Micrel MIC4104 100v half bridge mosfet drivers 3/2a sinking/sourcing current Datasheet

MIC4103/4104
100V Half Bridge MOSFET Drivers
3/2A Sinking/Sourcing Current
PRELIMINARY
General Description
Features
The MIC4103 and MIC4104 are high frequency, 100V Half
Bridge MOSFET drivers with faster turn-off characteristics
than the MIC4100 and MIC4101 drivers. They feature fast
24ns propagation delay times and 6ns driver fall times.
The low-side and high-side gate drivers are independently
controlled and matched to within 3ns typical. The MIC4103
has CMOS input thresholds and the MIC4104 has TTL
input thresholds. The MIC4103/4 include a high voltage
internal diode that charges the high-side gate drive
bootstrap capacitor.
A robust, high-speed, and low power level shifter provides
clean level transitions to the high side output. The robust
operation of the MIC4103/4 ensures 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 MIC4103 and MIC4104 are available in an 8-pin SOIC
and 8-pin 3mm × 3mm MLF® package with a operating
junction temperature range of –40°C to +125°C.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
• Asymmetrical, low impedance outputs drive 1000pF
load with 10ns rise times and 6ns fall times
• Bootstrap supply max voltage to 118V DC
• Supply voltage up to 16V
• Drives high- and low-side N-Channel MOSFETs with
independent inputs
• CMOS input thresholds (MIC4103)
• TTL input thresholds (MIC4104)
• On-chip bootstrap diode
• Fast 24ns propagation times
• Low power consumption
• Supply under-voltage protection
• Typical 2.5Ω pull up and 1.25Ω pull down output driver
resistance
• –40°C to +125°C junction temperature range
Applications
• High voltage buck converters
• Full- and half-bridge power topologies
• Active clamp forward converter
• Two switch forward topologies
• Interface to digital controllers
___________________________________________________________________________________________________________
Typical Application
100V Buck Regulator Solution
MLF and MicroLead Frame is a registered trademark of Amkor Technologies, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
October 2007
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MIC4103/4104
Ordering Information
Part Number
Input
Junction Temp. Range
Package
MIC4103YM
CMOS
–40° to +125°C
8-Pin SOIC
MIC4104YM
TTL
–40° to +125°C
8-Pin SOIC
MIC4103YML (coming soon)
CMOS
–40° to +125°C
8-Pin 3x3 MLF®
MIC4104YML (coming soon)
TTL
–40° to +125°C
8-Pin 3x3 MLF®
Pin Configuration
8-Pin 3mm × 3mm MLF® (ML)
8-Pin SOIC (M)
Pin Description
Pin Number
Pin Name
1
VDD
2
HB
High-Side Bootstrap supply. External bootstrap capacitor is required. Connect
positive side of bootstrap capacitor to this pin. Bootstrap diode is on-chip.
3
HO
High-Side Output. Connect to gate of High-Side power MOSFET.
4
HS
High-Side Source connection. Connect to source of High-Side power MOSFET.
Connect negative side of bootstrap capacitor to this pin.
5
HI
High-Side input.
6
7
VSS
8
LO
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LI
Pin Function
Positive Supply to lower gate drivers. Decouple this pin to VSS (Pin 7).
Bootstrap diode connected to HB (pin 2).
Low-Side input.
Chip negative supply, generally will be ground.
Low-Side Output. Connect to gate of Low-Side power MOSFET.
2
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MIC4103/4104
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VDD, VHB – VHS) ...................... -0.3V to 18V
Input Voltages (VLI, VHI) ......................... -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 110V
Voltage on HB ..............................................................118V
Average Current in VDD to HB Diode.......................100mA
Junction Temperature (TJ) ........................–55°C to +150°C
Storage Temperature (Ts) ..........................-60°C to +150°C
ESD Rating..........................................................See note 3
Supply Voltage (VDD)........................................ +9V to +16V
Voltage on HS ................................................... -1V to 100V
Voltage on HS (repetitive transient) .................. -5V to 105V
HS Slew Rate............................................................ 50V/ns
Voltage on HB ...................................VHS + 8V to VHS + 16V
and............................................ VDD - 1V to VDD + 100V
Junction Temperature (TJ) ........................ –40°C to +125°C
Junction Thermal Resistance
SOIC-8L (θJA)...................................................140°C/W
3mm × 3mm MLF® ............................................tbd°C/W
Electrical Characteristics(4)
VDD = VHB = 12V; VSS = VHS = 0V; No load on LO or HO; TA = 25°C; unless noted. Bold values indicate –40°C< TJ < +125°C.
