TPS43340-Q1 Datasheet, PDF (29/38 Pages) Texas Instruments – LOW IQ, 30 μA, HIGH VIN QUAD-OUTPUT POWER SUPPLY

TPS43340-Q1
www.ti.com
SLVSB16B – NOVEMBER 2011 – REVISED APRIL 2012
Buck3 Component Selection
Duty Cycle
1.8
D = = 0.36
5
(26)
Inductor Selection L_BUCK3
L_BUCK3
=
3.7 W
400 kHz
= 9.25 mH
(27)
Use 8.2 µH.
Inductor Ripple Current
DIL_RIPPLE
=
1.8 V
400 kHz x 8.2 mH
x
æçççè_{1 -}
1.8 V
5V
ö÷ø÷÷
= 0.46 A
(28)
Output Capacitor C_O
C_O
=
2 x 4.6 A
400 kHz x 0.075 V
= 30.7 mF
(29)
Use 100 µF.
Input Capacitor C_I
0.25 x 2.2 A
C_I = _{400 kHz x 0.05 V} = 5.76 mF
(30)
Use 10 µF.
Internal High-Side MOSFET
(2.2
A)²
x
0.28W
x
0.36
+
æçççè ₅
V
x 2.2
2
A _{÷ö÷÷ø}
x (20 ns + 20 ns) x 400 kHz = 0.58 W
(31)
Internal Low-Side MOSFET
(2.2 A)² x 0.28W x (1 - 0.36) 0.6 x 2.2 A x (2 x 20 ns) x 400 kHz = 0.89 W
(32)
Power Dissipation
The power dissipation is dependent on the MOSFET drive current and input voltage. The drive current is
proportional to the total gate charge of the external MOSFET.
Power Dissipation BUCK1 and BUCK2 (VBUCK1 and VBUCK2)
P_{Gate drive} = Qg x V_VREG x f_sw (Watts)
(33)
Assuming both high and low side MOSFETs are identical in a synchronous configuration, the total power
dissipation per BUCK is
P_BUCK1 = 2 x Qg x f_sw x V_VREG (Watts)
(34)
Power Dissipation of the Buck Converter (VBUCK3)
High-Side Switch
The power dissipation losses are applicable for positive output currents:
P_HS-CON = I_OUTr² x R_DS(on) x (V_OUT/V_IN) (Conduction losses)
(35)
P_{HS_SW} = ½ x VSUP x Iout x (tr + tf) x f_SW (Switching losses)
(36)
P_{HS_Gate} = 1nC x f_sw (Gate drive losses, valid at V_VREG = 5.8V, V_SUP = 4V)
(37)
P_{HS_Total} = P_HS-CON + P_{H_SW} + P_{HS_Gate}
(38)
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