MICREL MIC4604YMT

MIC4604
85V Half Bridge MOSFET Drivers with up to
16V Programmable Gate Drive
General Description
Features
The MIC4604 is an 85V Half Bridge MOSFET driver. The
MIC4604 features fast 39ns propagation delay times and
20ns driver rise/fall times for a 1nF capacitive load. The
low-side and high-side gate drivers are independently
controlled. The MIC4604 has TTL input thresholds. It
includes a high-voltage internal diode that helps charge
the high-side gate drive bootstrap capacitor.
• 5.5V to 16V gate drive supply voltage range.
• Drives high-side and low-side N-Channel MOSFETs
with independent inputs
• TTL input thresholds
• On chip bootstrap diode
• Fast 39ns propagation times
• Drives 1000pF load with 20ns rise and fall times
• Low power consumption
• Supplies undervoltage protection
• –40°C to +125°C junction temperature range
A robust, high-speed, and low-power level shifter provides
clean level transitions to the high-side output. The robust
operation of the MIC4604 ensures that the outputs are not
affected by supply glitches, HS ringing below ground, or
HS slewing with high-speed voltage transitions.
Undervoltage protection is provided on both the low-side
and high-side drivers.
The MIC4604 is available in an 8-pin SOIC package and a
tiny 10-pin 2.5mm × 2.5mm TDFN package. Both
packages have an operating junction temperature range of
–40°C to +125°C.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Applications
•
•
•
•
•
Power inverters
High-voltage step-down regulators
Half, full and 3-phase bridge motor drives
Distributed power systems
Computing peripherals
Typical Application
Motor Door Lock Solution
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
June 25, 2013
Revision 1.0
Micrel, Inc.
MIC4604
Ordering Information
Part Number
Part Marking
Input
Junction Temperature Range
Package
MIC4604YMT
463
TTL
–40° to +125°C
10-Pin 2.5mm × 2.5mm TDFN
MIC4604 YM
TTL
–40° to +125°C
8-Pin SOIC
MIC4604YM
Pin Configurations
MIC4604YMT
10-Pin 2.5mm x2.5mm TDFN (MT)
(Top View)
MIC4604YM
8-Pin SOIC (M)
(Top View)
Pin Description
Pin Number
TDFN
SOIC
Pin
Name
1
1
VDD
2, 10
Pin Function
Input supply for gate drivers. Decouple this pin to VSS with a >2.2µF capacitor. Anode
connection to internal bootstrap diode.
NC
No Connect
3
2
HB
High-side bootstrap supply. External bootstrap capacitor is required. Connect bootstrap
capacitor across this pin and HS. Cathode connection to internal bootstrap diode.
4
3
HO
High-side drive output. Connect to gate of the external high-side power MOSFET.
5
4
HS
High-side drive reference connection. Connect to source of the external high-side power
MOSFET. Connect this pin to the bootstrap capacitor.
6
5
HI
High-side drive input.
7
6
LI
Low-side drive input.
8
7
VSS
9
8
LO
EP
June 25, 2013
EPAD
Driver reference supply input. Connected to power ground of external circuitry and to source
of low-side power MOSFET.
Low-side drive output. Connect to gate of the external low-side power MOSFET.
Exposed pad. Connect to VSS.
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Micrel, Inc.
MIC4604
Operating Ratings(2)
Absolute Maximum Ratings(1, 4)
Supply Voltage (VDD) [decreasing VDD] ........... 5.25V to 16V
Supply Voltage (VDD) [increasing VDD] .............. 5.5V to 16V
Voltage on HS .................................................... −1V to 85V
Voltage on HS (repetitive transient) ................... −5V to 90V
HS Slew Rate ............................................................ 50V/ns
Voltage on HB ................................ VHS + 4.5V to VHS + 16V
and/or.......................................... VDD − 1V to VDD + 85V
Junction Temperature (TJ) ........................ –40°C to +125°C
Junction Thermal Resistance
2.5mm x 2.5mm TDFN-10L (θJA) ....................... 75°C/W
SOIC-8L (θJA) .................................................. 98.9°C/W
Supply Voltage (VDD, VHB – VHS) ..................... −0.3V to 18V
Input Voltages (VLI, VHI, VEN) ................. −0.3V to VDD + 0.3V
Voltage on LO (VLO) ............................. −0.3V to VDD + 0.3V
Voltage on HO (VHO) ..................... VHS − 0.3V to VHB + 0.3V
Voltage on HS (continuous) ............................... −1V to 90V
Voltage on HB .............................................................. 108V
Average Current in VDD to HB Diode ....................... 100mA
Storage Temperature (Ts) ......................... −60°C to +150°C
(3)
ESD Rating
HBM ...................................................................... 1.5kV
MM ......................................................................... 200V
Electrical Characteristics(4)
VDD = VHB = 12V; VSS = VHS = 0V; No load on LO or HO; TA = +25°C; unless otherwise noted.
