Linear Technology LTC1709 Datasheet

LTC1709

2-Phase, 5-Bit Adjustable,

High Efficiency, Synchronous Step-Down

FEATURES

■

Two Ouput Stages Operate Antiphase Reducing
Input Capacitance and Power Supply Noise

■

5-Bit VID Control (VRM 8.4 Compliant)
V

: 1.3V to 3.5V in 50mV/100mV Steps

OUT

■

Current Mode Control Ensures Current Sharing

■

True Remote Sensing Differential Amplifier

■

OPTI-LOOPTM Compensation Minimizes C

■

Programmable Fixed Frequency: 150kHz to

OUT

300kHz—Effective 300kHz to 600kHz Switching
Frequency

■

±

1% Output Voltage Accuracy

■

Wide VIN Range: 4V to 36V Operation

■

Adjustable Soft-Start Current Ramping

■

Internal Current Foldback

■

Short-Circuit Shutdown Timer with Defeat Option

■

Overvoltage Soft-Latch Eliminates Nuisance Trips

■

Low Shutdown Current: 20µA

■

Small 36-Lead Narrow (0.209") SSOP Package

U

APPLICATIO S

■

Desktop Computers

■

Internet/Network Servers

■

Large Memory Arrays

■

DC Power Distribution Systems

■

Battery Chargers

Switching Regulator

U

DESCRIPTIO

The LTC®1709 is a 2-phase, VID programmable, synchro­nous step-down switching regulator controller that drives
all N-channel external power MOSFET stages in a fixed
frequency architecture. The 2-phase controller drives its
two output stages out of phase at frequencies up to
300kHz to minimize the RMS ripple currents in both input
and output capacitors. The 2-phase technique effectively
multiplies the fundamental frequency by two, improving
transient response while operating each channel at a
optimum frequency for efficiency. Thermal design is also
simplified.

An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required in high current applications.

The RUN/SS pin provides soft-start and optional timed,
short-circuit shutdown. Current foldback limits MOSFET
dissipaton during short-circuit conditions when overcurrent
latchoff is disabled. OPTI-LOOP compensation allows the
transient response to be optimized for a wide range of
output capacitors and ESR values.

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

OPTI-LOOP is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

S

0.1µF

V

IN

RUN/SS

1.2nF

15k

5 VID BITS

I

TH

SGND

VID0–VID4

EAIN
FBOUT
SENSEIN
V

DIFFOUT

–

V

OS

+

V

OS

Q1–Q4 2× FAIRCHILD FDS7760A OR SILICONIX Si4874

TG1

SW1

BG1

PGND

TG2

SW2

BG2

S

S

+
–

S

S

S

CC

+
–

10µF

+

LTC1709

BOOST 1

SENSE1
SENSE1

BOOST2

INTV
SENSE 2
SENSE 2

Figure 1. High Current 2-Phase Step-Down Converter

0.47µF

S

U

0.47µF

V

IN

+

5V TO 28V

V

OUT

1.3V TO 3.5V
40A

C

OUT

1000µF
4V
×2

1709 TA01

100

90

80

70

EFFICIENCY (%)

60

50

10µF ×4

Q1

Q2

Q3

Q4

35V

0.002Ω

1µH

0.002Ω

1µH

Efficiency Curve

515

10

0

LOAD CURRENTS (A)

VIN = 5V
V
f

25 45

30

20

= 1.6V

OUT

= 200kHz

S

35

40

1709 TA01a

1

LTC1709

WW

W

U

ABSOLUTE AXI U RATI GS

(Note 1)

Input Supply Voltage (VIN).........................36V to –0.3V

Topside Driver Voltages (BOOST 1, 2).......42V to –0.3V

Switch Voltage (SW1, 2) .............................36V to –5 V

SENSE 1+, SENSE 2+, SENSE 1–,

SENSE 2– Voltages....................... (1.1)INTVCC to –0.3V

EAIN, V
AMPMD, V

VID0–VID4, Voltages ...................................7V to –0.3V

Boosted Driver Voltage (BOOST-SW) ..........7V to –0.3V

PLLFLTR, PLLIN, V

ITH Voltage................................................2.7V to –0.3V

Peak Output Current <1µs(TGL1, 2; BG1, 2).............. 3A

INTVCC RMS Output Current................................ 50mA

Operating Ambient Temperature Range

(Note 2) .................................................. – 40°C to 85°C

Junction Temperature (Note 3)............................. 125°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)..................300°C

