Linear Technology DC164, LTC1624 Demo Manual

DESCRIPTIO

U

DEMO MANUAL DC164

DESIGN READY SWITCHER

DEMO MANUAL DC164

LTC1624 Constant Frequency,

8-Pin N-Channel DC/DC Converter

Demonstration Circuit 164 is a constant-frequency step­down (buck) regulator implemented entirely in surface
mount, using the LTC®1624 switching regulator controller.
DC164 is usable in a wide range of portable, industrial,
computer and communications applications. The output
voltage is programmable to 2.5V, 3.3V or 5V via a jumper.
The input voltage can range from 4.8V to 28V (limited by the
external MOSFET). The circuit highlights the capabilities of
the LTC1624, which uses a current mode, constant-fre­quency architecture to switch an N-channel power MOSFET
while providing 95% maximum duty cycle. Operating effi-

This results in a power supply that has very high
efficiency, low ripple and fast transient response. At
low output currents the LTC1624 automatically switches
to Burst ModeTM operation to reduce switching losses
and maintain high operating efficiencies. Additionally,
the supply current can be shut down to less than
20µA (VIN = 10V). This feature is an absolute necessity to
maximize battery life in portable applications. Gerber files

for this circuit board are available. Call the LTC factory.

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

Burst Mode is a trademark of Linear Technology Corporation.

ciencies exceeding 90% are obtained.

UWWW

PERFORMANCE SUMM ARY

Input Voltage Range (Maximum Input Voltage Limited by External MOSFET and Input Capacitor) 4.8V to 28V
Output Output Voltage (Jumper Selectable) 2.5V, 3.3V, 5V

Max Output Current (Continuous) 3.0A
Max Output Current (Peak) 3.5A
Typical Output Ripple at 10MHz Bandwidth (Burst Mode Operation) IO = 100mA 50mV
Typical Output Ripple at 10MHz Bandwidth (Continuous) IO = 1A 35mV

V

IN

I

OUT

I

Q

V

ITH/RUN

Frequency Operating Frequency (Typical) 200kHz

Line Regulation 4.5V to 20V 0.002%/V
Load Regulation No Load to Full Rated Output –1%
Supply Current with No Load (Typical), V
Supply Current in Shutdown (Typical), V
Run Pin Threshold (Typical) 0.8V

Operating Temperature Range 0°C to 50°C.

= 10V 550µA

IN

= 10V 16µA

IN

P-P

P-P

UUW

TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO

Efficiency

100

VIN = 10V

90

V

= 5V

OUT

80

V

= 2.5V

70

EFFICIENCY (%)

60

50

1

OUT

V

= 3.3V

OUT

10 100

LOAD CURRENT (mA)

1000 3000

DC164 • TPC01

1

DEMO MANUAL DC164

WWU

PACKAGE AND SCHEMATIC DIAGRAMS

–

SENSE

1



I

/RUN

2

TH

V



3

FB

GND

4

D1

8-LEAD PLASTIC SO

R



S

0.033Ω
1%
1/2W

M1
Si4412DY

C2
1000pF

1

–

R2
11k
1%

2

3

4

R3
20k
1%

J2B

3.3V

SENSE

ITH/RUN

V

FB

GND

RX

U1

LTC1624

R4

32.4k
1%

J2C

2.5V

CC

RC

470pF

6.8k

J1

/RUN

I

TH

C3

100pF

J2A
5V

V

BOOST

SW

R5
OPEN

USER
PGM
J2D

8

IN

7

6

TG

5

C1

0.1µF

CB

0.1µF

MBRS340T3

TOP VIEW

S8 PACKAGE

L1

10µH

+

C

IN1

22µF
35V

+

C

OUT1

100µF
10V

35.7k

100pF

R1

1%

V

8

IN

BOOST

7

6

5

C4

TG
SW

+

+

LTC1624CS8

C

IN2

22µF
35V

C

OUT2

100µF
10V

+

C

IN3

OPTION

+

C

OUT3

OPTION

(E1)

V

IN

GND (E2)

V

OUT

R6
10Ω

V

OSENSE

GND (E5)

164 • SCHEMATIC

(E3)

(E4)

Figure 1. Demo Board Schematic

PARTS LIST

REFERENCE
DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE

C

C

C

, C

, (C

) 2 (3, 5A) TPSE226M035R0300 22µF 35V 20% Tantalum Capacitor AVX [phone]

