DC1126A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1126
3.3V/5A AND 2.5V/5A REGULATOR
LTC3850EUF
DESCRIPTION
Demonstration circuit 1126 is a high density 3.3V/5A
and 2.5V/5A step down converter featuring the
LTC3850EUF. The power components, excluding the bulk
output capacitors, fit within a 0.90” X 0.75” area on the
top layer and the control circuit resides in a 0.70” X
0.65” area on the bottom layer. The package style for the
LTC3850EUF is a 4mm X 4mm 28-lead QFN with an exposed ground pad.
tors to save cost and board space and to improve efficiency. Other stuffing options allow the converter to be
configured for either CCM (original setting), pulse skip
or Burst Mode operation, or to be synchronized to an
external clock.
The main features of the board include rail tracking, an
internal 5V linear regulator for bias, RUN pins for each
output and a PGOOD signal. An optional DCR sense circuit allows the converter to use the inductor’s DCR as
the sense element instead of the on-board sense resis-
Design files for this circuit board are available. Call
the LTC factory.
The input voltage range is 6.5V to 14V. For applications
that have a 5V +/- 0.5V input, the board has an optional
resistor to tie the INTVCC pin to the VIN pin.
Table 1. Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
6.5V
Maximum Input Voltage
14V
Output Voltage VOUT1
IOUT = 0A to 5A
3.3V ±2%
Output Voltage VOUT2
IOUT = 0A to 5A
2.5V ±2%
Nominal Switching Frequency
500kHz
Full Load Efficiency
VOUT1 = 3.3V, IOUT1 = 5A, VIN = 12V
91% Typical
(see Figure 3 for efficiency curves)
VOUT2 = 2.5V, IOUT2 = 5A, VIN = 12V
89% Typical
QUICK START PROCEDURE
Demonstration circuit 1126 is easy to set up to evaluate
the performance of the LTC3850EUF. 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
ON
JP2
ON
2. With power off, connect the input power supply
to VIN and GND.
3. Turn on the power at the input.
NOTE: Make
sure that the input voltage
does not exceed 15V.
4. Check for the proper output voltages.
VOUT1 = 3.234V to 3.366V,
VOUT2 = 2.450V to 2.550V
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1126
3.3V/5A AND 2.5V/5A REGULATOR
NOTE: If there is no output, temporarily
disconnect the load to make sure that
the load is not set too high.
5. Once the proper output voltages are established,
adjust the loads within the operating range and
observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
RAIL TRACKING
Demonstration circuit 1126 is setup for coincident rail
tracking where VOUT2 tracks VOUT1 and the ramp-rate
for VOUT1 is determined by the value of the TRK/SS1
capacitor at C11. See Figure 4.
to Tables 2 and 3 for tracking options and to the data
sheet for more details.
This board can be modified on the bench for external rail
tracking or for independent turn-on of the rails. For the
latter case, the ramp-rate for VOUT1 and VOUT2 will be
determined by their respective TRK/SS capacitors. Refer
Table 2. VOUT1 Tracking Options
TRACK1 DIVIDER
TRK/SS1 CAP
CONFIGURATION
R13
R15
C11
Soft Start Without Tracking (original board)
0Ω
Not Stuffed
10nF
External Coincident Tracking
63.4kΩ
20.0kΩ
Not Stuffed
Table 3. VOUT2 Tracking Options
TRACK2 DIVIDER
TRK/SS2 CAP
CONFIGURATION
R3
R5
C3
Soft Start Without Tracking
Not stuffed
Not stuffed
10nF
Coincident Tracking to VOUT1 (original board)
43.2kΩ
20.0kΩ
Not Stuffed
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1126
3.3V/5A AND 2.5V/5A REGULATOR
INDUCTOR DCR SENSING
Demonstration circuit 1126 provides an optional circuit
for DCR sensing. DCR 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, reduced board space and higher efficiency,
but the disadvantage is a less accurate current limit. If
DCR sensing is used, be sure to select an inductor current with a sufficiently high saturation current or use an
iron powder type.
Tables 4 and 5 show an example of how to modify the
DC1126 for DCR sensing using the parameters below:
VOUT1 = 3.3V / 5A
VOUT2 = 2.5V / 5A
VIN = 6.5V to 14V
Fsw = 500kHz, typical
L1,2 = Vishay IHLP2525CZ-11 2.2uH
(DCR = 15.7mΩ typ, 16.5mΩ max)
ILIM = INTVCC (R25 = 0Ω, R26 = OPEN)
Table 4. VOUT1 Configured for 3.3V/5A Using DCR Sensing and Discrete Sense Resistors
RSENSE
FILTER
RESISTORS
SENSE
FIILTER
CAP
DCR FILTER/DIVIDER
RESISTORS
TOP
BOTTOM
SENSE1- TO L1JUMPER
CONFIGURATION
RSNS1
L1
R7,R9
C4
R27
R29
R39
DCR Sensing
Short with
Cu strip or
very short &
thick piece
of wire
Vishay IHLP2525CZ-11
2.2uH
Open
0.1uF
2.7kΩ
2.7kΩ
0Ω
TDK RLF7030T –
2.2uH
10Ω
1nF
Open
Open
Open
Discrete RSENSE 8mΩ
(original board)
Table 5. VOUT2 Configured for 2.5V/5A Using DCR Sensing and Discrete Sense Resistors
RSENSE
FILTER
RESISTORS
SENSE
FIILTER
CAP
DCR FILTER/DIVIDER
RESISTORS
TOP
BOTTOM
SENSE2- TO L2JUMPER
CONFIGURATION
RSNS2
L2
R20,R21
C16
R34
R32
R40
DCR Sensing
Short with
Cu strip or
very short &
thick piece
of wire
Vishay IHLP2525CZ-11
2.2uH
Open
0.1uF
2.7kΩ
2.7kΩ
0Ω
TDK RLF7030T –
2.2uH
10Ω
1nF
Open
Open
Open
Discrete RSENSE 8mΩ
(original board)
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1126
3.3V/5A AND 2.5V/5A REGULATOR
Iin
Iout1
A
+
Vin
V
-
Vin
supply
A
+
V Vout1
+
-
-
V
+
Vout1
load
-
Vout2
+
A
Vout2
load
+
Iout2
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Output or Input Voltage Ripple
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1126
3.3V/5A AND 2.5V/5A REGULATOR
Vin = 12V, Fsw = 530kHz, CCM
100%
3.3Vout
Efficiency
90%
2.5Vout
80%
Each phase:
Q = Si4816BDY
L = TDK RLF7030 2.2uH
Rsense = 8mOhms
70%
60%
0
1
2
3
4
5
6
Load current (Amps)
Figure 3. Typical Efficiency vs Load Current
2msec / div
3.3V
2.5V
`
VOUT1,2
1V / DIV
Figure 4. Coincident Rail Tracking During Startup (original board).
5
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1126
3.3V/5A AND 2.5V/5A REGULATOR
6
Similar pages