OS

+

–

, V

, EXTVCC, INTVCC, RUN/SS,

OS

, ATTENIN, ATTENOUT,

BIAS

DIFFOUT

Voltages .... INTVCC to –0.3V

UUW

PACKAGE/ORDER I FOR ATIO

RUNN/SS
SENSE 1
SENSE 1

EAIN

PLLFLTR

PLLIN

SGND

V

DIFFOUT

VOS–
V

OS

SENSE 2
SENSE 2

ATTENOUT

ATTENIN

VID0
VID1

TOP VIEW

1

+

2

–

3
4
5
6
7

NC

8

I

TH

9
10
11
12

+

–

13

+

14
15
16
17
18

G PACKAGE

36-LEAD PLASTIC SSOP

T

= 125°C, θJA = 85°C/W

JMAX

36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19

NC
TG1
SW1
BOOST 1
V

IN

BG1
EXTV

CC

INTV

CC

PGND
BG2
BOOST 2
SW2
TG2
AMPMD
V

BIAS

VID4
VID3
VID2

ORDER PART

NUMBER

LTC1709EG

Consult factory for Industrial and Military grade parts.

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. V

A

= 15V, V

IN

= 5V unless otherwise noted.

RUN/SS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Main Control Loop

V

EAIN

V

SENSEMAX

I

INEAIN

V

LOADREG

V

REFLNREG

V

OVL

Regulated Feedback Voltage (Note 4); ITH Voltage = 1.2V ● 0.792 0.800 0.808 V
Maximum Current Sense Threshold V

–

= 5V ● 62 75 88 mV

SENSE

Feedback Current (Note 4) –5 –50 nA
Output Voltage Load Regulation (Note 4)

Measured in Servo Loop; ∆I
Measured in Servo Loop; ∆I

Voltage: 1.2V to 0.7V ● 0.1 0.5 %

TH

Voltage: 1.2V to 2V ● –0.1 –0.5 %

TH

Reference Voltage Line Regulation VIN = 3.6V to 30V (Note 4) 0.002 0.02 %/V
Output Overvoltage Threshold Measured at V

EAIN

● 0.84 0.86 0.88 V

UVLO Undervoltage Lockout VIN Ramping Down 3 3.5 4 V
g

m

g

mOL

I

Q

I

RUN/SS

V

RUN/SS

Transconductance Amplifier g

m

ITH = 1.2V; Sink/Source 5µA; (Note 4) 3 mmho
Transconductance Amplifier Gain ITH = 1.2V; (gmxZL; No Ext Load); (Note 4) 1.5 V/mV
Input DC Supply Current (Note 5)

Normal Mode EXTV

Shutdown V
Soft-Start Charge Current V
RUN/SS Pin ON Arming V

Tied to V

CC

= 0V 20 40 µA

RUN/SS

= 1.9V –0.5 –1.2 µA

RUN/SS

Rising 1.0 1.5 1.9 V

RUN/SS

OUT

; V

= 5V 470 µA

OUT

2

LTC1709

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. V

A

= 15V, V

IN

= 5V unless otherwise noted.

RUN/SS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

RUN/SSLO

I

SCL

I

SDLHO

I

SENSE

DF

MAX

RUN/SS Pin Latchoff Arming V
RUN/SS Discharge Current Soft Short Condition V

Shutdown Latch Disable Current V
Total Sense Pins Source Current Each Channel: V

Rising from 3V 4.1 4.5 V

RUN/SS

= 0.5V; 0.5 2 4 µA

= 4.5V

V

RUN/SS

= 0.5V 1.6 5 µA

EAIN

EAIN

SENSE1–, 2

– = V

SENSE1+, 2

+ = 0V –85 –60 µA

Maximum Duty Factor In Dropout 98 99.5 %
Top Gate Transition Time: (Note 6)

TG1, 2 t
TG1, 2 t

Rise Time C

r

Fall Time C

f

= 3300pF 30 90 ns

LOAD

= 3300pF 40 90 ns

LOAD

Bottom Gate Transition Time: (Note 6)

BG1, 2 t
BG1, 2 t

TG/BG t

BG/TG t

t

ON(MIN)

Rise Time C

r

Fall Time C

f

Top Gate Off to Bottom Gate On Delay (Note 6)

1D

Synchronous Switch-On Delay Time C
Bottom Gate Off to Top Gate On Delay (Note 6)

2D

Top Switch-On Delay Time C
Minimum On-Time Tested with a Square Wave (Note 7) 180 200 ns

