an1636

Application Note 1636
Author: Paul Orfanu
ISL85033-12VEVAL3Z Wide VIN Negative VOUT
Buck-Boost Regulator With Up to 5A Output Current
Hardware Description
Evaluating the Other Output Voltages
The ISL85033 is a wide input range, dual standard buck
converter that can be configured to provide a negative output
voltage. The ISL85033-12VEVAL3Z evaluation board is used in
this application note to demonstrate the negative
configuration. In this configuration, VIN can range from 4.5V to
(28V - VOUT).
The ISL85033-12VEVAL3Z kit output is preset to -12V;
however, output voltages can be adjusted from -3.3V to -15V.
The output voltage programming resistor, R3, depends on the
desired output voltage of the regulator. The value for the
feedback resistor is typically between 0Ω and 142kΩ as
shown in Equation 1.
The ISL85033 is offered in a 4mmx4mm 28 Ld TQFN package
with 1mm maximum height. The complete converter occupies
6.25cm2 area.
Key Features
• Wide Input Voltage Range from 4.5V to (28V - VOUT)
• Adjustable and Synchronizable Negative Output Voltage with
Continuous Output Current up to 5A, depending on VOUT and
VIN
VOUT
R3 = R2 ⎛ -------------- – 1⎞
⎝ VFB
⎠
Table 1 summarizes the external component selection for
VOUT = -5V, VOUT = -12V, and VOUT = -15V.
TABLE 1. COMPONENT SELECTION FOR VOUT
VOUT
-5V
• Current Mode Control
• Adjustable Switching Frequency from 300kHz to 2MHz
• Power-Good Detection (referenced to VOUT)
• Boot Undervoltage Detection
• Default Out-of-phase Channels Reduce Voltage Ripple and
Component Size. User-selectable Phase Operation.
Recommended Equipment
The following materials are recommended to perform testing:
• 0V to 30V power supply with at least 7A source current
capability or a 5V battery
EXTERNAL COMPONENTS
R3 = 43.2k; R5 = 20k; C4 = 2.7nF
C20 = 22µF (1210 ceramic)
C17 = 22µF (1210 ceramic)
C19 = 68µF (15mΩ polymer EEFUD0K680R)
-12V
R3 = 112k; R5 = 120k; C4 = 4.7nF
C14, C17 = 22µF (2210 ceramic)
C12, C19 = 68µF (70mΩ TaNbO2 TPSD686M020R0070)
C20 = DNP
-15V
R3 = 142k; R5 = 120k; C4 = 4.7nF
C14, C17 = 22µF (2210 ceramic)
C12, C19 = 68µF (70mΩ TaNbO2 TPSD686M020R0070)
C20 = DNP
• Externally Adjustable Soft-start Time
• Overcurrent and Hiccup Mode Short Circuit Protection,
Thermal Overload Protection, UVLO
(EQ. 1)
The curves in Figure 1 indicate the maximum output current
the converter can deliver as a function of the input voltage and
the selected output voltage configuration.
Figures 2, 3 and 4 show the efficiency for different VIN, VOUT
and load combinations.
• Electronic loads capable of sinking current up to 7A
• Digital multimeters (DMMs)
• 100MHz quad-trace oscilloscope
• Signal generator
Quick Setup Guide
1. Ensure that the circuit is correctly connected to the supply
and loads prior to applying any power.
2. Connect the bias supply to VIN1, the plus terminal to VIN1,
and the negative return to GND1.
3. Verify that the position is ON for S1.
4. Turn on the power supply.
5. Verify the output voltage is -12V for VOUT.
July 27, 2011
AN1636.1
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Copyright Intersil Americas Inc. 2011. All Rights Reserved.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.
Application Note 1636
6
95
EFFICIENCY (%)
VOUT = -5V
4
IOUT (A)
VIN = 12V
90
5
3
VOUT = -12V
2
VOUT = -15V
1
85
VIN = 5V
80
75
70
65
60
0
5
7
9
11
13
15
17
19
21
23
0
25
0.5
1.0
FIGURE 1. ISL85033-12VEVAL3Z BUCK BOOST: RECOMMENDED
MAXIMUM IOUT (VIN)
95
VIN = 6V
VIN = 15V
VIN = 12V
2.5
VIN = 12V
90
90
85
EFFICIENCY (%)
EFFICIENCY (%)
2.0
FIGURE 2. ISL85033-12VEVAL3Z EFFICIENCY: V OUT = -15V
95
VIN = 5V
80
75
70
85
VIN = 5V
80
VIN = 15V
75
70
65
65
60
0
1.5
IOUT (A)
VIN (V)
60
0.5
1.0
1.5
2.0
0
2.5
0.5
IOUT (A)
FIGURE 3. ISL85033-12VEVAL3Z EFFICIENCY: VOUT = -12V
If the output voltage desired is -0.8V, then R3 is shorted. The
value for R2 is typically between 1k and 10k. Note that if
VOUT < |2.5V| (i.e., -0.8V), the switching frequency and
compensation must be changed to accommodate the 300kHz
operation, due to minimum on-time limitation. Please refer to
the ISL85033 data sheet for further information.
