TPS40170-Q1_15 Datasheet, PDF (36/51 Pages) Texas Instruments – TPS40170-Q1 4.5-V to 60-V, Wide-Input, Synchronous PWM Buck Controller

TPS40170-Q1
SLVSB90B – JANUARY 2012 – REVISED DECEMBER 2014
www.ti.com
8.2.2.14 SCP Multiplier Selection (R5)
The TPS40170-Q1 controller uses a multiplier (A_OC) to translate the low-side overcurrent protection into a high-
side R_DS(on) pulse-by-pulse short-circuit protection. Ensure that Equation 41 is true.
(( )) _AOC
>
I_OCP(min)
I_OCP(min)
+
+
1
2
´
I_RIPPLE
1
2
´
I_RIPPLE
´ ^RDS(on)Q1
R_DS(on)Q2
=
8A +
8A +
1
2
1
2
´ 1.86
´ 1.86
A
A
´
11 mW
7.6 mW
= 1.45
(41)
A_OC = 3 is selected as the next-greater A_OC. The value of R5 is set to 10 kΩ.
8.2.2.15 Feedback Divider (R10, R11)
The TPS40170-Q1 controller uses a full operational amplifier with an internally fixed 0.6-V reference. The value
of R11 is selected between 10 kΩ and 50 kΩ for a balance of feedback current and noise immunity. With the
value of R11 set to 20 kΩ, the output voltage is programmed with a resistor divider given by Equation 42.
R10
=
V_FB ´ R11
(V_OUT - V_FB
)
=
0.600 V ´ 20.0kW
(5.0 V - 0.600 V)
=
2.73 kW
»
2.74 kW
(42)
8.2.2.16 Compensation: (R4, R13, C13, C14, C21)
Using the TPS40k Loop Stability Tool for a 60-kHz bandwidth and a 50° phase margin with an R10 value of 20
kΩ, the following values are obtained. The tool is available from the TI Web site, Literature Number SLUC263.
• C21 = C1 = 1500 pF
• C13 = C2 = 8200 pF
• C14 = C3 = 220 pF
• R13 = R2 = 511 Ω
• R4 = R3 = 3.83 kΩ
8.2.3 Application Curves
Figure 36 shows an efficiency graph for this design with 10-V to 60-V input and 5-V at 6-A output. Figure 37
shows a 24-V to 5-V at 6-A loop response, where V_IN = 24 V and I_OUT = 6 A, yielding 58-kHz bandwidth, 51°
phase margin. Figure 38 shows the output ripple 20 mV/div, 2 µs/div, 20 MHz bandwidth.
100
95
90
85
80
V_IN = 10 V
V_IN = 12 V
V_IN = 24 V
75
V_IN = 36 V
V_IN = 48 V
V_IN = 60 V
70
0
1
2
3
4
5
6
Load Current (A)
100
80
60
40
20
0
−20
−40
−60
0.1
Gain
Phase
1
10
100
Frequency (kHz)
225
180
135
90
45
0
−45
−90
−135
1000
Figure 36. Efficiency vs Load Current
Figure 37. Loop Response
36
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