Datasheet

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Modulator Frequency Setting (Terminal R
mod
)
Ground Terminal (PGND)
Enable Terminal (ENABLE)
Bootstrap Terminals (Cboot1 and Cboot2)
Functional Modes
Clock Modulator
Buck/Boost Transitioning
TPIC74100-Q1
BUCK/BOOST SWITCH-MODE REGULATOR
SLIS125 DECEMBER 2006
See the converter efficiency plots in the Typical Characteristics section to determine power dissipation.
The R
mod
terminal adjusts the clock modulator frequency. A resistor of R
mod
= 12 k generates a modulation
frequency of 28 kHz. The modulator function may be disabled by connecting R
mod
to GND and the device
operates with the nominal frequency. The modulator function cannot be activated during IC operation, only at IC
start-up.
The PGND terminal is the power ground for the device.
The ENABLE terminal allows the enabling and disabling of the switch mode regulator. A maximum of 40 V may
be applied to this terminal to enable the device and increasing it above the V
(driver)
input voltage does not affect
the device operation.
The functionality of the ENABLE terminal is described in the following table:
ENABLE Function
0 Vreg is off.
Open Undefined
1 Vreg is on.
An external bootstrap capacitor is required for driving the internal high-side MOSFET switch. A 4.7-nF ceramic
capacitor is typically required.
To minimize EMI issues associated with the switch-mode regulator, the device offers an integrated clock
modulator. The function of the clock modulator is to modulate the switching frequency and to distribute the
energy over the wave band.
The average switching frequency is 440 kHz (typical) and varies between 330 kHz and 550 kHz at a rate set by
the R
mod
resistor. A typical value of 12 k on the R
mod
terminal relates to a 28-kHz modulation frequency. The
clock modulator function can only be activated during IC start-up, not during IC operation.
The equation for the modulation frequency is as follows:
f
(mod)
(Hz) = (–2.2 × R
mod
) + 54.5 kHz, when R
mod
= 8 k to 16 k
The operation mode switches automatically between buck and boost modes depending on the input voltage of
V
(driver)
and output load conditions. During start up, when V
(driver)
is less than 5.8 V (typical), the device starts in
boost mode and continues to run in boost mode until V
(driver)
exceeds 5.8 V; at which time, the device switches
over to buck mode. In buck mode, the device continues to run in buck mode until it is required to switch back to
boost to hold regulation. This crossover window to switch to boost mode is when V
(driver)
is between 5.8 V and
5 V and depends on the loading conditions. When V
driver
drops below 5.8 V but the device is holding regulation
(~2%), the device remains in buck mode. However, when V
(driver)
is within the 5.8-V to 5-V window and V
OUT
drops to 4.9 V, the device crosses over to boost mode to hold regulation. In boost mode, the device remains in
boost mode until V
(driver)
exceeds 5.8 V; at which time, the device enters the buck mode. When the device is
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