TPS54352PWPRG4 Datasheet, PDF (8/37 Pages) Texas Instruments – 4.5-V TO 20-V INPUT, 3-A OUTPUT SYNCHRONOUS PWM

TPS54352, TPS54353
TPS54354, TPS54355
TPS54356, TPS54357
SLVS519A − MAY 2004 − REVISED OCTOBER 2004
FUNCTIONAL BLOCK DIAGRAM
BOOT
www.ti.com
VIN
PH
320 kΩ
UVLO
125 kΩ(1) _1.2V
UVLO
Hiccup
Current Limit
SYNC
RT
2x Oscillator
PWM Ramp
(FeedFoward)
Bias + Drive
Regulator
VBIAS
COMP
Z1
VSENSE
Z2
VBIAS2
Z3
Z4
Error
Amplifier
Reference
System
ENA
5 µA
PWM ^{S Q}
Comparator
R
Z5
Thermal
Shutdown
UVLO
Hiccup
Timer
Hiccup
Adaptive Deadtime
and
Control Logic
VBIAS
VSENSE
97% Ref
UVLO
Rising
Edge
Delay
LSG
PWRGD
TPS5435X
(1) _{75 kΩ for the TPS54357}
DETAILED DESCRIPTION
POWERPAD VBIAS
PGND
AGND
Undervoltage Lockout (UVLO)
The undervoltage lockout (UVLO) system has an internal
voltage divider from VIN to AGND. The defaults for the
start/stop values are labeled VIN and given in Table 1. The
internal UVLO threshold can be overridden by placing an
external resistor divider from VIN to ground. The internal
divider values are approximately 320 kΩ for the high side
resistor and 125 kΩ for the low side resistor. The divider
ratio (and therefore the default start/stop values) is quite
accurate, but the absolute values of the internal resistors
may vary as much as 15%. If high accuracy is required for
an externally adjusted UVLO threshold, select lower value
external resistors to set the UVLO threshold. Using a 1-kΩ
resistor for the low side resistor (R2 see Figure 1) is
recommended. Under no circumstances should the UVLO
pin be connected directly to VIN.
Table 1. Start/Stop Voltage Threshold
TPS54352−6
VIN (Default)
TPS54357
UVLO
START VOLTAGE THRESHOLD
4.49
6.65
1.24
STOP VOLTAGE THRESHOLD
3.69
5.45
1.02
The equations for selecting the UVLO resistors are:
R1
+
VIN(start)
1.24 V
1 kW
* 1kW
(1)
VIN(stop)
+
(R1
)
1 kW)
1 kW
1.02 V
(2)
8