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LTC3822-1

38221f

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

No R

SENSE

, Low Input

Voltage, Synchronous

Step-Down DC/DC Controller

The LTC

3822-1 is a synchronous step-down switching

regulator controller that drives external N-channel power

MOSFETs using few external components. The constant

frequency current mode architecture with MOSFET V

sensing eliminates the need for sense resistors and im-

proves efﬁ ciency.

Burst Mode operation provides high efﬁ ciency at light

loads. The 99% maximum duty cycle provides low dropout

operation, extending operating time in battery-powered

systems.

The operating frequency can be programmed up to 750kHz,

allowing the use of small surface mount inductors and ca-

pacitors. For noise sensitive applications, the LTC3822-1

can be synchronized to an external clock from 250kHz to

750kHz.

The LTC3822-1 is available in the tiny footprint thermally

enhanced 12-pin DFN package or 16-pin narrow SSOP

package.

■

Dual N-Channel MOSFET Synchronous Drive

■

No Current Sense Resistor Required

■

Optimized for 3.3V

and Li-Ion Applications

■

Constant Frequency Current Mode Operation for

Excellent Line and Load Transient Response

■

±1% 0.6V Reference

■

Low Dropout Operation: 99% Duty Cycle

■

Phase-Lockable or Adjustable Frequency:

250kHz to 750kHz

■

Internal Soft-Start Circuitry

■

Tracking and Adjustable Soft-Start Input

■

Selectable Maximum Peak Current Sense Threshold

■

Selectable Burst Mode

/ Forced Continuous/Pulse

Skipping Mode at Light Load

■

Digital RUN Control Pin

■

Output Overvoltage Protection

■

Micropower Shutdown: I

= 7.5µA

■

Tiny Thermally Enhanced 12-Pin (3mm × 3mm) DFN

or 16-Pin Narrow SSOP Packages

■

Single Cell Li-Ion Powered Systems

■

3.3V

Systems

IPRG

LTC3822-1

RUN

PLLLPF

0.1µF

1nF

10.2k

59k 118k

38221 TA01

0.47µH

47µF

×2

BOOST

TRACK/SS

SYNC/MODE

GND

47µF

×2

OUT

1.8V

3.3V

, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology

Corporation. No R

SENSE

is a trademark of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Protected by Patents, including 5481178, 5929620, 6580258, 6304066, 5847554,

6611131, 6498466, 5705919.

LTC3822-1 LTC3822

Light Load

Operation

Continuous, Discontinuous

or Burst Mode Operation

Discontinuous Mode

Package DD12 (3mm × 3mm), GN16 DD10 (3mm × 3mm),

MS10E

Tracking/Soft-Start Yes Internal Soft-Start Only

External Sync Yes No

PGOOD Pin GN16 Only No

Efﬁ ciency/Power Loss vs Load Current

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (W)

100 1000 10000

38221 TA01b

100

Burst Mode

EFFICIENCY

Burst Mode

POWER LOSS

0.1

0.01

0.001

= 3.3V

OUT

= 1.8V

FIGURE 10 CIRCUIT

Summary of content (24 pages)

