Sipex SP7651 Bedienungsanleitung

SP7651EB SCHEMATIC

Easy Evaluation for the SP7651ER

12V Input, 0 to 3A Output Synchronous

Buck Converter

Built in Low R

(

) Power FETs

UVLO Detects Both Vcc and V

Highly Integrated Design, Minimal

Components

High Efficiency: 88%

Feature Rich: UV

, Programmable

Softstart, External Vcc Supply and

Output Dead Short Circuit Shutdown

Protection

Solved by

SP7651

Evaluation Board Manual

Page 2 of 8

USING THE EVALUATION BOARD

1) Powering Up the SP7651EB Circuit

Connect the SP7651 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

OUT

ripple can best be seen touching the probe tip to the pad for C3 and the scope

GND collar touching the GND side of C3 using short wrapped wire around the collar –

avoid a GND lead on the scope which will increase noise pickup.

3) Using the Evaluation Board with Different Output Voltages

While the SP7651 Evaluation Board has been tested and delivered with the output set

to 3.30V, by simply changing one resistor, R2, the SP7651 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 V

, which is set to an internal reference voltage of 0.80V.

Standard 1% metal film resistors of surface mount size 0603 are recommended.

OUT

= 0.80V (R1 / R2 + 1) => R2 = R1 / [ ( Vout / 0.80V ) – 1 ]

Where R1 = 68.1KΩand for V

OUT

= 0.80V setting, simply remove R2 from the board.

Furthermore, one could select the value of the R1 & 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 SP7651 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

SP7651ER provides short circuit protection by sensing V

OUT

at GND.

POWER SUPPLY DATA

The SP7651ER is designed with a very accurate 1.0% reference over line, load and

temperature. Figure 1 data shows a typical SP7655 Evaluation Board Efficiency plot,

with efficiencies to 87% (including generation of 5V Vcc) and output currents to 3A.

SP7651ER Load Regulation is shown in Figure 2 to have only 0.5% change in output

voltage from 0.5A load to 3A load. Figures 3 and 4 illustrate a 1.5A to 3A and 0A to 3A

Load Step. Start-up Responses 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 SP7651ER is configured for

hiccup mode in response to an output dead short circuit condition and will Soft-start until

the over-load is removed. Figure 9 and 10 show output voltage ripple less than 25mV at

no load to 3A load.

While data on individual power supply boards may vary, the capability of the SP7651ER

of achieving high accuracy over a range of load conditions shown here is quite

impressive and desirable for accurate power supply design.

Page 3 of 8

Efficiency vs Load Current

100

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load current (A)

Efficiency (%)

Output Voltage vs Load Current

3.280

3.290

3.300

3.310

3.320

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load current (A)

Output Voltage (V)

Figure 1. Efficiency vs Load Figure 2. Load Regulation

Figure 3. Load Step Response: 1.5->3A Figure 4. Load Step Response: 0->3A

Figure 5. Start-Up Response: No Load Figure 6. Start-Up Response: 3A Load

Vout

Vin

SoftStart

Ichoke (0.5A/div)

Iout (2A/div)

Vout

Iout (1A/div)

Vout

Vin

SoftStart

Ichoke (2A/div)

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Page 4 of 8

Figure 7. Output Load Short Circuit Figure 8. Output Load Short Circuit (Zoom-in)

Figure 9. Output Ripple: No Load Figure 10. Output Ripple:3A Load

Ichoke (2A/div)

Vout ripple = 10mV

Ichoke (1A/div)

Vout ripple = 10mV

SoftStart

Ichoke

25A/div

SoftStart

Vout

Ichoke

25A/div

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Vi=12V

Vo=3.3V

Page 5 of 8

TYPE III LOOP COMPENSATION DESIGN

The open loop gain of the SP7651EB can be divided into the gain of the error amplifier

Gamp(s), PWM modulator Gpwm, buck converter output stage Gout(s), and feedback

resistor divider Gfbk. In order to cross over at the selecting frequency fco, the gain of

the error amplifier must compensate for the attenuation caused by the rest of the loop at

this frequency. The goal of loop compensation is to manipulate the open loop frequency

response such that its gain crosses over 0dB at a slope of –20dB/dec. The open loop

crossover frequency should be higher than the ESR zero of the output capacitors but

less than 1/5 to 1/10 of the switching frequency fs to insure proper operation. Since the

SP7651EB is designed with Ceramic Type output capacitors, a Type III compensation

circuit is required to give a phase boost of 180°in order to counteract the effects of the

output LC underdamped resonance double pole frequency.

(SRz2Cz2+1)(SR1Cz

3+1)

SR1Cz2(SRz3Cz3+1)(SRz2C

p1+1)

Vin

Vramp_p

(SResrCout+

[S^2LCout+S(Resr+Rdc)Co

ut+1]

(R1+R2

)

Vout

Vref

Vout

(Volts

)

Vref

(Volts

)

Type II

I Voltage

Loop

(Volts

)

Vfbk

Gout(S)

Gain Block

Compensation Gamp(S)