= 3300pF 30 90 ns

LOAD

= 3300pF 20 90 ns

LOAD

= 3300pF Each Driver 90 ns

LOAD

= 3300pF Each Driver 90 ns

LOAD

Internal VCC Regulator

V

INTVCC

V

LDO

V

LDO

V

EXTVCC

V

LDOHYS

Internal VCC Voltage 6V < VIN < 30V; V

INT INTVCC Load Regulation ICC = 0 to 20mA; V
EXT EXTVCC Voltage Drop ICC = 20mA; V

EXTVCC

EXTVCC Switchover Voltage ICC = 20mA, EXTV
EXTVCC Switchover Hysteresis ICC = 20mA, EXTV

= 4V 4.8 5.0 5.2 V

EXTVCC

= 4V 0.2 1.0 %

EXTVCC

= 5V 120 240 mV
Ramping Positive ● 4.5 4.7 V

CC

Ramping Negative 0.2 V

CC

VID Parameters

R

ATTEN

Resistance Between ATTENIN and 20 kΩ
ATTENOUT Pins

ATTEN

R

PULLUP

VID

THLOW

VID

THHIGH

VID

LEAK

Resistive Divider Worst-Case Error Programmed from 1.3V to 2.05V (VID4 = 0) ● –0.25 +0.25 %

ERR

Programmed from 2.1V to 3.5V (VID4 = 1)

● –0.35 +0.25 %

VID0–VID4 Pull-Up Resistance (Note 8) 40 kΩ
VID0–VID4 Logic Threshold Low 0.4 V
VID0–VID4 Logic Threshold High 1.6 V
VID0–VID4 Leakage V

< VID0–VID4 < 7V 1 µA

BIAS

Oscillator and Phase-Locked Loop

f

NOM

f

LOW

f

HIGH

R

PLLIN

I

PLLFLTR

R

RELPHS

Nominal Frequency V
Lowest Frequency V
Highest Frequency V

= 1.2V 190 220 250 kHz

PLLFLTR

= 0V 120 140 160 kHz

PLLFLTR

≥ 2.4V 280 310 360 kHz

PLLFLTR

PLLIN Input Resistance 50 kΩ
Phase Detector Output Current

Sinking Capability f

Sourcing Capability f

PLLIN
PLLIN

< f
> f

OSC
OSC

–15 µA
15 µA

Controller 2-Controller 1 Phase 180 Deg

Differential Amplifier/Op Amp Gain Block (Note 9)

A

DA

CMRR

Gain Differential Amp Mode 0.995 1 1.005 V/V
Common Mode Rejection Ratio Differential Amp Mode; 0V < VCM < 5V 46 55 dB

DA

3

LTC1709

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. V

A

= 15V, V

IN

= 5V unless otherwise noted.

RUN/SS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

R

IN

V

OS

I

B

A

OL

V

CM

CMRR
PSRR
I

CL

V

O(MAX)

GBW Gain-Bandwidth Product Op Amp Mode; I

Input Resistance Differential Amp Mode; Measured at VOS+ Input 80 kΩ
Input Offset Voltage Op Amp Mode; VCM = 2.5V; V

I

= 1mA

DIFFOUT

= 5V; 6 mV

DIFFOUT

Input Bias Current Op Amp Mode 30 200 nA
Open Loop DC Gain Op Amp Mode; 0.7V ≤ V

< 10V 5000 V/mV

DIFFOUT

Common Mode Input Voltage Range Op Amp Mode 0 3 V
Common Mode Rejection Ratio Op Amp Mode; 0V < VCM < 3V 70 90 dB

OA

Power Supply Rejection Ratio Op Amp Mode; 6V < VIN < 30V 70 90 dB

OA

Maximum Output Current Op Amp Mode; V
Maximum Output Voltage Op Amp Mode; I

= 0V 10 35 mA

DIFFOUT

= 1mA 10 11 V

DIFFOUT

= 1mA 2 MHz

DIFFOUT

SR Slew Rate Op Amp Mode; RL = 2k 5 V/µs
Note 1: Absolute Maximum Ratings are those values beyond which the

life of a device may be impaired.
Note 2: The LTC1709EG is guaranteed to meet performance specifications

from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: TJ is calculated from the ambient temperature TA and power
dissipation P

according to the following formulas:

D

LTC1709EG: TJ = TA + (PD • 85°C/W)
Note 4: The LTC1709 is tested in a feedback loop that servos V

specified voltage and measures the resultant V

EAIN

.