Symbol
Parameter
Condition
Min
Typ
Max
Units
40
150
200
µA
3.0
4.0
mA
25
150
200
µA
1.5
2.5
3
mA
0.05
1
30
µA
Supply Current
IDD
VDD Quiescent Current
LI = HI = 0V
IDDO
VDD Operating Current
f = 500kHz
IHB
Total HB Quiescent Current
LI = HI = 0V
IHBO
Total HB Operating Current
f = 500kHz
IHBS
HB to VSS Current, Quiescent
VHS = VHB = 110V
Input Pins: MIC4103 (CMOS Input )
4
3
VIL
Low Level Input Voltage
Threshold
VIH
High Level Input Voltage
Threshold
5.7
VIHYS
Input Voltage Hysteresis
0.4
RI
Input Pulldown Resistance
5.3
100
200
0.8
1.5
V
7
8
V
V
500
kΩ
Input Pins: MIC4104 (TTL Input )
VIL
Low Level Input Voltage
Threshold
VIH
High Level Input Voltage
Threshold
RI
Input Pulldown Resistance
V
1.5
2.2
V
100
200
500
kΩ
6.5
7.4
8.0
V
6.0
7.0
8.0
V
Under Voltage Protection
VDDR
VDD Rising Threshold
VDDH
VDD Threshold Hysteresis
VHBR
HB Rising Threshold
VHBH
HB Threshold Hysteresis
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0.5
0.4
3
V
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Symbol
MIC4103/4104
Parameter
Condition
Min
Typ
Max
Units
0.4
0.55
0.70
V
0.7
0.8
1.0
V
1.0
1.5
2.0
Ω
0.18
0.3
0.4
V
0.25
0.3
0.45
V
Bootstrap Diode
VDL
Low-Current Forward Voltage
IVDD-HB = 100µA
VDH
High-Current Forward Voltage
IVDD-HB = 100mA
RD
Dynamic Resistance
IVDD-HB = 100mA
LO Gate Driver
VOLL
Low Level Output Voltage
ILO = 160mA
VOHL
High Level Output Voltage
ILO = -100mA, VOHL = VDD - VLO
IOHL
Peak Sink Current
VLO = 0V
3
A
IOLL
Peak Source Current
VLO = 12V
2
A
HO Gate Driver
0.22
0.3
0.4
V
0.25
0.3
0.45
V
VOLH
Low Level Output Voltage
IHO = 160mA
VOHH
High Level Output Voltage
IHO = -100mA, VOHH = VHB – VHO
IOHH
Peak Sink Current
VHO = 0V
3
A
IOLH
Peak Source Current
VHO = 12V
2
A
Switching Specifications
tLPHL
Lower Turn-Off Propagation
Delay (LI Falling to LO Falling)
(MIC4103)
24
45
ns
tHPHL
Upper Turn-Off Propagation
Delay (HI Falling to HO Falling)
(MIC4103)
24
45
ns
tLPLH
Lower Turn-On Propagation
Delay (LI Rising to LO Rising)
(MIC4103)
24
45
ns
tHPLH
Upper Turn-On Propagation
Delay (HI Rising to HO Rising)
(MIC4103)
24
45
ns
tLPHL
Lower Turn-Off Propagation
Delay (LI Falling to LO Falling)
(MIC4104)
24
45
ns
tHPHL
Upper Turn-Off Propagation
Delay (HI Falling to HO Falling)
(MIC4104)
24
45
ns
tLPLH
Lower Turn-On Propagation
Delay (LI Rising to LO Rising)
(MIC4104)
24
45
ns
tHPLH
Upper Turn-On Propagation
Delay (HI Rising to HO Rising)
(MIC4104)
24
45
ns
tMON
Delay Matching: Lower Turn-On
and Upper Turn-Off
3
8
10
ns
tMOFF
Delay Matching: Lower Turn-Off
and Upper Turn-On
3
8
10
ns
tRC
Output Rise Time
CL = 1000pF
10
ns
tFC
Output Fall Time
CL = 1000pF
6
ns
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Symbol
MIC4103/4104
Parameter
Condition
Min
Typ
Max
Units
0.4
0.6
0.8
µs
0.2
0.3
0.4
µs
50
ns
Switching Specifications (cont.)
