1
Application Note 1636
Author: Paul Orfanu
ISL85033-12VEVAL3Z Wide VIN Negative VOUT
Buck-Boost Regulator With Up to 5A Output Current
Hardware Description
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 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
• Current Mode Control
• Adjustable Switching Frequency from 300kHz to 2MHz
• Power-Good Detection (referenced to VOUT)
• Externally Adjustable Soft-start Time
• Overcurrent and Hiccup Mode Short Circuit Protection,
Thermal Overload Protection, UVLO
• 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
• 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.
Evaluating the Other Output Voltages
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.
Table 1 summarizes the external component selection for
VOUT = -5V, VOUT = -12V, and VOUT = -15V.
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.
TABLE 1. COMPONENT SELECTION FOR VOUT
VOUT EXTERNAL COMPONENTS
-5V 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
R3 R2 VOUT
VFB
-------------- 1–
⎝⎠
⎛⎞
=(EQ. 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.
July 27, 2011
AN1636.1
Application Note 1636
2AN1636.1
July 27, 2011
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.
Frequency Control
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.
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.
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.
FIGURE 1. ISL85033-12VEVAL3Z BUCK BOOST: RECOMMENDED
MAXIMUM IOUT (VIN)
FIGURE 2. ISL85033-12VEVAL3Z EFFICIENCY: VOUT = -15V
FIGURE 3. ISL85033-12VEVAL3Z EFFICIENCY: VOUT = -12V FIGURE 4. ISL85033-12VEVAL3Z EFFICIENCY: VOUT = -5V
0
1
2
3
4
5
6
5 7 9 11 13 15 17 19 21 23 25
VIN (V)
IOUT (A)
VOUT = -5V
VOUT = -12V
VOUT = -15V
60
65
70
75
80
85
90
95
0 0.5 1.0 1.5 2.0 2.5
IOUT (A)
VIN = 5V
VIN = 12V
EFFICIENCY (%)
0 0.5 1.0 1.5 2.0 2.5
IOUT (A)
VIN = 12V
60
65
70
75
80
85
90
95
EFFICIENCY (%)
VIN = 15V
VIN = 5V
60
65
70
75
80
85
90
95
0 0.5 1.0 1.5 2.0 2.5
IOUT (A)
EFFICIENCY (%)
VIN = 12V
VIN = 15V
VIN = 5V
VIN = 6V
TABLE 2. SWITCH SETTINGS
S1 ON/OFF CONTROL
ON Enable VOUT
OFF Disable VOUT
Application Note 1636
3AN1636.1
July 27, 2011
ISL85033-12VEVAL3Z Schematic
VNEG
-12V
B340B
B340B
10UH
(ADJUSTABLE)
-12V
VNEG
10UH
ON
OFF
OPEN
113K
SS1
C3
PGOOD2
VNEG
8.06K
C13
ISL85033IRTZ
68UF
0.01UF
BOOT2
COMP2
VIN
FB2
FS
VIN
10UF
TBD
PGOOD1
4700PF
VNEG
VNEG
VCC
DNP
100UF
VCC
4.7UF
VNEG
DNP
0.01UF
OPEN
COMP1
VCC
SS2
VNEG
FS
VNEG
SYNCIN
PGOOD2
DNP
SYNCIN
0
OPEN
0
0
NC1
DNP
SS2
COMP2
VNEG
EN
OPEN
FB2
OPEN
SS1
VCC
OPEN
100K
FB1
120K
VNEG
DNP
VNEG
VNEG
DNP
0
5600PF
EN
VNEG
SS1
COMP1
OPEN
OPEN
VNEG
OPEN
OPEN
PGOOD1
DNP
22UF
10UF
68UF
SS1
BOOT1
VNEG
22PF
SS2
VNEG
22UF
FB1
EN
10UF
TBD
VNEG VNEG
5600PF
VNEG
U1
1
10
11
12
13
14
15
16
17
18
19
22 0
21
22
23
24
25
26
27
28
3
4
5
6
7
8
9
29
JVO2
2
3
4
1
VNEG1 VNEG2
VIN
