365
V
150
mA
+/-2
VOLTAGE BOOST
6.5
10
%
x input V
THERMAL
RESISTANCE, DC, junction to case
Full temperature range, f<60Hz
RESISTANCE, junction to air
Full temperature range
7.7
8.8
46
TEMPERATURE RANGE, case
0
°C/W
°C/W
70
°C
NOTES:
1. (All Min/Max characteristics and specifications are guaranteed over the Specified Operating Conditions. Typical performance characteristics and specifications are derived from measurements taken
at typical supply voltages and TC = 25°C).
2. Long term operation at the maximum junction temperature will result in reduced product life. Derate
power dissipation to achieve high MTTF.
3. Doubles for every 10oC of temperature increase.
4. +VS and –VS denote the positive and negative supply voltages to the output stage.
External Connections
Cboost
VIN
VIN
VBIAS
VIN
PGND Q2D
VIN
PGND Q2D
PGND Q2D
PGND
PGND
PGND
PGND Q2D
9 10 11 12 13 14 15 16 17 18 19 20
VB
8
PGND
LFIN
CC+
7
RSET
6
AGND
5
+VS
4
CR+
CR-
ILIM
3
OUT
2
+IN
1
+
C1
RLIM
-IN
-VS
CC-
TO LOAD
AND
FEEDBACK
42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21
CC-
Analog GND
MP400U
+
CIN
C C+
Power GND
10V-50V
42-Pin DIP
Package Style FC
3
MP400
P r o d u c t I n n o v a t i o nF r o m
Pin Descriptions
Pin #
Pin name
21 - 23, 25
24
12 – 15
VIN
Vbias
Q2D
8
VB
6
LFIN
4
+VS
34
RSET
26 – 33
35
PGND
AGND
41
-VS
39
40
1
+IN
-IN
VOUT
2
36
37
38
42
ILIM
C R+
CC+
CRCC-
Description
Input voltage pins for the on board high voltage switch mode power supply.
Input voltage pin for the boost controller circuitry. This pin is typically tied to VIN
Drain node of the SMPS MOSFET switch. An external RC snubber may be connect from this
node to power ground to reduce or eliminate overshoot and ringing at switch turn off, reducing
switching noise on the SMPS.
This is the output of the high voltage SMPS and typically is tied to pin 6, LFIN. Other loads can
be added to this pin as long as the maximum output power of the SMPS is not exceeded. For
proper operation, an external high voltage, low ESR capacitor must be connected to this pin.
Refer to the paragraph titled “SMPS Output Capacitor”.
The high voltage SMPS, VB , is connected to this pin to power the MP400FC amplifier through a
47 µH filter inductor. The supply current in to this pin can not exceed 200 mA.
MP400FC amplifier high voltage supply pin. This pin is used for external supply bypass. A high
quality ceramic capacitor of at least 1uF should be used. The high voltage SMPS, VB, can be
connected directly to this pin, bypassing the 47 µH filter inductor.
SMPS voltage set resistor. A resistor is connected from this pin to power ground to set the SMPS
voltage.
Power ground. SMPS switching circuits are referenced to ground through these pins.
Analog ground for MP400FC amplifier circuits. AGND and PGND are connected at one point on
the MP400FC. Avoid external connections between AGND and PGND.
This pin is typically connected to AGND. However, an external negative supply voltage can be
connected to this pin.
Amplifier non-inverting input
Amplifier inverting input
Amplifier output
Amplifier current limit. A current limit resistor must be connected between ILIM and VOUT. RLIM =
0.7/ILIM.
+ side compensation capacitor connection one.
+ side compensation capacitor connection two.
- side compensation capacitor connection one.
- side compensation capacitor connection two.
Unused pins should be left open. This is mandatory for pins 3, 5, 7, 9, 11 and 16.
Typical Application
The MP400FC is ideally suited to driving both piezo actuation and deflection
applications off of a single low voltage supply. The circuit above boosts a
system 24 V buss to 350 V to drive an
ink jet print head. The MP400FCs high
speed deflection amplifier is biased for
single supply operation by external resistors R2 – R6, so that a 0 to 5 V DAC
can be used as the input to the amplifier
to drive the print head from 0 to >300 V.
