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LTC3830/LTC3830-1

3830fa

High Power Step-Down

Synchronous DC/DC Controllers

for Low Voltage Operation

■

High Power Switching Regulator Controller

for 3.3V-5V to 1.xV-3.xV Step-Down Applications

■

No Current Sense Resistor Required

■

Low Input Supply Voltage Range: 3V to 8V

■

Maximum Duty Cycle >91% Over Temperature

■

All N-Channel External MOSFETs

■

Excellent Output Regulation: ±1% Over Line, Load

and Temperature Variations

■

High Efficiency: Over 95% Possible

■

Adjustable or Fixed 3.3V Output (16-Pin Version)

■

Programmable Fixed Frequency Operation: 100kHz to

500kHz

■

External Clock Synchronization

■

Soft-Start (16-Pin Version and LTC3830-1)

■

Low Shutdown Current: <10µA

■

Overtemperature Protection

■

Available in S8, S16 and SSOP-16 Packages

■

CPU Power Supplies

■

Multiple Logic Supply Generator

■

Distributed Power Applications

■

High Efficiency Power Conversion

The LTC

3830/LTC3830-1 are high power, high effi-

ciency switching regulator controllers optimized for

3.3V-5V to 1.xV-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 LTC3830/LTC3830-1 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 FET, providing an adjustable current limit

without a current sense resistor.

The LTC3830/LTC3830-1 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 200kHz

free-running clock frequency can be externally adjusted or

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

In shutdown mode, the LTC3830 supply current drops to

<10µA. The LTC3830-1 differs from the LTC3830 S8 ver-

sion by replacing shutdown with a soft-start function.

For a similar, pin compatible DC/DC converter with an

output voltage as low as 0.6V, please refer to the LTC3832.

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

Figure 1. High Efficiency 3V-6V to 1.8V Power Converter

0.01µF

15k

COMP

GND

CC2

CC1

LTC3830-1

3.3nF

0.1µF

4.7µF

Si7806DN

0.1µF

B320A

220µF

10V

1.8V

3.2µH

Si7806DN

L: SUMIDA CDEP105-3R2MC-88

OUT

: PANASONIC EEFUEOD271R

OUT

270µF

3830 F01

5.1Ω

3V TO 6V

12.7k 1%

5.36k 1%

MBR0520T1

LOAD CURRENT (A)

POWER LOSS (W)

EFFICIENCY (%)

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

100

87654321910

3830 TA02

= 3.3V

OUT

= 1.8V

Efficiency and Power Loss vs Load Current

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (24 pages)

