TPS43330-Q1 Datasheet, PDF (23/35 Pages) Texas Instruments – LOW IQ, SINGLE BOOST, DUAL SYNCHRONOUS BUCK CONTROLLER

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Output Ripple Voltage Due to Load
Transients, ∆V_O
Since the boost converter is active only during brief
events such as a cranking pulse and the buck
converters are high-voltage tolerant, a higher
excursion on the boost output may be tolerable in
some cases. In such cases, smaller component
choices for the boost output may be used.
Selection of Components for Type II
Compensation
The required loop gain for unity gain bandwidth
(UGB) is
TPS43330-Q1
TPS43332-Q1
SLVSA82A – MARCH 2011 – REVISED NOVEMBER 2011
Output Schottky Diode D1 Selection
A schottky diode with low forward conducting voltage
V_F over temperature and fast switching
characteristics is required to maximize efficiency. The
reverse breakdown voltage should be higher than the
maximum input voltage and the component should
have low reverse leakage current. Additionally the
peak forward current should be higher than the peak
inductor current The power dissipation in the Schottky
diode is given by :
Since this is activated for low input voltage profile
related to crank pulse the duration is less than 25ms
Low-Side MOSFET (BOT_SW3)
The boost converter error amplifier (OTA) has a Gm
that is proportional to the V_BAT voltage. This allows a
constant loop response across the input voltage
range and makes it easier to compensate by
removing the dependency on V_BAT.
G
10
R3 =
20 _{= 5.9k W}
85 *10^-6 *VO
10
10
C1 =
=
= 33nF
2p * fC * R3 2p * 8kHz * 5.9k W
C1
33nF
C2 =
=
= 265pF
2p * R3 *C1* (^fSW ) - 1 2p * 5.9k W * 33nF * ( ^200kHz ) - 1
2
2
Input Capacitor, C_I
The input ripple required is lower than 50 mV.
DVC1 = ^IRIPPLE = 10mV
8 * fSW *C1
DVESR = IRIPPLE * RESR = 40mV
Therefore our recommendation is 330µF with
10mOhm ESR.
The times t_r and t_f denote the rising and falling times
of the switching node and are related to the gate
driver strength of the TPS43330/2 and gate Miller
capacitance of the MOSFET. The first term denotes
the conduction losses which are minimized when the
on-resistance of the MOSFET is low. The second
term denotes the transition losses which arise due to
the full application of the input voltage across the
drain-source of the MOSFET as it turns on or off.
They are higher at high output currents and low input
voltages (due to the large input peak current) and
when the switching time is low.
Note: The on resistance R_DS(ON) has a positive
temperature coefficient which produces the
(TC=d*DeltaT) term that signifies the temperature
dependence.( Temperature coefficient d is available
as a normalized value from MOSFET data sheets
and can be assumed to be 0.005/degrees Celsius as
a starting value)
BUCKA Component Selection
Minimum ON Time, t_{ON min}
5
416
This is higher than the min duty cycle specified (100
ns typ). Hence the minimum duty cycle is achievable
at this frequency.
Copyright © 2011, Texas Instruments Incorporated
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Product Folder Link(s): TPS43330-Q1 TPS43332-Q1