Bold values indicate –40°C ≤ TJ ≤ +125°C
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
Supply Current
IDD
VDD Quiescent Current
LI = HI = 0V
48
200
µA
IDDO
VDD Operating Current
f = 20kHz
136
300
µA
IHB
Total HB Quiescent Current
LI = HI = 0V or LI = 0V and HI = 5V
20
75
µA
IHBO
Total HB Operating Current
f = 20kHz
29
200
µA
IHBS
HB to VSS Quiescent Current
VHS = VHB = 90V
0.5
5
µA
0.8
V
Input (LI, HI)
VIL
Low-Level Input Voltage
VIH
High-Level Input Voltage
VHYS
Input Voltage Hysteresis
RI
Input Pull-Down Resistance
2.2
V
0.05
V
100
240
500
kΩ
4.0
4.4
4.9
V
Undervoltage Protection
VDDF
VDD Falling Threshold
VDDH
VDD Threshold Hysteresis
VHBF
HB Falling Threshold
VHBH
HB Threshold Hysteresis
Rising VDD Threshold; VDDR = VDDF + VDDH
0.21
4.0
4.4
V
4.9
V
Rising VHB Threshold; VHBR = VHBF + VHBH
0.23
V
IVDD-HB = 100µA
0.42
0.70
V
Ω
Bootstrap Diode
VDL
Low-Current Forward Voltage
VDH
High-Current Forward Voltage
IVDD-HB = 50mA
0.75
1.0
RD
Dynamic Resistance
IVDD-HB = 50mA
2.8
5.0
V
Notes:
1. Exceeding the absolute maximum ratings may damage the device.
2. The device is not guaranteed to function outside its operating ratings.
3. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF.
4. Specification s are for packaged product only.
June 25, 2013
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Micrel, Inc.
MIC4604
Electrical Characteristics(4) (Continued)
VDD = VHB = 12V; VSS = VHS = 0V; No load on LO or HO; TA = +25°C; unless otherwise noted.
Bold values indicate –40°C ≤ TJ ≤ +125°C
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
LO Gate Driver
VOLL
Low-Level Output Voltage
ILO = 50mA
0.17
0.4
V
VOHL
High-Level Output Voltage
ILO = −50mA, VOHL = VDD – VLO
0.25
1.0
V
IOHL
Peak Sink Current
VLO = 5V
1
A
IOLL
Peak Source Current
VLO = 5V
1
A
HO Gate Driver
VOLH
Low-Level Output Voltage
IHO = 50mA
0.2
0.6
V
VOHH
High-Level Output Voltage
IHO = −50mA, VOHH = VHB – VHO
0.22
1.0
V
IOHH
Peak Sink Current
VHO = 5V
1.5
A
IOLH
Peak Source Current
VHO = 5V
1
A
(5)
Switching Specifications
tLPHL
Lower Turn-Off Propagation Delay
(LI Falling to LO Falling)
37
75
ns
tHPHL
Upper Turn-Off Propagation Delay
(HI Falling to HO Falling)
34
75
ns
tLPLH
Lower Turn-On Propagation Delay
(LI Rising to LO Rising)
39
75
ns
tHPLH
Upper Turn-On Propagation Delay
(HI Rising to HO Rising)
33
75
ns
tRC/FC
Output Rise/Fall Time
CL = 1000pF
20
ns
tR/F
Output Rise/Fall Time (3V to 9V)
CL = 0.1µF
0.8
µs
tPW
Minimum Input Pulse Width that
Changes the Output
50
ns
tBS
Bootstrap Diode Turn-On or Turn-Off
Time
10
ns
Note:
5. Guaranteed by design. Not production tested.
June 25, 2013
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MIC4604
Timing Diagrams
Note:
6. All propagation delays are measured from the 50% voltage level.
Block Diagram
Figure 1. MIC4604 Block Diagram
June 25, 2013
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Micrel, Inc.