4
Vin = 24V
100µF
Vboost
SMPS
CIRCUIT
Rset
0.0Ω
PGND
470µF
R4
0-5V
DAC
+350V
R2
124K
1W
402K
R3
124K
1W
5.62K
R5
5.62K
R1
CC
MP400
R6
402K
RCL
INK
DROPLETS
DEFLECTION
PLATE
CC
MP400U
MP400
P r o d u c t I n n o v a t i o nF r o m
TYPICAL PERFORMANCE GRAPHS
CURRENT LIMIT
POWER RESPONSE
200
150
100
50
NO COMPENSATION
INTERNAL POWER DISSIPATION, PD (W)
0
1
100
10
FREQUENCY, (KHz)
AMPLIFIER INTERNAL POWER DERATING
16
14
12
10
8
6
4
2
0
0
25
50
75
100
CASE TEMPERATURE, TC (°C)
EFFICIENCY Vs. SMPS CURRENT
EFFICIENCY (%)
EFFICIENCY (%)
60
VIN = 12V
VB = 120V
55
0.05
0.1
IO
0.15
CBOOST = 470uF
0.4
8V
=4
V IN
4V
=2
2V
=1
V IN
V IN
SMPS CURRENT, IS (A)
0.45
0.2
0.15
0.05 Limit of LFIN filter inductor,
and MP400 amplifier.
0
50 100 150 200 250 300 350
BOOST SUPPLY VOLTAGE, VB (V)
MP400U
4
6
8 10
RESISTOR (Ω)
12
14
OUTPUT VOLTAGE SWING
12
10
-VS SIDE DROP
8
6
+VS SIDE DROP
4
2
0
0
50
100
150
200
PEAK TO PEAK LOAD CURRENT (mA)
65
60
55
0.1
0.15
0.2
IO
70
100
-VS
80
+VS
60
40
20
0
100
1K
FREQUENCY, (Hz)
10K
COMMON MODE REJECTION
140
120
100
80
60
40
20
0
1
10
100
1K
10K 100K
FREQUENCY (Hz)
EFFICIENCY Vs. SMPS CURRENT
70
VIN = 48V
VB = 350V
50
0.05
0.2
SMPS OUTPUT POWER, PO (W)
0.5
0.1
2
VIN = 24V
VB = 240V
SMPS CURRENT VS. SMPS VOLTAGE
0.25
40
70
65
0.3
-VS
EFFICIENCY Vs. SMPS CURRENT
70
0.35
80
0
0
1000
POWER SUPPLY REJECTION (dB)
CURRENT LIMIT, ILIM (mA)
GAIN = -100
VOLTAGE DROP FROM SUPPLY (V)
OUTPUT VOLTAGE, (V)
250
+VS
120
COMMON MODE REJECTION (dB)
GAIN = -50
300
POWER SUPPLY REJECTION
160
EFFICIENCY (%)
350
65
60
55
0.05
0.1
0.15
0.2
IO
SMPS POWER DERATING
60
50
40
30
20
10
0
0
50
75
100
25
CASE TEMPERATURE, TC (°C)
5
MP400
P r o d u c t I n n o v a t i o nF r o m
SMALL SIGNAL OPEN LOOP GAIN
100
RC = OPEN, CC = 0pF
80
RC = 3.3K, CC = 1pF
RC = 3.3K, CC = 2.2pF
GAIN, Db
60
RC = 3.3K, CC = 5pF
40
CS = 68pF
PIN = -40dBm
RBIAS = OPEN
RS = 48.7Ω
VS = ±50V
20
0
-20
1
RC = 3.3K, CC = 10pF
RC = 3.3K, CC = 22pF
10
100
FREQUENCY, KHz
SMALL SIGNAL OPEN LOOP PHASE, VO = 250mVP-P
180
RC = 3.3K, CC = 10pF
120
PHASE, °
60
0 CS = 68pF
-30 PIN = -40dBm
R
= OPEN
-60 RBIAS
= 48.7Ω
S
-90
1
RC = 3.3K, CC = 5pF
RC = 3.3K, CC = 2.2pF
RC = 3.3K, CC = 1pF
RC = OPEN, CC = 0pF
10
100
FREQUENCY, KHz
1000
60
-5
-15
10
5 VP-P
50 VP-P
100
1K
FREQUENCY, KHz
10K
35
10
CC = 2.2pF
CC = 5pF
CC = 10pF
CC = 22pF
100
1K
FREQUENCY, KHz
10K
LARGE SIGNAL GAIN vs. COMPENSATION, VO = 50VP-P
CC = 0pF
25
15
A V = +26
RBIAS = 100K
RC = 3.3K
RF = 35.7K
RG = 1.5K
RL = 50K
VS = ±50V
-35
10
CC = 1pF
GAIN,dB
GAIN,dB
A V = +26
RBIAS = 100K
RF = 35.7K
RG = 1.5K
RL = 50K
VS = ±50V
-5
-35
25
6
1000
CC = 1pF
5
-25
CC = 0pF
35
-25
RC = OPEN, CC = 0pF
10
100
FREQUENCY, KHz
CC = 0pF
-15
SMALL SIGNAL GAIN vs. COMPENSATION, VO = 500mVP-P
45
-15
RC = 3.3K, CC = 1pF
15
