19-0628; Rev 2; 1/10
Single-Phase, Synchronous MOSFET Drivers
General Description
The MAX8791/MAX8791B are single-phase, synchro-
nous, noninverting MOSFET drivers. The MAX8791/
MAX8791B are intended to work with controller ICs like
the MAX8736 or MAX8786, in multiphase notebook
CPU core regulators.
The regulators can either step down directly from the
battery voltage to create the core voltage, or step down
from the main system supply. The single-stage conver-
sion method allows the highest possible efficiency, while
the 2-stage conversion at higher switching frequency
provides the minimum possible physical size.
The low-side drivers are optimized to drive 3nF capaci-
tive loads with 4ns/8ns typical fall/rise times, and the
high-side driver with 8ns/10ns typical fall/rise times.
Adaptive dead-time control prevents shoot-through cur-
rents and maximizes converter efficiency.
The MAX8791/MAX8791B are available in a small, lead-
free, 8-pin, 3mm x 3mm TQFN package.
Features
o
Single-Phase, Synchronous MOSFET Drivers
o
0.5Ω Low-Side On-Resistance
o
0.7Ω High-Side On-Resistance
o
8ns Propagation Delay
o
15ns Minimum Guaranteed Dead Time
o
Integrated Boost “Diode”
o
2V to 24V Input Voltage Range
o
Selectable Pulse-Skipping Mode
o
Low-Profile TQFN Package
MAX8791/MAX8791B
Applications
Notebooks/Desktops/Servers
CPU Core Power Supplies
Multiphase Step-Down Converters
PART
MAX8791GTA+
MAX8791BGTA+
Ordering Information
TEMP RANGE
-40
o
C to +105
o
C
-40 C to +105 C
o
o
PIN-PACKAGE
8 TQFN-EP*
8 TQFN-EP*
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Typical Operating Circuit
INPUT (V
IN
)*
5V TO 24V
Pin Configuration
SKIP
6
LX
7
PWM
DH
TOP VIEW
MAX8791
MAX8791B
PWM SKIP
+5V BIAS
SUPPLY
SKIP
BST
LX
V
DD
DL
V
OUT
(1.45V
AT 20A)
V
DD
5
4
DL
DH
8
+
MAX8791
MAX8791B
1
BST
2
PWM
3
GND
GND
PAD
TQFN
3mm
×
3mm
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Single-Phase, Synchronous MOSFET Drivers
MAX8791/MAX8791B
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND...............…………………….………….. -0.3V to +6V
SKIP
to GND..................………………………………-0.3V to +6V
PWM to GND ................……………………………….-0.3V to +6V
DL to GND ..................................................-0.3V to (V
DD
+ 0.3V)
BST to GND ............................................................-0.3V to +36V
DH to LX ....................................................-0.3V to (V
BST
+ 0.3V)
BST to V
DD
.............................................................-0.3V to +30V
BST to LX ................…………………………………...-0.3V to +6V
Continuous Power Dissipation (T
A
= +70°C)
8-Pin 3mm x 3mm TQFN
(derate 23.8mW/°C above +70°C) .............................1904mW
Operating Temperature Range .........................-40°C to +105°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
DD
= V
SKIP
= 5V, T
A
= -40°C to +105°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Input Voltage Range
V
DD
Undervoltage
Lockout Threshold
SYMBOL
V
DD
V
UVLO(VDD)
Rising edge, PWM disabled below this level
Falling edge, PWM disabled below this level
PWM = open; after the shutdown hold time has expired
Quiescent Supply
Current (V
DD
)
DRIVERS
PWM Pulse Width
DL Propagation Delay
DH Propagation Delay
DL-to-DH Dead Time
DH-to-DL Dead Time
DL Transition Time