1.5
2.0
2.5
IOUT (A)
FIGURE 4. ISL85033-12VEVAL3Z EFFICIENCY: VOUT = -5V
Disabling/Enabling Function
The ISL85033-12VEVAL3Z evaluation board contains an S1
switch that enables or disables both channels, thus allowing a
low quiescent current state. Table 2 details this function.
TABLE 2. SWITCH SETTINGS
Frequency Control
S1
The ISL85033-12VEVAL3Z evaluation board has an FS pin that
controls the frequency of operation. Programmable frequency
allows for optimization between efficiency and external
component size. Default switching frequency is 500kHz when FS
is tied to VCC (R9 = 0). By removing R9 and connecting R10 to
the most negative potential on the board (VOUT), the switching
frequency could be changed from 300kHz (R10 = 383k) to 2MHz
(R10 = 40.2k). See the ISL85033 data sheet for information
about calculating the value of R10. Do not leave this pin floating.
ON
Enable VOUT
OFF
Disable VOUT
2
1.0
ON/OFF CONTROL
NOTE: If driven externally, the EN signal (the same as all input
logic signals) is referenced to VOUT (the most negative potential
on the board) and not to GND. Therefore, the source cannot be
GND referenced, and input level shifting is required.
AN1636.1
July 27, 2011
ISL85033-12VEVAL3Z Schematic
VCC
PG1 FS VNEG SI SO PG2
DNP
PGOOD2
SYNCIN
VNEG
PGOOD1
FS
R12
NC1
R13
VIN
12
VNEG
C6
10UF
C7
10UF
DNP
A
PGOOD1
R20
A
AA
DNP
R7
R8
VNEG2
4
JLX2
GNDO2
3
VIN2
1
2
VNEG
FB1
A
C19
68UF
C20
TBD
R23
FB2
0
12
1
VNEG
-12V
(ADJUSTABLE)
A
COMP1
R24
COMP2
0
SS1
SS2
R17
DNP
SYNCIN
R10
R18
AN1636.1
July 27, 2011
DNP
VNEG
R25
DNP
FS
ON
S1 1 OPEN
OFF
VNEG
3
COMP2
22
24
23
SYNCOUT
PGOOD2
10UF
0
SS1
VNEG
0.01UF
C8
R9
OPEN
3
EN2
OPEN
VNEG
C17
EN
PGOOD2
OPEN
100K
C9
22UF
B340B
VCC
R4
5600PF
BOOT2
10UH
D2
VNEG
GND1
R19
SS2
R16
VIN
C18
VCC
C11
2
VIN
C2
A
SYNCIN
25
26
NC
SGND
27
FS
B340B
A
FB2
C10
L2
21
22UF
21
68UF
D1
4
R15
VNEG
10UH
C14
SS2
15
VNEG
A
OPEN
R11
16
OPEN
OPEN
0
17
1
2
C16
VNEG OPEN
OPEN
14
12
VIN2
EP
29
L1
C12
100UF
PHASE2
4.7UF
TBD
A
PHASE2
PHASE1
EN
VCC
EN
C1
PHASE1
C15
R14
18
BOOT2
ISL85033IRTZ
13
12
A
7
VNEG
GNDO1
BOOT1
6
VNEG
1
2
4
SS2
OPEN
19
FB2
PGND2
EN2
5
C5
21
COMP2
U1
PGND1
12
BOOT1
3
JLX1
SS1
4
0.01UF
-12V
FB1
VCC
3
EN1
VNEG
22
SS1
10
VNEG
5600PF
C3
VNEG
120K
COMP1
JVO2
0
VNEG
SS2
Application Note 1636
VNEG1
8.06K
1
11
4700PF
FB1
SS1
R2
R5
VIN1
C4
VIN1
C13
9
3
VNEG
113K
COMP1
22PF
8
R3
PGOOD1
28
DNP
A
Application Note 1636
Bill of Materials
PART NUMBER
REFERENCE
DESIGNATOR
QUANTITY
VALUE
TOLERANCE
VOLTAGE
POWER
PACKAGE
TYPE
JEDEC TYPE
MANUFACTURER
DESCRIPTION
CONN
TEK1314353-00
TEKTRONIX
Scope Probe Test Point
PCB Mount
SMD
CAP_TANT
AVX
TQC Series Hi-Volt Low
ESR Capacitor
SMD2
DO_SMA
DIODES
3A Low VF SCHOTTKY
BARRIER RECTIFIER
131-4353-00
JLX1, JLX2,
JVO2
3
TPSD686K020R00
070-T
C12, C19
2
B340B
D1, D2
2
C5750X7R1E226M
C14, C17
2
22µF
20%
25V
2220
CAP_2220
TDK
Ceramic Cap
EEE-FK1V101P-T
C2
1
100µF
20%
35V
SMD
CAPAE_315X
402
PANASONIC
AL LYTIC FK SERIES CAP
(RoHS COMP.)