PAGE 1
LTC3830/LTC3830-1 High Power Step-Down Synchronous DC/DC Controllers for Low Voltage Operation U FEATURES DESCRIPTIO ■ The LTC®3830/LTC3830-1 are high power, high efficiency switching regulator controllers optimized for 3.3V-5V to 1.xV-3.xV step-down applications. A precision internal reference and feedback system provide ±1% output regulation over temperature, load current and line voltage variations. The LTC3830/LTC3830-1 use a synchronous switching architecture with N-channel MOSFETs.
PAGE 2
LTC3830/LTC3830-1 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 (Note 11) ........................... 125°C Operating Temperature Range (Note 9) ..
PAGE 3
LTC3830/LTC3830-1 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 ● ● 14 0.
PAGE 4
LTC3830/LTC3830-1 U W TYPICAL PERFOR A CE CHARACTERISTICS 3.34 3.33 1.275 TA = 25°C REFER TO FIGURE 12 8 6 1.269 4 1.267 2 1.265 0 1.263 –2 1.261 –4 1.259 –6 1.257 –8 VFB (V) 1.271 3.30 3.29 3.28 3.27 3.26 –15 –10 –5 5 0 OUTPUT CURRENT (A) 10 1.255 15 4 3 6 7 5 SUPPLY VOLTAGE (V) 20 3.31 10 3.30 0 3.29 –10 3.28 –20 3.
PAGE 5
LTC3830/LTC3830-1 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 4.0 18 3.5 16 3.0 OUTPUT VOLTAGE (V) 100 IMAX Sink Current vs Temperature 14 12 10 8 91 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 4 – 50 – 25 125 0 50 75 25 TEMPERATURE (°C) 100 3830 G11 12 10 8 6 4 2.00 –9 1.
PAGE 6
LTC3830/LTC3830-1 U W TYPICAL PERFOR A CE CHARACTERISTICS PVCC Supply Current vs Gate Capacitance 200 TA = 25°C 40 VOUT 50mV/DIV 160 PVCC1,2 = 12V 30 20 PVCC1,2 = 5V 10 140 120 tf AT PVCC1,2 = 5V 100 60 40 0 1 2 3 4 5 6 7 8 9 10 GATE CAPACITANCE AT G1 AND G2 (nF) tf AT PVCC1,2 = 12V 0 50µs/DIV 3830 G22.
PAGE 7
LTC3830/LTC3830-1 U U U PI FU CTIO S FREQSET (Pin 11/NA/NA): Frequency Set. Use this pin to adjust the free-running frequency of the internal oscillator. With the pin floating, the oscillator runs at about 200kHz. A resistor from FREQSET to ground speeds up the oscillator; a resistor to VCC slows it down. IMAX (Pin 12/NA/NA): Current Limit Threshold Set. IMAX sets the threshold for the internal current limit comparator. If IFB drops below IMAX with G1 on, the LTC3830 goes into current limit.
PAGE 8
LTC3830/LTC3830-1 TEST CIRCUITS 5V PVCC + VSHDN VCC 10µF SHDN NC NC NC NC FB SS FREQSET COMP IMAX GND VCC PVCC2 PVCC1 IFB IFB VCOMP G1 VCC COMP 6800pF LTC3830 LTC3830 VFB G2 PGND G1 RISE/FALL G1 6800pF SENSE – 0.
PAGE 9
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO Similarly, the MAX comparator forces the output to 0% duty cycle if the feedback signal is greater than 40mV above the internal reference. To prevent these two comparators from triggering due to noise, the MIN and MAX comparators’ response times are deliberately delayed by two to three microseconds.
PAGE 10
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO The RDS(ON) of Q1 usually increases with temperature. To keep the current limit threshold constant, the internal 12µA sink current at IMAX is designed with a positive temperature coefficient to provide first order correction for the temperature coefficient of RDS(ON)Q1.
PAGE 11
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO External Clock Synchronization The LTC3830 SHDN pin doubles as an external clock input for applications that require a synchronized clock. An internal circuit forces the LTC3830 into external synchronization mode if a negative transition at the SHDN pin is detected.
PAGE 12
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO Input Supply Considerations/Charge Pump The 16-lead LTC3830 requires four supply voltages to operate: VIN for the main power input, PVCC1 and PVCC2 for MOSFET gate drive and a clean, low ripple VCC for the LTC3830 internal circuitry (Figure 6). The LTC3830-1 and the 8-lead LTC3830 have the PVCC2 and VCC pins tied together inside the package (Figure 7).
PAGE 13
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO The LTC3830/LTC3830-1 overcomes this problem by sensing the PVCC1 voltage when G1 is high. If PVCC1 is less than (VCC + 2.5V), the maximum G1 duty cycle is reduced to 70% by clamping the COMP pin at 1.8V (QC in BLOCK DIAGRAM). This increases the G2 on time and allows the charge pump capacitor to be refreshed.