DH Transition Time
DH Driver On-Resistance
DL Driver On-Resistance
DH Driver Source Current
DH Driver Sink Current
DL Driver Sink Current
Zero-Crossing Threshold
Boost On-Resistance
t
ON(MIN)
t
OFF(MIN)
t
PWM-DL
t
PWM-DH
t
DL-DH
t
DH-DL
t
F_DL
t
R_DL
t
F_DH
t
R_DH
R
ON(DH)
R
ON(DL)
Minimum on-time
Minimum off-time
PWM high to DL low
PWM low to DH low
DL falling to DH rising
DH falling to DL rising
Falling, 3.0nF load
Rising, 3.0nF load
Falling, 3.0nF load
Rising, 3.0nF load
BST-LX forced to 5V
DL, high state (pullup)
DL, low state (pulldown)
DH forced to 2.5V, BST - LX forced to 5V
DL forced to 2.5V
GND - LX,
SKIP
= GND
V
DD
= 5V, DH = LX = GND (pulldown state), I
BST
= 10mA
DH, high state (pullup)
DH, low state (pulldown)
T
A
= 0°C to +85°C
T
A
= -40°C to +105°C
T
A
= 0°C to +85°C
T
A
= -40°C to +105°C
15
15
15
15
12
14
8
10
0.9
0.7
0.7
0.5
2.2
2.7
2.7
8
3
5
12
2.5
2.3
1.8
1.2
30
50
300
10
14
30
ns
ns
ns
ns
ns
ns
ns
Ω
Ω
A
A
A
A
mV
Ω
I
DD
SKIP
= GND, PWM = GND,
LX = GND (after zero crossing)
SKIP
= GND or V
DD
, PWM = V
DD
, V
BST
= 5V
3.0
CONDITIONS
MIN
4.20
3.7
3.5
0.08
0.25
0.6
4.0
0.2
0.5
1.5
mA
TYP
MAX
5.50
UNITS
V
V
I
DH_SOURCE
DH forced to 2.5V, BST - LX forced to 5V
I
DH_SINK
I
DL_SINK
V
ZX
R
ON(BST)
DL Driver Source Current I
DL_SOURCE
DL forced to 2.5V
2
_______________________________________________________________________________________
Single-Phase, Synchronous MOSFET Drivers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
DD
= V
SKIP
= 5V, T
A
= -40°C to +105°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
High (DH = high; DL = low)
PWM Input Levels
Midlevel
Low (DH = low; DL = high)
PWM Input Current
Midlevel Shutdown Hold
Time
SKIP
Input Threshold
SKIP
Input Current
Thermal-Shutdown
Threshold
I
SKIP
T
SHDN
I
PWM
t
MID
Rising edge
Falling edge
Sink;
SKIP
forced to 0.8V to V
DD
, T
A
= +25°C
Hysteresis = 20°C
0.8
-4
Sink; PWM forced to V
DD
Source; PWM forced to GND
-400
80
120
-200
+200
300
1.7
1.5
-2
+160
-0.5
MIN
V
DD
-
0.4
V
DD
/2
- 0.4
V
DD
/2
+ 0.4
0.4
-80
400
600
2.4
µA
ns
V
µA
°C
V
TYP
MAX
UNITS
MAX8791/MAX8791B
Note 1:
Limits are 100% production tested at T
A
= +25°C. Maximum and minimum limits over temperature are guaranteed through
correlation using statistical-quality-control (SQC) methods.
Typical Operating Characteristics
(Circuit of Figure 1, V
DD
= 5V, C
DH
= 3nF, C
DL
= 3nF, T
A
= +25°C, unless otherwise noted.)
PACKAGE-POWER DISSIPATION
vs. PWM FREQUENCY
MAX8791 toc01
PACKAGE-POWER DISSIPATION
vs. CAPACITIVE LOAD ON DH AND DL
MAX8791 toc02
DL RISE AND FALL TIMES
vs. CAPACITIVE LOAD
MAX8791 toc03
300
250
B
200
PD (mW)
A
150
100
50
0
0
200
500
450
400
350
PD (mW)
300
250
200
150
100
A
A: 300kHz
B: 600kHz
C: 1MHz
1000
2500
4000 5500 7000
CAPACITANCE (pF)
B
C
30
25
RISE AND FALL TIME (ns)
RISE TIME
20
15
10
FALL TIME
5
C
DL
= C
DH
0
1000
2500
4000 5500 7000
CAPACITANCE (pF)
A: C
DH
= 3.3nF; C
DL
= 3.3nF
B: C
DH
= 1.5nF; C
DL
= 6.8nF
400
600
800 1000
PWM FREQUENCY (kHz)
1200
50
0
8500 10,000
8500 10,000
_______________________________________________________________________________________
3
Single-Phase, Synchronous MOSFET Drivers
MAX8791/MAX8791B
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
DD
= 5V, C
DH
= 3nF, C
DL
= 3nF, T
A
= +25°C, unless otherwise noted.)