MIC4604
Typical Characteristics
Quiescent Current
vs. Input Voltage
T = -40°C
T = 25°C
60
40
T = 125°C
20
HS = 0V
Freq = 20kHz
HS = 0V
VHB = VDD
250
VHB OPERATING CURRENT (µA)
VDD OPERATING CURRENT (µA)
T = -40°C
T = 25°C
200
150
100
T = 125°C
50
6
8
10
12
14
4
16
6
8
12
10
14
20
T = -40°C
4
6
8
10
12
14
INPUT VOLTAGE (V)
Quiescent Current
vs. Temperature
VDD Operating Current
vs. Temperature
VHB Operating Current
vs. Temperature
VDD = 12V
60
40
VDD = 9V
HS = 0V
0
250
VDD = 16V
200
VDD = 12V
150
VDD = 9V
100
50
0
25
50
75
100
125
Freq = 20kHz
HS = 0V
VHB = VDD
40
VHB = 16V
35
30
25
VHB = 12V
20
VHB = 9V
15
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
VDD Operating Current
vs. Frequency
VHB Operating Current
vs. Frequency
Low Level Output Voltage
vs. Temperature
8
VHB OPERATING CURRENT (mA)
T = -40°C
6
T = 25°C
4
2
T = 125°C
0
HS = 0V
ILO, IHO = 50mA
HS = 0V
VHB = VDD = 12V
400
0.6
T = 125°C
T = 25°C
0.4
400
600
FREQUENCY (kHz)
June 25, 2013
800
1000
VDD = 12V
VDD = 9V
300
200
0.2
VDD = 16V
100
T = -40°C
0
0
200
125
500
0.8
HS = 0V
VHB = VDD =12V
16
45
Freq = 20kHz
HS = 0V
VHB = VDD
VHB OPERATING CURRENT (µA)
VDD OPERATING CURRENT (µA)
80
0
30
INPUT VOLTAGE (V)
VDD = 16V
-25
T = 25°C
16
300
-50
T = 125°C
40
INPUT VOLTAGE (V)
100
20
Freq = 20kHz
HS = 0V
VHB = VDD
50
10
0
4
VOLL, VOLH (mV)
QUIESCENT CURRENT (µA)
80
0
QUIESCENT CURRENT (µA)
60
300
100
VDD OPERATING (mA)
VHB Operating Current
vs. Input Voltage
VDD Operating Current
vs. Input Voltage
0
200
400
600
FREQUENCY (kHz)
6
800
1000
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
Revision 1.0
Micrel, Inc.
MIC4604
Typical Characteristics (Continued)
High Level Output Voltage
vs. Temperature
500
HS = 0V
HS = 0V
4.7
THRESHOLDS (V)
VDD = 12V
VDD = 9V
300
200
0.26
VHB Rising
HYSTERESIS (V)
400
4.6
VDD Rising
4.5
VDD Falling
4.4
VHB Hysteresis
0.24
0.22
0.20
VDD Hysteresis
VDD = 16V
100
VHB Falling
4.3
0
0.18
0.16
4.2
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Propagation Delay
vs. Input Voltage
Propagation Delay
vs. Temperature
80
100
-50
125
DELAY (ns)
50
tLPHL
50
35
50
75
100
125
HS = 0V
tLPLH
tLPHL
40
tHPHL
30
tHPHL
25
1000
VDD = VHB = 12V
HS = 0V
tLPLH
0
Bootstrap Diode I-V
Characteristics
60
TAMB = 25°C
HS = 0V
65
-25
TEMPERATURE (°C)
FORWARD CURRENT (mA)
VOHL, VOHH (mV)
0.28
4.8
HS = 0V
ILO ,IHO = -50mA
DELAY (ns)
UVLO Hysteresis
vs. Temperature
UVLO Thresholds
vs. Temperature
tHPLH
T = 25°C
100
T = 125°C
10
T = -40°C
1
tHPLH
20
20
4
6
8
10
12
14
16
INPUT VOLTAGE (V)
0.1
-50
-25
0
25
50
75
TEMPERATURE (°C)
100
125
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
FORWARD VOLTAGE (V)
Bootstrap Diode
Reverse Current
100
REVERSE CURRENT (µA)
HS = 0V
10
1
T = 125°C
0.1
T = 85°C
0.01
T = 25°C
0.001
0.0001
0
10
20
30
40
50
60
70
80
90 100
REVERSE VOLTAGE (V)
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Micrel, Inc.
MIC4604
Functional Description
The MIC4604 is a high-voltage, non-inverting, dual
MOSFET driver that is designed to independently drive
both high-side and low-side N-Channel MOSFETs. The
block diagram of the MIC4604 is shown in Figure 1.