PAGE 14
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO PMAX should be calculated based primarily on required efficiency or allowable thermal dissipation. A typical high efficiency circuit designed for 5V input and 3.3V at 10A output might allow no more than 3% efficiency loss at full load for each MOSFET. Assuming roughly 90% efficiency at this current level, this gives a PMAX value of: (3.3V)(10A/0.9)(0.03) = 1.
PAGE 15
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO where LO is the inductor value in µH. With proper frequency compensation, the combination of the inductor and output capacitor values determine the transient recovery time. In general, a smaller value inductor improves transient response at the expense of ripple and inductor core saturation rating. A 2µH inductor has a 0.81A/µs rise time in this application, resulting in a 6.2µs delay in responding to a 5A load current step. During this 6.
PAGE 16
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO A common way to lower ESR and raise ripple current capability is to parallel several capacitors. A typical LTC3830 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.
PAGE 17
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO Figure 10b shows the Bode plot of the overall transfer function. When low ESR output capacitors (Sanyo OS-CON) are used, the ESR zero can be high enough in frequency that it provides little phase boost at the loop crossover frequency. As a result, the phase margin becomes inadequate and the load transient is not optimized.
PAGE 18
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO Table 3 shows the suggested compensation component values for 5V to 3.3V applications based on 470µF Sanyo POSCAP 4TPB470M output capacitors. Table 3. Recommended Compensation Network for 5V to 3.3V Applications Using Multiple Paralleled 470µF Sanyo POSCAP 4TPB470M Output Capacitors L1 (µH) 1.2 1.2 1.2 2.4 2.4 2.4 4.7 4.7 4.7 COUT (µF) 1410 2820 4700 1410 2820 4700 1410 2820 4700 RC (kΩ) 6.8 15 22 18 43 62 43 91 150 CC (nF) 4.7 2.2 2.2 10 2.2 2.
PAGE 19
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO 3. The small-signal resistors and capacitors for frequency compensation and soft-start should be located very close to their respective pins and the ground ends connected to the signal ground pin through a separate trace. Do not connect these parts to the ground plane! 4. The VCC, PVCC1 and PVCC2 decoupling capacitors should be as close to the LTC3830 as possible. The 4.
PAGE 20
LTC3830/LTC3830-1 U W U U APPLICATIO S I FOR ATIO 5V + 100Ω 1µF PVCC2 PVCC1 VCC 4.7µF 0.1µF NC SHUTDOWN C1 33pF IMAX SS 0.01µF RC 18k CC 0.01µF 0.1µF Q1 G1 1k LO 2.5µH 0.1µF LTC3830 IFB G2 FREQSET SHDN PGND COMP GND Q2 + COUT 470µF ×3 3.3V 10A SENSE + SENSE– FB 3.0 100 2.5 90 2.0 80 1.5 70 1.0 60 50 0.5 VIN = 5V VOUT = 3.
PAGE 21
LTC3830/LTC3830-1 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 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) .0532 – .0688 (1.35 – 1.75) 2 3 4 5 6 7 8 .004 – .0098 (0.102 – 0.249) 0° – 8° TYP .
PAGE 22
LTC3830/LTC3830-1 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 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .053 – .069 (1.346 – 1.752) .014 – .019 (0.
PAGE 23
LTC3830/LTC3830-1 U PACKAGE DESCRIPTIO S Package 16-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .386 – .394 (9.804 – 10.008) NOTE 3 .045 ±.005 .050 BSC 16 N 15 14 13 12 11 10 9 N .245 MIN .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) 1 .030 ±.005 TYP 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .010 – .020 × 45° (0.254 – 0.508) 2 3 4 5 6 .053 – .069 (1.346 – 1.752) .008 – .010 (0.203 – 0.254) NOTE: 1.
PAGE 24
LTC3830/LTC3830-1 U TYPICAL APPLICATIO Typical 3.3V to 2.5V, 14A Application 12V 3.3V + CIN 330µF ×2 + COUT 470µF ×3 0.1µF 10µF 100Ω PVCC1 PVCC2 4.7µF 0.1µF SHDN C1 33pF LO 1.3µH 1k LTC3830 IFB D1 PGND SHDN 2.5V 14A 16.5k 1% GND COMP RC 18k CC 1500pF Q2 G2 FREQSET 130k Q1 IMAX SS 0.01µF 6.8k G1 VCC SENSE + SENSE – NC FB NC CIN: SANYO POSCAP 6TPB330M COUT: SANYO POSCAP 4TPB470M D1: MBRS330T3 LO: SUMIDA CDEP105-1R3 Q1, Q2: VISHAY Si7892DP 16.