DH RISE AND FALL TIMES
vs. CAPACITIVE LOAD
MAX8791 toc04
DH AND DL RISE AND FALL TIMES
vs. TEMPERATURE
MAX8791 toc05
PACKAGE-POWER DISSIPATION
vs. PWM FREQUENCY
B
50
A
40
I
DD
(mW)
MAX8791 toc06
40
35
RISE AND FALL TIME (ns)
30
25
20
FALL TIME
15
10
5
C
DL
= C
DH
0
1000
2500
4000 5500 7000
CAPACITANCE (pF)
RISE TIME
40
DL RISE
35
RISE AND FALL TIME (ns)
30
DH RISE
25
DH FALL
20
DL FALL
15
10
DL IS DRIVING 2 SI7336ADP
DH IS DRIVING 1 SI7892ADP
-40
-15
10
35
60
TEMPERATURE (°C)
85
60
30
20
10
0
A: C
DH
= 3.3nF; C
DL
= 3.3nF
B: C
DH
= 1.5nF; C
DL
= 6.8nF
0
200
400
600
800 1000
PWM FREQUENCY (kHz)
1200
8500 10,000
110
PROPAGATION DELAY TIME
vs. TEMPERATURE
15
PROPOGATION DELAY TIME (ns)
14
13
12
11
10
9
V
DH
8
-40
-15
10
35
60
TEMPERATURE (°C)
85
110
PWM RISE TO DL FALL
V
DL
V
LX
PWM FALL TO DH FALL
MAX8791 toc07
TYPICAL APPLICATION CIRCUIT
SWITCHING WAVEFORMS
MAX8791 toc08
16
V
PWM
5V/div
10V/div
5V/div
20V/div
100ns/div
DH FALL AND DL RISE WAVEFORMS
MAX8791 toc09
DH RISE AND DL FALL WAVEFORMS
MAX8791 toc10
V
PWM
5V/div
V
PWM
5V/div
V
LX
10V/div
V
LX
10V/div
V
DL
5V/div
V
DL
5V/div
10V/div
V
DH
20ns/div
10V/div
V
DH
20ns/div
4
_______________________________________________________________________________________
Single-Phase, Synchronous MOSFET Drivers
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
DD
= 5V, C
DH
= 3nF, C
DL
= 3nF, T
A
= +25°C, unless otherwise noted.)
MAX8791/MAX8791B
SWITCHING WAVEFORMS
(PWM = MID TO LOW TO MID)
MAX8791 toc11
SWITCHING WAVEFORMS
(PWM = HIGH TO MID TO HIGH)
MAX8791 toc12
V
PWM
5V
5V/div
0
5V
5V/div
0
0
10V/div
V
PWM
V
DL
5V
5V/div
0
0
5V/div
10V
10V/div
0
15V
V
DL
V
LX
V
LX
V
DH
0
10V/div
V
DH
10V/div
0
Pin Description
PIN
1
NAME
BST
FUNCTION
Boost Flying-Capacitor Connection. Gate-drive power supply for DH high-side gate driver. Connect a 0.1µF or
0.22µF capacitor between BST and LX.
PWM Input Pin. Noninverting DH control input from the controller IC:
Logic high: DH = high (BST), DL = low (PGND).
Midlevel: After the midlevel hold time expires, the controller enters standby mode. DH and DL pulled low.
Logic low: DH = low (LX), DL = high (V
DD
) when
SKIP
= high.
Internal pullup and pulldown resistors create the midlevel and prevent the controller from triggering an on-time if
this input is left unconnected (not soldered properly) or driven by a high impedance.
Power Ground for the DL Gate Drivers and Analog Ground. Connect exposed pad to GND.
PWM Low-Side Gate-Driver Output. Swings between GND and V
DD
. DL forced high in shutdown.
Supply Voltage Input for the DL Gate Drivers. Connect to 4.2V to 5.5V supply and bypass to GND with a 1µF
ceramic capacitor.
Pulse-Skipping Mode Pin. Enable pulse-skipping mode (zero-crossing comparator enabled) when the driver is
operating in SKIP mode:
SKIP
= V
DD
PWM mode
SKIP
= GND SKIP mode
An internal pulldown current pulls the controller into the low-power pulse-skipping state if this input is left
unconnected (not soldered properly) or driven by a high impedance.
Switching Node and Inductor Connection. Low-power supply for the DH high-side gate driver. LX connects to
the skip-mode zero-crossing comparator.
External High-Side nMOSFET Gate-Driver Output. Swings between LX and BST.
Exposed Pad. Connect to ground through multiple vias to reduce the thermal impedance.
2
PWM
3
4
5
GND
DL
V
DD
6
SKIP
7
8
—
LX
DH
EP
_______________________________________________________________________________________
5
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