Both drivers contain an input buffer with hysteresis, a
UVLO circuit, and an output buffer. The high-side output
buffer includes a high-speed level-shifting circuit that is
referenced to the HS pin. An internal diode is used as part
of a bootstrap circuit to provide the drive voltage for the
high-side output.
Startup and UVLO
The UVLO circuit forces the driver output low until the
supply voltage exceeds the UVLO threshold. The low-side
UVLO circuit monitors the voltage between the VDD and
VSS pins. The high-side UVLO circuit monitors the voltage
between the HB and HS pins. Hysteresis in the UVLO
circuit prevents noise and finite circuit impedance from
causing chatter during turn-on.
Figure 2. Low-Side Driver Block Diagram
High-Side Driver and Bootstrap Circuit
A block diagram of the high-side driver and bootstrap
circuit is shown in Figure 3. This driver is designed to drive
a floating N-channel MOSFET, whose source terminal is
referenced to the HS pin.
Input Stage
Both the HI and LI pins of the MIC4604 are referenced to
the VSS pin. The voltage state of the input signal does not
change the quiescent current draw of the driver.
The MIC4604 has a TTL-compatible input range and can
be used with input signals with amplitude less than the
supply voltage. The threshold level is independent of the
VDD supply voltage and there is no dependence between
IVDD and the input signal amplitude with the MIC4604. This
feature makes the MIC4604 an excellent level translator
that will drive high-threshold MOSFETs from a low-voltage
PWM IC.
Low-Side Driver
A block diagram of the low-side driver is shown in
Figure 2. The low-side driver is designed to drive a ground
(VSS pin) referenced N-channel MOSFET. Low driver
impedances allow the external MOSFET to be turned on
and off quickly. The rail-to-rail drive capability of the output
ensures a low RDsON from the external MOSFET.
Figure 3. High-Side Driver and Bootstrap Circuit Block
Diagram
A high level applied to LI pin causes the upper driver
MOSFET to turn on and VDD voltage is applied to the gate
of the external MOSFET. A low level on the LI pin turns off
the upper driver and turns on the low side driver to ground
the gate of the external MOSFET.
June 25, 2013
A low-power, high-speed, level-shifting circuit isolates the
low side (VSS pin) referenced circuitry from the high-side
(HS pin) referenced driver. Power to the high-side driver
and UVLO circuit is supplied by the bootstrap circuit while
the voltage level of the HS pin is shifted high.
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Micrel, Inc.
MIC4604
The bootstrap circuit consists of an internal diode and
external capacitor, CB. In a typical application, such as the
synchronous buck converter shown in Figure 4, the HS pin
is at ground potential while the low-side MOSFET is on.
The internal diode allows capacitor CB to charge up to
VDD-VF during this time (where VF is the forward voltage
drop of the internal diode). After the low-side MOSFET is
turned off and the HO pin turns on, the voltage across
capacitor CB is applied to the gate of the upper external
MOSFET. As the upper MOSFET turns on, voltage on the
HS pin rises with the source of the high-side MOSFET until
it reaches VIN. As the HS and HB pin rise, the internal
diode is reverse biased preventing capacitor CB from
discharging.
(total of 10.8V) to exceed the minimal VDD range. As an
additional benefit, the low 5.5V gate drive capability allows
a longer run time. This is because the Li-ion battery can
run down to 5.5V, which is just above its 4.8V minimum
recommended discharge voltage. This is also a benefit in
higher current power tools that use five or six cells. The
driver can be operated up to 16V to minimize the RDSON of
the MOSFETs and use as much of the discharge battery
pack as possible for a longer run time. For example, an
18V battery pack can be used to the lowest operating
discharge voltage of 13.5V.
Application Information
Power Dissipation Considerations
Power dissipation in the driver can be separated into three
areas:
Internal diode dissipation in the bootstrap circuit
•
Internal driver dissipation
•
Quiescent current dissipation used to supply the
internal logic and control functions.
Bootstrap Circuit Power Dissipation
Power dissipation of the internal bootstrap diode primarily
comes from the average charging current of the CB
capacitor multiplied by the forward voltage drop of the
diode. Secondary sources of diode power dissipation are
the reverse leakage current and reverse recovery effects
of the diode.