PAGE 1
LTC3822-1 No RSENSETM, Low Input Voltage, Synchronous Step-Down DC/DC Controller DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Dual N-Channel MOSFET Synchronous Drive No Current Sense Resistor Required Optimized for 3.3VIN and Li-Ion Applications Constant Frequency Current Mode Operation for Excellent Line and Load Transient Response ±1% 0.
PAGE 2
LTC3822-1 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (VIN) ........................ –0.3V to 4.5V BOOST Voltage .......................................... –0.3V to 10V PLLLPF, RUN, IPRG, SYNC/MODE, TRACK/SS Voltages .......................–0.3V to (VIN + 0.3V) VFB, ITH Voltages ....................................... –0.3V to 2.4V SW Voltage ............................................ –2V to VIN + 1V Operating Temperature Range (Note 2) ...
PAGE 3
LTC3822-1 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 3.3V unless otherwise noted. PARAMETER CONDITIONS MIN Output Voltage Load Regulation ITH = 1.3V to 0.9V (Note 5) ITH = 1.3V to 1.7V TRACK/SS Pull-Up Current TRACK/SS = 0V VFB Input Current (Note 5) Overvoltage Protect Threshold Measured at VFB TYP MAX UNITS 0.1 –0.1 0.5 –0.5 % % 0.65 1 1.35 µA 10 50 nA 0.66 0.
PAGE 4
LTC3822-1 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency/Power Loss vs Load Current 100 10 80 EFFICIENCY EFFICIENCY (%) 1 60 50 0.1 40 POWER LOSS 30 POWER LOSS (W) 70 VOUT AC COUPLED 200mV/DIV VOUT AC COUPLED 200mV/DIV INDUCTOR CURRENT 2A/DIV INDUCTOR CURRENT 2A/DIV FIGURE 10 CIRCUIT 0.01 Burst Mode OPERATION PULSE SKIPPING CONTINUOUS MODE 0.001 100 1000 10000 LOAD CURRENT (mA) 20 10 0 10 Load Step (Pulse Skip Mode) Load Step (Continuous Mode) 100 VIN = 3.3V, VOUT = 1.
PAGE 5
LTC3822-1 TYPICAL PERFORMANCE CHARACTERISTICS Shutdown Quiescent Current vs Input Voltage Maximum Current Sense Voltage vs ITH Pin Voltage Oscillator Frequency vs Input Voltage 100 80 CURRENT LIMIT (%) 3 2 1 0 –1 –2 –3 18 Burst Mode OPERATION (ITH RISING) Burst Mode OPERATION (ITH FALLING) FORCED CONTINUOUS MODE PULSE SKIPPING MODE 4 60 40 16 SHUTDOWN CURRENT (µA) 5 NORMALIZED FREQUENCY SHIFT (%) TA = 25°C unless otherwise noted. 20 0 14 12 10 8 6 4 2 –4 –5 2.5 –20 3.0 3.5 4.
PAGE 6
LTC3822-1 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted. Pulse Skip Mode Operation Burst Mode Operation VSW 2V/DIV VSW 2V/DIV VOUT 20mV/DIV AC COUPLED VOUT 20mV/DIV AC COUPLED IL 2A/DIV IL 2A/DIV 2µs/DIV FIGURE 10 CIRCUIT VIN = 3.3V VOUT = 1.8V, 100mA PIN FUNCTIONS 38221 G18 10µs/DIV FIGURE 10 CIRCUIT VIN = 3.3V VOUT = 1.8V, 100mA 38221 G19 (DD/GN) PLLLPF (Pin 1/Pin 2): This pin serves as the frequency select input and PLL lowpass ﬁlter compensation point.
PAGE 7
LTC3822-1 PIN FUNCTIONS (DD/GN) BG (Pin 8/Pin 11): Bottom Gate Driver Output. This pin drives the gate of the external bottom-side MOSFET. This pin has an output swing from GND to BOOST. TG (Pin 9/Pin 12): Top Gate Driver Output. This pin drives the gate of the external topside MOSFET. This pin has an output swing from GND to BOOST. BOOST (Pin 10/Pin 13): Positive Supply Pin for the Gate Driver Circuitry.
PAGE 8
LTC3822-1 FUNCTIONAL DIAGRAM DB VIN VIN CB CIN SENSE – VOLTAGE REFERENCE BOOST IPRG VREF 0.6V TG SLOPE CLK + UNDERVOLTAGE LOCKOUT Q GND R ICMP SENSE+ M1 S SWITCHING LOGIC AND BLANKING CIRCUIT – VIN L VOUT COUT BOOST VIN BG M2 UVSD 0.7µA RUN GND BG t = 1ms INTERNAL SOFT-START BOOST REFRESH TIMEOUT CLK FCB IREV TRK/SS MUX TRACK/SS + SW – GND RICMP + 1µA SW ANTI-SHOOTTHROUGH SLEEP VIN 0.
