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General Description

The MAX5099 offers a dual-output, high-switching-fre-

quency DC-DC buck converter with an integrated high-

side switch. The MAX5099 integrates two low-side

MOSFET drivers to allow each converter to drive an

external synchronous-rectifier MOSFET. Converter 1

delivers up to 2A output current, and converter 2 can

deliver up to 1A of output current. The MAX5099 inte-

grates load-dump protection circuitry that is capable of

handling load-dump transients up to 80V for automotive

applications. The load-dump protection circuit utilizes

an internal charge pump to drive the gate of an external

n-channel MOSFET. When an overvoltage or load-

dump condition occurs, the series protection MOSFET

absorbs the high voltage transient to prevent damage

to lower voltage components.

The DC-DC converter operates over a wide 4.5V to 19V

operating voltage range. The MAX5099 operates 180°

out-of-phase with an adjustable switching frequency to

minimize external components while allowing the ability

to make trade-offs between the size, efficiency, and

cost. The high switching frequency also allows these

devices to operate outside the AM band for automotive

applications. These regulators can be protected

against high voltage transients such as a load-dump

condition by using the integrated overvoltage controller.

This device utilizes voltage-mode control for stable

operation and external compensation, so that the loop

gain is tailored to optimize component selection and

transient response. The MAX5099 has a maximum duty

cycle of 92.5% and is synchronized to an external clock

fed at the SYNC input.

Additional features include internal digital soft-start,

individual enable for each DC-DC regulator (EN1 and

EN2), open-drain power-good outputs (PGOOD1 and

PGOOD2), and shutdown input (ON/OFF).

Other features of the MAX5099 include overvoltage pro-

tection and short-circuit (hiccup current limit) and ther-

mal protection. The MAX5099 is available in a thermally

enhanced, exposed pad 5mm x 5mm, 32-pin TQFN

package and operates over the automotive -40°C to

+125°C temperature range.

Applications

Automotive AM/FM Radio Power Supply

Automotive Instrument Cluster Display

Features

♦ Wide 4.5V to 5.5V or 5.2V to 19V Input Voltage

Range with 80V Load-Dump Protection

♦ Dual-Output DC-DC Converter with Integrated

Power MOSFETs

♦ Adjustable Outputs from 0.8V to 0.9V

♦ Output Current Capability Up to 2A and 1A

♦ Switching Frequency Programmable from 200kHz

to 2.2MHz

♦ Synchronization Input (SYNC)

♦ Individual Converter Enable Input and Power-

Good Output

♦ Low-I

(7µA) Standby Current (ON/OFF)

♦ Internal Digital Soft-Start and Soft-Stop

♦ Short-Circuit Protection on Outputs and

Maximum Duty-Cycle Limit

♦ Overvoltage Protection on Outputs with Auto

Restart

♦ Thermal Shutdown

♦ Thermally Enhanced 32-Pin TQFN Package

Dissipates Up to 2.7W at +70°C

MAX5099

Dual, 2.2MHz, Automotive Synchronous Buck

Converter with 80V Load-Dump Protection

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-4112; Rev 0; 5/08

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.

Pin Configuration appears at end of data sheet.

EVALUATION KIT

AVAILABLE

Denotes a lead-free package.

EP = Exposed pad.

PART TEMP RANGE PIN-PACKAGE

MAX5099ATJ+

-40°C to +125°C

32 TQFN-EP*

Summary of content (27 pages)