tR
Output Rise Time (3V to 9V)
CL = 0.1µF
tF
Output Fall Time (3V to 9V)
CL = 0.1µF
tPW
Minimum Input Pulse Width that
Changes the Output
Note 6
tBS
Bootstrap Diode Turn-On or
Turn-Off Time
10
ns
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
4. Specification for packaged product only.
5. All voltages relative to pin 7, VSS unless otherwise specified
6. Guaranteed by design. Not production tested.
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Timing Diagrams
Note: All propagation delays are measured from the 50% voltage level.
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Typical Characteristics
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Typical Characteristics
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Functional Characteristics
Figure 1. MIC4103/4 Functional Block Diagram
Functional Description
where the input signal is noisy or where the input signal
swings the full range of voltage (from VDD to GND). There
is typically 400mV of hysteresis on the input pins
throughout the VDD range. The hysteresis improves noise
immunity and prevents input signals with slow rise times
from falsely triggering the output. The threshold voltage of
the MIC4103 varies proportionally with the VDD supply
voltage.
The MIC4103 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 MIC4103 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.
The amplitude of the input signal affects the VDD supply
current. Vin voltages that are a diode drop less than the
VDD supply voltage will cause an increase in the VDD pin
current. The graph in Figure 2 shows the typical
dependence between IVDD and Vin for Vdd=12V.
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.
Input Stage
The MIC4103 and MIC4104 have different input stages,
which lets these parts cover a wide range of driver
applications. Both the HI and LI pins are referenced to the
VSS pin.
The MIC4103 has a high impedance, CMOS compatible
input threshold and is recommended for applications
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Figure 2. MIC4103 Supply Current vs. Input Voltage
The MIC4104 has a TTL compatible input range and is
recommended for use with inputs signals whose amplitude
is 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 MIC4104. This feature makes the MIC4104 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
3. 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 full enhancement of the external MOSFET.
Figure 4. High-Side Driver and Bootstrap Circuit Block
Diagram
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.
A high level applied to LI pin causes the upper driver FET
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.
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 5, 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-VD during this time (where VD 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.
Vdd
LO
External
FET
Vss
CB
CVDD
Figure 3. Low-Side Driver Block Diagram
HI
High-Side Driver and Bootstrap Circuit
A block diagram of the high-side driver and bootstrap
circuit is shown in Figure 4. This driver is designed to drive
a floating N-channel MOSFET, whose source terminal is
referenced to the HS pin.
Vin
HB
Vdd
Q1
Level
shift
Lout
HO
HS
LI
Q2
LO
Vss
Figure 5. High-Side Driver and Bootstrap Circuit
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Application Information
The total diode power dissipation is:
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.
Pdiode total = Pdiode fwd + Pdiode RR
An optional external bootstrap diode may be used instead
of the internal diode (Figure 6). 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.
A 100V Schottky diode will work for most 72Vinput telecom
applications. 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:
Bootstrap Circuit Power Dissipation
Power dissipation of the internal bootstrap diode primarily
comes from the average charging current of the CB
capacitor times 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.
The average current drawn by repeated charging of the
high-side MOSFET is calculated by:
Pdiode REV = I R × VREV × (1 − D )
where : IR = Reverse current flow at VREV and TJ
I F ( AVE ) = Qgate × fS
where : Q gate = Total Gate Charge at VHB
fS = gate drive switching frequency
VREV = Diode Reverse Voltage
D = Duty Cycle = t ON / fS
fs = switching frequency of the power supply
The average power dissipated by the forward voltage drop
of the diode equals:
The on-time is the time the high-side switch is conducting.