GND1
JLX2
2
3
4
1
GNDO2
VNEG
SS2
PG1 FS SI SO PG2
EN
C11
JLX1
2
3
41
GNDO1
R9
R18
D1
21
D2
21
R8R7
R5
R11 C10
C4
C6 C8
R19 R20
C14 C17
S1
23
1
R17
R10
R25
R24
R23
R4
C9
C5
C7
C15
R2
R15
C16
R16
R3 R14
R13
R12
L2
12
C18
L1
12
C2
12
C12
12
C19
12
C20C1
EP
SS1
PGND1
PHASE1
PGOOD1
NC
FS
SYNCIN
SGND
SYNCOUT
PGOOD2
COMP2
FB2
SS2
PGND2
BOOT2
PHASE2
PHASE2
VIN2
VIN2
EN2
VCC
EN1
VIN1
VIN1
PHASE1
FB1
BOOT1
COMP1
A
AA
A A
A
A
A
A
A
AA
Application Note 1636
4AN1636.1
July 27, 2011
Bill of Materials
PART NUMBER
REFERENCE
DESIGNATOR QUANTITY VALUE TOLERANCE VOLTAGE POWER
PACKAGE
TYPE JEDEC TYPE MANUFACTURER DESCRIPTION
131-4353-00 JLX1, JLX2,
JVO2
3 CONN TEK131-
4353-00
TEKTRONIX Scope Probe Test Point
PCB Mount
TPSD686K020R00
070-T
C12, C19 2 68µF 20% 20V SMD CAP_TANT AVX TQC Series Hi-Volt Low
ESR Capacitor
B340B D1, D2 2 SMD2 DO_SMA DIODES 3A Low VF SCHOTTKY
BARRIER RECTIFIER
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
H1044-00220-
50V5
C13 1 22PF 5% 50V 402 CAP_0402 GENERIC Multilayer Cap
H1044-00472-
50V10
C4 1 4700PF 10% 50V 402 CAP_0402 GENERIC Multilayer Cap
H1044-OPEN C10, C15, C16 3 OPEN OPEN OPEN 402 CAP_0402 GENERIC Multilayer Cap
H1045-00103-
50V10
C5, C9 2 0.01µF 10% 50V 603 CAP_0603 GENERIC Multilayer Cap
H1045-00562-
50V10
C3, C11 2 5600PF 10% 50V 603 CAP_0603 GENERIC Multilayer Cap
H1046-00475-
10V20
C7 1 4.7µF 20% 10V 805 CAP_0805 GENERIC Multilayer Cap
H1065-00106-
25V10-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-DNP-
R1
R12, R13,
R19, R20,
R25
5 DNP 0.10% DNP 603 RES_0603 GENERIC Metal Film Chip Resistor
(Do Not Populate)
H2510-01133-
1/16W1
R3 1 113k 1% 1/16W 402 RES_0402 GENERIC Thick Film Chip Resistor
H2510-01203-
1/16W1
R5 1 120k 1% 1/16W 402 RES_0402 GENERIC Thick Film Chip Resistor
H2510-08061-
1/16W1
R2 1 8.06k 1% 1/16W 402 RES_0402 GENERIC Thick Film Chip Resistor
H2510-ROPEN-
OPEN
R7, R8, R11,
R14-R16
6 OPEN 1% OPEN 402 RES_0402 GENERIC Thick Film Chip Resistor
H2511-00R00-
1/16W
R23, R24 2 0 0% 1/16W 603 RES_0603 GENERIC Thick Film Chip Resistor
H2511-00R00-
1/16W1
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
Application Note 1636
5AN1636.1
July 27, 2011
PAD_150 VIN, GND1,
GNDO1,
GNDO2,
VNEG1,
VNEG2
6 THOLE PAD-150 GENERIC 0.150 Pad with 0.110
Plated Thru Hole
SQ1004 L1, L2 2 10µH 25% 4.8A SMD IND_SQ10XX FALCO SMT SHIELDED POWER
INDUCTOR
Bill of Materials (Continued)
PART NUMBER
REFERENCE
DESIGNATOR QUANTITY VALUE TOLERANCE VOLTAGE POWER
PACKAGE
TYPE JEDEC TYPE MANUFACTURER DESCRIPTION
ISL85033-12VEVAL3Z Layout
FIGURE 5. TOP LAYER COMPONENTS FIGURE 6. TOP LAYER ETCH
FIGURE 7. SECOND LAYER ETCH FIGURE 8. THIRD LAYER ETCH
Application Note 1636
6
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
AN1636.1
July 27, 2011
FIGURE 9. BOTTOM LAYER ETCH FIGURE 10. BOTTOM LAYER COMPONENTS
ISL85033-12VEVAL3Z Layout (Continued)
