Datasheet

ƒ
z
+
1
2 p Cc Rc
Cƒƒ +
1
2 p ƒ
z
R1
+
1
2 p 10 kHz R1
V
out
+ 1.146 V
ǒ
1 )
R1
R2
Ǔ
I
avg
+
(
1 * D
)
lsw +
Vin
Vout
2.8 A with lsw + minimum switch current of the TPS65161 (2.8 A).
Vin
D = 1 -
Vout
TPS65161
TPS65161A, TPS65161B
www.ti.com SLVS617E –APRIL 2006–REVISED MARCH 2013
Table 3. Output Capacitor Selection (Boost Converter)
CAPACITOR VOLTAGE RATING COMPONENT SUPPLIER
22 μF/1812 16 V Taiyo Yuden EMK432BJ226MM
Rectifier Diode Selection (Boost Converter)
To achieve high efficiency, a Schottky diode should be used. The reverse voltage rating should be higher than
the maximum output voltage of the converter. The average rectified forward-current rating needed for the
Schottky diode is calculated as the off-time of the converter times the maximum switch current of the TPS65161:
Usually, a Schottky diode with 2-A maximum average rectified forward-current rating is sufficient for most
applications. Secondly, the Schottky rectifier has to be able to dissipate the power. The dissipated power is the
average rectified forward current times the diode forward voltage.
P
D
= I
avg
× V
F
= Isw × (1 - D) × V
F
(with Isw = minimum switch current of the TPS65161 (2.8 A).
Table 4. Rectifier Diode Selection (Boost Converter)
CURRENT RATING
Vr V
forward
R
θJA
SIZE COMPONENT SUPPLIER
I
avg
3 A 20 V 0.36 at 3 A 46°C/W SMC MBRS320, International Rectifier
2 A 20 V 0.44 V at 3 A 75°C/W SMB SL22, Vishay Semiconductor
2 A 20 V 0.5 at 2 A 75°C/W SMB SS22, Fairchild Semiconductor
Setting the Output Voltage and Selecting the Feedforward Capacitor (Boost Converter)
The output voltage is set by the external resistor divider and is calculated as:
Across the upper resistor, a bypass capacitor is required to achieve a good load transients response and to have
a stable converter loop. Together with R1, the bypass capacitor Cƒƒ sets a zero in the control loop. Depending
on the inductor value, the zero frequency needs to be set. For a 6.8-μH or 10-μH inductor, f
z
= 10 kHz and for a
22-μH inductor, f
z
= 7 kHz.
A value coming closest to the calculated value should be used.
Compensation (COMP) (Boost Converter)
The regulator loop can be compensated by adjusting the external components connected to the COMP pin. The
COMP pin is the output of the internal transconductance error amplifier. A single capacitor connected to this pin
sets the low-frequency gain. Usually, a 22-nF capacitor is sufficient for most of the applications. Adding a series
resistor sets an additional zero and increases the high-frequency gain. The following formula calculates at what
frequency the resistor increases the high-frequency gain.
Lower input voltages require a higher gain and therefore a lower compensation capacitor value.
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