Intersil ISL8088EVAL1Z Application Note

ISL8088EVAL1Z REVA Dual 800mA Low Quiescent
Current 2.25MHz High Efficiency Synchronous Buck
Regulator

Description

The ISL8088EVAL1Z kit is intended for use by individuals with
requirements for Point-of-Load applications sourcing from 2.75V
to 5.5V. The ISL8088EVAL1Z evaluation board is used to
demonstrate the performance of the ISL8088 low quiescent
current mode converter.
The ISL8088 is offered in a 3mmx3mm 10 Ld DFN package with
1mm maximum height. The complete converter occupies less
2
than 1.8cm area.

Key Features:

• Dual 800mA High Efficiency Synchronous Buck Regulator with
up to 97% Efficiency
• 800mA Guaranteed Output Current per channel
• Power-Good (PG) output with 1ms Delay
• 2.75V to 5.5V Supply Voltage
• 3% Output Accuracy Over-Temperature/Load/Line
• Start-up with Pre-biased Output
• Internal Digital Soft-Start - 2ms
• Soft-Stop Output Discharge During Disabled
• 30µA Quiescent Supply Current in PFM Mode
• Selectable Forced PWM Mode and PFM Mode
• External Synchronization up to 4MHz
• Typical 6.5µA Logic Controlled Shutdown Current
• 100% Maximum Duty Cycle for Lowest Dropout
• Internal Current Mode Compensation
• Peak Current Limiting.
• Over-Temperature Protection
• Independent Enable

Recommended Equipment

The following materials are recommended to perform testing:
• 0V to 10V Power Supply with at least 3A source current
capability or 5V battery
• Electronic Loads capable of sinking current up to 3A
• Digital Multimeters (DMMs)
• 100MHz quad-trace oscilloscope
• Signal generator
February 14, 2014
AN1492.2
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774
Application Note 1492

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 VIN. Plus terminal to VIN and
negative return to PGND.
3. Verify that position is ON for SW2 and SW3.
4. Turn on the power supply.
5. Verify the output voltage is 2.5V for V

Evaluating the Other Output Voltage

The ISL8088EVAL1Z kit output is preset to 2.5V for V
1.8V for V ; however, output voltages can be adjusted from
OUT2
0.6V to 3.3V. The output voltage programming resistor, R2 (or R5
in Channel 2), will depend on the desired output voltage of the
regulator. The value for the feedback resistor is typically between
0Ω and 750kΩ as shown in Equation 1.
Let's set R3 = 100kΩ, then R2 will be:
⎛ ⎞
VOUT
----------------- - 1
R2 = R3 –
⎝ ⎠
VFB
If the output voltage desired is 0.6V, then R3 is left unpopulated
and short R2. For faster response performance, add 10pF in
parallel to R2.

Mode Control

The ISL8088 has a SYNC pin that controls the operation mode.
SYNC pin connect to logic high or input voltage VIN for PFM
mode; connect to logic low or ground for forced PWM mode.
Connect to an external function generator for Synchronization.
Negative edge trigger. Do not leave this pin floating.
TABLE 1. SWITCH SETTINGS
SW2&3 ENABLE
1 OFF Disable V
3 ON Enable V
SW1 SKIP
1 PWM Fixed PWM frequency at light load
3 PFM Force continuous mode
|
Copyright Intersil Americas LLC 2009, 2010, 2014. All Rights Reserved
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.
Author: Huong Doan
and 1.8V for V
OUT1 OUT2.
and
OUT1
(EQ. 1)
ON/OFF CONTROL
OUT
OUT
FUNCTION