GAIN,dB
GAIN, dB
A V = +51
RBIAS = 100K
RC = OPEN
RF = 75K
RG = 1.5K
RL = 50K
VS = ±50V
5
-5
RC = 3.3K, CC = 2.2pF
SMALL SIGNAL GAIN vs. COMPENSATION, VO = 5VP-P
35
500 mVP-P
15
5
RC = 3.3K, CC = 5pF
25
25
15
30
CS = 68pF
0 PIN = -40dBm
-30 RBIAS = 100K
R = 48.7Ω
-60 V S = ±50V
S
-90
1
35
-25
RC = 3.3K, CC = 10pF
90
GAIN vs. INPUT/OUTPUT SIGNAL LEVEL
45
RC = 3.3K, CC = 22pF
150
120
90
30
SMALL SIGNAL OPEN LOOP PHASE
180
RC = 3.3K, CC = 22pF
150
PHASE, °
1000
CC = 2.2pF
CC = 5pF
-25
CC = 22pF
100
1K
FREQUENCY, KHz
-5
-15
CC = 10pF
10K
CC = 1pF
5
-35
10
A V = +26
RBIAS = 100K
RF = 35.7K
RG = 1.5K
RL = 50K
VS = ±50V
CC = 2.2pF
CC = 5pF
CC = 10pF
CC = 22pF
100
1K
FREQUENCY, KHz
10K
MP400U
MP400
P r o d u c t I n n o v a t i o nF r o m
SR+/SR- (25% - 75%)
A V = +26
C = 8pF
800 RL = 35.6K
F
RG = 1.5K
600 RL = 50K
VS = ±150V
SRSR+
A V = +101
CL = 8pF
RF = 25K
RG = 250Ω
RL = 50K
VS = ±150V
400
200
0
2
4
6
8
10
12
PEAK-TO-PEAK INPUT VOLTAGE
14
400
0
16
0
2
4
6
8
10
12
PEAK-TO-PEAK INPUT VOLTAGE
14
A V = +51
CL = 8pF
RF = 75K
RG = 1.5K
RL = 50K
VS = ±150V
0.8
SRA V = +51
CL = 8pF
RF = 75K
RG = 1.5K
RL = 50K
VS = ±150V
200
0
2
4
6
8
10
12
PEAK-TO-PEAK INPUT VOLTAGE
TRANSIENT RESPONSE
10
5
input1
0
0
16
0
-0.8
-100
6
8
10
TRANSIENT RESPONSE
30
A V = +26
CC = 2.2pF 1
CL = 8pF
RC = 3.3K 0.5
RF = 35.7K
RG = 1.5K 0
RL = 50K
input2
10
0
-10
-0.5
-20
-1
-30
-4
MP400U
-2
0
2
4
TIME, µs
6
8
10
-150
-4
16
8
A V = +26
CC = 2.2pF
CL = 8pF
RC = 3.3K
RF = 35.7K
RG = 1.5K
RL = 50K
input10
6
4
2
0
-2
-4
-6
-2
0
2
4
6
TIME, µs
8
10
-8
12
PULSE RESPONSE vs. CC AND RC
1.5
2VP-P
20
-1.2
12
INPUT VOLTAGE, V
4
TIME, µs
10VP-P
0
-10
2
14
TRANSIENT RESPONSE
50
-50
0
4
6
8
10
12
PEAK-TO-PEAK INPUT VOLTAGE
100
-0.4
-2
2
150
-5
-15
-4
OUTPUT VOLTAGE, V
TR
0.2
1.2
A V = +26
CC = 2.2pF 0.8
CL = 8pF
RC = 3.3K 0.4
RF = 35.7K
RG = 1.5K 0
RL = 50K
1VP-P
TF
0.4
-1.5
12
150
Out - 0pF
120 input
90
60
Out - 1pF & 3.3K
30
0
-30
-60
Out - 5pF & 3.3K
-90
-120
-150
-2
-1
0
1
2
3
4
TIME, µs
A V = +51
CC = 68pF
CL = 330pF
RC = 48Ω
RF = 75K
RG = 1.5K
RL = OPEN
VS = ±150V
OUTPUT VOLTAGE, V
OUTPUT VOLTAGE, V
15
14
0.6
INPUT VOLTAGE, V
OUTPUT VOLTAGE, V
400
0
Time, µs
SR, V/µs
600
16
RISE AND FALL TIME (10% - 90%)
1
SR+
800
SR-
200
SR+/SR- (25% -75%)
1000
SR+
SR, V/µs
SR, V/µs
600
INPUT VOLTAGE, V
800
0
SR+/SR- (25% - 75%)
1000
5
6
7
3.0
2.4
1.8
1.2
0.6
0
-0.6
-1.2
-1.8
-2.4
-3.0
INPUT VOLTAGE, V
1000
8
7
MP400
P r o d u c t I n n o v a t i o nF r o m
PULSE RESPONSE vs. CAP LOAD
PULSE RESPONSE vs. CAP LOAD
140
120
100
80
60
40
20
0
-20
-40
-60
-80
-6 -4 -2 0
A V = -50
RF = 75K
RG = 1.5K
RL = 50K
VS = ±150V
2
4
6
300pF, 1VP-P
200pF, 1VP-P
100pF, 1VP-P
OUTPUT, V
300pf, 3VP-P
200pf, 3VP-P
100pf, 3VP-P
OUTPUT, V
140
120
100
80
60
40
20
0
-20
-40
-60
-80
-6 -4 -2 0
