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LT8610

8610fa

For more information www.linear.com/LT8610

TYPICAL APPLICATION

FEATURES DESCRIPTION

42V, 2.5A Synchronous

Step-Down Regulator

with 2.5µA Quiescent

Current

The LT

8610 is a compact, high efficiency, high speed

synchronous monolithic step-down switching regulator

that consumes only 2.5µA of quiescent current. Top and

bottom power switches are included with all necessary

circuitry to minimize the need for external components.

Low ripple Burst Mode operation enables high efficiency

down to very low output currents while keeping the output

ripple below 10mV

P-P

. A SYNC pin allows synchronization

to an external clock. Internal compensation with peak cur-

rent mode

topology allows the use of small inductors and

results

in fast transient response and good loop stability.

The EN/UV pin has an accurate 1V threshold and can be

used to program V

undervoltage lockout or to shut down

the LT8610 reducing the input supply current to 1µA. A

capacitor on the TR/SS pin programs the output voltage

ramp rate during start-up. The PG flag signals when V

OUT

is within ±9% of the programmed output voltage as well

as fault conditions. The LT8610 is available in a small

16-lead MSOP package with exposed pad for low thermal

resistance.

5V 2.5A Step-Down Converter 12V

to 5V

OUT

Efficiency

APPLICATIONS

Wide Input Voltage Range: 3.4V to 42V

Ultralow Quiescent Current Burst Mode

Operation:

2.5μA I

Regulating 12V

to 3.3V

OUT

Output Ripple < 10mV

P-P

High Efficiency Synchronous Operation:

96% Efficiency at 1A, 5V

OUT

from 12V

94% Efficiency at 1A, 3.3V

OUT

from 12V

Fast Minimum Switch-On Time: 50ns

Low Dropout Under All Conditions: 200mV at 1A

Allows Use Of Small Inductors

Low EMI

Adjustable and Synchronizable: 200kHz to 2.2MHz

Current Mode Operation

Accurate 1V Enable Pin Threshold

Internal Compensation

Output Soft-Start and Tracking

Small Thermally Enhanced 16-Lead MSOP Package

Automotive and Industrial Supplies

General Purpose Step-Down

GSM Power Supplies

L, LT , LT C , LT M , Burst Mode, Linear Technology and the Linear logo are registered trademarks

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

owners.

BSTV

EN/UV

SYNC

INTV

TR/SS

LT8610

GND

PGND

BIAS

8610 TA01a

0.1µF

OUT

2.5A

4.7µF

5.5V TO 42V

1µF

10nF

10pF

4.7µH

243k

= 700kHz

60.4k

47µF

LOAD CURRENT (A)

EFFICIENCY (%)

100

8610 G01

0.5

1.5

2.5

= 12V

= 24V

= 700kHz

Summary of content (22 pages)

