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MAX8791/MAX8791B

Single-Phase, Synchronous MOSFET Drivers

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-0628; Rev 2; 1/10

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.

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

Applications

Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

PART TEMP RANGE PIN-PACKAGE

MAX8791GTA+ -40

C to +105

C 8 TQFN-EP*

MAX8791BGTA+ -40

C to +105

C 8 TQFN-EP*

Single-Phase, Synchronous MOSFET Drivers

0.5Ω Low-Side On-Resistance

0.7Ω High-Side On-Resistance

8ns Propagation Delay

15ns Minimum Guaranteed Dead Time

Integrated Boost “Diode”

2V to 24V Input Voltage Range

Selectable Pulse-Skipping Mode

Low-Profile TQFN Package

Notebooks/Desktops/Servers

CPU Core Power Supplies

Multiphase Step-Down Converters

SKIP

PWM

BST

GND

TQFN

3mm × 3mm

MAX8791

MAX8791B

TOP VIEW

Pin Configuration

MAX8791

MAX8791B

PWM

BST

GND

PAD

PWM

+5V BIAS

SUPPLY

SKIP

INPUT (V

5V TO 24V

OUT

(1.45V

AT 20A)

Typical Operating Circuit

Summary of content (12 pages)

PAGE 1
9-0628; Rev 2; 1/10 Single-Phase, Synchronous MOSFET Drivers The MAX8791/MAX8791B are single-phase, synchronous, 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.
PAGE 2
MAX8791/MAX8791B Single-Phase, Synchronous MOSFET Drivers ABSOLUTE MAXIMUM RATINGS VDD 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 (VDD + 0.3V) BST to GND ............................................................-0.3V to +36V DH to LX ....................................................-0.3V to (VBST + 0.3V) BST to VDD .....
PAGE 3
Single-Phase, Synchronous MOSFET Drivers (Circuit of Figure 1, VDD = V SKIP = 5V, TA = -40°C to +105°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN VDD/2 - 0.4 Midlevel Low (DH = low; DL = high) PWM Input Current IPWM Midlevel Shutdown Hold Time tMID ISKIP Thermal-Shutdown Threshold TSHDN VDD/2 + 0.4 V -400 -200 -80 80 +200 400 120 300 600 1.7 2.4 Falling edge 0.8 1.5 Sink; SKIP forced to 0.
PAGE 4
Typical Operating Characteristics (continued) (Circuit of Figure 1, VDD = 5V, CDH = 3nF, CDL = 3nF, TA = +25°C, unless otherwise noted.) DH AND DL RISE AND FALL TIMES vs. TEMPERATURE 25 20 FALL TIME 15 10 35 A 30 40 DH RISE 25 DH FALL 20 20 DL IS DRIVING 2 SI7336ADP DH IS DRIVING 1 SI7892ADP CDL = CDH 10 0 1000 2500 4000 5500 7000 CAPACITANCE (pF) -40 8500 10,000 -15 A: CDH = 3.3nF; CDL = 3.3nF B: CDH = 1.5nF; CDL = 6.
PAGE 5
Single-Phase, Synchronous MOSFET Drivers (Circuit of Figure 1, VDD = 5V, CDH = 3nF, CDL = 3nF, TA = +25°C, unless otherwise noted.) SWITCHING WAVEFORMS (PWM = HIGH TO MID TO HIGH) SWITCHING WAVEFORMS (PWM = MID TO LOW TO MID) MAX8791 toc12 MAX8791 toc11 VPWM 5V 5V/div 0 VDL 5V 5V/div 0 VLX 0 10V/div VDH 0 10V/div 5V 5V/div 0 VPWM VDL 0 5V/div 10V 10V/div 0 VLX 15V VDH 10V/div 0 Pin Description PIN NAME FUNCTION 1 BST Boost Flying-Capacitor Connection.
PAGE 6
MAX8791/MAX8791B Single-Phase, Synchronous MOSFET Drivers PWM DH BST PWM SKIP SKIP MAX8791 MAX8791B LX DL +5V BIAS SUPPLY VDD CDH 3nF CBST 0.1µF CDL 3nF GND C1 1.0µF PAD Figure 1. Test Circuit tPWM-DH tPWM-DL tMID tPWM-DL tMID PWM tF_DL tR_DL tF_DL tR_DL DL tDH-DL tDL-DH DH tR_DH tR_DH tR_DH tR_DH tPWM-DH Figure 2.
PAGE 7
Single-Phase, Synchronous MOSFET Drivers MAX8791/MAX8791B INPUT (VIN) CIN PWM SKIP +5V BIAS SUPPLY PWM DH SKIP BST VDD MAX8791 MAX8791B NH 2x 10µF L1 0.36µH CBST 0.22µF LX CVDD 1.0µF DL NL OUTPUT (VOUT) COUT 2x 330µF 6mΩ DL GND PAD Figure 3. Typical MOSFET-Driver Application Circuit Table 1.
PAGE 8
MAX8791/MAX8791B Single-Phase, Synchronous MOSFET Drivers VDD BST PWM DRV DH DRIVER LOGIC AND DEAD-TIME CONTROL THERMAL SHUTDOWN LX UVLO DRV# VDD SKIP DL LX GND ZX DETECTION PAD Figure 4. Overview Block Diagram Adaptive Shoot-Through Protection The DH and DL drivers are optimized for driving moderately sized high-side and larger low-side power MOSFETs. This is consistent with the low duty factor seen in the notebook CPU environment, where a large VIN - VOUT differential exists.
PAGE 9
Single-Phase, Synchronous MOSFET Drivers Input Undervoltage Lockout When VDD is below the UVLO threshold, DH and DL are held low. Once VDD is above the UVLO threshold and while PWM is low, DL is driven high and DH is driven low. This prevents the output of the converter from rising before a valid PWM signal is applied. Low-Power Pulse Skipping The MAX8791/MAX8791B enter into low-power pulseskipping mode when SKIP is pulled low.
PAGE 10
MAX8791/MAX8791B Single-Phase, Synchronous MOSFET Drivers Switching losses in the high-side MOSFET can become an insidious heat problem when maximum AC adapter voltages are applied due to the squared term in the switching-loss equation above. If the high-side MOSFET chosen for adequate RDS(ON) at low battery voltages becomes extraordinarily hot when biased from VIN(MAX), consider choosing another MOSFET with lower parasitic capacitance.
PAGE 11
Single-Phase, Synchronous MOSFET Drivers PROCESS: BiCMOS For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
PAGE 12
MAX8791/MAX8791B Single-Phase, Synchronous MOSFET Drivers Revision History REVISION NUMBER REVISION DATE DESCRIPTION PAGES CHANGED 0 8/06 Initial release 1 11/06 Updated Electrical Characteristics and PWM Input section. 3, 7 — 2 1/10 Added the MAX8791B to entire data sheet. 1–12 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.