LM27222
LM27222 High-Speed 4.5A Synchronous MOSFET Driver
Literature Number: SNVS306A
LM27222
High-Speed 4.5A Synchronous MOSFET Driver
General Description
The LM27222 is a dual N-channel MOSFET driver designed
to drive MOSFETs in push-pull configurations as typically
used in synchronous buck regulators. The LM27222 takes
the PWM output from a controller and provides the proper
timing and drive levels to the power stage MOSFETs. Adap-
tive shoot-through protection prevents damaging and effi-
ciency reducing shoot-through currents, thus ensuring a ro-
bust design capable of being used with nearly any MOSFET.
The adaptive shoot-through protection circuitry also reduces
the dead time down to as low as 10ns, ensuring the highest
operating efficiency. The peak sourcing and sinking current
for each driver of the LM27222 is about 3A and 4.5Amps
respectively with a Vgs of 5V. System performance is also
enhanced by keeping propagation delays down to 8ns. Effi-
ciency is once again improved at all load currents by sup-
porting synchronous, non-synchronous, and diode emulation
modes through the LEN pin. The minimum output pulse
width realized at the output of the MOSFETs is as low as
30ns. This enables high operating frequencies at very high
conversion ratios in buck regulator designs. To support low
power states in notebook systems, the LM27222 draws only
5µA from the 5V rail when the IN and LEN inputs are low or
floating.
Features
nAdaptive shoot-through protection
n10ns dead time
n8ns propagation delay
n30ns minimum on-time
n0.4Ωpull-down and 0.9Ωpull-up drivers
n4.5A peak driving current
nMOSFET tolerant design
n5µA quiescent current
n30V maximum input voltage in buck configuration
n4V to 6.85V operating voltage
nSO-8 and LLP packages
Applications
nHigh Current Buck And Boost Voltage Converters
nFast Transient DC/DC Power Supplies
nSingle Ended Forward Output Rectification
nCPU And GPU Core Voltage Regulators
Typical Application
20117902
FIGURE 1.
March 2006
LM27222 High-Speed 4.5A Synchronous MOSFET Driver
© 2006 National Semiconductor Corporation DS201179 www.national.com
Connection Diagram
20117901
Top View
SO-8 (NS Package # M08A) θ
JA
= 172˚C/W
or
LLP-8 (NS Package # SDC08A) θ
JA
= 39˚C/W
Ordering Information
Order Number Size NSC Drawing # Package Type Supplied As
LM27222M SO-8 M08A Rail 95 Units/Rail
LM27222MX Tape and Reel 2500 Units/Reel
LM27222SD LLP-8 SDC08A Tape and Reel 1000 Units/Reel
LM27222SDX Tape and Reel 4500 Units/Reel
Pin Descriptions
Pin # Pin Name Pin Function
1 SW High-side driver return. Should be connected to the common node of high and low-side MOSFETs.
2 HG High-side gate drive output. Should be connected to the high-side MOSFET gate. Pulled down
internally to SW with a 10K resistor to prevent spurious turn on of the high-side MOSFET when the
driver is off.
3 CB Bootstrap. Accepts a bootstrap voltage for powering the high-side driver.
4 IN Accepts a PWM signal from a controller. Active High. Pulled down internally to GND with a 150K
resistor to prevent spurious turn on of the high-side MOSFET when the controller is inactive.
5 LEN Low-side gate enable. Active High. Pulled down internally to GND with a 150K resistor to prevent
spurious turn-on of the low-side MOSFET when the controller is inactive.
6V
CC
Connect to +5V supply.
7 LG Low-side gate drive output. Should be connected to low-side MOSFET gate. Pulled down internally to
GND with a 10K resistor to prevent spurious turn on of the low-side MOSFET when the driver is off.