ITH

to a

Note 5: Dynamic supply current is higher due to the gate charge being

Note 6: Rise and fall times are measured using 10% and 90% levels. Delay

times are measured using 50% levels.
Note 7: The minimum on-time condition corresponds to the on inductor

peak-to-peak ripple current ≥40% I

(see Minimum On-Time

MAX

Considerations in the Applications Information section).
Note 8: Each built-in pull-up resistor attached to the VID inputs also has a

series diode to allow input voltages higher than the VIDV

supply without

CC

damage or clamping (see the Applications Information section).
Note 9: When the AMPMD pin is high, the IC pins are connected directly to

the internal op amp inputs. When the AMPMD pin is low, internal MOSFET
switches connect four 40k resistors around the op amp to create a
standard unity-gain differential amp.

delivered at the switching frequency. See Applications Information.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Efficiency vs Output Current
(Figure 12)

100

80

60

40

EFFICIENCY (%)

20

0

0.1 1 10 100

VIN = 5V
VIN = 8V
VIN = 12V
VIN = 20V

V
V
f = 200kHz

OUTPUT CURRENT (A)

OUT
EXTVCC

= 2V

= 0V

1709 G01

Efficiency vs Output Current
(Figure 12)

100

V

= 2V

OUT

= 12V

V

IN

f = 200kHz

80

60

40

EFFICIENCY (%)

20

0

0.1

INTERNAL LDO VS EXTERNALLY
APPLIED 5V OVERALL EFFICIENCY
(FIGURE 12)

V

EXTVCC

V

EXTVCC

1 10 100

OUTPUT CURRENT (A)

= 5V
= 0V

4

1709 G02

Efficiency vs Input Voltage
(Figure 12)

100

V

= 3.3V

OUT

= 5V

V

EXTVCC

= 20A

I

OUT

90

EFFICIENCY (%)

80

70

5

10 15 20

VIN (V)

1709 G03

UW

TEMPERATURE (°C)

–50

INTV

CC

AND EXTV

CC

SWITCH VOLTAGE (V)

4.95

5.00

5.05

25 75

1709 G06

4.90

4.85

–25 0

50 100 125

4.80

4.70

4.75

INTVCC VOLTAGE

EXTVCC SWITCHOVER THRESHOLD

TYPICAL PERFOR A CE CHARACTERISTICS

LTC1709

Supply Current vs Input Voltage
and Mode EXTVCC Voltage Drop

1000

800

600

400

SUPPLY CURRENT (µA)

200

0

05

ON

SHUTDOWN

15

10

INPUT VOLTAGE (V)

20

25

30

35

1709 G04

250

200

150

100

VOLTAGE DROP (mV)

CC

EXTV

50

0

10

0

Maximum Current Sense Threshold

Internal 5V LDO Line Reg

5.1
I

= 1mA

LOAD

5.0

4.9

4.8

VOLTAGE (V)

4.7

CC

INTV

4.6

4.5

4.4

0

510

15 25

INPUT VOLTAGE (V)

20 30 35

1709 G07

vs Duty Factor

75

50

(mV)

SENSE

V

25

0

0

20 40 60 80

30

20

CURRENT (mA)

DUTY FACTOR (%)

INTVCC and EXTVCC Switch
Voltage vs Temperature

40

50

1709 G05

Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)

80

70

60

50

(mV)

40

SENSE

V

30

20

10

100

1709 G08

0

0

PERCENT ON NOMINAL OUTPUT VOLTAGE (%)

25

50

75

100

1709 G09

80

60

(mV)

40

SENSE

V

20

0

Maximum Current Sense Threshold
vs V

V

SENSE(CM)

0

(Soft-Start)

RUN/SS

= 1.6V

1234

V

(V)

RUN/SS

56

1709 G10

Maximum Current Sense Threshold
vs Sense Common Mode Voltage

80

76

72

(mV)

SENSE

68

V

64

60

1

0

COMMON MODE VOLTAGE (V)

3

2

Current Sense Threshold
vs ITH Voltage

90
80
70
60
50
40

(mV)

30
20

SENSE

V

10

0
–10
–20

4

1709 G11

–30

5

0.5

0

1.5

2

1

V

(V)

ITH

2.5

1709 G12

5

LTC1709

TEMPERATURE (°C)

–50 –25

0

EXTV

CC

SWITCH RESISTANCE (Ω)

