HR1000A – RESONANT HALF-BRIDGE CONTROLLER
FUNCTIONAL DESCRIPTION
Oscillator
source-1 (IS-1) to charge the CT capacitor. Here,
the current mirror ratio inside the HR1000A is
1A/A. When a switching cycle starts, IS-1
charges the CT capacitor until the voltage
triggers the peak threshold voltage. Then the
discharge current source (IS-2) with twice the
source current of the Fset pin turns on.
Therefore, the CT capacitor discharges with the
source current of the Fset pin. When the
voltage on the CT capacitor drops to the valley
threshold voltage, the IS-2 turns off and then a
new switching cycle is enabled.
The charge/discharge time of the CT capacitor
determines the oscillator frequency. The
voltage on the CT capacitor fluctuates between
the peak threshold and valley threshold to form
a triangle waveform. Figure 2 shows the
detailed waveform during steady state.
Based on the block diagram shown in Figure 3,
the Fset RC network functions as described:
1. Rfmin from the Fset pin to GND sets the
maximum resistance of external RC network
when the phototransistor is blocked,
therefore setting the Fset minimum source
current, which sets the minimum switching
frequency;
Figure 2: CT Waveform and Gate Signal
The network connecting the Fset pin
charges/discharges the current on the CT
capacitor, as Figure 3 shows. The source
current of the Fset pin controls the current
Figure 3: Oscillator Block Diagram
HR1000A Rev. 1.01
8/30/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
13
MPS [ MONOLITHIC POWER SYSTEMS ]