In most power supply topologies, the diode is reverse
biased during the switching cycle off-time.
Pdiode fwd = I F ( AVE ) × VF
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 and will yield a good
approximation of diode power dissipation.
CB
HB
Vdd
HI
The reverse leakage current of the internal bootstrap diode
is typically 11µA at a reverse voltage of 100V and 125°C.
Power dissipation due to reverse leakage is typically much
less than 1mW and can be ignored.
Vin
Level
shift
HO
HS
LI
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:
LO
Vss
Figure 6. Optional Bootstrap Diode
I RR ( AVE ) = 0.5 × I RRM × t rr × fS
Pdiode RR = I RR ( AVE ) × VREV
Gate Driver Power Dissipation
Power dissipation in the output driver stage is mainly
caused by charging and discharging the gate to source
where : IRRM = Peak Reverse Recovery Current
t rr = Reverse Recovery Time
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MIC4103/4104
and gate to drain capacitance of the external MOSFET.
Figure 7 shows a simplified equivalent circuit of the
MIC4103 driving an external MOSFET.
External
FET
HB
Vdd
Cgd
Ron
CB
HO
Rg
Roff
Rg_fet
Cgs
HS
Figure 8. Typical Gate Charge vs. VGS
Figure 7. MIC4103 Driving an External MOSFET
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:
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 MIC4103.
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 trace can be ignored since they are
much less than RON and RG_FET.
Edriver = QG × VGS
and
Pdriver = QG × VGS × fs
where
Edriver is the energy dissipated per switching cycle
Pdriver is the power dissipated by switching the MOSFET on and off
QG is the total gate charge at Vgs
VGS is the gate to source voltage on the MOSFET
fs is the switching frequency of the gate drive circuit
The effective capacitance of CGD and CGS is difficult to
calculate since they vary non-linearly with ID, VGS, and VDS.
Fortunately, most power MOSFET specifications include a
typical graph of total gate charge vs. VGS. Figure 8 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
The power dissipated inside the MIC4103/4 is equal to the
ratio of RON & ROFF to the external resistive losses in RG
and RG_FET. Letting RON =ROFF, the power dissipated in the
MIC4103 due to driving the external MOSFET is:
Pdiss drive = Pdriver
RON
RON
+ RG + RG _ FET
Supply Current Power Dissipation
Power is dissipated in the MIC4103 even if there is nothing
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.
× Ciss × Vgs 2
but
Q = C× V
so
E = 1/2 × Qg × Vgs
where
Ciss is the total gate capacitance of the MOSFET
The power dissipated by the MIC4103 due to supply
current is:
Pdiss sup ply = VDD × I DD + VHB × I HB
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MIC4103/4104
must be allowed for the CB capacitor to charge up before
the high-side driver is turned on.
Total power dissipation and Thermal Considerations
Total power dissipation in the MIC4103 or MIC4104 is
equal to the power dissipation caused by driving the
external MOSFETs, the supply current, and the internal
bootstrap diode.
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 as well as minimize the voltage ripple on these
pins. The capacitor from HB to HS serves double duty by
providing decoupling for the high-side circuitry as well as
providing 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 due to the large change in capacitance over
temperature and voltage. A minimum value of 0.1uf 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
minimum capacitance value should be increased if low
voltage capacitors are used since even good quality
dielectric capacitors, such as X5R, will lose 40% to 70% of
their capacitance value at the rated voltage.
Pdiss total = Pdiss supply + Pdiss drive + Pdiode total
The die temperature may be calculated once the total
power dissipation is known.
TJ = T A + Pdiss total × θ JA
where :
TA is the maximum ambient temperature
TJ is the junction temperature (°C)
Pdisstotal is the power dissipation of the MIC4103/4
θJC is the thermal resistance from junction to ambient air (°C/W)
Propagation Delay and Delay Matching and other
Timing Considerations
Propagation delay and signal timing is an important
consideration in a high performance power supply. The
MIC4103 is designed not only to minimize propagation
delay but to minimize the mismatch in delay between the
high-side and low-side drivers.
