Application Note 1636
Author: Paul Orfanu
ISL85033-12VEVAL3Z Wide V Negative V
Buck-Boost Regulator With Up to 5A Output Current
IN
OUT
Evaluating the Other Output Voltages
The ISL85033-12VEVAL3Z kit output is preset to -12V;
Hardware Description
The ISL85033 is a wide input range, dual standard buck
however, output voltages can be adjusted from -3.3V to -15V.
converter that can be configured to provide a negative output
The output voltage programming resistor, R3, depends on the
voltage. The ISL85033-12VEVAL3Z evaluation board is used in
desired output voltage of the regulator. The value for the
this application note to demonstrate the negative
feedback resistor is typically between 0Ω and 142kΩ as
configuration. In this configuration, V can range from 4.5V to
IN
shown in Equation 1.
(28V - V
).
OUT
VOUT
VFB
⎛
⎝
⎞
– 1
The ISL85033 is offered in a 4mmx4mm 28 Ld TQFN package
with 1mm maximum height. The complete converter occupies
(EQ. 1)
--------------
R3 = R2
⎠
2
6.25cm area.
Table 1 summarizes the external component selection for
= -5V, V = -12V, and V = -15V.
V
OUT
OUT OUT
Key Features
TABLE 1. COMPONENT SELECTION FOR V
EXTERNAL COMPONENTS
OUT
• Wide Input Voltage Range from 4.5V to (28V - V
)
OUT
• Adjustable and Synchronizable Negative Output Voltage with
Continuous Output Current up to 5A, depending on V and
V
OUT
-5V
R3 = 43.2k; R5 = 20k; C4 = 2.7nF
C20 = 22µF (1210 ceramic)
C17 = 22µF (1210 ceramic)
OUT
V
IN
• Current Mode Control
• Adjustable Switching Frequency from 300kHz to 2MHz
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
• Power-Good Detection (referenced to V
• Externally Adjustable Soft-start Time
)
OUT
• Overcurrent and Hiccup Mode Short Circuit Protection,
Thermal Overload Protection, UVLO
-15V R3 = 142k; R5 = 120k; C4 = 4.7nF
C14, C17 = 22µF (2210 ceramic)
C12, C19 = 68µF (70mΩ TaNbO2 TPSD686M020R0070)
C20 = DNP
• Boot Undervoltage Detection
• Default Out-of-phase Channels Reduce Voltage Ripple and
Component Size. User-selectable Phase Operation.
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.
Recommended Equipment
The following materials are recommended to perform testing:
Figures 2, 3 and 4 show the efficiency for different V , V
IN OUT
and load combinations.
• 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 V
.
OUT
July 27, 2011
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Copyright Intersil Americas Inc. 2011. All Rights Reserved.
1
AN1636.1
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.
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