Figure 4. High-Side Driver and Bootstrap Circuit Block
Diagram
The average current drawn by repeated charging of the
high-side MOSFET is calculated by:
Programmable Gate Drive
The MIC4604 offers programmable gate drive, which
means the MOSFET gate drive (gate to source voltage)
equals the VDD voltage. This feature offers designers
flexibility in driving the MOSFETs. Different MOSFETs
require different VGS characteristics for optimum RDSON
performance. Typically, the higher the gate voltage (up to
16V), the lower the RDSON achieved. For example, a 4899
MOSFET can be driven to the ON state at 4.5V gate
voltage but RDSON is 7.5mΩ. If driven to 10V gate voltage,
RDSON is 4.5mΩ. In low-current applications, the losses due
to RDSON are minimal, but in high-current applications such
as power hand tools, the difference in RDSON can cut into
the efficiency budget.
IF( AVE ) = Q gate × f S
Eq. 1
Where:
Qgate = total gate charge at VHB
fs = gate drive switching frequency
The average power dissipated by the forward voltage drop
of the diode equals:
Pdiode fwd = IF( AVE ) × VF
Eq. 2
Where:
VF = diode forward voltage drop
The value of VF should be taken at the peak current
through the diode; however, this current is difficult to
calculate because of differences in source impedances.
The peak current can either be measured or the value of
VF at the average current can be used, which will yield a
good approximation of diode power dissipation.
In portable hand tools and other battery-powered
applications, the MIC4604 offers the ability to drive motors
at a lower voltage compared to the traditional MOSFET
drivers because of the wide VDD range (5.5V to 16V).
Traditional MOSFET drivers typically require a VDD
greater than 9V. The MIC4604 drives a motor using only
two Li-ion batteries (total 7.2V) compared to traditional
MOSFET drivers which will require at least three cells
June 25, 2013
•
The reverse leakage current of the internal bootstrap diode
is typically 2µA at a reverse voltage of 85V at 125C. Power
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MIC4604
dissipation due to reverse leakage is typically much less
than 1mW and can be ignored.
Reverse recovery time is the time required for the injected
minority carriers to be swept away from the depletion
region during turn-off of the diode. Power dissipation due
to reverse recovery can be calculated by computing the
average reverse current due to reverse recovery charge
times the reverse voltage across the diode. The average
reverse current and power dissipation due to reverse
recovery can be estimated by:
IRR( AVE ) = 0.5 × IRRM × t rr × f S
Pdiode RR = IRR( AVE ) × VREV
Eq. 3
Where:
IRRM = peak reverse recovery current
trr = reverse recovery time
The total diode power dissipation is:
Pdiode total = Pdiode fwd + Pdiode RR
Eq. 4
Figure 5. Optional Bootstrap Diode
An optional external bootstrap diode may be used instead
of the internal diode (Figure 5). An external diode may be
useful if high gate charge MOSFETs are being driven and
the power dissipation of the internal diode is contributing to
excessive die temperatures. The voltage drop of the
external diode must be less than the internal diode for this
option to work. The reverse voltage across the diode will
be equal to the input voltage minus the VDD supply
voltage. The above equations can be used to calculate
power dissipation in the external diode; however, if the
external diode has significant reverse leakage current, the
power dissipated in that diode due to reverse leakage can
be calculated as:
Pdiode REV = IR × VREV × (1 − D)
Gate Driver Power Dissipation
Power dissipation in the output driver stage is mainly
caused by charging and discharging the gate to source
and gate to drain capacitance of the external MOSFET.
Figure 6 shows a simplified equivalent circuit of the
MIC4604 driving an external MOSFET.
Eq. 5
Where:
IR = reverse current flow at VREV and TJ
VREV = diode reverse voltage
D = duty cycle = tON × fS
The on-time is the time the high-side switch is conducting.
In most topologies, the diode is reverse biased during the
switching cycle off-time.
Figure 6. MIC4604 Driving an External MOSFET
Dissipation during the External MOSFET Turn-On
Energy from capacitor CB is used to charge up the input
capacitance of the MOSFET (Cgd and Cgs). The energy
delivered to the MOSFET is dissipated in the three
resistive components, Ron, Rg and Rg_fet. Ron is the on
resistance of the upper driver MOSFET in the MIC4604.
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MIC4604
Rg is the series resistor (if any) between the driver IC and
the MOSFET. Rg_fet is the gate resistance of the
MOSFET. Rg_fet is usually listed in the power MOSFET’s
specifications. The ESR of capacitor CB and the resistance
of the connecting etch can be ignored since they are much
less than Ron and Rg_fet.
