MIC4101YM [MICROCHIP]
2A HALF BRDG BASED MOSFET DRIVER, PDSO8;
| 型号： | MIC4101YM |
| 厂家： | 
MICROCHIP |
| 描述： | 2A HALF BRDG BASED MOSFET DRIVER, PDSO8 驱动 光电二极管 接口集成电路 驱动器 |
| 文件： | 总18页 (文件大小：706K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC4100/1
100V Half Bridge MOSFET Drivers
General Description
Features
The MIC4100/1 are high frequency, 100V Half Bridge
MOSFET driver ICs featuring fast 30ns propagation delay
times. The low-side and high-side gate drivers are
independently controlled and matched to within 3ns
typical. The MIC4100 has CMOS input thresholds, and the
MIC4101 has TTL input thresholds. The MIC4100/1
include a high voltage internal diode that charges the high-
side gate drive bootstrap capacitor.
• 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 (MIC4100)
• TTL input thresholds (MIC4101)
• On-chip bootstrap diode
• Fast 30ns propagation times
• Drives 1000pF load with 10ns rise and fall times
• Low power consumption
• Supply under-voltage protection
• 3Ω pull up , 3Ω pull down output resistance
• Space saving SOIC-8L package
• –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 MIC4100/1 ensures the outputs are not
affected by supply glitches, HS ringing below ground, or
HS slewing with high speed voltage transitions. Under-
voltage protection is provided on both the low-side and
high-side drivers.
The MIC4100 is available in the SOIC-8L package with a
junction operating range from –40°C to +125°C.
Applications
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
• High voltage buck converters
• Push-pull converters
• Full- and half-bridge converters
• Active clamp forward converters
___________________________________________________________________________________________________________
Typical Application
9V to 16V Bias
100V Supply
VDD
HB
MIC4100
SO-8
HI
LI
PWM
Controller
HO
HS
VOUT
GND
LO
100V Buck Regulator 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
M9999-031506
March 2006
Micrel, Inc.
MIC4100/1
Ordering Information
Part Number
Standard
Pb-Free
Input
CMOS
TTL
Junction Temp. Range
–40° to +125°C
Package
MIC4100BM
MIC4101BM
MIC4100YM
MIC4101YM
SOIC-8L
SOIC-8L
–40° to +125°C
Pin Configuration
VDD
HB
1
2
3
4
8
7
6
5
LO
VSS
LI
HO
HS
HI
SOIC-8L (M)
Pin Description
Pin Number
Pin Name
Pin Function
1
VDD
Positive Supply to lower gate drivers. Decouple this pin to VSS (Pin 7). Bootstrap
diode connected to HB (pin 2).
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
4
HO
HS
High-Side Output. Connect to gate of High-Side power MOSFET.
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
LI
Low-Side input.
VSS
LO
Chip negative supply, generally will be ground.
Low-Side Output. Connect to gate of Low-Side power MOSFET.
8
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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
EDS Rating(3)..............................................................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
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.
Parameter
Symbol Condition
Min
Typ
Max
Units
Supply Current
40
150
VDD Quiescent Current
VDD Operating Current
Total HB Quiescent Current
IDD
LI = HI = 0V
f = 500kHz
LI = HI = 0V
µ
A
200
3.4
150
200
2.5
3
IDDO
IHB
2.5
25
mA
µ
A
1.4
Total HB Operating Current
IHBO
f = 500kHz
mA
0.05
10
1
HB to VSS Current, Quiescent
HB to VSS Current, Operating
IHBS
VHS = VHB = 110V
f = 500kHz
µ
µ
A
A
IHBSO
Input Pins: MIC4100 (CMOS Input )
4
5.3
5.7
Low Level Input Voltage
Threshold
VIL
V
3
7
High Level Input Voltage
Threshold
VIH
V
V
8
Input Voltage Hysteresis
Input Pulldown Resistance
Input Pins: MIC4101 (TTL)
VIHYS
0.4
100
0.8
200
500
RI
K
Ω
Low Level Input Voltage
Threshold
1.5
1.5
200
VIL
V
V
High Level Input Voltage
Threshold
2.2
VIH
RI
100
500
Input Pulldown Resistance
K
Ω
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Parameter
Symbol Condition
Min
Typ
Max
Units
Under Voltage Protection
VDD Rising Threshold
VDD Threshold Hysteresis
HB Rising Threshold
HB Threshold Hysteresis
Bootstrap Diode
VDDR
VDDH
VHBR
VHBH
6.5
7.4
8.0
V
V
V
V
0.5
7.0
0.4
6.0
8.0
0.4
0.7
1.0
0.55
0.70
0.8
Low-Current Forward Voltage
High-Current Forward Voltage
VDL
VDH
RD
V
V
Ω
IVDD-HB = 100µA
IVDD-HB = 100mA
IVDD-HB = 100mA
1.0
1.5
Dynamic Resistance
LO Gate Driver
2.0
0.22
0.25
0.3
0.4
Low Level Output Voltage
VOLL
ILO = 100mA
V
V
0.3
High Level Output Voltage
VOHL
ILO = -100mA, VOHL = VDD - VLO
0.45
Peak Sink Current
Peak Source Current
HO Gate Driver
IOHL
IOLL
VLO = 0V
2
2
A
A
VLO = 12V
0.22
0.25
0.3
0.4
Low Level Output Voltage
High Level Output Voltage
VOLH
IHO = 100mA
V
V
0.3
VOHH
IHO = -100mA, VOHH = VHB – VHO
0.45
Peak Sink Current