GMK325BJ106KN
C6, C8
2
10µF
10%
35V
1210
CAP_1210
TAIYO YUDEN
Ceramic Chip Cap
GT13MCBE
S1
1
SW
SW_GT13MC
BE
C&K
SPDT On-Off-On
Ultraminiature
Toggle Switch
H1044-0022050V5
C13
1
22PF
5%
50V
402
CAP_0402
GENERIC
Multilayer Cap
H1044-0047250V10
C4
1
4700PF
10%
50V
402
CAP_0402
GENERIC
Multilayer Cap
68µF
20%
20V
H1044-OPEN
C10, C15, C16
3
OPEN
OPEN
OPEN
402
CAP_0402
GENERIC
Multilayer Cap
H1045-0010350V10
C5, C9
2
0.01µF
10%
50V
603
CAP_0603
GENERIC
Multilayer Cap
H1045-0056250V10
C3, C11
2
5600PF
10%
50V
603
CAP_0603
GENERIC
Multilayer Cap
H1046-0047510V20
C7
1
4.7µF
20%
10V
805
CAP_0805
GENERIC
Multilayer Cap
H1065-0010625V10-T
C18
1
10µF
10%
25V
SMD
CAP_1206
VENKEL
Multilayer Cap
H1082-TBD-TBD
C1, C20
2
TBD
TBD
TBD
1210
CAP_1210
GENERIC
Ceramic Chip Cap
H2505-01003-1/
16WR1
R4
1
100k
0.10%
1/16W
603
RES_0603
GENERIC
Metal Film Chip Resistor
H2505-DNP-DNP-1
R10, R17
2
DNP
1%
DNP
603
RES_0603
GENERIC
Metal Film Chip Resistor
(Do Not Populate)
H2505-DNP-DNPR1
R12, R13,
R19, R20,
R25
5
DNP
0.10%
DNP
603
RES_0603
GENERIC
Metal Film Chip Resistor
(Do Not Populate)
H2510-011331/16W1
R3
1
113k
1%
1/16W
402
RES_0402
GENERIC
Thick Film Chip Resistor
H2510-012031/16W1
R5
1
120k
1%
1/16W
402
RES_0402
GENERIC
Thick Film Chip Resistor
H2510-080611/16W1
R2
1
8.06k
1%
1/16W
402
RES_0402
GENERIC
Thick Film Chip Resistor
H2510-ROPENOPEN
R7, R8, R11,
R14-R16
6
OPEN
1%
OPEN
402
RES_0402
GENERIC
Thick Film Chip Resistor
H2511-00R001/16W
R23, R24
2
0
0%
1/16W
603
RES_0603
GENERIC
Thick Film Chip Resistor
H2511-00R001/16W1
R9, R18
2
0
1%
1/16W
603
RES_0603
GENERIC
Thick Film Chip Resistor
ISL85033IRTZ
U1
1
QFN
QFN28_157X
157_157_EP
INTERSIL
WIDE VIN DUAL
STANDARD BUCK
REGULATOR (Pb-FREE)
PAD_100
EN, FS, SI, SO,
PG1, PG2,
SS1,
SS2, VNEG
9
THOLE
PAD-100
GENERIC
0.100 Pad with 0.037
Plated Thru Hole
4
AN1636.1
July 27, 2011
Application Note 1636
Bill of Materials (Continued)
PART NUMBER
REFERENCE
DESIGNATOR
QUANTITY
PAD_150
VIN, GND1,
GNDO1,
GNDO2,
VNEG1,
VNEG2
6
SQ1004
L1, L2
2
VALUE
TOLERANCE
10µH
VOLTAGE
POWER
25%
4.8A
PACKAGE
TYPE
JEDEC TYPE
MANUFACTURER
DESCRIPTION
THOLE
PAD-150
GENERIC
0.150 Pad with 0.110
Plated Thru Hole
SMD
IND_SQ10XX
FALCO
SMT SHIELDED POWER
INDUCTOR
ISL85033-12VEVAL3Z Layout
FIGURE 5. TOP LAYER COMPONENTS
FIGURE 6. TOP LAYER ETCH
FIGURE 7. SECOND LAYER ETCH
FIGURE 8. THIRD LAYER ETCH
5
AN1636.1
July 27, 2011
Application Note 1636
ISL85033-12VEVAL3Z Layout (Continued)
FIGURE 9. BOTTOM LAYER ETCH
FIGURE 10. BOTTOM LAYER COMPONENTS
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is
cautioned to verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
6
AN1636.1
July 27, 2011
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