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LTC4449

4449fa

4V to 6.5V V

Operating Voltage

38V Maximum Input Supply Voltage

Adaptive Shoot-Through Protection

Rail-to-Rail Output Drivers

3.2A Peak Pull-Up Current

4.5A Peak Pull-Down Current

8ns TG Rise Time Driving 3000pF Load

7ns TG Fall Time Driving 3000pF Load

Separate Supply to Match PWM Controller

Drives Dual N-Channel MOSFETs

Undervoltage Lockout

Low Proﬁ le (0.75mm) 2mm × 3mm DFN Package

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

High Speed Synchronous

N-Channel MOSFET Driver

The LTC

4449 is a high frequency gate driver that

is designed to drive two N-Channel MOSFETs in a

synchronous DC/DC converter. The powerful rail-to-rail

driver capability reduces switching losses in MOSFETs

with high gate capacitance.

The LTC4449 features a separate supply for the input logic

to match the signal swing of the controller IC. If the input

signal is not being driven, the LTC4449 activates a shutdown

mode that turns off both external MOSFETs. The input logic

signal is internally level-shifted to the bootstrapped supply,

which functions at up to 42V above ground.

The LTC4449 contains undervoltage lockout circuits on

both the driver and logic supplies that turn off the external

MOSFETs when an undervoltage condition is present. An

adaptive shoot-through protection feature is also built-in

to prevent the power loss resulting from MOSFET cross-

conduction current.

The LTC4449 is available in the 2mm × 3mm DFN

package.

Synchronous Buck Converter Driver

Distributed Power Architectures

High Density Power Modules

LTC4449 Driving 3000pF Capacitive Loads

BOOST

TO 38V

GND

LOGIC

LTC4449

BGPWM

4V TO 6.5V

OUT

4449 TA01a

TOP GATE

(TG - TS)

5V/DIV

INPUT (IN)

5V/DIV

4449 TA01b

BOTTOM GATE

(BG) 5V/DIV

10ns/DIV

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Summary of content (14 pages)