IOHH
IOLH
VHO = 0V
2
2
A
A
Peak Source Current
VHO = 12V
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Parameter
Symbol Condition
Min
Typ
Max
Units
Switching Specifications
Lower Turn-Off Propagation
Delay (LI Falling to LO Falling)
27
45
45
45
45
55
55
55
55
tLPHL
tHPHL
tLPLH
tHPLH
tLPHL
tHPHL
tLPLH
tHPLH
(MIC4100)
(MIC4100)
(MIC4100)
(MIC4100)
(MIC4101)
(MIC4101)
(MIC4101)
(MIC4101)
ns
ns
ns
ns
ns
ns
ns
ns
Upper Turn-Off Propagation
Delay (HI Falling to HO Falling)
27
27
27
31
31
31
31
3
Lower Turn-On Propagation
Delay (LI Rising to LO Rising)
Upper Turn-On Propagation
Delay (HI Rising to HO Rising)
Lower Turn-Off Propagation
Delay (LI Falling to LO Falling)
Upper Turn-Off Propagation
Delay (HI Falling to HO Falling)
Lower Turn-On Propagation
Delay (LI Rising to LO Rising)
Upper Turn-On Propagation
Delay (HI Rising to HO Rising)
8
10
8
Delay Matching: Lower Turn-On
and Upper Turn-Off
tMON
ns
3
Delay Matching: Lower Turn-Off
and Upper Turn-On
tMOFF
ns
ns
10
Either Output Rise/Fall Time
tRC , tFC
tR , tF
tPW
tBS
CL = 1000pF
10
0.4
0.6
Either Output Rise/Fall Time
(3V to 9V)
CL = 0.1
µF
µs
0.8
Minimum Input Pulse Width that
Changes the Output
Note 6
50
ns
ns
Bootstrap Diode Turn-On or
Turn-Off Time
10
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 pin7, VSS unless otherwise specified
6. Guaranteed by design. Not production tested.
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MIC4100/1
Timing Diagrams
LI
HI
HI,LI
tHPLH
tLPLH
tHPLH
tLPLH
LO
HO,LO
tMON
tMOFF
HO
Note: All propagation delays are measured from the 50% voltage level.
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Typical Characteristics
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Typical Characteristics (cont.)
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Functional Diagram
HV
HB
HO
HS
DRIVER
LEVEL
SHIFT
UVLO
UVLO
HI
VDD
LO
DRIVER
LI
VSS
Figure 1. MIC4100 Functional Block Diagram
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MIC4100/1
Functional Description
The MIC4100 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 MIC4100 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
Figure 2
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.
The MIC4101 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 MIC4101. This feature makes the MIC4101 an
excellent level translator that will drive high threshold
MOSFETs from a low voltage PWM IC.
Input Stage
The MIC4100 and MIC4101 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 voltage state of the input signal does not
change the quiescent current draw of the driver.
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 a low Rdson from the external MOSFET.
The MIC4100 has a high impedance, CMOS compatible
input range and is recommended for applications 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
MIC4100 varies proportionally with the VDD supply
voltage.
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 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.
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MIC4100/1
Vdd
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.
External
FET
LO
Vin
CB
HB
Vdd
CVDD
HI
Q1
Q2
Level
shift
Lout
HO
Vss
Vout
Cout
HS
LO
Figure 3
LI
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.
Vss
Figure 5
Vdd
HB
CB
External
FET
HO
HS
Figure 4
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.
The bootstrap circuit consists of an internal diode and
external capacitor, CB. In a typical application, such as the
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MIC4100/1
IRR( AVE) = 0.5× IRRM ×trr × fS
PdiodeRR = IRR( AVE) ×VREV
Application Information
Power Dissipation Considerations
Power dissipation in the driver can be separated into three
areas:
where : IRRM = Peak Reverse RecoveryCurrent
trr = Reverse RecoveryTime
•
•
•
Internal diode dissipation in the bootstrap circuit
Internal driver dissipation
The total diode power dissipation is:
Quiescent current dissipation used to supply the
internal logic and control functions.
Pdiodetotal = Pdiode fwd + PdiodeRR
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:
IF ( AVE) = Qgate × fS
where : Qgate = TotalGateCharge at VHB
fS = gate driveswitching frequency
PdiodeREV = IR ×VREV × (1− D)
where : IR = Reverse current flow at VREV and TJ
VREV = Diode Reverse Voltage
The average power dissipated by the forward voltage drop
of the diode equals:
Pdiodefwd = IF ( AVE) ×VF
D = Duty Cycle = tON / fS
where : VF = Diode forward voltagedrop
fs = switching frequency of the power supply
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.
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.
