Datasheet

COMPx
+
-
VIN
VREF
7V
10 V
12 V
C 1
C 2
R3
C
O
R
ESR
OTA-gm
EA
TPS43330-Q1
TPS43332-Q1
SLVSA82E –MARCH 2011–REVISED APRIL 2013 www.ti.com
APPLICATION INFORMATION
The following example illustrates the design process and component selection for the TPS43330-Q1. Table 3
lists the design-goal parameters.
Table 3. Application Example
PARAMETER V
BuckA
V
BuckB
BOOST
V
IN
= 6 V to 30 V V
IN
= 6 V to 30 V V
BAT
= 5 V (cranking
Input voltage
12 V - typical 12 V - typical pulse input) to 30 V
Output voltage, V
OUTx
5 V 3.3 V 10 V
Maximum output current, I
OUTx
3 A 2 A 2.5 A
Load-step output tolerance, ∆V
OUT
+ ±0.5 V
±0.2 V ±0.12 V
∆V
OUT(Ripple)
Current output load step, ∆I
OUTx
0.1 A to 3 A 0.1 A to 2 A 0.1 A to 2.5 A
Converter switching frequency, f
SW
400 kHz 400 kHz 200 kHz
This is a starting point and theoretical representation of the values for use in the application; improving the
performance of the device may require further optimization of the derived components.
Boost Component Selection
A boost converter operating in continuous-conduction mode (CCM) has a right-half-plane (RHP) zero in its
transfer function. The RHP zero relates inversely to the load current and inductor value and directly to the input
voltage. The RHP zero limits the maximum bandwidth achievable for the boost regulator. If the bandwidth is too
close to the RHP zero frequency, the regulator may become unstable.
Thus, for high-power systems with low input voltages, choose a low inductor value. A low value increases the
amplitude of the ripple currents in the N-channel MOSFET, the inductor, and the capacitors for the boost
regulator. Select these components with the ripple-to-RHP zero trade-off in mind and considering the power
dissipation effects in the components due to parasitic series resistance.
A boost converter that operates always in the discontinuous mode does not contain the RHP zero in its transfer
function. However, designing for the discontinuous mode demands an even lower inductor value that has high
ripple currents. Also, ensure that the regulator never enters the continuous-conduction mode; otherwise, it may
become unstable.
Figure 26. Boost Compensation Components
This design assumes operation in continuous-conduction mode. During light load conditions, the boost converter
operates in discontinuous mode without affecting stability. Hence, the assumptions here cover the worst case for
stability.
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