Linear Technology DEMO CIRCUIT 1672A User manual

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DESCRIPTION
Demonstration circuit 1672A is a high efficiency,
single phase, synchronous buck converter for Intel
IMVP-6/IMVP-6.5 CPUs. It can supply 25A maxi-
mum load current at up to 1.5V output with 4.5V to
28V input range. The demo board features the
LTC®3816EUHF controller. The LTC3816 is a sin-
gle-phase synchronous buck controller in a con-
stant-frequency voltage mode architecture. The con-
troller’s leading edge modulation topology allows
extremely low output voltages and supports a phase-
lockable switching frequency up to 550kHz. The
output voltage is programmed using a 7-bit VID
code. The default VID jumpers (VID6 to VID0) are
set to be 0110000 for 0.9V output. The LTC3816
features all of the IMVP-6/IMVP-6.5 requirements,
including start-up to a preset boot voltage, differen-
tial remote output voltage sensing with programma-
ble active voltage positioning, Imon output current
reporting, power optimization during sleep state, and
slow slew rate sleep state exit. Fault protection fea-
tures include input undervoltage lockout, cycle-by-
cycle current limit, output overvoltage protection,
and power-good (PWRGD) and overtemperature
flags. The LTC3816 supports wide input range (4.5V
to 36V) with optional line feedforward compensation,
temperature compensated inductor DCR or sense
resistor output current monitoring. The LTC3816
can provide high efficiency, high power density and
versatile power solutions for embedded computing,
mobile computers, internet devices and navigation
displays. The controller is available in 38-pin ther-
mally enhanced eTSSOP and 5mm × 7mm QFN
packages.
The VRON pin (JP15) provides enable feature. To
shut down the converter, one simple way is to force
the VRON pin below 0.65V (JP15: OFF). Use JP19
jumper to select pulse-skipping or forced continuous
mode operation. Switching frequency is pre-set at
about 400KHz, and it can be easily modified from
150KHz to 550KHz. JP20~JP26 (VID0~VID7) are
used to set the output voltage based on the IMVP-
6/IMVP-6.5 VID code, as shown in table 2. JP1 and
JP18 are used to select either IMVP6 or IMVP6.5
specification. For detailed information, please see
LTC3816 data sheet and Intel IMVP-6/IMVP-6.5 spe-
cification.
Design files for this circuit board are available. Call
the LTC factory.
DEMO CIRCUIT 1672A
QUICK START GUIDE
LTC3816EUHF
HIGH EFFICIENCY SINGLE PHASE BUCK CONVERTER
FOR INTEL IMVP-6/IMVP-6.5 CPUs
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER CONDITION VALUE
Input Voltage Range 4.5V to 28V
Output Voltage, VOUT V
IN = 4.5-28V, IOUT = 0A to 23A, VID6-0=0110000 0.9V ±1.5%
Maximum Output Current, IOUT V
IN = 4.5-28V, VOUTMAX = 1.5V 25A
Typical Efficiency VIN = 12V, VOUT = 1.5V, IOUT = 23A 86.7%
Typical Switching Frequency 400kHz

LTC3816EUHF
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Table 2 . IMVP-6/IMVP-6.5 VID Output Voltage Programming

LTC3816EUHF
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QUICK START PROCEDURE
Demonstration circuit 1672A is easy to set up to eva-
luate the performance of the LTC3816EUHF. Refer to
Figure 1 for the proper measurement equipment se-
tup and jumpers’ location, and follow the procedure
below:
1. With power off, connect the input power
supply to Vin (4.5V-28V) and GND (input re-
turn).
2. Set VID jumpers VID6-0: 0110000 for 0.9V ou-
put.
3. Connect the output load between Vout and
GND (Initial load: no load).
4. Connect the DVMs to the input and outputs.
5. Turn on the input power supply and check for
the proper output voltages. Vout should be
within 0.885 V to 0.915V .
6. Once the proper output voltages are estab-
lished, adjust the loads within the operating
range and observe the output voltage regula-
tion, ripple voltage and other parameters.
Note: When measuring the output or input voltage
ripple, do not use the long ground lead on the oscil-
loscope probe. See Figure 2 for the proper scope
probe technique. Short, stiff leads need to be sol-
dered to the (+) and (-) terminals of an output capaci-
tor. The probe’s ground ring needs to touch the (-)
lead and the probe tip needs to touch the (+) lead.

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Figure 1. Proper Measurement Equipment Setup
VOUT GND
COUT
+-
Figure 2.
Measuring Output Voltage Ripple

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l
Figure 3.
Efficiency vs load current

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DC1672A