8 10 12 14 16 18 20 22 24 26 28 30
TIME, µs
A V = -50
RF = 75K
RG = 1.5K
RL = 50K
VS = ±150V
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30
TIME, µs
PULSE RESPONSE vs. CAP LOAD
300pF, 2VP-P
200pF, 2VP-P
100pF, 2VP-P
OUTPUT, V
A V = -50
RF = 75K
RG = 1.5K
RL = 50K
VS = ±150V
CL = 8pF
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30
TIME, µs
PULSE RESPONSE
0.2
300
IS, A
0.15
0.1
OUTPUT VOLTAGE, V
A V = +51
CL = 8pF
RF = 75K
RG = 1.5K
RL = 50K
VS = ±150V
0.05
1
2
3
TIME,µs
4
-300
-6
6
5
30
A V = +51
CL = 8pF
CS = 68pF
RF = 75K
RG = 1.5K
RL = 50K
RS = 48.7Ω
VS = ±150V
14
12
10
8
6
25
20
IS, mA
16
IS, mA
0
IS vs. VIN
18
1
200
SR+/SR- V/µs
2
3
4
5
6
VIN, VP-P (100KHz sine wave)
SR+/SR- (25%-75%)
SR+(A V = -25)
SR-(A V = -25)
SR+(A V = +26)
SR-(A V = +26)
7
8
-4
OUTPUT
2
0
-2
-2
1600
0
2
4
TIME, µs
6
8
-6
12
10
SUPPLY CURRENT vs. FREQUENCY
A V = +51
CL = 8pF
CS = 68pF
RF = 75K
RG = 1.5K
RL = 50K
RS = 48.7Ω
VS = ±150V
0
10
9
VIN = 6VP
VIN = 3VP
100
Frequency, (KHz sine wave)
1000
SR+/SR- (25%-75%)
R = 75K
1400 RF = 1.5K
G
1200 RL = 50K
VS = ±150V
1000 C = 8pF
L
V/µs
0
RF = 75K
1000 RG = 1.5K
RL = 50K
800 VS = ±150V
CL = 8pF
400
4
-4
5
2
600
15
10
4
8
0
6
INPUT
-200
-0.05
-1
1200
100
-100
0
0
200
OVERDRIVE RECOVERY
A V = +51
CC = OPEN
CL = 8pF
RC = OPEN
RF = 75K
RG = 1.5K
RL = 50K
VS = ±150V
INPUT VOLTAGE, V
140
120
100
80
60
40
20
0
-20
-40
-60
-80
-6 -4 -2 0
800
600
400
200
MP400U
SR+(A V = -50)
SR-(A V = -50)
SR+(A V = +51)
IS, mA
1
2
7
8
RF = 75K
1000 RG = 1.5K
RL = 50K
800 VS = ±150V
CL = 8pF
SR+(A V = -25)
SR-(A V = -25)
SR+(A V = +26)
SR-(A V = +26)
600
100
Frequency, (KHz sine wave)
800
SR+(A V = -50)
SR-(A V = -50)
SR+(A V = +51)
SR-(A V = +51)
200
0
1
2
3
4 5 6 7 8 9 10 11 12 13 14 15
PEAK TO PEAK INPUT VOLTAGE
1000
R = 75K
1400 RF = 1.5K
G
1200 RL = 50K
VS = ±150V
1000 C = 8pF
L
400
200
MP400
SR+/SR- (25%-75%)
1600
600
400
0
0
10
9
SR+/SR- (25%-75%)
1200
SR+/SR- V/µs
3
4
5
6
VIN, VP-P (100KHz sine wave)
VIN = 6VP
VIN = 3VP
5
P r o d u c t I n n o v a t i o nF r o m
2
0
15
10
4
0
CS = 68pF
RF = 75K
RG = 1.5K
RL = 50K
RS = 48.7Ω
VS = ±150V
20
V/µs
IS, mA
14 CS = 68pF
RF = 75K
12
RG = 1.5K
10 RL = 50K
8 RS = 48.7Ω
VS = ±150V
6
0
0
1
2
3 4 5 6 7 8 9 10 11 12 13 14 15
INPUT VOLTAGE, VOLTS PEAK-TO-PEAK
GENERAL
Please read Application note 1 “General operating considerations” which covers stability, power supplies,
heat sinking, mounting, current limit, SOA interpretation, and specification interpretation. Visit www.cirrus.com for
design tools that help automate tasks such as calculations for stability, internal power dissipation, and current limit.
There you will also find a complete application notes library, technical seminar workbook, and evaluation kits.
Theory of Operation
