DEMO CIRCUIT 1510A
LTC3858EUH
Demo Manual
LTC3858EUH
POLYPHASE HIGH VOUT SYNC. BUCK CONVERTER
DESCRIPTION
Demonstration circuit 1510A is a high output voltage,
high efficiency synchronous poly-phase buck converter
featuring the LTC3858EUH. The demo circuit is available
in two versions. The input voltage of both versions is
16V to 26V. DC1510A-A is configured using 2 piece of
LTC3858EUH with 4 phase interleaving operation which
provides 12V/50A output, while the DC1510A-B is confi-
gured with 1 piece of LTC3858EUH with 2 phase inter-
leaving operation which provides 12V/25A output.
The board has a Mode selection jumper that allows the
converter to run in Forced CCM Mode, Pulse Skip Mode
or Burst Mode operation. Synchronization to an external
clock (frequency range 150kHz to 500kHz) is also possi-
ble on this board.
The demo circuit senses inductor current with sensing
resistor but also has an optional DCR sense circuit that
allows using the inductor’s DCR as the current sensing
element to save cost, footprint and improve efficiency.
The LTC3858EUH datasheet gives a complete description
of these parts, operation and application information and
must be read in conjunction with this quick start guide
for Demonstration circuit 1510A.
Design files for this circuit board are available. Call
the LTC factory.
L
, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower SwitcherCAD, Multimode
Dimming, No Latency
ΔΣ,
No Latency Delta-Sigma, No R SENSE , Operational Filter, PanelPro-
tect, PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
Table 1. Performance Summary (T
A
=25°C)
PARAMETER
Input Supply Range
Output Voltage Range
Nominal Switching Frequency
Full Load Efficiency
(See Figure 3 for efficiency curves)
CONDITIONS
V
IN
= 24V, V
OUT
= 12 V
V
IN
= 24V, V
OUT
= 12V,
I
LOAD
= 50A (-A) / 25A (-B)
MIN
16
11.82
TYP
12
250
97.3
MAX
26
12.18
UNITS
V
V
kHz
%
QUICK START PROCEDURE
Demonstration circuit 1510A is easy to set up to evaluate
the performance of the LTC3858EUH. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
NOTE.
When measuring the input or output voltage ripple, care must be
taken to avoid a long ground lead on the oscilloscope probe. Measure the
input or output voltage ripple by touching the probe tip directly across the
Vin or Vout and GND terminals. See Figure 2 for proper scope probe
technique.
1.
Place jumpers in the following positions:
JP1 MODE
CCM
JP2 RUN
ON
JP3 RUN
ON
2.
With power off, connect the input power supply to
VIN and GND. Connect the load to the output. The
load current should be smaller than 50A for
DC1510A-A and smaller than 25A for DC1510A-B.
1
LTC3858EUH
3.
Turn on the power at the input.
NOTE.
Make sure that the input voltage does not exceed 36V.
the output voltage regulation, ripple voltage, efficien-
cy and other parameters.
6.
Different operating modes can be evaluated by
changing the position of JP1
MODE
jumper and are
discussed in the next section.
4.
Check for the proper output voltage. VOUT = 11.82V
to 12.18V
5.
Once the proper output voltages are established, ad-
just the loads within the operating range and observe
Vin
Supply
+
A
-
Vin
GND (J6, J12)
VIN (J11, J5)
+
V
-
VOUT (J1, J2, J7, J8)
Iout
GND (J3, J4, J9, J10)
-
V
+
A
Vout
load
+
-
Figure 1. Proper Measurement Equipment Setup
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LTC3858EUH
Figure 2. Measuring Input or Output Ripple
FREQUENCY SYNCHRONIZATION AND MODE SELECTION
Demonstration circuit 1510A’s Mode selector allows
the converter to run in Forced CCM Mode, Pulse Skip
Mode or Burst Mode operation by changing position
of
JP1 MODE
jumper. For synchronizing to an external
clock source,
JP1 MODE
jumper needs to be removed.
Table 2. Mode Selection and Synchronizing Operation Options
CONFIGURATION
Forced CCM Mode Operation
Pulse Skip Mode Operation
Burst Mode Operation
Synchronize to Ext. clock (Ext. clock apply to MODE/PLLIN turret)
Apply the external clock (frequency range 150kHz to
500kHz) from the
PLL/MODE1
turret to
GND
. Refer to
Table 2 and to the data sheet for more details.
Note:
Please don’t use Burst Mode in 4 phase inter-
leaving operation
PLL/MODE1 JUMPER
“CCM”
“PULSE SKIP”
“BURST MODE”
Remove Jumper
OPTIONAL INDUCTOR DCR CURRENT SENSING
Demonstration circuit 1510A provides an optional cir-
cuit for Inductor DCR Current Sensing. Inductor DCR
Current Sensing uses the DCR of the inductor to sense
the inductor current instead of discrete sense resistors.
The advantages of DCR sensing are lower cost, re-
duced board space and higher efficiency, but the dis-
advantage is a less accurate current limit. If DCR sens-
ing is used, be sure to select an inductor current with a
sufficiently high saturation current or use an iron
powder type. Refer to the datasheet for more details.
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LTC3858EUH
Figure 3. Efficiency Curve for Demonstration Circuit 1510A
4
DC1510A-A Schematic
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LTC3858EUH
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