8 GND Ground.
LM27222
www.national.com 2
Block Diagram
20117903
LM27222
www.national.com3
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
CC
to GND -0.3V to 7V
CB to GND -0.3V to 36V
CB to SW -0.3V to 7V
SW to GND (Note 2) -2V to 36V
LEN, IN, LG to GND -0.3V to V
CC
+ 0.3V ≤7V
HG to GND -0.3V to 36V
Junction Temperature +150˚C
Power Dissipation (Note 3) 720mW
Storage Temperature −65˚ to 150˚C
ESD Susceptibility
Human Body Model 2kV
Operating Ratings (Note 1)
VCC 4V to 6.85V
Junction Temperature Range −40˚ to 125˚C
CB (max) 33V
Electrical Characteristics (Note 4)
VCC = CB = 5V, SW = GND = 0V, unless otherwise specified. Typicals and limits appearing in plain type apply for T
A
=T
J
=
+25˚C. Limits appearing in boldface type apply over the entire operating temperature range (-40˚C ≤T
J
≤125˚C).
Symbol Parameter Conditions Min Typ Max Units
POWER SUPPLY
I
q_op
Operating Quiescent Current IN = 0V, LEN = 0V 5 15 µA
30
IN = 0V, LEN = 5V 500 540 650 µA
825
HIGH-SIDE DRIVER
Peak Pull-up Current 3 A
R
H-pu
Pull-up Rds_on I
CB
=I
HG
= 0.3A 0.9 2.5 Ω
Peak Pull-down Current 4.5 A
R
H-pd
Pull-down Rds_on I
SW
=I
HG
= 0.3A 0.4 1.5 Ω
t
4
Rise Time Timing Diagram, C
LOAD
= 3.3nF 17 ns
t
6
Fall Time Timing Diagram, C
LOAD
= 3.3nF 12 ns
t
3
Pull-up Dead Time Timing Diagram 9.5 ns
t
5
Pull-down Delay Timing Diagram 16.5 ns
t
on_min
Minimum Positive Output
Pulse Width
30 ns
LOW-SIDE DRIVER
Peak Pull-up Current 3.2 A
R
L-pu
Pull-up Rds_on I
VCC
=I
LG
= 0.3A 0.9 2.5 Ω
Peak Pull-down Current 4.5 A
R
L-pd
Pull-down Rds_on I
GND
=I
LG
= 0.3A 0.4 1.5 Ω
t
8
Rise Time Timing Diagram, C
LOAD
= 3.3nF 17 ns
t
2
Fall Time Timing Diagram, C
LOAD
= 3.3nF 14 ns
t
7
Pull-up Dead Time Timing Diagram 11.5 ns
t
1
Pull-down Delay Timing Diagram 7.7 ns
PULL-DOWN RESISTANCES
HG-SW Pull-down Resistance 10k Ω
LG-GND Pull-down
Resistance
10k Ω
LEN-GND Pull-down
Resistance
150K Ω
IN-GND Pull-down Resistance 150K Ω
LEAKAGE CURRENTS
I
leak_IN
IN pin Leakage Current IN = 0V, Source Current 50 nA
IN = 5V, Sink Current 33 µA
LM27222
www.national.com 4
Electrical Characteristics (Note 4) (Continued)
VCC = CB = 5V, SW = GND = 0V, unless otherwise specified. Typicals and limits appearing in plain type apply for T
A
=T
J
=
+25˚C. Limits appearing in boldface type apply over the entire operating temperature range (-40˚C ≤T
J
≤125˚C).
Symbol Parameter Conditions Min Typ Max Units
I
leak_LEN
LEN pin Leakage Current LEN = 0V, Source Current 200 nA
LEN = 5V, Sink Current 33 µA
LOGIC
V
IH_LEN
LEN Low to High Threshold Low to High Transition 65 %ofV
CC
V
IL_LEN
LEN High to Low Threshold High to Low Transition 30 %ofV
CC
V
IH_IN
IN Low to High Threshold Low to High Transition 65 %ofV
CC
V
IL_IN
IN High to Low Threshold High to Low Transition 30 %ofV
CC
Threshold Hysteresis 0.7 V
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating ratings are conditions under which the device operates
correctly. Operating Ratings do not imply guaranteed performance limits.
