ST AN2565 APPLICATION NOTE
AN2565
Application note
PM6680A evaluation kit
dual step-down controller with auxiliary voltages
Introduction
PM6680A evaluation kit order code: STEVAL-ISA053V2.
The PM6680A is a dual step-do wn controller with adjustab le outp ut v oltages . The PM6680A
evaluation kit is designed to test the performance of the PM 6680A by employing a typical
application circuit that allows testing of all th e PM6680A device functions. The kit features
two switching sections, with (typically) 3.3 V and 1.8 V outputs, from a 6 V to 36 V input
voltage. The typi cal oper ating switching frequency of the two switching sections is 200 kHz /
300 kHz, respectively. Each switching section delivers more than 2.5 A of output current.
Moreover, an internal linear regulator can provide 5 V @ 100 mA peak current.
Figure 1. PM6680A evaluation kit
April 2008 Rev 2 1/29
www.st.com
Contents AN2565
Contents
1 Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Evaluation kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3 Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Evaluation board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5 I/O interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Recommended equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7 Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8 Jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9 Feedback output connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10 Test setup and performance summary . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1 Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.2 Power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.3 Soft-start and shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.4 OUT1 and OUT2 output efficiency vs. load current . . . . . . . . . . . . . . . . . 19
10.5 Power consumption analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.6 Switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.7 Linear regulator output voltages vs. output current . . . . . . . . . . . . . . . . . 24
10.8 Load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
11 Representative waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
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AN2565 List of figures
List of figures
Figure 1. PM6680A evaluation kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. Evaluation kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 3. PM6680A eval board layout - top layer (PGND plane and component side) . . . . . . . . . . . . 8
Figure 4. PM6680A eval board layout - inn er layer 1 (SGND layer and V
Figure 5. PM6680A eval board layout - inner layer 2 (SGND layer and signals). . . . . . . . . . . . . . . . . 9
Figure 6. PM6680A eval board layout - bottom layer (PM6680A and component side) . . . . . . . . . . . 9
Figure 7. Test setup connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 8. Power-up sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 9. Section 1 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 10. Section 2 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 11. Section 1 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 12. Section 2 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 13. OUT1 efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 14. OUT2 efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 15. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 16. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 17. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 18. Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 19. Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 20. OUT1 switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 21. OUT2 switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 22. LDO5 output vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 23. OUT1 load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 24. OUT2 load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 25. SMPS pulse skip mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 26. SMPS no-audible skip mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 27. SMPS PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
plane). . . . . . . . . . . . . . . 8
IN
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Main features AN2565
1 Main features
● Constant on-time control allows very fast load transients
● 6 V to 36 V input voltage range
● 5 V auxiliary output voltage
● Adjustable switching outputs
● Lossless current sensing using low side MOSFET R
●
Negative current limit
● Soft-start internally fixed at 2.8 ms
● Soft-end for output discharge
● 200 kHz / 300 kHz, 300 kHz / 400 kHz, 400 kHz / 500 kHz (OUT1 / OUT2 selectable
switching frequency)
● Selectable pulse skip and no-audible skip modes at light loads
● Independent power good signals
DS(on)
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AN2565 Evaluation kit schematic