PAGE 9
LTC3822-1 OPERATION (Refer to Functional Diagram) Main Control Loop The LTC3822-1 uses a constant frequency, current mode architecture. During normal operation, the top external N-channel power MOSFET is turned on when the clock sets the RS latch, and is turned off when the current comparator (ICMP) resets the latch. The peak inductor current at which ICMP resets the RS latch is determined by the voltage on the ITH pin, which is driven by the output of the error ampliﬁer (EAMP).
PAGE 10
LTC3822-1 OPERATION (Refer to Functional Diagram) signal goes low and the controller resumes normal operation by turning on the top N-channel MOSFET on the next cycle of the internal oscillator. When the controller is enabled for Burst Mode or pulse skipping operation, the inductor current is not allowed to reverse. Hence, the controller operates discontinuously. The reverse current comparator RICMP senses the drainto-source voltage of the bottom N-channel MOSFET.
PAGE 11
LTC3822-1 OPERATION (Refer to Functional Diagram) Undervoltage Lockout To prevent operation of the MOSFETs below safe input voltage levels, an undervoltage lockout is incorporated in the LTC3822-1. When the input supply voltage (VIN) drops below 2.25V, the external MOSFETs and all internal circuits are turned off except for the undervoltage block, which draws only a few microamperes.
PAGE 12
LTC3822-1 APPLICATIONS INFORMATION The typical LTC3822-1 application circuit is shown on the front page of this data sheet. External component selection for the controller is driven by the load requirement and begins with the selection of the inductor and the power MOSFETs. Power MOSFET Selection The LTC3822-1’s controller requires external N-channel power MOSFETs for the topside (main) and bottom (synchronous) switches.
PAGE 13
LTC3822-1 APPLICATIONS INFORMATION gate drive (VIN) voltage, the MOSFETs ultimately should be evaluated in the actual LTC3822-1 application circuit to ensure proper operation. ρT NORMALIZED ON RESISTANCE 2.0 1.5 Shoot-through between the MOSFETs can most easily be spotted by monitoring the input supply current. As the input supply voltage increases, if the input supply current increases dramatically, then the likely cause is shoot-through. 1.0 0.
PAGE 14
LTC3822-1 APPLICATIONS INFORMATION an external voltage VX, according to a ratio set by a resistor divider at TRACK/SS pin (Figure 4a). The ratiometric relation between VOUT and VX is (Figure 4c): VOUT RTA RA + RB = • VX RA RTA + RTB For coincident tracking (VOUT = VX during start-up), RTA = RA, RTB = RB Table 1.
PAGE 15
LTC3822-1 APPLICATIONS INFORMATION over temperature and process variations, to be between 250kHz and 750kHz. A simpliﬁed block diagram is shown in Figure 6. If the external clock frequency is greater than the internal oscillator’s frequency, fOSC, then current is sourced continuously from the phase detector output, pulling up the PLLLPF pin. When the external clock frequency is less than fOSC, current is sunk continuously, pulling down the PLLLPF pin.
PAGE 16
LTC3822-1 APPLICATIONS INFORMATION Burst Mode Operation Considerations The choice of RDS(ON) and inductor value also determines the load current at which the LTC3822-1 enters Burst Mode operation.