The PA78 is designed specifically as a high speed pulse amplifier. In order to achieve high slew rates with low idle
current, the internal design is quite different from traditional voltage feedback amplifiers. Basic op amp behaviors
like high input impedance and high open loop gain still apply. But there are some notable differences, such as signal
dependent supply current, bandwidth and output impedance, among others. The impact of these differences varies
depending on application performance requirements and circumstances. These different behaviors are ideal for
some applications but can make designs more challenging in other circumstances.
Supply Current and Bypass Capacitance
A traditional voltage feedback amplifier relies on fixed current sources in each stage to drive the parasitic capacitances of the next stage. These currents combine to define the idle or quiescent current of the amplifier. By design,
these fixed currents are often the limiting parameter for slew rate and bandwidth of the amplifier. Amplifiers which
are high voltage and have fast slew rates typically have high idle currents and dissipate notable power with no signal applied to the load. At the heart of the PA78 design is a signal dependent current source which strikes a new
balance between supply current and dynamic performance. With small input signals, the supply current of the PA78
is very low, idling at less than 1 mA. With large transient input signals, the supply currents increase dramatically to
allow the amplifier stages to respond quickly. The Pulse Response plot in the typical performance section of this
datasheet describes the dynamic nature of the supply current with various input transients.
Choosing proper bypass capacitance requires careful consideration of the dynamic supply currents. High frequency
ceramic capacitors of 0.1 µF or more should be placed as close as possible to the amplifier supply pins. The inductance of the routing from the supply pins to these ceramic capacitors will limit the supply of peak current during
transients, thus reducing the slew rate of the PA78. The high frequency capacitance should be supplemented by
additional bypass capacitance not more than a few centimeters from the amplifier. This additional bypass can be
a slower capacitor technology, such as electrolytic, and is necessary to keep the supplies stable during sustained
output currents. Generally, a few microfarad is sufficient.
Small Signal Performance
The small signal performance plots in the typical performance section of this datasheet describe the behavior when
the dynamic current sources described previously are near the idle state. The selection of compensation capacitor
directly affects the open loop gain and phase performance.