2 Evaluation kit schematic
Figure 2. Evaluation kit schematic
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Component list AN2565
3 Component list
Table 1. Component list
Qty Reference Description Value Package Part number
3 C1, C2, C3 Ceramic capacitor 10 µF, 50 V 1210 Tayio Yuden - UMK325BJ106KM
1 C4 Ceramic capacitor 10 µF, 50 V 1210
2 C5, C6 Ceramic capacitor 100 nF, 50 V 0805
1 C19 Ceramic capacitor 100 nF, 50 V 0805
1 C7 Tantalum capacitor N.M. 7343 N.M.
2 C9, C10 Ceramic capacitor N.M. 0805 N.M.
1 C11 Tantalum capacitor N.M. 7343 N.M.
1 C8 Tantalum capacitor
1 C12 Tantalum capacitor
2 C13, C14 Ceramic capacitor 10 nF, 50 V 0603
2 C15, C16 Ceramic capacitor 1.5 nF, 50 V 0603
220 µF,
25 mΩ, 6.3 V
150 µF,
18 mΩ, 4 V
7343 Sanyo POSCAP - 6TPE220M
7343 Sanyo POSCAP - 4TPE150MI
2 C17, C18 Ceramic capacitor 47 pF, 50 V 0603
1 C20 Ceramic capacitor 1 µF, 10 V 0805
1 C21 Tantalum capacitor 4.7 µF, 16 V 3216
1 C22 Ceramic capacitor 220 nF, 10 V 0805
1 C23 Ceramic capacitor 10 pF, 50 V 0805
1 CIN Tantalum capacitor N.M. D = 10 mm
1 CREF Ceramic capacitor 100 nF, 50 V 0805
1 C26 Ceramic capacitor 4.7 µF, 50 V 1210 Taiyo-Y uden - UMK325F475ZH
1 C24, C25 Ceramic capacitor 10 µF, 6.3 V 0805
1 C27 Tantalum capacitor N.M. 0805
1 C28 Tantalum capacitor N.M. 3216
1D1
2D2, D3
1 IC1 PM6680A VFQFPN-32 5x5 ST - PM6680A
1 L1 Power inductor 4.7 µH, 4 A 10 mm x 10 mm Wurth - TPC 7440650047
1 L2 Power inductor 8.2 µH, 3 A 10 mm x 10 mm Wurth - TPC 7440650082
Dual Schottky
diode
Power Schottky
rectifier
SOT23 ST - BAS70
SMA STPS1L30M
4M1, M2
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>40 V N-channel
MOSFET
SO-8 ST - STS5NF60L
AN2565 Component list
Table 1. Component list (continued)
Qty Reference Description Value Package Part number
4M3, M4
1 R3 Resistor 1% 20 kΩ 0805
1 R4 Resistor 1% 47 kΩ 0805
1 R5 Resistor 1% 2.2 kΩ 0805
1 R6 Resistor 1% 1.1 kΩ 0805
2 R7, R8 Resistor 1% 390 Ω 0805
1 R9 Resistor 1% 47 Ω 0805
2 R10, R11 Resistor 1% 10 Ω 0805
4 R12:R15 Resistor 1% 100 kΩ 0805
1 R16 Resistor 1% 43 kΩ 0805
1 R17 Resistor 1% 510 kΩ 0805
2 R18, R19 Resistor 1% N.M. 0805
R20, R21,
4
R22, R23
1 R24 Resistor 1% 1.1 kΩ 0805
1 R25 Resistor 1% 820 Ω 0805
1 R26 Resistor 1% 3.9 Ω 1206
> 40 V N-channel
MOSFET
Resistor 1% 0Ω 0805
SO-8 ST - STS7NF60L
1 R27 Resistor 1% 10 kΩ 0805
1 R29 Resistor 1% 10 kΩ 0805
1 R28 Resistor 1% 27 kΩ 0805
1 R30 Resistor 1% 10 kΩ 0805
1 R31 Resistor 1% N.M: 0603
1 R32 Resistor 1% N.M. 0603
1 R33 Resistor 1% N.M. 0805
1
RLD5V,
RLD3V
Resistor N.M. 0805
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Evaluation board layout AN2565
4 Evaluation board layout
Figure 3. PM6680A eval board layout - top layer (PGND plane and component side)
Figure 4. PM6680A eval board layout - inner layer 1 (SGND layer and V
plane)
IN
8/29
AN2565 Evaluation board layout
Figure 5. PM6680A eval board layout - inner layer 2 (SGND layer and signals)
Figure 6. PM6680A eval board layout - bottom layer (PM6680A and component
side)
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