The same energy is dissipated by Roff, Rg and Rg_fet
when the driver IC turns the MOSFET off. Assuming Ron
is approximately equal to Roff, the total energy and power
dissipated by the resistive drive elements is:
Edriver = Qg × Vgs
and
Pdriver = Qg × Vgs × fs
The effective capacitances of Cgd and Cgs are difficult to
calculate because they vary non-linearly with Id, Vgs, and
Vds. Fortunately, most power MOSFET specifications
include a typical graph of total gate charge versus Vgs.
Figure 7 shows a typical gate charge curve for an arbitrary
power MOSFET. This chart shows that for a gate voltage
of 10V, the MOSFET requires about 23.5nC of charge.
The energy dissipated by the resistive components of the
gate drive circuit during turn-on is calculated as:
E=
1
2
× Ciss × Vgs
Where:
Edriver = energy dissipated per switching cycle
Pdriver = power dissipated per switching cycle
Qg = total gate charge at Vgs
Vgs = gate to source voltage on the MOSFET
fs = switching frequency of the gate drive circuit
The power dissipated inside the MIC4604 is equal to the
ratio of Ron and Roff to the external resistive losses in Rg
and Rg_fet. Letting Ron = Roff, the power dissipated in the
MIC4604 due to driving the external MOSFET is:
2
but
Q = C× V
Eq. 6
so
E = 1/2 × Qg × Vgs
Pdiss drive = Pdriver
Where
Ciss = total gate capacitance of the MOSFET
VGS - Gate-to-Source Voltage (V)
Ron
Ron + Rg + Rg _ fet
Eq. 8
Supply Current Power Dissipation
Power is dissipated in the MIC4604 even if nothing is
being driven. The supply current is drawn by the bias for
the internal circuitry, the level shifting circuitry, and shootthrough current in the output drivers. The supply current is
proportional to operating frequency and the VDD and VHB
voltages. The typical characteristic graphs show how
supply current varies with switching frequency and supply
voltage.
Gate Charge
10
VDS = 50V
ID = 6.9A
8
Eq. 7
6
The power dissipated by the MIC4604 due to supply
current is
4
2
Pdiss sup ply = VDD × IDD + VHB × IHB
Eq. 9
0
0
5
10
15
20
Total Power Dissipation and Thermal Considerations
Total power dissipation in the MIC4604 is equal to the
power dissipation caused by driving the external
MOSFETs, the supply current and the internal bootstrap
diode.
25
Qg - Total Gate Charge (nC)
Figure 7. Typical Gate Charge vs. VGS
Pdiss total = Pdiss sup ply + Pdiss drive + Pdiode total
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The die temperature can be calculated after the total
power dissipation is known.
TJ = TA + Pdiss total × θ JA
minimum capacitance value should be increased if low
voltage capacitors are used because even good quality
dielectric capacitors, such as X5R, will lose 40% to 70% of
their capacitance value at the rated voltage.
Eq. 11
Placement of the decoupling capacitors is critical. The
bypass capacitor for VDD should be placed as close as
possible between the VDD and VSS pins. The bypass
capacitor (CB) for the HB supply pin must be located as
close as possible between the HB and HS pins. The etch
connections must be short, wide, and direct. The use of a
ground plane to minimize connection impedance is
recommended. Refer to the section on Grounding,
Component Placement and Circuit Layout for more
information.
Where:
TA = maximum ambient temperature
TJ = junction temperature (°C)
Pdisstotal = power dissipation of the MIC4604
θJA = thermal resistance from junction to ambient air
Propagation Delay and Other Timing Considerations
Propagation delay and signal timing are important
considerations. Many power supply topologies use two
switching MOSFETs operating 180° out of phase from
each other. These MOSFETs must not be on at the same
time or a short circuit will occur, causing high peak
currents and higher power dissipation in the MOSFETs.
The MIC4604 output gate drivers are not designed with
anti-shoot-through protection circuitry. The output drive
signals simply follow the inputs. The power supply design
must include timing delays (dead-time) between the input
signals to prevent shoot-through.
The voltage on the bootstrap capacitor drops each time it
delivers charge to turn on the MOSFET. The voltage drop
depends on the gate charge required by the MOSFET.
Most MOSFET specifications specify gate charge versus
Vgs voltage. Based on this information and a
recommended ΔVHB of less than 0.1V, the minimum value
of bootstrap capacitance is calculated as:
CB ≥
Make sure the input signal pulse width is greater than the
minimum specified pulse width. An input signal that is less
than the minimum pulse width may result in no output
pulse or an output pulse whose width is significantly less
than the input.
