Datasheet

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LTC3832/LTC3832-1

sn3832 3832fs

High Power Step-Down

Synchronous DC/DC Controllers

for Low Voltage Operation

■

OUT

as Low as 0.6V

■

High Power Switching Regulator Controller

for 3.3V-5V to 0.6V-3.xV Step-Down Applications

■

No Current Sense Resistor Required

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Low Input Supply Voltage Range: 3V to 8V

■

Maximum Duty Cycle >91% Over Temperature

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All N-Channel External MOSFETs

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Excellent Output Regulation: ±1% Over Line, Load

and Temperature Variations

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High Efficiency: Over 95% Possible

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Adjustable or Fixed 2.5V Output (LTC3832)

■

Programmable Fixed Frequency Operation: 100kHz to

500kHz

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External Clock Synchronization

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Soft-Start

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Low Shutdown Current: <10µA

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Overtemperature Protection

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Available in SO-8 and SSOP-16 Packages

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CPU Power Supplies

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Multiple Logic Supply Generator

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Distributed Power Applications

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High Efficiency Power Conversion

The LTC

3832/LTC3832-1 are high power, high effi-

ciency switching regulator controllers optimized for

3.3V-5V to 0.6V-3.xV step-down applications. A preci-

sion internal reference and feedback system provide

±1% output regulation over temperature, load current

and line voltage variations. The LTC3832/LTC3832-1 use

a synchronous switching architecture with N-channel

MOSFETs. Additionally, the chip senses output current

through the drain-source resistance of the upper

N-channel MOSFET, providing an adjustable current limit

without a current sense resistor.

The LTC3832/LTC3832-1 operate with an input supply

voltage as low as 3V and with a maximum duty cycle of

>91% over temperature. They include a fixed frequency

PWM oscillator for low output ripple operation. The 300kHz

free-running clock frequency can be externally adjusted or

synchronized with an external signal from 100kHz to 500kHz.

In shutdown mode, the LTC3832 supply current drops to

<10µA. The LTC3832-1 is the SO-8 version without current

limit, frequency adjustment and shutdown functions.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Figure 1. High Efficiency 3.3V to 1V Power Converter

0.01µF

15k

COMP

GND

/PV

CC2

CC1

LTC3832-1

680pF

0.1µF

4.7µF

MBR0520T1

Si9426DY

OUT

3.2µH

Si9426DY

L1: SUMIDA CDEP105-3R2MC-88

OUT

: PANASONIC EEFUEOD271R

OUT

270µF

3832 F01

0.1µF

5.1Ω

3V TO 7V

6.49k

4.32k

LOAD CURRENT (A)

EFFICIENCY (%)

100

2468

3832 F01b

10103579

= 3.3V

OUT

= 2.5V

OUT

= 1V

Efficiency

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (24 pages)