Depending on the configuration of the amplifier, these plots show that the phase margin can diminish to very low
levels when left uncompensated. This is due to the amount of bias current in the input stage when the part is in
standby. An increase in the idle current in the output stage of the amplifier will improve phase margin for small signals although will increase the overall supply current.
MP400U
9
MP400
P r o d u c t I n n o v a t i o nF r o m
Current can be injected into the output stage by adding a resistor, RBIAS, between CC- and VS+. The size of RBIAS will
depend upon the application but 500 µA (50 V V+ supply/100K) of added bias current shows significant improvement in the small signal phase plots. Adding this resistor has little to no impact on small signal gain or large signal
performance as under these conditions the current in the input stage is elevated over its idle value. It should also
be noted that connecting a resistor to the upper supply only injects a fixed current and if the upper supply is fixed
and well bypassed. If the application includes variable or adjustable supplies, a current source diode could also be
used. These two terminal components combine a JFET and resistor connected within the package to behave like
a current source.
As a second stability measure, the PA78 is externally compensated and performance can be optimized to the application. Unlike the RBIAS technique, external phase compensation maintains the low idle current but does affect
the large signal response of the amplifier. Refer to the small and large signal response plots as a guide in making
the tradeoffs between bandwidth and stability. Due to the unique design of the PA78, two symmetric compensation
networks are required. The compensation capacitor CC must be rated for a working voltage of the full operating
supply voltage (+VS to –VS). NPO capacitors are recommended to maintain the desired level of compensation over
temperature.
The PA78 requires an external 33 pF capacitor between CC- and -VS to prevent oscillations in the falling edge of the
output. This capacitor should be rated for the full supply voltage (+VS to -VS).
Large Signal Performance
As the amplitude of the input signal increases, the internal dynamic current sources increase the operation bandwidth of the amplifier. This unique performance is apparent in its slew rate, pulse response, and large signal performance plots. Recall the previous discussion about the relationships between signal amplitude, supply current, and
slew rate. As the amplitude of the input amplitude increases from 1 VP-P to 15 VP-P, the slew rate increases from 50
V/µs to well over 350 V/µs.
Notice the knee in the Rise and Fall times plot, at approximately 6 VP-P input voltage. Beyond this point the output
becomes clipped by the supply rails and the amplifier is no longer operating in a closed loop fashion. The rise and
fall times become faster as the dynamic current sources are providing maximum current for slewing. The result of
this amplifier architecture is that it slews fast, but allows good control of overshoot for large input signals. This can
be seen clearly in the large signal Transient Response plots.
Heatsinking and Safe Operating Area
OUTPUT CURRENT (mA)
SOA
The MOSFET output stage of the PA78 is not limited by second break160
down considerations as in bipolar output stages. Only thermal considerations of the package and current handling capabilities limit the
140
Safe Operating Area. The SOA plots include power dissipation limita120
25°C
tions which are dependent upon case temperature. Keep in mind that
100
the dynamic current sources which drive high slew rates can increase
75°C
the operating temperature of the amplifier during periods of repeated
80
slewing. The plot of supply current vs. input signal amplitude for a 100
60
125°C
kHz signal provides an indication of the supply current with repeated
40
slewing conditions. This application dependent condition must be considered carefully.
20
The output stage is self-protected against transient flyback by the para0
sitic body diodes of the output stage. However, for protection against
10
100
1000
sustained high energy flyback, external, fast recovery diodes must be SUPPLY TO OUTPUT DIFFERENTIAL, VS-VO (V)
used.
Current Limit
For proper operation, the current limit resistor, RLIM, must be connected as shown in the external connections diagram. For maximum reliability and protection, the largest resistor value should be used. The maximum practical
value for RLIM is about 12 Ω. However, refer to the SOA curves for each package type to assist in selecting the optimum value for Rlim in the intended application. Current limit may not protect against short circuit conditions with
supply voltages over 200 V.
10
MP400U
MP400
P r o d u c t I n n o v a t i o nF r o m
Layout Considerations
The PA78 is built on a dielectrically isolated process and the package tab is therefore not electrically connected
to the amplifier. For high speed operation, the package tab should be connected to a stable reference to reduce
capacitive coupling between amplifier nodes and the floating tab. It is often convenient to directly connect the tab
to GND or one of the supply rails, but an AC connection through a 1µF capacitor to GND is also sufficient if a DC
connection is undesirable
Care should be taken to position the RC / CC compensation networks close
SMPS Output vs. RSET
to the amplifier compensation pins. Long loops in these paths pick up noise 100000
and increase the likelihood of LC interactions and oscillations.