Fast propagation delay between the input and output drive
waveform is desirable. It improves overcurrent protection
by decreasing the response time between the control
signal and the MOSFET gate drive. Minimizing
propagation delay also minimizes phase shift errors in
power supplies with wide bandwidth control loops.
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 bootstrap
capacitor (CB) for the HB supply pin must be located as
close as possible between the HB and HS pins. The trace
connections must be short, wide, and direct. The use of a
ground plane to minimize connection impedance is
recommended. Refer to the section on layout and
component placement for more information.
Many power supply topologies use two switching
MOSFETs operating 180º 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 MIC4103
and MIC4104 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 MIC4103 &
MIC4104 drivers specify delay matching between the two
drivers to help improve power supply performance by
reducing the amount of dead-time required between the
input signals.
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 vs. Vgs
voltage. Based on this information and a recommended
∆VHB of less than 0.1V, the minimum value of bootstrap
capacitance is calculated as:
CB ≥
∆VHB
where : Q gate = Total Gate Charge at VHB
Care must be taken to insure 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.
∆ HB = Voltage drop at the HB pin
The decoupling capacitor for the Vdd input may be
calculated with the same formula, however, the two
capacitors are usually equal in value.
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
October 2007
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Grounding, Component Placement, and Circuit Layout
Nanosecond switching speeds and ampere peak currents
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low impedance connections are important during turn-off
for the same reasons given in the turn-on explanation.
Remember that during turn-off current flowing through the
internal diode replenishes charge in the bootstrap
capacitor, CB.
in and around the MIC4103 and MIC4104 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.
Figure 9 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 where it should be turned on.
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 trace 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
which fights the turn-on of the MOSFET.
Figure 10. Turn-Off Current Paths
The following circuit guidelines should be adhered to for
optimum circuit performance:
1. The VDD and HB bypass capacitors must be
placed close to the supply and ground pins. It is
critical that the trace length between the high side
decoupling capacitor (CB) and the HB & HS pins
be minimized to reduce trace inductance.
2. A ground plane should be used to minimize
parasitic inductance and impedance of the return
paths. The MIC4103 is capable of greater than 2A
peak currents and any impedance between the
MIC4103, the decoupling capacitors, and the
external MOSFET will degrade the performance of
the driver.
3. Trace out the high di/dt and dv/dt paths, as shown
in Figures 9 and 10 and minimize trace 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.
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.
Low -side drive turn-on
current path
LO
Vdd
gnd
plane
CVdd
HB
Vss
HO
CB
HS
LI
Level
shift
gnd
plane
HI
High-side drive turn-on
current path
Figure 9. Turn-On Current Paths
Figure 10 shows the critical current paths when the driver
outputs go low and turn off the external MOSFETs. Short,
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MIC4103/4104
CB
CVDD
HI
A typical layout of a synchronous Buck converter power
stage (Figure 11) is shown in Figure 12.
The circuit is configured as a synchronous buck power
stage. The high-side MOSFET drain connects to the input
supply voltage 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) would connect
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 which minimizes the
impedance of that current path. The decoupling capacitors,
CB and CVDD are placed to minimize trace 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 0.025” wide or
greater to reduce impedance. Cin is used to decouple the
high current path through the MOSFETs.
Vin
HB
Vdd
Level
shift
HO
HS
High-Side
Fet
HS (switch) Node
Low-Side Fet
LI
Cin
LO
MIC4103
Vss
Figure 11. Synchronous Buck Converter Power Stage
Top Side
Bottom Side
Figure 12. Typical Layout of a Synchronous Buck Converter Power Stage
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MIC4103/4104
Package Information
8-Pin SOIC (M)
®
8-Pin MLF (ML)
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M9999-100107-B
Micrel
MIC4103/4104
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
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2006 Micrel, Incorporated.
October 2007
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