RT6296A
Operation
Power Saving Mode
The RT6296A automatically enters into power saving
mode (PSM) at light load to improve efficiency. In PSM,
the RT6296A disable the internal CLK when V
FB
is
above the V
REF
x 1.005 (typ.). In other words, the
device automatically skip the PWM pulse at light load.
While V
FB
falls below the V
REF
x 1.005, the RT6296A
enables the internal CLK again and hence the new
switching cycle is activated. When the internal switches
are activated, for each cycle the device detects the
peak inductor current (I
L_PEAK
) and keeps high-side
switch on until the I
L
reaches its minimum peak current
MPC (A)
I
L
MPC
SW
Figure 1. Minimum Peak Current at PSM
MPC vs. TTH Voltage
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
level (from TTH setting).
When low-side switch is
turn-on, the
zero-current detection is also activated to
prevent that I
L
becomes negative and
enables the
higher efficiency at light load. During the period that
both switches are off, the device turns off the most of
the internal circuit to reduce the quiescent power
consumption further.
With lower output loading, the non-switching period is
longer, so the effective switching frequency becomes
lower to reduce the switching loss and switch driving
loss.
Transition Threshold (TTH)
V
IN
= 12V, V
OUT
= 3.3V, L = 5.6μH
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
TTH Voltage (V)
Figure 2 Relation between MPC and V
TTH
Frequency vs. Ouput Current
1000
TTH
2.5V
Frequency (kHz)1
In power saving mode, the minimum peak current
(MPC) of each switching pulse, can be adjusted by
voltage of TTH (V
TTH
) to set the PSM/Force PWM
transition threshold as shown in the Figure 1.
Figure 2 shows the actual minimum peak current
versus the TTH setting voltage. When V
TTH
is
connected to ground, the MPC will be < 20mA. The
device clamps the minimum peak current at 3.2A (typ.)
if the V
TTH
is set higher than 1.2V. The RT6296A
maintains forced CCM operation if the V
TTH
is set
higher than 2.5V (typ.). In PWM, the switching
frequency maintains fixed and the output voltage ripple
maintains smaller even at light load. As shown Figure 3
and Figure 4, smaller MPC sets the mode transition
current lower and enables higher switching frequency
at PSM.
100
TTH = 0.5V
TTH = 1.2V
10
V
IN
= 12V, V
OUT
= 3.3V,
L = 5.6μH, C
OUT
= 22μF x 2
1
0.01
0.1
1
10
Ouput Current (A)
Figure 3. Frequency vs Output Current, V
OUT
= 3.3V
Copyright © 2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6296A-04
January 2018
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