PAGE 1
LT8610 42V, 2.5A Synchronous Step-Down Regulator with 2.5µA Quiescent Current DESCRIPTION FEATURES Wide Input Voltage Range: 3.4V to 42V n Ultralow Quiescent Current Burst Mode® Operation: 2.5μA IQ Regulating 12VIN to 3.3VOUT Output Ripple < 10mVP-P n High Efficiency Synchronous Operation: 96% Efficiency at 1A, 5VOUT from 12VIN 94% Efficiency at 1A, 3.
PAGE 2
LT8610 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION VIN, EN/UV, PG...........................................................42V BIAS...........................................................................30V BST Pin Above SW Pin................................................4V FB, TR/SS, RT, INTVCC ................................................4V SYNC Voltage ..............................................................6V Operating Junction Temperature Range (Note 2) LT8610E................
PAGE 3
LT8610 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS Oscillator Frequency RT = 221k, ILOAD = 1A RT = 60.4k, ILOAD = 1A RT = 18.2k, ILOAD = 1A Top Power NMOS On-Resistance ISW = 1A MIN TYP MAX UNITS l l l 180 665 1.85 210 700 2.00 240 735 2.15 kHz kHz MHz l 3.5 4.8 2.5 3.3 120 Top Power NMOS Current Limit Bottom Power NMOS On-Resistance VINTVCC = 3.
PAGE 4
LT8610 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency at 5VOUT Efficiency at 3.3VOUT 95 95 90 90 90 80 85 85 80 75 70 65 fSW = 700kHz VIN = 12V VIN = 24V 60 55 50 0.5 0 1.5 1 LOAD CURRENT (A) 2 EFFICIENCY (%) 100 EFFICIENCY (%) 100 EFFICIENCY (%) 100 80 75 70 65 55 50 2.5 0.5 0 1.5 1 LOAD CURRENT (A) 2 Efficiency at 3.3VOUT 90 30 0 0.001 0.01 2.5 Reference Voltage VOUT = 3.3V 0.982 EFFICIENCY (%) 92 50 40 30 0.1 1 10 100 1000 10000 LOAD CURRENT (mA) 0.
PAGE 5
LT8610 TYPICAL PERFORMANCE CHARACTERISTICS No Load Supply Current 25 VOUT = 3.3V IN REGULATION 4.5 20 INPUT CURRENT (µA) INPUT CURRENT (µA) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Top FET Current Limit vs Duty Cycle 6.0 VOUT = 3.3V VIN = 12V IN REGULATION 5.5 CURRENT LIMIT (A) No Load Supply Current 5.0 15 10 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 0 –55 45 Top FET Current Limit 65 5 95 35 TEMPERATURE (°C) –25 125 2.0 155 250 3.4 3.5 3.0 3.2 3.0 2.8 5 35 65 TEMPERATURE (°C) 95 2.
PAGE 6
LT8610 TYPICAL PERFORMANCE CHARACTERISTICS Switching Frequency 700 730 600 500 400 300 200 RT = 60.4k 720 710 700 690 680 670 100 0 Burst Frequency 800 SWITCHING FREQUENCY (kHz) 740 SWITCHING FREQUENCY (kHz) DROPOUT VOLTAGE (mV) Dropout Voltage 800 0 1 0.5 1.5 2 2.5 LOAD CURRENT (A) 95 65 35 TEMPERATURE (°C) 5 125 8610 G19 VOUT = 5V fSW = 700kHz SWITCHING FREQUENCY (kHz) 20 600 25 30 35 INPUT VOLTAGE (V) 40 1.0 500 400 300 0 45 0.2 0 0.2 0.4 0.
PAGE 7
LT8610 TYPICAL PERFORMANCE CHARACTERISTICS RT Programmed Switching Frequency Bias Pin Current 3.6 225 3.4 4.75 3.2 4.50 INPUT VOLTAGE (V) 175 150 125 100 75 5.00 BIAS PIN CURRENT (mA) 200 RT PIN RESISTOR (kΩ) VIN UVLO 250 3.0 2.8 2.6 2.4 50 2.2 25 0 0.2 0.6 1.4 1.8 1 SWITCHING FREQUENCY (MHz) 2.2 2.0 –55 –25 BIAS PIN CURRENT (mA) 4.00 3.75 3.50 95 65 35 TEMPERATURE (°C) 5 125 155 3.
PAGE 8
LT8610 TYPICAL PERFORMANCE CHARACTERISTICS Transient Response Start-Up Dropout Performance ILOAD 1A/DIV VIN VIN 2V/DIV VOUT 200mV/DIV 50µs/DIV 50mA TO 1A TRANSIENT 12VIN, 5VOUT COUT = 47µF 8610 G36 VIN 2V/DIV VOUT VOUT 2V/DIV 100ms/DIV 2.5Ω LOAD (2A IN REGULATION) Start-Up Dropout Performance VOUT 2V/DIV 8610 G37 VIN VOUT 100ms/DIV 20Ω LOAD (250mA IN REGULATION) 8610 G38 PIN FUNCTIONS SYNC (Pin 1): External Clock Synchronization Input.
PAGE 9
LT8610 PIN FUNCTIONS BIAS (Pin 14): The internal regulator will draw current from BIAS instead of VIN when BIAS is tied to a voltage higher than 3.1V. For output voltages of 3.3V and above this pin should be tied to VOUT. If this pin is tied to a supply other than VOUT use a 1µF local bypass capacitor on this pin. PG (Pin 15): The PG pin is the open-drain output of an internal comparator. PG remains low until the FB pin is within ±9% of the final regulation voltage, and there are no fault conditions.
PAGE 10
LT8610 OPERATION The LT8610 is a monolithic, constant frequency, current mode step-down DC/DC converter. An oscillator, with frequency set using a resistor on the RT pin, turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. The peak inductor current at which the top switch turns off is controlled by the voltage on the internal VC node.
PAGE 11
LT8610 APPLICATIONS INFORMATION Achieving Ultralow Quiescent Current To enhance efficiency at light loads, the LT8610 operates in low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimizing output voltage ripple. In Burst Mode operation the LT8610 delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor.