PAGE 1
9-4112; Rev 0; 5/08 KIT ATION EVALU E L B A IL AVA Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection The MAX5099 offers a dual-output, high-switching-frequency DC-DC buck converter with an integrated highside switch. The MAX5099 integrates two low-side MOSFET drivers to allow each converter to drive an external synchronous-rectifier MOSFET. Converter 1 delivers up to 2A output current, and converter 2 can deliver up to 1A of output current.
PAGE 2
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection ABSOLUTE MAXIMUM RATINGS V+ to SGND............................................................-0.3V to +25V V+ to IN_HIGH...........................................................-19V to +6V IN_HIGH to SGND ..................................................-0.3V to +19V IN_HIGH Maximum Input Current .......................................60mA BYPASS to SGND..................................................-0.
PAGE 3
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection (VDRV = VL, V+ = VL = IN_HIGH = 5.2V or V+ = IN_HIGH = 5.2V to 19V, EN_ = VL, SYNC = GND, IVL = 0mA, PGND = SGND, CBYPASS = 0.22μF (low ESR), CVL = 4.7μF (ceramic), CV+ = 1μF (low ESR), CIN_HIGH = 1μF (ceramic), RIN_HIGH = 3.9kΩ, ROSC = 10kΩ, TJ = -40°C to +125°C, unless otherwise noted.
PAGE 4
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection ELECTRICAL CHARACTERISTICS (continued) (VDRV = VL, V+ = VL = IN_HIGH = 5.2V or V+ = IN_HIGH = 5.2V to 19V, EN_ = VL, SYNC = GND, IVL = 0mA, PGND = SGND, CBYPASS = 0.22μF (low ESR), CVL = 4.7μF (ceramic), CV+ = 1μF (low ESR), CIN_HIGH = 1μF (ceramic), RIN_HIGH = 3.9kΩ, ROSC = 10kΩ, TJ = -40°C to +125°C, unless otherwise noted.
PAGE 5
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection (VDRV = VL, V+ = VL = IN_HIGH = 5.2V or V+ = IN_HIGH = 5.2V to 19V, EN_ = VL, SYNC = GND, IVL = 0mA, PGND = SGND, CBYPASS = 0.22μF (low ESR), CVL = 4.7μF (ceramic), CV+ = 1μF (low ESR), CIN_HIGH = 1μF (ceramic), RIN_HIGH = 3.9kΩ, ROSC = 10kΩ, TJ = -40°C to +125°C, unless otherwise noted.
PAGE 6
Typical Operating Characteristics (V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means that N1 is shorted externally.) OUTPUT2 EFFICIENCY vs. LOAD CURRENT VIN = 14V 50 40 VIN = 8V 20 60 40 VOUT = 5V fSW = 1.85MHz 30 40 30 VOUT = 3.3V fSW = 1.85MHz VOUT = 5V fSW = 300kHz L1 = 18μH 10 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 OUTPUT2 EFFICIENCY vs. LOAD CURRENT OUTPUT1 VOLTAGE vs. LOAD CURRENT OUTPUT2 VOLTAGE vs.
PAGE 7
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection CONVERTER 1 LOAD-TRANSIENT RESPONSE LINE-TRANSIENT RESPONSE (BUCK CONVERTER) MAX5099 toc11 MAX5099 toc10 0V VIN 5V/div VOUT1 = 5.0V AC-COUPLED 200mV/div 0V VOUT1 = 5.0V/1.5A AC-COUPLED 200mV/div IOUT1 1A/div VOUT2 = 3.3V/0.75A AC-COUPLED 200mV/div 0A 100μs/div 1ms/div CONVERTER 2 LOAD-TRANSIENT RESPONSE SOFT-START/SOFT-STOP FROM EN1 MAX5099 toc13 MAX5099 toc12 fSW = 1.85MHz EN1 5V/div 0V VOUT2 = 3.
PAGE 8
Typical Operating Characteristics (continued) (V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means that N1 is shorted externally.
PAGE 9
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection BYPASS VOLTAGE vs. BYPASS CURRENT SOURCE1, ISOURCE1, DL1, IIDL1 TA = +85°C TA = +125°C BYPASS VOLTAGE (V) 1.998 TA = +135°C MAX5099 toc22 MAX5099 toc23 2.000 SOURCE1 10V/div 0V 1.996 DL1 10V/div OV TA = -40°C 1.994 TA = +25°C ISOURCE1 1A/div 1.992 0A 1.990 0 10 20 30 40 50 60 70 80 90 100 200ns/div BYPASS CURRENT (μA) V+ SWITCHING SUPPLY CURRENT vs.
PAGE 10