The reverse leakage current of the internal bootstrap diode
is typically 11uA at a reverse voltage of 100V and 125C.
Power 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:
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MIC4100/1
external
diode
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 MIC4100.
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.
Vin
CB
HB
Vdd
Level
shift
HO
HS
HI
LI
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:
LO
Vss
Figure 6
Gate Driver Power Dissipation
2
1
E = ×Ciss ×Vgs
2
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 7 shows a simplified equivalent circuit of the
MIC4100 driving an external MOSFET.
but
Q = C× V
so
E = 1/2× Qg ×Vgs
where
External
FET
Ciss is the total gate capacitance of the MOSFET
HB
Vdd
Gate Charge
Cgd
Ron
Roff
10
CB
VDS = 50V
HO
ID = 6.9A
8
Rg
Rg_fet
Cgs
6
4
2
0
HS
Figure 7
0
5
g
10
15
20
25
Q
- Total Gate Charge (nC)
Figure 8
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:
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Edirver = Qg×Vgs
consideration in a high performance power supply. The
MIC4100 is designed not only to minimize propagation
delay but to minimize the mismatch in delay between the
high-side and low-side drivers.
and
P
= Qg×Vgs × fs
driver
where
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.
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
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 MIC4100
and MIC4101 output gate drivers are not designed with
anti-shoot-through protection circuitry. The output drives
signals simply follow the inputs. The power supply design
must include timing delays (dead-time) between the input
The power dissipated inside the MIC4100/1 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
MIC4100 due to driving the external MOSFET is:
Ron
Pdissdrive = P
driver
Ron + Rg + Rg _ fet
signals to prevent shoot-through. The MIC4100
&
Supply Current Power Dissipation
MIC4101 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.
Power is dissipated in the MIC4100 even if is there is
nothing being driven. The supply current is drawn by the
bias for the internal circuitry, the level shifting circuitry and
shoot-through 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.
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.
The power dissipated by the MIC4100 due to supply
current is
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.
Pdisssup ply = Vdd × Idd +Vhb × Ihb
Total power dissipation and Thermal Considerations
Total power dissipation in the MIC4100 or MIC4101 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
Pdisstotal = Pdisssup ply + Pdissdrive + Pdiodetotal
The die temperature may be calculated once the total
power dissipation is known.
TJ = TA + Pdisstotal ×θJA
where:
TA is the maximumambient temperature
TJ is the junction temperature(°C)
Pdisstotal is the power dissipation of the MIC4100/1
θJC is the thermalresistancefrom junction to ambient air (°C/W)
Propagation Delay and Delay Matching and other
Timing Considerations
Propagation delay and signal timing is an important
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capacitors are recommended for most applications. The
minimum capacitance value should be increased if low
voltage capacitors are use since even good quality
dielectric capacitors, such as X5R, will lose 40% to 70% of
their capacitance value at the rated voltage.
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
which fights the turn-on of the MOSFET.
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 layout and
component placement for more information.
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 high-
side drive circuitry.
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:
Low-side drive turn-on
current path
LO
Vdd
HB
CVdd
gnd
plane
Vss
LI
gnd
plane
Qgate
CB ≥
HO
HS
∆VHB
where : Qgate = TotalGateChargeat VHB
∆VHB = Voltage drop at the HB pin
CB
Level
shift
HI
High-side drive turn-on
current path
The decoupling capacitor for the Vdd input may be
calculated in with the same formula; however, the two
capacitors are usually equal in value.
Turn-On Current Paths
Figure 9
Grounding, Component Placement and Circuit Layout
Nanosecond switching speeds and ampere peak currents
in and around the MIC4100 and MIC4101 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 10 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.
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
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MIC4100/1
Low-side drive turn-off
current path
Vin
CB
LO
Vdd
HB
HB
Vdd
CVDD
HI
High-Side Fet
CVdd
Level
shift
HO
HS
Vss
LI
HS (switch) Node
Cin
Low-Side Fet
HO
HS
LI
LO
CB
Level
shift
HI
MIC4100
High-side drive turn-on
current path
Vss
Turn-Off Current Paths
Figure 11
Figure 10
The following circuit guidelines should be adhered to for
optimum circuit performance:
1. The Vcc and HB bypass capacitors must be
placed close to the supply and ground pins. It is
critical that the etch length between the high side
decoupling capacitor (CB) and the HB & HS pins
be minimized to reduce lead inductance.
2. A ground plane should be used to minimize
parasitic inductance and impedance of the return
paths. The MIC4100 is capable of greater than 2A
peak currents and any impedance between the
MIC4100, 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 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 11) is shown in Figure 12.
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MIC4100/1
The circuit is configured as a synchronous buck 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) 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 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
0.025” wide or greater to reduce impedance. Cin is used to
decouple the high current path through the MOSFETs.
Vin (FET Drain)
High-side FET
Low-side FET
HS Node
(switching node)
CIN
GND
GND
(FET Source)
Cvdd
MIC4100
LO
Vss
CB
LI
HI
HO trace
HS
HO
HB
Vdd
Figure 12
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Package Information
8-Pin SOIC (M)
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.
© 2004 Micrel, Incorporated.
March 2006
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