PAGE 12
LT8610 APPLICATIONS INFORMATION FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the resistor values according to:  V  R1= R2  OUT – 1  0.970V  (1) Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain output voltage accuracy. If low input quiescent current and good light-load efficiency are desired, use large resistor values for the FB resistor divider.
PAGE 13
LT8610 APPLICATIONS INFORMATION The LT8610 is capable of a maximum duty cycle of greater than 99%, and the VIN-to-VOUT dropout is limited by the RDS(ON) of the top switch. In this mode the LT8610 skips switch cycles, resulting in a lower switching frequency than programmed by RT.
PAGE 14
LT8610 APPLICATIONS INFORMATION current. This allows use of a physically smaller inductor, or one with a lower DCR resulting in higher efficiency. Be aware that low inductance may result in discontinuous mode operation, which further reduces maximum load current. For more information about maximum output current and discontinuous operation, see Linear Technology’s Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.
PAGE 15
LT8610 APPLICATIONS INFORMATION A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LT8610. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (underdamped) tank circuit. If the LT8610 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8610’s rating. This situation is easily avoided (see Linear Technology Application Note 88).
PAGE 16
LT8610 APPLICATIONS INFORMATION Output Power Good When the LT8610’s output voltage is within the ±9% window of the regulation point, which is a VFB voltage in the range of 0.883V to 1.057V (typical), the output voltage is considered good and the open-drain PG pin goes high impedance and is typically pulled high with an external resistor. Otherwise, the internal pull-down device will pull the PG pin low. To prevent glitching both the upper and lower thresholds include 1.3% of hysteresis.
PAGE 17
LT8610 APPLICATIONS INFORMATION D1 VIN VIN LT8610 GND EN/UV GND 8610 F03 1 16 TR/SS 2 15 RT 3 14 BIAS 4 13 INTVCC 5 12 6 11 7 10 8 9 SYNC Figure 3. Reverse VIN Protection PCB Layout EN/UV For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 4 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT8610’s VIN pins, PGND pins, and the input capacitor (C1).
PAGE 18
LT8610 TYPICAL APPLICATIONS 5V Step-Down Converter VIN 5.5V TO 42V VIN 4.7µF BST EN/UV LT8610 0.1µF 2.5µH SW SYNC BIAS TR/SS PG 10nF 3.3V Step-Down Converter VOUT 5V 47µF 2.5A VIN 3.8V TO 27V (42V TRANSIENT) INTVCC RT PGND GND FB 1M POWER GOOD INTVCC RT PGND GND 4.7µF BST EN/UV LT8610 SYNC 0.1µF 10µH SW BIAS 10nF TR/SS PG INTVCC RT PGND GND 110k fSW = 400kHz FB 1M 8610 TA04 3.3V Step-Down Converter VIN 3.8V TO 42V 4.7µF VOUT 5V 2.5A 68µF VIN BST EN/UV PG SYNC LT8610 0.
PAGE 19
LT8610 TYPICAL APPLICATIONS 12V Step-Down Converter VIN 12.5V TO 42V 4.7µF VIN BST EN/UV LT8610 SYNC 1.8V Step-Down Converter VIN 3.4V TO 42V 0.1µF 10µH VOUT 12V 47µF 2.5A SW BIAS 10nF 4.7µF TR/SS PG INTVCC RT PGND GND FB 41.2k 1M LT8610 0.1µF 4.7µH SW BIAS SYNC VOUT 1.8V 120µF 2.5A 10nF POWER GOOD 1µF TR/SS INTVCC RT PGND GND 10pF FB 110k 88.7k fSW = 1MHz BST EN/UV PG 100k 1µF VIN 4.7pF 1M fSW = 400kHz 8610 TA09 866k 8610 TA07 1.8V 2MHz Step-Down Converter VIN 3.
PAGE 20
LT8610 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev E) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ± 0.102 (.112 ± .004) 5.23 (.206) MIN 2.845 ± 0.102 (.112 ± .004) 0.889 ± 0.127 (.035 ± .005) 8 1 1.651 ± 0.102 (.065 ± .004) 1.651 ± 0.102 3.20 – 3.45 (.065 ± .004) (.126 – .136) 0.305 ± 0.038 (.0120 ± .0015) TYP 16 0.50 (.0197) BSC 4.039 ± 0.
PAGE 21
LT8610 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 10/13 Added H-grade version ABS Max table, Order Information 2 Clarified Feedback Voltage specification to 150°C 2 Clarified 3.3V and 5V Efficiency graphs 4 Clarified RT Programmed Switching Frequency graph 7 8610fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 22
LT8610 TYPICAL APPLICATION 3.3V and 1.8V with Ratio Tracking VIN 3.8V TO 42V 4.7µF VIN BST EN/UV PG LT8610 Ultralow IQ 2.5V, 3.3V Step-Down with LDO VIN 3.8V TO 27V 0.1µF 5.6µH SW SYNC 10nF VIN 4.7µF VOUT1 3.3V 47µF 2.5A BST EN/UV PG LT8610 SYNC 0.1µF 1.8µH VOUT1 3.3V 47µF 2.5A SW BIAS 10nF 1µF BIAS TR/SS INTVCC RT PGND GND FB 232k TR/SS 1µF 4.7pF 88.7k INTVCC RT PGND GND 97.6k 18.2k fSW = 500kHz fSW = 2MHz FB 1M 4.7pF IN 412k OUT LT3008-2.5 VOUT2 2.5V 2.