Note 2: The SW pin can have -2V to -0.5 volts applied for a maximum duty cycle of 10% with a maximum period of 1 second. There is no duty cycle or maximum
period limitation for a SW pin voltage range of -0.5V to 30 Volts.
Note 3: Maximum allowable power dissipation is a function of the maximum junction temperature, TJMAX, the junction-to-ambient thermal resistance, θJA, and the
ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using: PMAX =(T
JMAX-TA)/θJA. The junction-to-
ambient thermal resistance, θJA, for the LM27222M, it is 165˚C/W. For a TJMAX of 150˚C and TAof 25˚C, the maximum allowable power dissipation is 0.76W. The
θJA for the LM27222SD is 42˚C/W. For a TJMAX of 150˚C and TA of 25˚C, the maximum allowable power dissipation is 3W.
Note 4: Min and Max limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical
Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL).
Timing Diagram
20117904
LM27222
www.national.com5
Typical Waveforms
The typical waveforms are from a circuit similar to Figure 1 with:
Q1: 2 x Si7390DP
Q2: 2 x Si7356DP
L1: 0.4 µH
V
IN
: 12V
20117907
FIGURE 2. PWM Low-to-High Transition at IN Input
20117908
FIGURE 3. PWM High-to-Low Transition at IN Input
20117909
FIGURE 4. LEN Operation
LM27222
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Application Information
GENERAL
The LM27222 is designed for high speed and high operating
reliability. The driver can handle very narrow, down to zero,
PWM pulses in a guaranteed, deterministic way. Therefore,
the HG and LG outputs are always in predictable states. No
latches are used in the HG and LG control logic so the
drivers cannot get "stuck" in the wrong state. The driver
design allows for powering up with a pre-biasing voltage
being present at the regulator output. To reduce conduction
losses in DC-DC converters with low duty factors the
LM27222 driver can be powered from a 6.5V ±5% power
rail.
It is recommended to use the same power rail for both the
controller and driver. If two different power rails are used,
never allow the PWM pulse magnitude at the IN input or the
control voltage at the LEN input to be above the driver V
CC
voltage or unpredictable HG and LG outputs pulse widths
may result.
MINIMUM PULSE WIDTH
As the input pulse width to the IN pin is decreased, the pulse
width of the high-side gate drive (HG-SW) also decreases.
However, for input pulse widths 60ns and smaller, the
HG-SW remains constant at 30ns. Thus the minimum pulse
width of the driver output is 30ns. Figure 5 shows an input
pulse at the IN pin 20ns wide, and the output of the driver, as
measured between the nodes HG and SW is a 30ns wide
pulse. Figure 6 shows the variation of the SW node pulse
width vs IN pulse width. At the IN pin, if a falling edge is
followed by a rising edge within 5ns, the HG may ignore the
rising edge and remain low until the IN pin toggles again. If a
rising edge is followed by a falling edge within 5ns, the pulse
may be completely ignored.
ADAPTIVE SHOOT-THROUGH PROTECTION
The LM27222 prevents shoot-through power loss by ensur-
ing that both the high- and low-side MOSFETs are not con-
ducting at the same time. When the IN signal rises, LG is first
pulled down. The adaptive shoot-through protection circuit
waits for LG to reach 0.9V before turning on HG. Similarly,
when IN goes low, HG is pulled down first, and the circuit
turns LG on only after the voltage difference between the
high-side gate and the switch node, i.e. HG-SW, has fallen to
0.9V.
It is possible in some applications that at power-up the
driver’s SW pin is above 3V in either buck or boost com-
verter applications. For instance, in a buck configuration a
pre-biasing voltage can be either a voltage from anothert
power rail connected to the load, or a leakage voltage
through the load, or it can be an output capacitor pre-
charged above 3V while no significant load is present. In a
boost application it can be an input voltage rail above 3V.
In the case of insufficient initial CB-SW voltage (less than
2V) such as when the output rail is pre-biased, the shoot-
through protection circuit holds LG low for about 170ns,
beginning from the instant when IN goes high. After the
170ns delay, the status of LG is dictated by LEN and IN.
