Datasheet

SLUU111 – June 2002
8
1-MHz, 3.3-V, High-Efficiency Synchronous Buck Converter With TPS43000 PWM Controller
2.6 Current Limiting
Two types of current limiting can be selected from the controller. Detailed information is
available in the datasheet (TI Literature No. SLUS489). A jumper, JP2, is used to choose
different current limiting. By tying the CCS pin to VIN, the controller enters pulse-by-pulse
current limiting and the current-limiting threshold is calculated by equation (6):
I
MAX
ǒ
p*p
Ǔ
+
150 mV
R
DS(on)
in which R
DS(on)
is the on-resistance of Q2. In this design, the threshold is approximately
2.3 A. This value may change with temperature.
By tying the CCS pin to ground, the controller enters hiccup-mode overcurrent limiting . The
current-limiting threshold is calculated in equation (7). The threshold in this case is
approximately 3.8 A. This value may change with temperature.
I
MAX
(
hu
)
+
250 mV
R
DS(on)
2.7 Voltage Sense Resistor
R1 and R6 operate as the output voltage divider. The internal reference voltage is 0.8 V. The
relationship between the output voltage and divider is described in equation (8).
V
REF
R6
+
V
OUT
R1 ) R6
With an R1 value of 100 kΩ and 3.3-V voltage regulation, R6 is calculated at 32.4 kΩ.
(6)
(7)
(8)