
G009
1k
10
0.01
1
100
I
–
D
ra
in
-t
o
-So
u
rce
C
u
rre
n
t
–
A
D
S
0.1
0.01
0.1
10
100
1
Single Pulse
R
= 94C/W (min Cu)
θ
JA
1ms
10ms
100ms
1s
DC
Area Limited
by R
DS(on)
V
– Drain-to-Source Voltage – V
DS
2
ENTHRESH
VCC
1
2
R
V
R
=
+
OUT
VCC
CHG
C
V
t
I
D =
SLVSAL2C
– JANUARY 2011 – REVISED MAY 2011
Figure 35. CSD16403Q5 SOA Curve
STEP 5. Calculate the Retry-Mode Duty Ratio
In retry mode, the TPS24711/13 is on for one charging cycle and off for 16 charge/discharge cycles, as can be
seen in Figure 32. The first CT charging cycle is from 0 V to 1.35 V, which gives 7.56 ms. The first CT discharging cycle is from 1.35 V to 0.35 V, which gives 5.6 ms. Therefore, the total time is 7.56 ms + 33
× 5.6 ms = 192.36
ms. As a result, the retry mode duty ratio is 7.56 ms/192.36 ms = 3.93%.
STEP 6. Select R1 and R2 for UV
Next, select the values of the UV resistors, R1 and R2, as shown in the typical application diagram on the front
page. From the TPS24710/11/12/13 electrical specifications, VENTHRESH = 1.35 V. The VUV is the undervoltage
trip voltage, which for this example equals 10.7 V.
(12)
Assume R1 is 130 k and use Equation 12 to solve for the R2 value of 18.7 k. STEP 7. Choose RGATE, R4, R5 and C1
In the typical application diagram on the front page, the gate resistor, RGATE, is intended to suppress
high-frequency oscillations. A resistor of 10
Ω will serve for most applications, but if M1 has a CISS below 200 pF,
then 33
Ω is recommended. Applications with larger MOSFETs and very short wiring may not require RGATE. R4
and R5 are required only if PGb and FLTb are used; these resistors serve as pullups for the open-drain output
drivers. The current sunk by each of these pins should not exceed 2 mA (see the RECOMMENDED
OPERATING CONDITIONS table). C1 is a bypass capacitor to help control transient voltages, unit emissions,
and local supply noise while in the disabled state. Where acceptable, a value in the range of 0.001
μF to 0.1 μF
is recommended.
ALTERNATIVE DESIGN EXAMPLE: GATE CAPACITOR (dV/dt) CONTROL IN INRUSH MODE
The TPS24710/11/12/13 can be used in applications that expect a constant inrush current. This current is
controlled by a capacitor connected from the GATE terminal to GND. A resistor of 1 k
placed in series with this
capacitor will prevent it from slowing a fast-turnoff event. In this mode of operation, M1 operates as a source
follower, and the slew rate of the output voltage approximately equals the slew rate of the gate voltage (see
To implement a constant-inrush-current circuit, choose the time to charge,
(13)
where COUT is the output capacitance, VVCC is the input voltage, and ICHG is the desired charge current. Set PLIM
to a value greater than VVCC × ICHG to prevent power limiting from affecting the desired current.
Copyright
2011, Texas Instruments Incorporated
25