Once LG goes high and SW goes low, the bootstrap capaci-
tor will be charged up (assuming SW is grounded for long
enough time). As a result, CB-SW will be close to 5V and the
LM27222 will now fully support synchronous operation.
The dead-time between the high- and low-side pulses is kept
as small as possible to minimize conduction through the
body diode of the low-side MOSFET(s).
20117905
FIGURE 5. Min On Time
20117906
FIGURE 6.
LM27222
www.national.com7
Application Information (Continued)
POWER DISSIPATION
The power dissipated in the driver IC when switching syn-
chronously can be calculated as follows:
where f
SW
= switching frequency
V
CC
= voltage at the V
CC
pin,
Q
G_H
= total gate charge of the (parallel combination of the)
high-side MOSFET(s)
Q
G_L
= total gate charge of the (parallel combination of the)
low-side MOSFET(s)
R
G_H
= gate resistance of the (parallel combination of the)
high-side MOSFET(s)
R
G_L
= gate resistance of the (parallel combination of the)
low-side MOSFET(S)
R
H_pu
= pull-up R
DS_ON
of the high-side driver
R
H_pd
= pull-down R
DS_ON
of the high-side driver
R
L_pu
= pull-up R
DS_ON
of the low-side driver
R
L_pd
= pull-down R
DS_ON
of the low-side driver
PC BOARD LAYOUT GUIDELINES
1. Place the driver as close to the MOSFETs as possible.
2. HG, SW, LG, GND: Run short, thick traces between the
driver and the MOSFETs. To minimize parasitics, the
traces for HG and SW should run parallel and close to
each other. The same is true for LG and GND.
3. Driver V
CC
: Place the decoupling capacitor close to the
V
CC
and GND pins.
4. The high-current loop between the high-side and low-
side MOSFETs and the input capacitors should be as
small as possible.
5. There should be enough copper area near the MOS-
FETs and the inductor for heat dissipation. Vias may
also be added to carry the heat to other layers.
TYPICAL APPLICATION CIRCUIT DESCRIPITON
The Application Example on the following page shows the
LM27222 being used with National’s LM27212, a 2-phase
hysteretic current mode controller. Although this circuit is
capable of operating from 5V to 28V, the components are
optimized for an input voltage range of 9V to 28V. The
high-side FET is selected for low gate charge to reduce
switching losses. For low duty cycles, the average current
through the high-side FET is relatively small and thus we
trade off higher conduction losses for lower switching losses.
The low-side FET is selected solely on R
DS_ON
to minimize
conduction losses. If the input voltage range were 4V to 6V,
the MOSFET selection should be changed. First, much lower
voltage FETs can be used, and secondly, high-side FET
R
DS_ON
becomes a larger loss factor than the switching
losses. Of course with a lower input voltage, the input ca-
pacitor voltage rating can be reduced and the inductor value
can be reduced as well. For a 4V to 6V application, the
inductor can be reduced to 200nH to 300nH. The switching
frequency of the LM27212 is determined by the allowed
ripple current in the inductor. This circuit is set for approxi-
mately 300kHz. At lower input voltages, higher frequencies
are possible without suffering a significant efficiency loss.
Although the LM27222 can support operating frequencies up
to 2MHz in many applications, the LM27212 should be lim-
ited to about 1MHz. The control architecture of the LM27212
and the low propagation times of the LM27222 potentially
gives this solution the fastest transient response in the
industry.
LM27222
www.national.com 8
Application Example
20117920
* Q1, Q3: 2 x Si7390DP
** Q2, Q4: 2 x Si7356DP
LM27222
www.national.com9
Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead Small Outline Package
Order Number: LM27222M, LM27222MX
NS Package Number M08A
8-Lead LLP Package
Order Number: LM27222SD, LM27222SDX
NS Package Number SDC08A
LM27222
www.national.com 10
Notes
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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LM27222 High-Speed 4.5A Synchronous MOSFET Driver
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