SP7652
Evaluation Board Manual
Easy Evaluation for the
SP7652EU 0 to 28V Input, 0 to 8A
Output Synchronous Buck
Converter
Built in Low Rds(on) Power FETs
UVLO Detects Both VCC and VIN
High Integrated Design, Minimal
Components
High Efficiency: 90%
Feature Rich: UVIN, Programmable
Softstart, External VCC Supply and
Output Dead Short Circuit Shutdown
SP7652EB SCHEMATIC
Rev 07/07/04
SP7652 Evaluation Manual
Copyright 2004 Sipex Corporation
USING THE EVALUATION BOARD
1) Powering Up the SP7652EB Circuit
Connect the SP7652 Evaluation Board with an external +12V power supply. Connect
with short leads and large diameter wire directly to the “VIN” and “GND” posts. Connect
a Load between the VOUT and GND2 posts, again using short leads with large
diameter wire to minimize inductance and voltage drops.
2) Measuring Output Load Characteristics
It’s best to GND reference scope and digital meters using the Star GND post in the
center of the board. VOUT ripple can best be seen touching probe tip to the pad for C3
and scope GND collar touching Star GND post – avoid a GND lead on the scope which
will increase noise pickup.
3) Using the Evaluation Board with Different Output Voltages
While the SP7652 Evaluation Board has been tested and delivered with the output set
to 3.30V, by simply changing one resistor, R2, the SP7652 can be set to other output
voltages. The relationship in the following formula is based on a voltage divider from the
output to the feedback pin VFB, which is set to an internal reference voltage of 0.80V.
Standard 1% metal film resistors of surface mount size 0603 are recommended.
Vout = 0.80V ( R1 / R2 + 1 ) => R2 = R1 / [ ( Vout / 0.80V ) – 1 ]
Where R1 = 68.1KΩ and for Vout = 0.80V setting, simply remove R2 from the board.
Furthermore, one could select the value of R1 and R2 combination to meet the exact
output voltage setting by restricting R1 resistance range such that 50KΩ
≤
R1
≤
100KΩ
for overall system loop stability.
Note that since the SP7652 Evaluation Board design was optimized for 12V down
conversion to 3.30V, changes of output voltage and/or input voltage will alter
performance from the data given in the Power Supply Data section. In addition, the
SP7652EU provides short circuit protection by sensing Vout at GND.
POWER SUPPLY DATA
The SP7652EU is designed with a very accurate 1.0% reference over line, load and
temperature. Figure 1 data shows a typical SP7652 Evaluation Board Efficiency plot,
with efficiencies to 90% and output currents to 8A. SP7652EU Load Regulation is
shown in Figure 2 of only 0.4% change in output voltage from no load to 8A load.
Figures 3 and 4 illustrate a 4A to 8A and 0A to 8A Load Step. Start-up Response in
Figures 5, 6 and 7 show a controlled start-up with different output load behavior when
power is applied where the input current rises smoothly as the Softstart ramp increases.
In Figure 8 the SP7652EU is configured for hiccup mode in response to an output dead
short circuit condition and will Softstart until the over-load is removed. Figure 9 and 10
show output voltage ripple less than 50mV at no load to 8A load.
While data on individual power supply boards may vary, the capability of the SP7652EU
of achieving high accuracy over a range of load conditions shown here is quite
impressive and desirable for accurate power supply design.
2
Vin=12V
Vout=3.3V
Vin=12V
Vout=3.3V
Figure 1. Efficiency vs Load
Figure 2. Load Regulation
Vout
Vin
Vout
Vin
Iout (5A/div)
Vin=12V
Vout=3.3V
Iout (5A/div)
Vin=12V
Vout=3.3V
Figure 3. Load Step Response: 4->8A
Figure 4. Load Step Response: 0->8A
Vout
Vout
Vin
SoftStart
Vin
SoftStart
Iout (5A/div)
Iout (5A/div)
Figure 5. Start-Up Response: No Load
Vout
Figure 6. Start-Up Response: 4A Load
SoftStart
Vin
Vout
Iout (5A/div)
Ichoke (5A/div)
Figure 7. Start-Up Response: 8A Load
Figure 8. Output Load Short Circuit
3
+5V BIAS SUPPLY APPLICATION SCHEMATIC
In this application example, the SP7652EU is power by an external +5V bias supply
which current consumption of 20mA Maximum. If this supply is not available than it is
recommend Sipex SPX5205 Low-Noise LDO Voltage Regulator which is included on
the SP7652 Evaluation Board.
Vout ripple = 30mV
Vout ripple = 50mV
Vin
Vin
Ichoke (5A/div)
Ichoke(5A/div)
Figure 9. Output Ripple: No Load
Figure 10. Output Ripple: 8A Load
4
DIFFERENT +5V BIAS SUPPLY SCHEMES APPLICATION SCHEMATIC
The SP7652EU VCC Bias Supply can be derived from Vin or external bias with several
biasing options. The transistor plus zener diode +5V bias supply could also be used as
shown in Figure 11.
Figure 11. Transistor plus Zener Diode +5V Supply Application Schematic
Table 1: SP7652EB Suggested Components and Vendor Lists
5