IN3

, (C

OUT2

) 2 (3, 5A) TPSD107M010R0065 100µF 10V 20% Tantalum Capacitor AVX [phone]

OUT3

C

IN1

OUT1

IN2

, C

C3, C4 2 08055A101KAT1A 100pF 50V 10% Chip Capacitor NPO AVX [phone]
C8, C1 2 08055C104MAT2A 0.1µF 50V 20% Chip Capacitor X7R AVX [phone]
C2 1 08055A102MAT2A 1000pF 50V 20% Chip Capacitor NPO AVX [phone]
D1 1 MBRS340T3 BVR = 40V Schottky Diode Motorola [phone]

E1, E2, E3, E4, E5 5 2502-2 Turret Terminal Keystone [phone]
JP1, JP2A, 5 2802S-03-G2 2mm Pin Header COMM CON [phone]

JP2B, JP2C, JP2D
J1, J2A, J2B, J2C, J2D 2 CCIJ2MM-138-G Jumper COMM CON [phone]
L1 1 CDRH125-10 10µH Inductor Sumida [phone]

1 08055A471MAT1A 470pF 50V 10% Chip Capacitor NPO AVX [phone]

08055A681MAT1A (5A) 680pF 50V 10% Chip Capacitor NPO AVX [phone]

MBRD835L (5A) BVR = 35V Schottky Diode Motorola [phone]

CDRH127-10 (5A) 10µH Inductor (Alternate) Sumida [phone]

2

DEMO MANUAL DC164

J2D

USER

DEFINED

J2C

2.5V

J2B

3.3V

J2A

5V

164 • F02

PARTS LIST

REFERENCE
DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE

M1 1 Si4412DY N-Channel MOSFET Siliconix [phone]

Si4410DY (5A) N-Channel MOSFET Siliconix [phone]
R1 1 TAD CR10-3572F-T 35.7k 1/10W 1% Resistor Chip TAD [phone]
R2 1 TAD CR10-1102F-T 11k 1/10W 1% Resistor Chip TAD [phone]
R3 1 TAD CR10-2002F-T 20k 1/10W 1% Resistor Chip TAD [phone]
R4 1 TAD CR10-3242F-T 32.4k 1/10W 1% Resistor Chip TAD [phone]
R5 1 User Defined User Defined 1/10W 1% Resistor Chip TAD [phone]
R6 1 TAD CR10-100J-T 10Ω 1/10W 1% Resistor Chip TAD [phone]
R

C

R

S

U1 1 LTC1624CS LTC1624CS8 IC LTC [phone]

1 TAD CR10-682J-T 6.8k 1/10W 5% Resistor Chip TAD [phone]

TAD CR10-332J-T (5A) 3.3k 1/10W 5% Resistor Chip TAD [phone]

1 WSL-2010 0.033Ω 1/2W 1% Resistor Dale [phone]

WSL-2010 (5A) 0.02Ω 1/2W 1% Resistor Dale [phone]

QUICK START GUIDE

This demonstration board is easily set up to evaluate the
performance of the LTC1624. Please follow the proce­dure outlined below for proper operation.

• Refer to Figure 3 for board orientation and proper
measurement equipment setup.

• Connect the input power supply to the VIN and GND
terminals on the left side of the board. Do not increase
VIN over 28V or the MOSFET, M1, will be damaged.

• Connect the load between the V
on the right side of the board.

• The ITH/RUN pin can be left unconnected. To shut
down the LTC1624, connect a jumper from this pin to
ground at J1. (A spare jumper installed in position D
in J2 is supplied for this purpose).

• Do not short or load the V

OSENSE

is used for remote output voltage sensing only.

and GND terminals

OUT

pin. The V

OSENSE

pin

• Set the desired output voltage with jumper J2 as
shown in Figure 2/Table 1.

Table 1. Output Voltage Selection

POSITION OUTPUT VOLTAGE

A5V
B 3.3V
C 2.5V

D User Defined

Figure 2. Output Voltage Selection (J2) (3.3V Position Shown)

3

DEMO MANUAL DC164

U

OPERATIO

The circuit in Figure 1 highlights the capabilities of the
LTC1624 configured as a step-down switching regulator.
The application circuit is set up for a variety of output
voltages. Output voltages from 2.5V to 5V are available by
selecting the appropriate jumper position. An additional
jumper position is also available for a user-selectable
output voltage by adding the appropriate feedback divider
resistor at R5.

