ISL85033-12VEVAL3Z Datasheet, PDF (1/6 Pages) Intersil Corporation – Wide VIN Negative VOUT Buck-Boost Regulator With Up to 5A Output Current

Application Note 1636
Author: Paul Orfanu
ISL85033-12VEVAL3Z Wide V_IN Negative V_OUT
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, V_IN can range from 4.5V to
(28V - V_OUT).
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 - V_OUT)
• Adjustable and Synchronizable Negative Output Voltage with
Continuous Output Current up to 5A, depending on V_OUT and
V_IN
• Current Mode Control
• Adjustable Switching Frequency from 300kHz to 2MHz
• Power-Good Detection (referenced to V_OUT)
• 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 V_OUT.
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.
R3
=
R
2_⎝⎛
V_----O_-----U_----T_-
VFB
–
1_⎠⎞
(EQ. 1)
Table 1 summarizes the external component selection for
V_OUT = -5V, V_OUT = -12V, and V_OUT = -15V.
TABLE 1. COMPONENT SELECTION FOR V_OUT
V_OUT
-5V
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
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 V_IN, V_OUT
and load combinations.
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.
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