QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 432
HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN REGULATOR
1
LTC1875 or LTC1879
DESCRIPTION
Demonstration circuit 432 is a step-down converter, fea-
turing either the LTC1875 or LTC1879 high frequency
monolithic switching regulators. With an input voltage
range from 2.65V to 6V, the LTC1875 is ideal for Li-Ion
applications, such as PDAs, cellular phones, and digital
cameras. For applications with higher input voltages, the
LTC1879 is the choice with its maximum input voltage
limit of 10V. Both devices have switch current limits over
1A (LTC1875-1.6A, LTC1879-1.8A), which allows these
ICs to deliver high(er) power to small, low-profile appli-
cations. While the standard operating frequency of both
parts is 550 kHz, the switching can be externally set as
high as 750 kHz. All these features make the LTC1879
(DC432A) or LTC1875 (DC432B) perfectly suited for bat-
tery-powered, surface mount applications.
Design files for this circuit board are available. Call
the LTC factory.
Table 1. Performance Summary
PARAMETER CONDITION VALUE
Minimum Input Voltage 2.65V
Maximum Input Voltage
(
LTC1875)
Maximum Input Voltage (LTC1879)
6V
10V
V
OUT (
LTC1875)
V
OUT
(LTC1879)
I
OUT
= 0A to 1.5A
I
OUT
= 0A to 1.2A
0.8V ±2% to V
IN
±2%
0.8V ±2% to V
IN
±2%
I
OUT (
LTC1875)
I
OUT
(LTC1879)
1.5A
1.2A
Nominal Switching Frequency 550kHz
QUICK START PROCEDURE
Demonstration circuit 432 is easy to set up to evaluate
the performance of the LTC1875 or LTC1879. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscil-
loscope probe. Measure the input or output voltage rip-
ple by touching the probe tip directly across the Vin or
Vout and GND terminals. Refer to Figure 2 for proper
placement of the scope probe.
1.
Place jumper JP2 in the SHDN position.
2.
Select the desired output voltage, using jumper JP3.
The fixed output options are 1.8V, 2.5V, and 3.3V. Too
set the output voltage to a custom value, insert a re-
sistor into RFB5.
3.
Connect the load between the Vout and GND termi-
nals on the bottom right-side of the board.
4.
With power off, connect the input power supply to Vin
and GND (which are at the bottom left-side of the
board). Turn on the power at the input.
NOTE:
If evaluating the LTC1875, do not exceed 6V in-
put; if evaluating the LTC1879, do not exceed 10V in.
5.
Place jumper JP2 in the RUN position.
6.
Check for the proper output voltages.
If there is no output, temporarily disconnect the load
to make sure that the load is not set too high.
7.
Once the proper output voltages are established, ad-
just the loads within the operating range and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 432
HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN REGULATOR
2
+
–
+
–
+
–
+
–
+
–
+
–
LOAD
Figure 1. Proper Measurement Equipment Setup for both versions of the board:
LTC1879 (DC432A) and LTC1875 (DC432B)
VIN
GND
Figure 2. Scope Probe Placement for
Measuring Input or Output Ripple
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 432
HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN REGULATOR
3
JP3 OPEN3.3V2.5V
1.8V
Vin
Vout
SYNC
RUN
PG
**
**
Space Provided for an Optional Resistor to Program a Custom Output Voltage
PCB SILKSCREEN
CSS
RSS
CFFW
RFB1
CC1
RC
CC2
CPL
RPL
CBYP RIN
RPG
L1
COUTCIN2
U1
CIN1
D1
SHDN
Pulse - skipBurst Mod e
(Opt. )
VERSION TABLE
DC432A
DC432B
Assembly Type Cin1, Cin2
10uF , 10V
10uF , 16V
U1
LTC1875EGN
LTC1879EGN
*
**
*
*
*
Vin
2. 65-6V
2.65-10V
Iout(A)
1.5
1.2
Iout
1.8V / 2.5V / 3.3V
RUN
Cin 2
10uF
Rpl
10K
E3
E8
Rpg
100K
Rin
10
Rc
150K
U1
2
15
16
14
4
1
7
3
13
11
6
12
5
9
8
10
RUN/SS
SYNC/MODE
PLL_LPF
PGOOD
ITH
SGND
PGND
Vfb
SVin
SWN2
SWN1
SWP2
SWP1
PVin2
PVin1
PGND
Cc1
47pF
Rfb3
412K
Co ut
47uF
6.3V
Rfb4
280K
Cpl
2200p F
Rfb5
optional
D1
MBR052 0
E4
E5
Cc2
220pF
Cffw
22pF
E6
E7
Rss
1M
JP2
1
2
3
Rfb1
887K
E2
Cin 1
10uF
JP1
1
2
3
Cbyp
0.1uF
Css
0. 1uF
L1
4.7u H
Rfb2
698K
E1
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
JP3 OPEN3.3V2.5V
1.8V
Vin
Vout
SYNC
RUN
PG
**
**
Space Provided for an Optional Resistor to Program a Custom Output Voltage.