The LTC1624 is a current mode switching regulator con­troller that drives an external N-channel power MOSFET
using a fixed-frequency architecture. Burst Mode opera­tion provides high efficiency at low load currents. Operat­ing efficiencies typically exceed 90% over two decades of
load current range. A maximum duty cycle limit of 95%
provides low dropout operation that extends operating
time in battery-operated systems.

Small spring-clip leads are very convenient for small­signal bench testing and voltage measurements but should
not be used with the high currents associated with this
circuit. Soldered wire connections are required to properly
ascertain the performance of the PC board.

This demonstration unit is intended for the evaluation of
the LTC1624 switching regulator IC and was not designed
for any other purpose. Further detailed information and
alternate topology applications are shown in the LTC1624
data sheet.

LTC1624 CONTROLLER DESCRIPTION

Main Control Loop

The LTC1624 uses a constant-frequency, current mode
architecture. During normal operation, the top MOSFET is
turned on during each cycle when the oscillator sets a
latch, and turned off when the main current comparator
resets the latch. The peak inductor current that resets the
latch is controlled by the voltage on the ITH/RUN pin, which
is the output of the error amplifier. VFB allows the error
amplifier to receive an output feedback voltage from an
external resistive divider. When the load current increases,
it causes a slight decrease in VFB relative to the 1.19V
reference, which in turn causes the ITH/RUN voltage to
increase until the average inductor current matches the
new load current. While the top MOSFET is off, an internal
bottom MOSFET is turned on for approximately 300ns to
400ns to recharge the bootstrap capacitor CB.

The top MOSFET driver is biased from the floating boot­strap capacitor CB, which is recharged during each off
cycle. The dropout detector counts the number of oscilla­tor cycles that the top MOSFET remains on and periodi­cally forces a brief off period to allow CB to recharge.

The main control loop is shut down by pulling ITH/RUN
below its 1.19V clamp voltage. Releasing ITH/RUN allows
an internal 2.5µ A current source to charge compensation
capacitor CC. When the ITH/RUN pin voltage reaches 0.8V,

I

IN

A

+

+

V

–

–

4

V

IN

V

IN

STEP-DOWN CONVERTER

J1

GND

J2

DCBA

DEMO CIRCUIT 164A

LTC1624CS

Figure 3. Proper Measurement Setup

LINEAR TECHNOLOGY

[phone]

V

OSENSE

V

GND

OUT

I

OUT

A

V

V

OUT

+

LOAD

–

OPTIONAL 
REMOTE V
SENSE CONNECTION

OUT



OPERATIO

DEMO MANUAL DC164

U

the main control loop is enabled with the ITH/RUN voltage
pulled up by the error amp.

A built-in comparator guards against transient output
overshoots >7.5% by turning off the top MOSFET and
keeping it off until the output decreases.

Low Current Operation

The LTC1624 is capable of Burst Mode operation, in which
the external MOSFET operates intermittently based on
load demand. The transition to low current operation
begins when a comparator detects that the ITH/RUN volt­age is below 1.5V. If the voltage across R

SENSE

does not
exceed approximately 20mV for one full cycle, the top and
internal bottom drives will be disabled on the following
cycles. This continues until the ITH voltage exceeds 1.5V,
which causes drive to be returned to TG on the next cycle.

INTVCC Power/Boost Supply (CB, DB)

Power for the top and internal bottom MOSFET drivers is
derived from VIN. An internal regulator supplies the power.
To power the top driver in step-down applications, an
internal high voltage diode recharges the bootstrap ca­pacitor CB during each off cycle from the internal supply.
A small internal N-channel MOSFET pulls the switch node
(SW) to ground each cycle after the top MOSFET has
turned off, ensuring that the bootstrap capacitor is kept
fully charged.

When the top side MOSFET is to be turned on, the driver
places the CB voltage across the gate-source of the MOSFET.
This enhances the MOSFET and turns on the top-side
switch. The switch node voltage SW rises to VIN and the
BOOST pin rises to VIN + 5V.

Significant efficiency gains can be realized by supplying
top-side driver operating voltage from the output, since
the VIN current resulting from the driver and control
currents will be scaled by a factor of (Duty Cycle)/(Effi­ciency). For 5V regulators this simply means connecting
the BOOST pin though a small Schottky diode (such as a
CMDH-3) to V

OUT

.

exceed the maximum voltage on the BOOST to SW pins of

7.8V.

ITH / RUN Function

The ITH/RUN pin is a dual purpose pin that provides the
loop compensation and a means to shut down the LTC1624.