10000
The MP400FC is designed to operate off of a standard voltage rail. Typical values include 12 V, 24 V, or 48 V. The addition of the on-board SMPS
eliminates the need to design or purchase a high voltage power supply. The
only inputs required by the SMPS are the VIN source. Input and output filter
capacitor, and boost voltage set resistor (RSET).
The SMPS output can be adjusted between a minimum of 50 V to a maximum of 350 V. The voltage boost adjustment is independent of VIN. Adjustment to the boost level is made through a resistor from the RSET pin to
ground. The resistor value is:
RSET =
RSET (Ω)
SMPS Operation
1000
100
10
1
50
100 150 200 250 300 350
VBoost (V)
1.85 • 105
- 615
VBOOST - 49.95
Where VBOOST = desired SMPS voltage.
Example:
1) Desired VBOOST = 160 V
2) RSET = 1K (1066 by equation)
If RSET is open, VBOOST will be 50 V. If RSET is shorted to ground VBOOST will be limited to 350 V.
Note that while the MP400 SMPS generates a positive voltage from 50 V to 350 V, the amplifier may operate from
a variety of supply voltages. Symmetric, asymmetrical and single supply configurations can be used so long as the
total supply voltage from +VS to -VS does not exceed 350 V. The amplifier performance graphs in this datasheet
include some plots taken with symmetrical supplies, but those plots generally apply to all supply configurations.
SMPS Output Capacitor
An external SMPS output filter capacitor is required for proper operation. ESR considerations prevail in the choice
of the output filter capacitor. Select the highest value capacitor that meets the following ESR requirement. The
minimum value for CBOOST is 100 µF.
ESR = dVo/ILPK
Where,
dVo
ILPK
L
VIN
ton
VBOOST
IO
FSW
MP400U
= The maximum acceptable output ripple voltage
= Peak inductor current = (1/L) • VIN • ton
= 10-6 if the internal inductor is used.
= Input voltage of the application.
= √(2 • Io • L • ((Vo + 0.6 - VIN)/(FSW • VIN2)))
= The boost supply voltage of the application.
= The maximum continuous output current for the application.
= 100 KHz switching frequency of the MP400FC boost supply.
11
MP400
P r o d u c t I n n o v a t i o nF r o m
SMPS Input Capacitor
An external input capacitor is required. This capacitor should be at least 100 µF.
Thermal Considerations
For reliable operation the MP400FC will require a heatsink for most applications. When choosing the heatsink the
power dissipation in the op amp and the SMPS MOSFET switch (Q2) are both considered. The power dissipation of
the op amp is determined in the same manner as any power op amp. The power dissipation of the MOSFET switch
(Q2) is the sum of the power dissipation due to conduction and the switching power.
PD(Q2) = (IIN(pk)2 • RDS(ON) • D) + (IIN(pk) • VIN • tr • FSW)
Where:
VIN
VB
IO
FSW
RDS(ON)
tr D
t1 =
= SMPS input voltage
= SMPS output voltage
= Total SMPS output current
= 100 KHz
= 0.621 Ω
= 82 x 10-9s
= t1 • FSW
2 • IO • 10 x 10-6 •
IIN(pk) =
td = t1 •
(
VB - VIN
FSW • VIN2
)
VB • td
10 x 10-6
(
VB
VB - VIN
)
- t1
Contacting Cirrus Logic Support
For all Apex Precision Power product questions and inquiries, call toll free 800-546-2739 in North America.
For inquiries via email, please contact [email protected]
International customers can also request support by contacting their local Cirrus Logic Sales Representative.
To find the one nearest to you, go to www.cirrus.com
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Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable. However, the information is subject
to change without notice and is provided "AS IS" without warranty of any kind (express or implied). Customers are advised to obtain the latest version of relevant
information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale
supplied at the time of order acknowledgment, including those pertaining to warranty, indemnification, and limitation of liability. No responsibility is assumed by Cirrus
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does not extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
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All other brand and product names in this document may be trademarks or service marks of their respective owners.
12
MP400U