4

10

0

50

75

1709 G22

2

8

6

25

100

125

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Load Regulation V

0.0

–0.1

(%)

OUT

–0.2

NORMALIZED V

–0.3

–0.4

0

1

2

LOAD CURRENT (A)

FCB = 0V
V

= 15V

IN

FIGURE 1

3

4

5

1709 G13

Maximum Current Sense
Threshold vs Temperature

80

78

76

(mV)

SENSE

74

V

72

70

–50 –25

50

25

0

TEMPERATURE (°C)

75

100

125

1709 G17

vs V

ITH

RUN/SS

2.5
V

= 0.7V

OSENSE

2.0

1.5

(V)

ITH

V

1.0

0.5

0

0

234

1

V

RUN/SS

(V)

RUN/SS Current vs Temperature

1.8

1.6

1.4

1.2

1.0

0.8

0.6

RUN/SS CURRENT (µA)

0.4

0.2

0

–50 –25

0 25 125

TEMPERATURE (°C)

56

75 10050

1709 G14

1709 G18

SENSE Pins Total Source Current

100

50

(µA)

0

SENSE

I

–50

–100

0

24

V

COMMON MODE VOLTAGE (V)

SENSE

Soft-Start Up (Figure 12)

V

ITH

1V/DIV

V

OUT

2V/DIV

V

RUNSS

2V/DIV

100ms/DIV

6

1709 G15

1629 G19

V

OUT

50mV/DIV

I

OUT

10A/DIV

6

Load Step Response Using Active
Voltage Positioning (Figure 12)

20A

0A

20µs/DIV

1709 G20

Current Sense Pin Input Current
vs Temperature

35

EXTVCC = 5V

33

31

29

27

CURRENT SENSE INPUT CURRENT (µA)

25

–50 –25

0

TEMPERATURE (°C)

50

25

EXTVCC Switch Resistance
vs Temperature

100

125

1709 G21

75

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC1709

Oscillator Frequency
vs Temperature

350

300

250

200

150

FREQUENCY (kHz)

100

50

0

–50

–25 0

V

= 5V

FREQSET

V

= OPEN

FREQSET

V

= 0V

FREQSET

50 100 125

25 75

TEMPERATURE (°C)

1709 G23

Undervoltage Lockout
vs Temperature

3.50

3.45

3.40

3.35

3.30

UNDERVOLTAGE LOCKOUT (V)

3.25

3.20
–50

–25 0

TEMPERATURE (°C)

UUU

PI FU CTIO S

RUN/SS (Pin 1): Combination of Soft-Start, Run Control
Input and Short-Circuit Detection Timer. A capacitor to
ground at this pin sets the ramp time to full current output.
Forcing this pin below 0.8V causes the IC to shut down all
internal circuitry. All functions are disabled in shutdown.

SENSE 1+, SENSE 2+ (Pins 2,14): The (+) Input to Each
Differential Current Comparator. The ITH pin voltage and
built-in offsets between SENSE– and SENSE+ pins in
conjunction with R

SENSE 1–, SENSE 2– (Pins 3, 13): The (–) Input to the
Differential Current Comparators.

EAIN (Pin 4): Input to the Error Amplifier that compares
the feedback voltage to the internal 0.8V reference voltage.
This pin is normally connected to a resistive divider from
the output of the differential amplifier (DIFFOUT).

PLLFLTR (Pin 5): The Phase-Locked Loop’s Low Pass
Filter is tied to this pin. Alternatively, this pin can be driven
with an AC or DC voltage source to vary the frequency of
the internal oscillator.

PLLIN (Pin 6): External Synchronization Input to Phase
Detector. This pin is internally terminated to SGND with
50kΩ. The phase-locked loop will force the rising top gate
signal of controller 1 to be synchronized with the rising
edge of the PLLIN signal.

set the current trip threshold.

SENSE

V

Shutdown Latch

RUN/SS

Thresholds vs Temperature

4.5

LATCH ARMING

LATCHOFF

THRESHOLD

0 25 125

TEMPERATURE (°C)

75 10050

1709 G25

50 100 125

25 75

1709 G24

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

SHUTDOWN LATCH THRESHOLDS (V)

0

–50 –25

NC (Pins 7, 36): Do not connect.

ITH (Pin 8): Error Amplifier Output and Switching Regula-

tor Compensation Point. Both current comparator’s thresh­olds increase with this control voltage. The normal voltage
range of this pin is from 0V to 2.4V

SGND (Pin 9): Signal Ground, common to both control­lers. Route separately to the PGND pin.