PWM Stage

Output Stage

Gain Block

Gpwm

Gain Block

Gfbk

Voltage Feedback

Resr := Output Capacitor Equivalent Series Resitance

Definition

Rdc := Output

Inductor DC Resistance

Vramp_pp := SP7651 Internal RAMP Amplitude Peak to Peak Voltage

Output Load Resistance >> Resr and Rdc

Cz2 >> Cp1 and R1 >> Rz3

Condition

Figure 11. Voltage Mode Control Loop with Loop Dynamic for Type III Compensation

Page 6 of 8

The simple guidelines for positioning the poles and zeros and for calculating the

component values for Type III compensation are as follows:

a. Choose fco = fs / 5

b. Calculate fp_LC

fp_LC = 1 / [2π(L ●C) ^ 1/2 ]

c. Calculate fz_ESR

fz_ESR = 1 / 2π(R

ESR

) ●(C

OUT

)

d. Select R1 component value such that 50kΩ≤R1 ≤100kΩ

e. Calculate R2 base on the desired V

OUT

R2 = R1 / [(V

OUT

/ 0.80V) – 1]

f. Select the ratio of Rz2 / R1 gain for the desired gain bandwidth

Rz2 = R1 (V

RAMP

/ V

MAX

) (fco / fp_LC)

g. Calculate Cz2 by placing the zero at ½ of the output filter pole frequency

Cz2 = 1 / [π(Rz2) ●(fp_LC) ]

h. Calculate Cp1 by placing the first pole at ESR zero frequency

Cp1 = 1 / [2π(Rz2) ●(fz_ESR) ]

i. Calculate Rz3 by setting the second pole at ½ of the switching frequency and the

second zero at the output filter double pole frequency

Rz3 = 2 (R1) (fp_LC) / fs

j. Calculate Cz3 from Rz3 component value above

Cz3 = 1 / π(Rz3) ●(fs)

k. Choose 100pF ≤Cf1 ≤220pF to stabilize the SP7651ER internal Error Amplifier

Note: Loop Compensation component calculations discussed in this section are

further elaborated in the application note #ANP16, “Loop Compensation of

Voltage-Mode Buck Converters”.

These calculations shown here can be quickly iterated with the Type III Loop

Compensation Calculator on the web at:

www.sipex.com/files/Application-Notes/TypeIIICalculator.xls

Page 7 of 8

PCB LAYOUT DRAWINGS

Figure 12. SP7651EB Layout Top Side & Component Placement

Figure 13. SP7651EB PC Layout Bottom Side & Component Placement

Figure 14. SP7651EB PC Layout Inner Layer 1

Figure 15. SP7651EB PC Layout Inner Layer 2

Page 8 of 8

Table 1: SP7651EB List of Materials

REF. DES.

QTY

MANUFACTURER

NAME Manufacturer Part Number SIZE DESCRIPTION

U1 1 SIPEX SP7651ER DFN-26 2-FETs Buck Ctrl

U2 1 Sipex SPX5205M5-5.0

SOT-23-5

150mA LDO Voltage Regulator

DBST 1 Diodes Inc. SD101AWS-7

SOD-323

Schottky Diode, 15mA

L1 1 Intertechnical SC7232-2R2M 7 X 7mm

Inductor, 2.2uH, 8A, 10.4mohm

C3 1 TDK CORPORATION C3225X5R0J226M 1210 Capacitor, Ceramic, 22uF, 6.3V, X5R, 20%

C4 1 TDK CORPORATION C3225X5R1C226M 1210 Capacitor, Ceramic, 22uF, 16V, X5R, 20%

CVCC 1 TDK CORPORATION C1608X5R1A225K 0603 Capacitor, Ceramic, 2.2uF, 10V, X5R, 10%

C2 1 TDK CORPORATION C1608X7R1H104K 0603 Capacitor, Ceramic, 0.1uF, 50V, X7R, 10%

CBST 1 AVX CORPORATION 06035C682KAT2A 0603 Capacitor, Ceramic, 6.8nF, 50V, X7R, 10%

CSS 1 ROHM MCH185CN153KK 0603 Capacitor, Ceramic, 15nF, 50V, X7R, 10%

CP1 1 AVX CORPORATION 06035A100JAT2A 0603 Capacitor, Ceramic, 10pF, 50V, C0G, 5%

CZ2 1 AVX CORPORATION 06035A391JAT2A 0603 Capacitor, Ceramic, 390pF, 50V, C0G, 5%

CZ3 1 AVX CORPORATION 06035A101JAT2A 0603 Capacitor, Ceramic, 100pF, 50V, C0G, 5%

CF1 1 ROHM MCH185A101JK 0603 Capacitor, Ceramic, 100pF, 50V, C0G, 5%

RZ2 1 VISHAY DALE CRCW0603-1502FRT1 0603 Resistor, 15K, 1/16W, 1%

R2 1 SEI ELECTRONICS RMC-1/16W-21.5K-1%-TR 0603 Resistor, 21.5K, 1/16W, 1%

RZ3 1 VISHAY DALE CRCW0603-2001FRT1 0603 Resistor, 2K, 1/16W, 1%

R1 1 VISHAY DALE CRCW0603-6812FRT1 0603 Resistor, 68.1K, 1/16W, 1%

R3 1 VISHAY DALE CRCW0603-2003FRT1 0603 Resistor, 200K, 1/16W, 1%

R4 1 VISHAY DALE CRCW0603-1003FRT1 0603 Resistor, 100K, 1/16W, 1%

RBST 1 ROHM MCR03EZPEFX20R0 0603 Resistor, 20, 1/16W, 1%

VIN,VOUT,

GND,GND2

4 Vector Electronic K24C/M .042 Dia Input/Output Terminal Posts

ORDERING INFORMATION

Model Temperature Range Package Type

SP7651EB…................................-40°C to +85°C...............…SP7651 Evaluation Board

SP7651ER..............................…. -40°C to +85°C.................................……26-pin DFN

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