PAGE 17
LTC3822-1 APPLICATIONS INFORMATION The selection of COUT is driven by the effective series resistance (ESR). Typically, once the ESR requirement is satisﬁed, the capacitance is adequate for ﬁltering. The output ripple (ΔVOUT) is approximated by: VOUT ⎛ 1 ≈ IRIPPLE • ⎜ESR + 8• f •C ⎝ OUT VOUT LTC3822-1 RB CFF VFB RA ⎞ ⎟⎠ 38221 F07 Figure 7.
PAGE 18
LTC3822-1 APPLICATIONS INFORMATION If the duty cycle falls below what can be accommodated by the minimum on-time, the LTC3822-1 will begin to skip cycles. The output voltage will continue to be regulated, but the ripple current and ripple voltage will increase. The minimum on-time for the LTC3822-1 is typically about 170ns. However, as the peak sense voltage (IL(PEAK) • RDS(ON)) decreases, the minimum on-time gradually increases up to about 260ns.
PAGE 19
LTC3822-1 APPLICATIONS INFORMATION components, including a review of control loop theory, refer to Application Note 76. A second, more severe transient is caused by switching in loads with large (>1µF) supply bypass capacitors. The discharged bypass capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem if the load switch resistance is low and it is driven quickly.
PAGE 20
LTC3822-1 APPLICATIONS INFORMATION VIN CIN M1 GND L1 SW M2 VOUT COUT GND U1 AND OTHER SMALL-SIGNAL COMPONENTS GND SENSE TRACE 38221 F09 Figure 9. LTC3822-1 Suggested PCB Floorplan 10.2k TRACK/SS IPRG VIN SYNC/MODE RUN TG PLLLPF LTC3822EDD-1 SW ITH BOOST 27pF 1000pF GND 59k 1% BG 22µF ×2 FDS6898A 0.22µF IHLP-2525CZ-01 0.47µH VIN 2.75V TO 4.5V VOUT 1.8V 47µF* 8A ×2 D OPTIONAL VFB 118k 1% 38221 F10 *TDK C3216X5R0JL176M 27pF Figure 10. 3.3VIN 1.
PAGE 21
LTC3822-1 APPLICATIONS INFORMATION 1M TRACK/SS IPRG VIN SYNC/MODE RUN TG PGOOD – SENSE PLLLPF SW LTC3822EGN-1 ITH BOOST 33pF Si7882DP 47µF ×2 0.56µH** VOUT 1.8V 100µF* 12A ×2 0.22µF 13.7k 680pF GND 59k 1% BG VIN 3.3V Si7882DP VFB 118k 1% 38221 F07 *TAIYO YUDEN JMK325BJ107MM **TOKO FDU0650 68pF Figure 11. 3.3VIN 1.
PAGE 22
LTC3822-1 APPLICATIONS INFORMATION EXTERNAL OSCILLATOR 700kHz 10nF 10k 64.9k TRACK/SS IPRG VIN SYNC/MODE RUN TG PLLLPF LTC3822EDD-1 SW ITH BOOST 22µF ×2 Si7940DP VIN 3.3V 0.20µH** 0.20µF 10µF X5R 33pF VOUT 1.1V 220µF* 8A 470pF GND 59k 1% BG Si7940DP VFB 49.9k 1% 38221 F12a *SANYO 2R5TPE220M9 **TOKO FDV0630 82pF Figure 12. Externally Synchronized 700kHz, 3.3VIN, 1.
PAGE 23
LTC3822-1 PACKAGE DESCRIPTION DD Package 12-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1725 Rev A) R = 0.115 TYP 7 0.40 ± 0.10 12 0.70 ±0.05 3.50 ±0.05 2.10 ±0.05 2.38 ±0.05 1.65 ±0.05 2.38 ±0.10 3.00 ±0.10 (4 SIDES) 1.65 ± 0.10 PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) PACKAGE OUTLINE 6 0.25 ± 0.05 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 0.200 REF 0.45 BSC 2.25 REF 2.25 REF (DD12) DFN 0106 REV A 0.00 – 0.
PAGE 24
LTC3822-1 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1628/LTC3728 Dual High Efﬁciency, 2-Phase Synchronous Step Down Controllers Constant Frequency, Standby, 5V and 3.3V LDOs, VIN to 36V, 28-Lead SSOP LTC1735 High Efﬁciency Synchronous Step-Down Controller Burst Mode Operation, 16-Pin Narrow SSOP, Fault Protection, 3.5V ≤ VIN ≤ 36V LTC1778 No RSENSE, Synchronous Step-Down Controller Current Mode Operation Without Sense Resistor, Fast Transient Response, 4V ≤ VIN ≤ 36V LTC3411 1.