PAGE 1
LTC4449 High Speed Synchronous N-Channel MOSFET Driver FEATURES DESCRIPTION n The LTC®4449 is a high frequency gate driver that is designed to drive two N-Channel MOSFETs in a synchronous DC/DC converter. The powerful rail-to-rail driver capability reduces switching losses in MOSFETs with high gate capacitance. n n n n n n n n n n n 4V to 6.5V VCC Operating Voltage 38V Maximum Input Supply Voltage Adaptive Shoot-Through Protection Rail-to-Rail Output Drivers 3.2A Peak Pull-Up Current 4.
PAGE 2
LTC4449 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Supply Voltage VLOGIC ...................................................... –0.3V to 7V VCC........................................................... –0.3V to 7V BOOST – TS ............................................. –0.3V to 7V BOOST Voltage .......................................... –0.3V to 42V TS ................................................................. –5V to 38V IN Voltage ....................................................
PAGE 3
LTC4449 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating junction temperature range, otherwise speciﬁcations are at TA = 25°C. VCC = VLOGIC = VBOOST = 5V, VTS = GND = 0V, unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX VIH(TG) TG Turn-On Input Threshold VLOGIC ≥ 5V, IN Rising VLOGIC = 3.3V, IN Rising VIL(TG) TG Turn-Off Input Threshold VIH(BG) UNITS l l 3 1.9 3.5 2.2 4 2.6 V V VLOGIC ≥ 5V, IN Falling VLOGIC = 3.
PAGE 4
LTC4449 TYPICAL PERFORMANCE CHARACTERISTICS Input Thresholds vs VLOGIC Supply Voltage Input Thresholds for VLOGIC ≥ 5V vs Temperature Input Thresholds for VLOGIC = 3.3V vs Temperature 4.0 3.0 VIH(TG) 5 VLOGIC = 3.3V VLOGIC ≥ 5V 2.5 2.0 VIL(BG) 1.5 VIH(BG) 1.0 2.0 VIL(TG) 1.5 VIL(BG) 1.0 3.5 4.0 4.5 5.0 5.5 VLOGIC SUPPLY (V) 6.0 0.5 –40 6.5 –10 20 50 80 TEMPERATURE (°C) 0.25 0.20 0.15 0.10 0.05 0 3.0 3.5 4.0 4.5 5.0 5.5 VLOGIC SUPPLY (V) 6.0 6.5 0.8 0.30 VLOGIC = 5V 0.25 0.20 0.
PAGE 5
LTC4449 TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Input Frequency Switching Supply Current vs Load Capacitance 100 SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) NO LOAD VLOGIC = VCC = 5V 5 TS = GND 4 IVCC 3 2 15 VLOGIC = VCC = 5V TS = GND CLOAD = 3.3nF TS = GND ICC fIN = 500kHz 10 RISE/FALL TIME (ns) 6 ICC fIN = 100kHz ILOGIC fIN = 500kHz 1 10 0 0 200k 400k 600k tr(BG) 5 tf(BG) 0.
PAGE 6
LTC4449 PIN FUNCTIONS TG (Pin 1): High Side Gate Driver Output (Top Gate). This pin swings between TS and BOOST. TS (Pin 2): High Side MOSFET Source Connection (Top Source). BG (Pin 3): Low Side Gate Driver Output (Bottom Gate). This pin swings between VCC and GND. GND (Pin 4, Exposed Pad Pin 9): Chip Ground. The exposed pad must be soldered to PCB ground for optimal electrical and thermal performance. IN (Pin 5): Input Signal. Input referenced to an internal supply baised off of VLOGIC (Pin 6) and GND.
PAGE 7
LTC4449 TIMING DIAGRAM IN TG VIL(TG) VIL(BG) VIL(BG) 90% 10% tr(TG) tf(TG) 90% BG 10% tr(BG) tpLH(BG) tpLH(TG) tf(BG) tpHL(BG) 4449 TD tpHL(TG) OPERATION Overview The LTC4449 receives a ground-referenced, low voltage digital input signal to drive two N-channel power MOSFETs in a synchronous power supply conﬁguration. The gate of the low side MOSFET is driven either to VCC or GND, depending on the state of the input.
PAGE 8
LTC4449 OPERATION The hysteresis between the corresponding VIH and VIL voltage levels eliminates false triggering due to noise during switch transitions; however, care should be taken to keep noise from coupling into the IN pin, particularly in high frequency, high voltage applications. VIN LTC4449 Q1 BOOST CGD P1 HIGH SIDE POWER MOSFET TG CGS N1 TS Undervoltage Lockout The LTC4449 contains undervoltage lockout detectors that monitor both the VCC and VLOGIC supplies. When VCC falls below 3.
PAGE 9
LTC4449 OPERATION The LTC4449’s powerful parallel combination of the N-channel MOSFET (N2) and NPN (Q3) on the BG pull-down generates a phenomenal 4ns fall time on BG while driving a 3nF load. Similarly, the 0.8Ω pull-down MOSFET (N1) on TG results in a rapid 7ns fall time with a 3nF load. These powerful pull-down devices minimize the power loss associated with MOSFET turn-off time and cross-conduction current.
PAGE 10
LTC4449 APPLICATIONS INFORMATION Bypassing and Grounding The LTC4449 requires proper bypassing on the VLOGIC, VCC and VBOOST – TS supplies due to its high speed switching (nanoseconds) and large AC currents (amperes). Careless component placement and PCB trace routing may cause excessive ringing and under/overshoot. To obtain the optimum performance from the LTC4449: • Mount the bypass capacitors as close as possible between the VLOGIC and GND pins, the VCC and GND pins, and the BOOST and TS pins.
PAGE 11
1.33k RUN2 CLKOUT 20k 20k VDIFF1 1.5nF RUN1 VCC 5V VIN 7V TO 14V 45k SS1 FREQ SET FOR 600kHz VCC VDIFF1 VOS1N VOS1P FB1 COMP1 VSNSOUT VSNSN VSNSP COMP2 FB2 0.1μF TRACK/SS1 100k VCC LTC3860 7V TO 14V IN AND 1.2V OUT AT 50A fSW = 600kHz, DCR SENSING 220pF 12.7k 33pF 1μF 470μF 50k ILIM1 ISNS1P ISNS1N ISNS2N ISNS2P ILIM2 RUN2 PWM1 100pF VCC TRACK/SS1 VINSNS IAVG PGOOD1 PWM1 RUN1 PWM2 TRACK/SS2 FREQ CLKIN CLKOUT PHSMD PGOOD2 PWM2 VCC 4.7μF 1μF 4.7μF 1μF VCC 2.2Ω 0.22μF 0.
PAGE 12
LTC4449 PACKAGE DESCRIPTION DCB Package 8-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1718 Rev A) R = 0.115 TYP R = 0.05 5 TYP 2.00 p0.10 (2 SIDES) 0.40 p 0.10 8 0.70 p0.05 1.35 p0.10 3.50 p0.05 1.65 p 0.10 3.00 p0.10 (2 SIDES) 2.10 p0.05 1.35 p0.05 1.65 p 0.05 PIN 1 NOTCH R = 0.20 OR 0.25 s 45o CHAMFER PIN 1 BAR TOP MARK (SEE NOTE 6) PACKAGE OUTLINE (DCB8) DFN 0106 REV A 4 0.200 REF 1 0.23 p 0.05 0.45 BSC 0.75 p0.05 1.35 REF BOTTOM VIEW—EXPOSED PAD 0.00 – 0.05 NOTE: 1.
PAGE 13
LTC4449 REVISION HISTORY REV DATE DESCRIPTION A 6/10 Updated Temperature Range in Order Information section PAGE NUMBER Updates to Electrical Characteristics section 2 2, 3 Updates to Pin Functions 6 Added Typical Application and updated Related Parts 14 4449fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 14
LTC4449 TYPICAL APPLICATION VIN LTC4449 IN GND VLOGIC TG VCC TS BOOST BG PWM1 VCC VIN 470μF VCC 1μF VOUT 1nF 220Ω 33pF 20k 20k 220pF 0.1μF 12.7k PWM1 VINSNS VCC FREQ FB2 ILIM2 LTC3860 FB1 COMP1,2 SS1,2 VSNSOUT VSNSN VSNSP SGND RUN1,2 ILIM1 ISNS1P ISNS1N ISNS2N ISNS2P 50k TG1 SW1 0.3μH BG1 0.22μF 2.32k VOUT 1.2V 330μF 50A s4 0.22μF 0.22μF VIN LTC4449 IN GND VLOGIC TG VCC TS BOOST BG PWM2 PWM2 VCC IAVG CLKIN 100pF 2.32k TG2 SW2 0.3μH 4449 TA03 BG2 0.