Typical Operating Characteristics (continued) (V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means that N1 is shorted externally.) IN_HIGH CLAMP VOLTAGE vs. CLAMP CURRENT TA = +125°C 20.2 TA = +85°C TA = +25°C 20.1 TA = -40°C 20.0 19.9 5 V+ TO IN_HIGH CLAMP VOLTAGE (V) MAX5099 toc28 IN_HIGH CLAMP VOLTAGE (V) TA = +135°C MAX5099 toc29 V+ TO IN_HIGH CLAMP VOLTAGE vs. GATE SINK CURRENT 20.
PAGE 11
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection PIN NAME FUNCTION 1, 32 SOURCE2 Converter 2 Internal MOSFET Source Connection. For buck converter operation, connect SOURCE2 to the switched side of the inductor. For boost operation, connect SOURCE2 to PGND (Figure 5). 2, 3 DRAIN2 Converter 2 Internal MOSFET Drain Connection. For buck converter operation, use the MOSFET as a highside switch and connect DRAIN2 to the DC-DC converters supply input rail.
PAGE 12
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection Pin Description (continued) PIN NAME FUNCTION Signal Ground. Connect SGND to exposed pad and to the board signal ground plane. Connect the board signal ground and power ground planes together at a single point. 15 SGND 16 BYPASS Reference Output Bypass Connection. Bypass to SGND with a 0.22μF or greater ceramic capacitor. 17 FSEL_1 Converter 1 Frequency Select Input.
PAGE 13
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection V+ MAX5099 1.8V IN_HIGH GATE CHARGE PUMP ON/OFF 20V SHUNT REGULATOR OVERVOLTAGE STARTUP CIRCUIT/ PROTECTION CIRCUIT/ CHARGE PUMP CONVERTER 1 VL MAX DUTY-CYCLE CONTROL CLK1 VL LDO BST1/VDD1 CURRENT LIMIT OSCILLATOR DRAIN1 FREQUENCY CONTROL BYPASS R S FSEL_1 FREQUENCY DIVIDER PWM COMPARATOR SOURCE1 Q VDRV DL1 FSW/4 PGOOD1 Q TRANSCONDUCTANCE ERROR AMPLIFIER PGND 0.
PAGE 14
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection Detailed Description PWM Controller The MAX5099 dual DC-DC converters use a pulse-widthmodulation (PWM) voltage-mode control scheme. On each converter the device includes one integrated nchannel MOSFET switch and requires an external low-forward-drop Schottky diode for output rectification.
PAGE 15
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection Internal Oscillator/ Out-of-Phase Operation The internal oscillator generates the 180° out-of-phase clock signal required by each regulator. The switching frequency of each converter (fSW) is programmable from 200kHz to 2.2MHz using a single 1% resistor at ROSC. See the Setting the Switching Frequency section. With dual-synchronized out-of-phase operation, the MAX5099’s internal MOSFETs turn on 180° out-ofphase.
PAGE 16
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection VIN VIN VL VL OUTPUT2 N VL DRAIN2 V+ DRAIN1 SOURCE2 SOURCE1 DL2 FB2 MAX5099 OUTPUT1 OUTPUT2 N DL1 N FB1 VL DRAIN2 V+ DRAIN1 SOURCE2 SOURCE1 DL2 MAX5099 DL1 FB2 FB1 EN2 EN1 OUTPUT1 N R2 VL EN2 VL EN1 R1 VL C2 PGOOD1 SEQUENCING—OUTPUT 2 DELAYED WITH RESPECT TO OUTPUT 1. VL C1 R1/C1 AND R2/C2 ARE SIZED FOR REQUIRED SEQUENCING. Figure 1.
PAGE 17
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection Applications Information Setting the Switching Frequency The controller generates the clock signal by dividing down the internal oscillator fOSC or the SYNC input signal when driven by an external oscillator. The switching frequency equals half the internal oscillator frequency (fSW = fOSC/2). The internal oscillator frequency is set by a resistor (ROSC) connected from OSC to SGND.
PAGE 18