PAGE 1
LTC3832/LTC3832-1 High Power Step-Down Synchronous DC/DC Controllers for Low Voltage Operation U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®3832/LTC3832-1 are high power, high efficiency switching regulator controllers optimized for 3.3V-5V to 0.6V-3.xV step-down applications. A precision internal reference and feedback system provide ±1% output regulation over temperature, load current and line voltage variations.
PAGE 2
LTC3832/LTC3832-1 W W W AXI U U ABSOLUTE RATI GS (Note 1) Supply Voltage VCC ....................................................................... 9V PVCC1,2 ................................................................ 14V Input Voltage IFB, IMAX ............................................... – 0.3V to 14V SENSE+, SENSE–, FB, SHDN, FREQSET ....................... – 0.3V to VCC + 0.3V Junction Temperature ........................................... 125°C Operating Temperature Range (Note 9) ..
PAGE 3
LTC3832/LTC3832-1 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC, PVCC1, PVCC2 = 5V, unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS TYP MAX IVCC Supply Current Figure 2, VSHDN = VCC VSHDN = 0V ● ● MIN 0.7 1 1.6 10 mA µA IPVCC PVCC Supply Current Figure 2, VSHDN = VCC (Note 3) VSHDN = 0V ● ● 20 0.
PAGE 4
LTC3832/LTC3832-1 U W TYPICAL PERFOR A CE CHARACTERISTICS 0.605 2.54 TA = 25°C 2.53 REFER TO FIGURE 12 3 0.602 2 0.601 1 0.600 0 0.599 –1 0.598 –2 0.597 –3 0.596 –4 VFB (V) VOUT (V) 2.48 2.47 –10 –5 5 0 OUTPUT CURRENT (A) 10 0.595 15 4 3 6 7 5 SUPPLY VOLTAGE (V) 3832 G01 40 2.52 20 2.51 10 2.50 0 2.49 –10 2.48 –20 2.47 –30 2.46 –40 VOUT (V) 30 50 25 0 75 TEMPERATURE (°C) 100 ∆VOUT (mV) 2.53 2.
PAGE 5
LTC3832/LTC3832-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Maximum G1 Duty Cycle vs Temperature VFB = 0V REFER TO FIGURE 3 98 IMAX SINK CURRENT (µA) MAXIMUM G1 DUTY CYCLE (%) 99 97 96 95 94 93 Output Overcurrent Protection 20 3.0 18 2.5 16 OUTPUT VOLTAGE (V) 100 IMAX Sink Current vs Temperature 14 12 10 1.
PAGE 6
LTC3832/LTC3832-1 U W TYPICAL PERFOR A CE CHARACTERISTICS PVCC Supply Current vs Gate Capacitance 80 G1 Rise/Fall Time vs Gate Capacitance 200 TA = 25°C VOUT 50mV/DIV 160 60 G1 RISE/FALL TIME (ns) PVCC SUPPLY CURRENT (mA) TA = 25°C 180 70 Transient Response 50 PVCC1,2 = 12V 40 30 PVCC1,2 = 5V 20 140 120 tf AT PVCC1,2 = 5V 100 60 40 10 tf AT PVCC1,2 = 12V 20 0 0 1 2 3 4 5 6 7 8 9 10 GATE CAPACITANCE AT G1 AND G2 (nF) 0 50µs/DIV 3832 G21 tr AT PVCC1,2 = 12V 0 1 2 3 4 5 6 7 8 9 10 G
PAGE 7
LTC3832/LTC3832-1 U U U PI FU CTIO S VCC (Pin 14/Pin 7): Power Supply Input. All low power internal circuits draw their supply from this pin. Connect this pin to a clean power supply, separate from the main VIN supply at the drain of Q1. This pin requires a 4.7µF bypass capacitor. The LTC3832-1has VCC and PVCC2 tied together at Pin 7 and requires a 10µF bypass capacitor to GND. FREQSET (Pin 11/NA): Frequency Set. Use this pin to adjust the free-running frequency of the internal oscillator.
PAGE 8
LTC3832/LTC3832-1 W BLOCK DIAGRA (LTC3832-1) DISABLE GATE DRIVE THERMAL SHUTDOWN INTERNAL OSCILLATOR POWER DOWN PVCC1 – + COMP PWM S Q G1 R Q VCC/PVCC2 G2 FFG2 12µA S SS Q ENABLE G2 QSS MAX ERR + R + – – POR PGND FB VREF 2.2V VREF + 10% QC 1.2V + PVCC1 – VCC + 2.
PAGE 9
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO Also included in the LTC3832 is an internal soft-start feature that requires only a single external capacitor to operate. In addition, the LTC3832 features an adjustable oscillator that can free run or synchronize to external signal with frequencies from 100kHz to 500kHz, allowing added flexibility in external component selection. The LTC3832-1 does not include current limit, frequency adjustability, external synchronization and the shutdown function.
PAGE 10
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO remains at a reduced voltage until the overload is removed. Serious overloads generate a large overdrive at CC, allowing it to pull SS down quickly and preventing damage to the output components. By using the RDS(ON) of Q1 to measure the output current, the current limiting circuit eliminates an expensive discrete sense resistor that would otherwise be required. This helps minimize the number of components in the high current path.
PAGE 11
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO Connecting a 82k resistor from FREQSET to ground forces 15µA out of the pin, causing the internal oscillator to run at approximately 450kHz. Forcing an external 20µA current into FREQSET cuts the internal frequency to 100kHz. An internal clamp prevents the oscillator from running slower than about 50kHz. Tying FREQSET to V CC forces the chip to run at this minimum speed. The LTC3832-1 does not have this frequency adjustment function.
PAGE 12
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO VCC PVCC2 PVCC1 VIN G1 Q1 LO INTERNAL CIRCUITRY VOUT G2 + COUT Q2 LTC3832 3832 F6 Figure 6. LTC3832 Power Supplies VCC/PVCC2 PVCC1 VIN G1 Q1 LO INTERNAL CIRCUITRY VOUT G2 + Q2 LTC3832-1 COUT 3832 F7 Figure 7. LTC3832-1 Power Supplies In many applications, VCC can be powered from VIN through an RC filter. This supply can be as low as 3V.