PCB SILKSCREEN
CSS
RSS
CFFW
RFB1
CC1
RC
CC2
CPL
RPL
CBYP RIN
RPG
L1
COUTCIN2
U1
CIN1
D1
SHDN
Pulse -skipBurst Mode
(Opt.)
VERSION TABLE
DC432A
DC432B
Assembly Type Cin1, Cin2
10uF, 10V
10uF, 16V
U1
LTC1875EGN
LTC1879EGN
*
**
*
*
*
Vin
2.65-6V
2.65-10V
Iout(A)
1.5
1.2
Iout
1.8V / 2.5V / 3.3V
RUN
A
Demo Circuit 432A / 432B
Wednesday, June 05, 2002
11
LTC1879EGN/LTC1875EGN, High Efficiency Synchronous Step-Down Regulator
June Wu 5/22/01
TOM GROSS5/22/01
SIZE
SCALE:
CAGE CODE DWG NO REV
SHEET OF
FILENAME:
TITLE
CONTRACT NO.
APPROVALS DATE
DRAWN
CHECKED
APPROVED
ENGINEER
DESIGNER
TECHNOLOGY
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
Cin2
10uF
Rpl
10K
E3
E8
Rpg
100K
Rin
10
Rc
150K
U1
2
15
16
14
4
1
7
3
13
11
6
12
5
9
8
10
RUN/SS
SYNC/MODE
PLL_LPF
PGOOD
ITH
SGND
PGND
Vfb
SVin
SWN2
SWN1
SWP2
SWP1
PVin2
PVin1
PGND
Cc1
47pF
Rfb3
412K
Cout
47uF
6.3V
Rfb4
280K
Cpl
2200pF
Rfb5
optional
D1
MBR0520
E4
E5
Cc2
220pF
Cffw
22pF
E6
E7
Rss
1M
JP2
1
2
3
Rfb1
887K
E2
Cin1
10uF
JP1
1
2
3
Cbyp
0.1uF
Css
0.1uF
L1
4.7uH
Rfb2
698K
E1
Linear Technology Corporation
LTC1879EGN
Bill Of Material
Demo Bd. #432A
6/17/2005
10:05 AM
Item Qty Reference Part Description Manufacture / Part #
1 2 Cbyp,Css CAP., X7R, 0.1uF, 16V, 20% 0603 AVX, 0603YC104MAT
2 1 Cc1 CAP., NPO, 47pF, 50V, 10% 0402 AVX, 04025A470KAT
3 1 Cc2 CAP., X7R, 220pF, 50V, 20% 0402 AVX, 04025C221MAT
4 1 Cffw CAP., NPO, 22pF, 50V, 10% 0402 AVX, 04025A220KAT
5 2 Cin1,Cin2 CAP., X5R, 10uF, 16V, 20% 1210 TAIYO YUDEN, EMK325BJ106MN
6 1 Cout CAP., X5R, 47uF, 6.3V, 20% 1812 TDK, C4532X5R0J476M
7 1 Cpl CAP., X7R, 2200pF, 50V, 20% 0402 AVX, 04025C222MAT
8 0 D1 (OPT.) DIODE, MBR0520
9 8 E1-E7 TURRET, MILL-MAX2501-2
10 2 JP1,JP2 JUMPER, 0.079, 3 PIN COMM CON2802S-03G1
11 1 JP3 JUMPER, DOUBLE ROW 0.079X4 COMM CON2202S-08G1
12 3 JP1,JP2,JP3 SHUNT, COMM CON. CCIJ2MM-138G
13 1 L1 INDUCTOR,4.7uH, D63LCB TOKO, A921CY-4R7M
14 1 Rc RES.,CHIP, 150K, 1/16W, 5% 0402 AAC, CR05-154JM
15 1 Rfb1 RES.,CHIP, 887K, 1/16W, 1% 0402 AAC, CR05-8873FM
16 1 Rfb2 RES.,CHIP, 698K, 1/16W, 1% 0402 AAC, CR05-6983FM
17 1 Rfb3 RES.,CHIP, 412K, 1/16W, 1% 0402 AAC, CR05-4123FM
18 1 Rfb4 RES.,CHIP, 280K, 1/16W, 1% 0402 AAC, CR05-2803FM
19 0 Rfb5 (optional) RES.,CHIP, 0402
20 1 Rin RES.,CHIP, 10, 1/16W, 1% 0402 AAC, CR05-10R0FM
21 1 Rpg RES.,CHIP, 100K, 1/16W, 5% 0402 AAC, CR05-104JM
22 1 Rpl RES.,CHIP, 10K, 1/16W, 5% 0402 AAC, CR05-103JM
23 1 Rss RES.,CHIP, 1M, 1/16W, 5% 0402 AAC, CR05-105JM
24 1 U1 I.C., LTC1879EGN, SSOP-16GN LINEAR, LTC1879EGN
25 1 PRINTED CIRCUIT BOARD DEMO BOARD DC432A
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