An internal 2.5µA current source charges the external
capacitor CC (Figure 4). When the voltage on ITH/RUN
reaches 0.8V, the LTC1624 begins operating. At this point
the error amplifier pulls up the ITH/RUN pin to its maxi­mum of 2.4V (assuming V

is starting low). Soft start

OUT

can also be implemented with this pin, as shown in Figure
4c. Soft start reduces surge currents from VIN by gradually
increasing the internal current limit. Power supply
sequencing can also be accomplished using this pin.

During normal operation the voltage on the ITH/RUN pin
will vary from 1.19V to 2.4V, depending on the load
current. Pulling the ITH/RUN pin below 0.8V puts the
LTC1624 into a low quiescent current shutdown (IQ <
30µA). This pin can be driven directly from logic, as shown
in Figures 4a and 4b.

The operating frequency is set internally to 200kHz.
In addition to shutdown, the dual function pin ITH/RUN

allows external compensation for optimum load-step

3.3V 

OR 5V

(4a) (4b)

/RUN

I

TH

D1

J1

C

C

R

C

R1

C1

I

TH

D1

J1

/RUN

I

/RUN

TH

J1

C

C

R

C

C

C

R

C

For low input voltage operation (V

IN

diode can be connected from VIN to BOOST to increase the
external MOSFET gate drive voltage. Be careful not to

< 7V), a Schottky

(4c)

Figure 4. ITH/RUN Pin Interfacing

164 • F04

5

DEMO MANUAL DC164

U

OPERATIO

response. Compensation is provided by RC and CC. The
operating current level is user-programmable via an exter­nal current sense resistor (RS) and is set to 3.0A. Short­circuit current limit is set to approximately 4A.

This demo board is optimized for 3.3V outputs. A wide
input supply range allows operation from 4.8V to 28V for
V

voltages of 3.3V and 2.5V. For 5V outputs the

OUT

minimum input voltage is 5.4V at full load.
The lowest operating input voltage is limited by the exter-

nal MOSFET M1. For operation below 4.8V, subthreshold­level MOSFETs should be substituted. The minimum input
voltage of the LTC1624 is 3.5V.

Remote Output Voltage Sensing

Remote output voltage sensing can be accomplished by
externally connecting a sense lead from V

OSENSE

directly

to the load. To prevent the output from overshooting in
case of a sense-lead fault, a 10Ω resistor (R6) is con­nected on the printed circuit board across the V
V

OSENSE

Connect the external load only to V

terminals. This prevents V

OUT

OSENSE

, not to V

from floating.

OSENSE

OUT

and

. The

surface mount 10Ω resistor mentioned above cannot
handle the load current that would pass though it should
the load be incorrectly connected to V

OSENSE

.

How to Measure Voltage Regulation

When trying to measure voltage regulation, remember
that all measurements must be taken at the point of
regulation. This point is where the LTC1624’s control loop
looks for the information to keep the output voltage
constant. In this demonstration board this information
point occurs between the signal ground and the output
side of R1. These points correspond to the GND (E5) and
V

OSENSE

(E4) terminals of the board. Output voltage test
leads should be attached directly to these terminals. The
load should be placed across V

(E3) to GND (E5).

OUT

Measurements should not be taken at the end of test leads
at the load; refer to Figure 3 for the proper monitoring
equipment configuration.

This applies to line regulation (input to output voltage
regulation) as well as load regulation tests. In doing line
regulation tests always look at the input voltage across the
input terminals.

For the purposes of these tests the demonstration circuit
should be fed from a regulated DC bench supply so
additional variation on the DC input does not add an error
to the regulation measurements.

Output Voltage Programming

The jumper (J2) selects the output voltage according to
Table 1. Output voltages of 5V, 3.3V, 2.5V and one user
programmable output voltage are jumper selectable. Re­sistor R5 (see Figure 1) is left unstuffed so a user select­able output voltage can easily be programmed.

The output voltage is set by a resistive divider according
to the following formula (refer to Figure 1):

R

1

VV

=+

OUT



119 1

.










RX

R1 is set to 35.7k; jumper J2 selects the value of RX. If no
jumpers are in place for J2 or if only jumper J2D is selected
without a resistor in place for R5, the output voltage will be

1.19V (since the equivalent value of RX will be infinite). Be
careful not to exceed the output capacitor's maximum
voltage rating of 10V when selecting R5.