∆VHB
Eq. 12
Where:
Qgate = total gate charge at VHB
∆VHB = voltage drop at the HB pin
The maximum duty cycle (ratio of high side on-time to
switching period) is controlled by the minimum pulse width
of the low side and by the time required for the CB
capacitor to charge during the off-time. Adequate time
must be allowed for the CB capacitor to charge up before
the high-side driver is turned on.
The decoupling capacitor for the VDD input may be
calculated in with the same formula; however, the two
capacitors are usually equal in value.
Grounding, Component Placement and Circuit Layout
Nanosecond switching speeds and ampere peak currents
in and around the MIC4604 drivers require proper
placement and trace routing of all components. Improper
placement may cause degraded noise immunity, false
switching, excessive ringing, or circuit latch-up.
Decoupling and Bootstrap Capacitor Selection
Decoupling capacitors are required for both the low side
(VDD) and high side (HB) supply pins. These capacitors
supply the charge necessary to drive the external
MOSFETs and also minimize the voltage ripple on these
pins. The capacitor from HB to HS has two functions: it
provides decoupling for the high-side circuitry and also
provides current to the high-side circuit while the high-side
external MOSFET is on. Ceramic capacitors are
recommended because of their low impedance and small
size. Z5U type ceramic capacitor dielectrics are not
recommended because of the large change in capacitance
over temperature and voltage. A minimum value of 0.1µF
is required for each of the capacitors, regardless of the
MOSFETs being driven. Larger MOSFETs may require
larger capacitance values for proper operation. The
voltage rating of the capacitors depends on the supply
voltage, ambient temperature and the voltage derating
used for reliability. 25V rated X5R or X7R ceramic
capacitors are recommended for most applications. The
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Q gate
Figure 8 shows the critical current paths when the driver
outputs go high and turn on the external MOSFETs. It also
helps demonstrate the need for a low impedance ground
plane. Charge needed to turn-on the MOSFET gates
comes from the decoupling capacitors CVDD and CB.
Current in the low-side gate driver flows from CVDD through
the internal driver, into the MOSFET gate, and out the
source. The return connection back to the decoupling
capacitor is made through the ground plane. Any
inductance or resistance in the ground return path causes
a voltage spike or ringing to appear on the source of the
MOSFET. This voltage works against the gate drive
voltage and can either slow down or turn off the MOSFET
during the period when it should be turned on.
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Current in the high-side driver is sourced from capacitor CB
and flows into the HB pin and out the HO pin, into the gate
of the high side MOSFET. The return path for the current
is from the source of the MOSFET and back to capacitor
CB. The high-side circuit return path usually does not have
a low-impedance ground plane so the etch connections in
this critical path should be short and wide to minimize
parasitic inductance. As with the low-side circuit,
impedance between the MOSFET source and the
decoupling capacitor causes negative voltage feedback
that fights the turn-on of the MOSFET.
It is important to note that capacitor CB must be placed
close to the HB and HS pins. This capacitor not only
provides all the energy for turn-on but it must also keep HB
pin noise and ripple low for proper operation of the highside drive circuitry.
Figure 9. Turn-Off Current Paths
DC Motor Applications
MIC4604 MOSFET drivers are widely used in DC motor
applications. They address brushed motors in both halfbridge and full-bridge motor topologies as well as 3-phase
brushless motors. As shown in Figure 10, Figure 11, and
Figure 12, the drivers switch the MOSFETs at variable
duty cycles that modulate the voltage to control motor
speed. In the half-bridge topology, the motor turns in one
direction only. The full-bridge topology allows for
bidirectional control. 3-Phase motors are more efficient
compared to the brushed motors but require three halfbridge switches and additional circuitry to sense the
position of the rotor.
The MIC4604 85V operating voltage offers the engineer
margin to protect against Back Electromotive Force (EMF)
which is a voltage spike caused by the rotation of the rotor.
The Back EMF voltage amplitude depends on the speed of
the rotation. It is good practice to have at least twice the
HV voltage of the motor supply. 85V is plenty of margin for
12V, 24V, and 40V motors.
Figure 8. Turn-On Current Paths
Figure 9 shows the critical current paths when the driver
outputs go low and turn off the external MOSFETs. Short,
low-impedance connections are important during turn-off
for the same reasons given in the turn-on explanation.
Current flowing through the internal diode replenishes
charge in the bootstrap capacitor, CB.