PAGE 13
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO Diagram). This increases the G2 on-time and allows the charge pump capacitors to be refreshed. For applications using an external supply to PVCC1, this supply must also be higher than VCC by at least 2.5V to ensure normal operation. For applications with a 5V or higher VIN supply, PVCC2 can be tied to VIN if a logic level MOSFET is used. PVCC1 can be supplied using a doubling charge pump as shown in Figure␣ 9.
PAGE 14
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO Note that the required RDS(ON) for Q2 is roughly three times that of Q1 in this example. Note also that while the required RDS(ON) values suggest large MOSFETs, the power dissipation numbers are only 0.83W per device or less; large TO-220 packages and heat sinks are not necessarily required in high efficiency applications.
PAGE 15
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO requirements. Peak current in the inductor will be equal to the maximum output load current plus half of the peak-topeak inductor ripple current. Ripple current is set by the inductor value, the input and output voltage and the operating frequency. The ripple current is approximately equal to: IRIPPLE = ( VIN − VOUT ) • ( VOUT ) fOSC • LO • VIN fOSC = LTC3832 oscillator frequency = 300kHz LO = Inductor value Solving this equation with our typical 3.
PAGE 16
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO LTC3832 application might exhibit 5A input ripple current. Sanyo OS-CON capacitors, part number 10SA220M (220µF/10V), feature 2.3A allowable ripple current at 85°C; three in parallel at the input (to withstand the input ripple current) meet the above requirements. Similarly, Sanyo POSCAP 4TPB470M (470µF/4V) capacitors have a maximum rated ESR of 0.04Ω; three in parallel lower the net output capacitor ESR to 0.013Ω.
PAGE 17
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO between the top of the resistor divider network and the V FB pin to create a pole-zero pair in the loop compensation. The zero location is prior to the pole location and thus, phase lead can be added to boost the phase margin at the loop crossover frequency. The pole and zero locations are located at: fZC2 = 1/[2π(R2)(C2)] and fPC2 = 1/[2π(R1||R2)(C2)] where R1||R2 is the parallel combination resistance of R1 and R2.
PAGE 18
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO 1. In general, layout should begin with the location of the power devices. Be sure to orient the power circuitry so that a clean power flow path is achieved. Conductor widths should be maximized and lengths minimized. After you are satisfied with the power path, the control circuitry should be laid out. It is much easier to find routes for the relatively small traces in the control circuits than it is to find circuitous routes for high current paths. 2.
PAGE 19
LTC3832/LTC3832-1 U W U U APPLICATIO S I FOR ATIO + OPTIONAL DZ 12V 1N5242 1N5817 1N5817 CIN 330µF ×2 VIN 3.3V 1N5817 + 10µF 100Ω + PVCC2 PVCC1 VCC 1µF NC SHDN C1 180pF Q1A, Q1B 2 IN PARALLEL G1 SS 0.01µF IMAX 0.1µF 1k LO 1.3µH LTC3832 IFB SHDN PGND COMP GND RC 18k CC 1500pF Q2 G2 FREQSET D1 + SENSE + SENSE – FB COUT 470µF ×3 VOUT 2.
PAGE 20
LTC3832/LTC3832-1 U TYPICAL APPLICATIO S Typical 3.3V to 5V, 5A Synchronous Boost Converter VIN 3.3V + CIN 330µF 5mΩ MBR0520 10µF MBR0520 10Ω 10µF PVCC1 PVCC2 VCC 2.2µF NC SHUTDOWN C1 68pF RC 6.8k CC 0.01µF NC 5.6k 0.1µF SS 0.47µF 0.1µF IMAX LO 1.3µH MBR330T3 Q2 100Ω LTC3832 IFB G1 FREQSET SHDN PGND COMP GND SENSE + SENSE– NC Q1 10µF + 93.1k 1% COUT 330µF ×2 VOUT 5V 5A 12.
PAGE 21
LTC3832/LTC3832-1 U TYPICAL APPLICATIO S Typical 3.3V to – 5V, 5A Positive-to-Negative Converter VIN 3.3V + MBR0520 CIN 330µF 100Ω 1µF 10µF PVCC1 PVCC2 1µF IMAX SS 0.01µF NC SHUTDOWN C1 180pF RC 15k CC 1.5nF 1k LO 1.3µH 0.1µF LTC3832 IFB FREQSET Q2 G2 13V SHDN COMP NC Q1 0.1µF G1 VCC DZ 8.2V 3.5k + 10µF COUT 330µF 93.1k 1% FB SENSE + SENSE– NC 12.
PAGE 22
LTC3832/LTC3832-1 U PACKAGE DESCRIPTIO GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .045 ±.005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ± .0015 .150 – .157** (3.810 – 3.988) .0250 TYP RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) .053 – .068 (1.351 – 1.727) 2 3 4 5 6 7 8 .004 – .0098 (0.102 – 0.249) 0° – 8° TYP .016 – .
PAGE 23
LTC3832/LTC3832-1 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 7 6 5 N N .245 MIN .160 ±.005 1 .030 ±.005 TYP .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 2 3 4 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) 0°– 8° TYP .016 – .
PAGE 24
LTC3832/LTC3832-1 U TYPICAL APPLICATIO Typical 5V to 3.3V, 10A Application 5V + MBR0530T1 + 100Ω 1µF + VCC 0.1µF 4.7µF NC C1 180pF IMAX LO 1.3µH 0.1µF Q2 G2 PGND SHDN + COUT 470µF ×3 3.3V 10A 45k 1% GND COMP RC 18k CC 0.01µF 1k LTC3832 IFB FREQSET SHUTDOWN Q1A, Q1B 2 IN PARALLEL 0.1µF G1 SS 0.