At high input-to-output differential voltages, the on-time
becomes very small. Due to internal gate delays and
response times of the internal circuitry, the minimum
recommended on-time is 450ns. Because this board
allows for a wide output voltage range and the operating
frequency remains constant at 200kHz, a potential duty
cycle limitation exists when low output voltages are
selected (V

< 2.5V). When the duty cycle is less than

OUT

9%, cycle skipping may occur; this increases the inductor
ripple current but does not cause V

to lose regulation.

OUT

Avoiding cycle skipping imposes a limit on the input
voltage for a given output voltage only when V

V

IN(MAX)

= 11.1V

+ 5V For DC > 9%.

OUT

OUT

< 2.2V.

Modification For 5A Output Current

The DC164 demo board has provisions for higher output
currents. Additional pad locations are available for adding
one extra input and output capacitor together with a larger
footprint for a Schottky diode. The following list shows the

6

OPERATIO

DEMO MANUAL DC164

U

component changes necessary for a 5A output current
version:

L1 Sumida CDRH127-10
M1 Siliconix Si4410DY
D1 Motorola MBRD835L
R
C
R

add: C

C

S

C

C
IN3
OUT3

0.02Ω
680pF

3.3k
AVX TPSE226M035R0300
AVX TPSD107M010R0065

At high input voltages the duty cycle decreases and the
Schottky diode is on for a higher percentage of the cycle.
This increases the diode's power dissipation. At higher
input voltages together with high output currents, the

Table 1. List of Alternative Component Manufacturers

MANUFACTURER DEVICE PHONE FAX

AVX Capacitors [phone] [phone]
Central Semiconductor Diodes [phone] [phone]
Coilcraft Inductors [phone] [phone]
Coiltronics Inductors [phone] [phone]
COMM CON Connectors [phone] [phone]
Dale Inductors/Sense Resistors [phone] [phone]
International Rectifier MOSFETs/Diodes [phone] [phone]
IRC Sense Resistors [phone] [phone]
KRL Sense Resistors [phone] [phone]
Motorola MOSFETs/Diodes [phone] [phone]
Murata-Erie Capacitors [phone] [phone]
Sanyo Capacitors/MOSFETs [phone] [phone]

Siliconix MOSFETs [phone] [phone]
Sprague Capacitors [phone] [phone]
Sumida Inductor [phone] [phone]

TDK Inductors [phone] [81] 03-3278-5358

Schottky diode will dissipate a couple of watts and heat
sinking will be needed. Remember that the most stressful
condition on the Schottky diode is a short circuit. For
applications greater than 5A, synchronous operation may
be preferred. Refer to the LTC1435 data sheet and demo
board DC094.

Component Manufacturers

Table 1 is a partial list of alternate component manufactur­ers that can be used in LTC1624 applications. Using
components other than the ones supplied on the demon­stration board will require careful analysis to verify that no
component specifications are exceeded. Finally,
recharacterizing the circuit for efficiency is necessary.

[81] 0952-82-3959 [81] 0952-82-4655

[81] 03-3607-5111 [81] 03-3607-5144

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

7



DEMO MANUAL DC164



UW

PCB LAYOUT A D FIL

Component Side Silkscreen Component Side Component Side Mask

Solder Side Solder Side Mask Pastemask Top

U

PC FAB DRAWI G

A

A

BB

B

B

2.000

B

NOTES: UNLESS OTHERWISE SPECIFIED
 1. MATERIAL:  FR4 OR EQUIVALENT EPOXY, 2 OZ. 

B

B

B

B

A

A

 COPPER CLAD THICKNESS 0.062 ±0.006 TOTAL OF TWO LAYERS
 2. FINISH:  ALL PLATED HOLES 0.001 MIN, 0.0015 MAX 

 COPPER PLATE ELECTRODEPOSITED TIN-LEAD COMPOSITION
 BEFORE REFLOW, SOLDER MASK OVER BARE COPPER (SMOBC)

 3. SOLDER MASK: BOTH SIDES USING SR1020 OR EQUIVALENT
 4. SILKSCREEN:  USING WHITE NONCONDUCTIVE EPOXY INK

2.000
 5. ALL DIMENSIONS ARE IN INCHES


 NUMBER
SYMBOL DIAMETER OF HOLES

 A 0.020 9
 B 0.095 4
 TOTAL 13

164 • FAB DWG

Linear Technology Corporation

8

1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● [phone]
FAX: [phone]

●

TELEX: 499-3977 ● www.linear-tech.com

dc164f LT/TP 1097 500 • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1997

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Analog Devices Inc.:
DC164A