IO Output Current mA
9.8
9.9
10.0
10.1
10.2
30
40
50
60
70
80
90
100
V
O
Output
V
oltage
V
G013
VI = 2.9 V
VI = 2.3 V
L = 4.7
H
VO = Vpos + |Vneg| = 10 V
TA = 85°C
VI = 2.5 V
DETAILED DESCRIPTION
www.ti.com ............................................................................................................................................................. SLVS831A – APRIL 2008 – REVISED JULY 2008
MAXIMUM OUTPUT CURRENT
4.7
H, LPF3010-4R7
Figure 13.
The TPS65136 operates with a four-switch buck-boost converter topology, generating a negative and a positive
output voltage with a single inductor. The device uses the SIMO regulator technology featuring best-in-class
line-transient regulation, buck-boost mode for the positive and negative outputs, and highest efficiency over the
entire load-current range. High efficiency over the entire load-current range is implemented by reducing the
converter switching frequency. Out-of-audio mode avoids the switching frequency going below 20 kHz.
sets the output voltage for the positive output, OUTP. The ground error amplifier regulates FBG to typically 0 V.
Using the external feedback divider allows setting the output voltage of the negative output, OUTN. In principle,
the converter topology operates just like any other buck-boost converter topology with the difference that the
output voltage across the inductor is the sum of the positive and negative output voltages. With this
consideration, all calculations of the buck-boost converter apply for this topology as well. During the first switch
cycle, M1 and M2 are closed, connecting the inductor from VIN to GND. During the second switch cycle, the
inductor discharges to the positive and negative outputs by closing switches M4 and M3. Because the inductor is
discharged to both of the outputs simultaneously, the output voltages can be higher or lower than the input
voltage. In addition to that, the converter operates best when the current out of OUTP is equal to the current
flowing into OUTN. This is usually the case when driving an AMOLED panel. Any asymmetries in load current
can be canceled out by the ground error amplifier connected to FBG. However, this is only possible for current
asymmetries of typically 30%. During light load current in discontinuous conduction mode, the converter operates
in peak-current-mode control with the switching cycle given by the internal voltage-controlled oscillator (VCO). As
the load current increases, the converter operates in continuous-conduction mode. In this mode, the converter
moves to peak-current control with the switch cycle given by the fixed off-time. The SIMO regulator topology has
excellent line transient regulation when operating in discontinuous conduction mode. As the load current
increases, entering continuous conduction mode, the line transient performance is linearly decreased.
Copyright 2008, Texas Instruments Incorporated
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