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Figure 10. Half Bridge DC Motor
Figure 12. 3-Phase Brushless DC Motor Driver – 24V Block
Diagram
The MIC4604 is offered in a small 2.5mm × 2.5mm TDFN
package for applications that are space constrained and
an SOIC-8 package for ease of manufacturing. The motor
trend is to put the motor control circuit inside the motor
casing, which requires small packaging because of the
size of the motor.
The MIC4604 offers low UVLO threshold and
programmable gate drive, which allows for longer
operation time in battery operated motors such as power
hand tools.
Cross conduction across the half bridge can cause
catastrophic failure in a motor application. Engineers
typically add dead time between states that switch
between high input and low input to ensure that the lowside MOSFET completely turns off before the high-side
MOSFET turns on and vice versa. The dead time depends
on the MOSFET used in the application, but 200ns is
typical for most motor applications.
Power Inverter
Power inverters are used to supply AC loads from a DC
operated battery system, mainly during power failure. The
battery voltage can be 12VDC, 24VDC, or up to 36VDC,
depending on the power requirements. There two popular
conversion methods, Type I and Type II, that convert the
battery energy to AC line voltage (110VAC or 230VAC).
Figure 11. Full Bridge DC Motor
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Figure 13. Type I Inverter Topology
As shown in Figure 13, Type I is a dual-stage topology
where line voltage is converted to DC through a
transformer to charge the storage batteries. When a power
failure is detected, the stored DC energy is converted to
AC through another transformer to drive the AC loads
connected to the inverter output. This method is simplest
to design but tends to be bulky and expensive because it
uses two transformers.
•
Use a ground plane to minimize parasitic inductance
and impedance of the return paths. The MIC4604 is
capable of greater than 1A peak currents and any
impedance between the MIC4604, the decoupling
capacitors, and the external MOSFET will degrade the
performance of the driver.
•
Trace out the high di/dt and dv/dt paths, as shown in
Figure 14 and Figure 15, and minimize etch length and
loop area for these connections. Minimizing these
parameters decreases the parasitic inductance and
the radiated EMI generated by fast rise and fall times.
A typical layout of a synchronous Buck converter power
stage (Figure 14) is shown in Figure 15 .
Type II is a single-stage topology that uses only one
transformer to charge the bank of batteries to store the
energy. During a power outage, the same transformer is
used to power the line voltage. The Type II switches at a
higher frequency compared to the Type I topology to
maintain a small transformer size.
Both types require a half bridge or full bridge topology to
boost the DC to AC. This application can use two
MIC4604s. The 85V operating voltage offers enough
margin to address all of the available banks of batteries
commonly used in inverter applications. The 85V operating
voltage allows designers to increase the bank of batteries
up to 72V, if desired. The MIC4604 can sink as much as
1A, which is enough current to overcome the MOSFET’s
input capacitance and switch the MOSFET up to 50kHz.
This makes the MIC4604 an ideal solution for inverter
applications.
Figure 14. Synchronous Buck Converter Power Stage
The high-side MOSFET drain connects to the input supply
voltage (drain) and the source connects to the switching
node. The low-side MOSFET drain connects to the
switching node and its source is connected to ground. The
buck converter output inductor (not shown) connects to the
switching node. The high-side drive trace, HO, is routed on
top of its return trace, HS, to minimize loop area and
parasitic inductance. The low-side drive trace LO is routed
over the ground plane to minimize the impedance of that
current path. The decoupling capacitors, CB and CVDD, are
placed to minimize etch length between the capacitors and
their respective pins. This close placement is necessary to
efficiently charge capacitor CB when the HS node is low.
All traces are 0.025in wide or greater to reduce
impedance. CIN is used to decouple the high current path
through the MOSFETs.
As with all half bridge and full bridge topologies, cross
conduction is a concern to inverter manufactures because
it can cause catastrophic failure. This can be remedied by
adding the appropriate dead time between transitioning
from the high-side MOSFET to the low-side MOSFET and
vice versa.
Layout Guidelines
Use the following layout guidelines for optimum circuit
performance:
•
Place the VDD and HB bypass capacitors close to the
supply and ground pins. It is critical that the etch
length between the high side decoupling capacitor (CB)
and the HB and HS pins be minimized to reduce lead
inductance.
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MIC4604
Top Side
Bottom Side
Figure 15. Typical Layout of a Synchronous Buck Converter Power Stage
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Package Information and Recommended Land Pattern(7)
8-Pin SOIC (M)
Note:
7. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.
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MIC4604
Package Information and Recommended Land Pattern (Continued)(7)
2.5mm × 2.5mm 10-Pin TDFN (MT)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
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whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
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© 2013 Micrel, Incorporated.
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