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection VOUT_ VOUT_ SOURCE_ BYPASS RA RC FB_ FB_ MAX5099 RB MAX5099 RA SOURCE_ VOUT_ ≥ 0.8V VOUT_ < 0.8V capacitance requirement. Note that the two converters of the MAX5099 run 180° out-of-phase, thereby effectively doubling the switching frequency at the input. The input ripple waveform would be unsymmetrical due to the difference in load current and duty cycle between converter 1 and converter 2.
PAGE 19
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection ΔVESR ΔIL ΔIL COUT = 8 × ΔVQ × fSW ESROUT = ΔVESR ISTEP ×t I COUT = STEP RESPONSE ΔVQ ESROUT = where I STEP is the load step and t RESPONSE is the response time of the controller. Controller response time depends on the control-loop bandwidth. Boost Converter The MAX5099 can be configured for step-up conversion since the internal MOSFET can be used as a lowside switch.
PAGE 20
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection where where ΔIL = (VIN − VDS ) × D L × fSW where VDS is the voltage drop across the internal MOSFET switch. ΔIL is the peak-to-peak inductor ripple current as calculated above. ΔVQ is the portion of input ripple due to the capacitor discharge, and ΔVESR is the contribution due to ESR of the capacitor.
PAGE 21
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection 2) Select the unity-gain crossover frequency: f fC ≤ SW 20 If the fZERO,ESR is lower than fC and close to fLC, use a Type II compensation network where RFCF provides a midband zero fMID,ZERO, and RFCCF provides a highfrequency pole. 3) Calculate modulator gain G M at the crossover frequency.
PAGE 22
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection Procedure 2 (See Figure 4) If the output capacitor used is a low-ESR ceramic type, the ESR frequency is usually far away from the targeted unity crossover frequency (fC). In this case, Type III compensation is recommended. Type III compensation provides two-pole zero pairs. The locations of the zero and poles should be such that the phase margin peaks around fC.
PAGE 23
Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection CF = 1 at 0.75 × fLC. 2 π × RF × CF 1 2π × 0.75 × fLC × RF where RF ≥ 10kΩ. 3) Calculate CI for a target crossover frequency, fC: 2 VOSC ⎡⎢(1 − D) + ω C2L OCO ⎤⎥ ⎣ ⎦ CI = ω CRF VIN where ωC = 2π x fC. 4) Place a pole fP1 = 1 at fZERO,RHP 2 π × RI × CI Choose a suitable power MOSFET that can safely operate in the saturation region.
PAGE 24
MAX5099 Dual, 2.2MHz, Automotive Synchronous Buck Converter with 80V Load-Dump Protection PCB Layout Guidelines Layout Procedure Careful PCB layout is critical to achieve low switching losses and clean, stable operation. This is especially true for dual converters where one channel can affect the other. Refer to the MAX5098A/MAX5099 Evaluation Kit data sheet for a specific layout example. Use a multilayer board whenever possible for better noise immunity.
PAGE 25
SGND PGND VOUT1 R22 C7 R8 R6 C8 L1 R7 D2 VL C20 C9 4 R11 N2 6 5 21 C6 D1 R9 3 2 1 IN_HIGH JU4 17 20 21 18 19 28 FSEL_1 EN1 PGOOD1 COMP1 FB1 DL1 25 SOURCE1 24 SOURCE1 26 BST1/VDD1 OSC 8 R12 ON/OFF BYPASS 16 C11 10 GATE 11 13 MAX5099 V+ 12 15 C19 VDRV C12 27 22 23 VIN DRAIN1 DRAIN1 VDRV C1 C4 2 3 C13 SYNC EN2 PGOOD2 COMP2 FB2 PGND DL2 SOURCE2 SOURCE2 BST2/VDD2 14 VL PGND SGND DRAIN2 DRAIN2 VIN 9 5 4 7 6 29 30 32 1 31 C15 R18
PAGE 26
VOUT1 = 5V AT 2A SGND PGND VOUT1 R22 10kΩ 1% R8 976Ω 1% C8 270pF R6 52.3kΩ 1% C7 22μF D2 R7 10kΩ 1% L1 4.7μH VL R11 C20 33pF 2 1 C9 R9 2700pF 12.7Ω 4 N2 6 5 21 C6 0.1μF D1 3 12 JU4 17 20 21 18 19 28 FSEL_1 EN1 PGOOD1 COMP1 FB1 DL1 25 SOURCE1 24 SOURCE1 26 BST1/VDD1 OSC 8 11 R12 6.49Ω ON/OFF VDRV IN_HIGH R1 3.9kΩ C2 4.7μF 35V 16 BYPASS C1 22μF 100V C11 0.22μF 10 GATE PGND MAX5099 15 13 C3 150μF 25V VDRV V+ N1 VDRV C12 2.
PAGE 27
Dual, 2.