V

DIFFOUT

(Pin 10): Output of a Differential Amplifier that

provides true remote output voltage sensing. This pin
normally drives an external resistive divider that sets the
output voltage.

–

V

OS

+

, V

(Pins 11, 12): Inputs to an Operational Ampli-

OS

fier. Internal precision resistors capable of being elec­tronically switched in or out can configure it as a differen­tial amplifier or an uncommitted Op Amp.

ATTENOUT (Pin 15): Voltage Feedback Signal Resistively
Divided According to the VID Programming Code.

ATTENIN (Pin 16): The Input to the VID Controlled Resis­tive Divider.

VID0–VID4 (Pins 17,18, 19, 20, 21): VID Control Logic
Input Pins.

V

(Pin 22): Supply Pin for the VID Control Circuit.

BIAS

7

LTC1709

PI FU CTIO S

UUU

AMPMD (Pin 23): This Logic Input pin controls the
connections of internal precision resistors that configure
the operational amplifier as a unity-gain differential
amplifier.

TG2, TG1 (Pins 24, 35): High Current Gate Drives for Top
N-Channel MOSFETS. These are the outputs of floating
drivers with a voltage swing equal to INTVCC superim­posed on the switch node voltage SW.

SW2, SW1 (Pins 25, 34): Switch Node Connections to
Inductors. Voltage swing at these pins is from a Schottky
diode (external) voltage drop below ground to VIN.

BOOST 2, BOOST 1 (Pins 26, 33): Bootstrapped Supplies
to the Topside Floating Drivers. External capacitors are
connected between the Boost and Switch pins, and Schottky
diodes are connected between the Boost and INTVCC pins.

BG2, BG1 (Pins 27, 31): High Current Gate Drives for
Bottom N-Channel MOSFETS. Voltage swing at these pins
is from ground to INTVCC.

PGND (Pin 28): Driver Power Ground, connect to sources
of bottom N-channel MOSFETS and the (–) terminals of
CIN.

INTVCC (Pin 29): Output of the Internal 5V Linear Low
Dropout Regulator and the EXTVCC Switch. The driver and
control circuits are powered from this voltage source.

Decouple to power ground with a 1µF ceramic capacitor
placed directly adjacent to the IC and minimum of 4.7µF
additional tantalum or other low ESR capacitor.

EXTVCC (Pin 30): External Power Input to an Internal
Switch . This switch closes and supplies INTV
ing the internal low dropout regulator whenever EXTVCC is
higher than 4.7V. See EXTVCC Connection in the Applica­tions Information section. Do not exceed 7V on this pin
and ensure V

VIN (Pin 32): Main Supply Pin. Should be closely decoupled
to the IC’s signal ground pin.

EXTVCC

≤ VIN.

bypass-

CC,

8

LTC1709

UU

W

FU CTIO AL DIAGRA

PLLIN

F

IN

R

LP

C

LP

PLLFLTR

V

OS

V

OS

AMPMD

DIFFOUT

V

IN

V

IN

EXTV

INTV

5V

+

SGND

PHASE DET

50k

0.8V

+
–

CLK1
CLK2

TO

SECOND

CHANNEL

A1

–
+

V

REF

5V
LDO
REG

INTERNAL

SUPPLY

OSCILLATOR

–

+

0V POSITION

4.7V

CC

CC

DUPLICATE FOR
SECOND CHANNEL

V

IN

1.2µA

6V

4(VFB)

I1

SLOPE

COMP

SRQ

INTV

BOOST

INTV

CC

30k

30k

CC

TG

SW

BG

PGND*

SENSE

SENSE

EAIN

I

TH

RUN/SS

+

–

R

SENSE

C

C

DROP

OUT
DET

BOT

FORCE BOT

Q

SHDN

–

+–

+

45k

SHDN

RST

4(VFB)

45k

2.4V

RUN

SOFT-

START

EA

OV

SWITCH

LOGIC

–

+

+

–

TOP

BOT

INTV

V

FB

0.80V

0.86V

V

CC

IN

D

B

C

B

L

+

C

IN

C

OUT

+

V

OUT

R

C

ATTENIN

ATTENOUT

R2

20k

R1 R1 VARIABLE

5-BIT VID DECODER

VID0 VID1 VID2 VID4

VID3

TYPICAL ALL
VID PINS

40k

C

SS

V

BIAS

1709 FBD

9