UC1846-SP_15 Datasheet, PDF (15/29 Pages) Texas Instruments – Current-Mode PWM Controller

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8 Application and Implementation
UC1846-SP
SLUS871C – JANUARY 2009 – REVISED OCTOBER 2015
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
UC1846-SP can be used as a controller to design various topologies such as push-pull, half-bridge, full bridge,
and flyback.
The following sections highlight the topologies for oscillators, error amplifiers, and parallel configurations
(paralleling two EVMs).
8.2 Typical Applications
8.2.1 Oscillator Circuit Application
V_REF
9
Comp
Sawtooth
8
(Pin 8)
7.5 mA
R_T
Oscillator
C_T
(Pin 10)
10
Sync
Output Deadtime (τ_d)
A. Output deadtime is determined by the external capacitor, CT, according to the formula:
W_d (µs)
145CT (µF)
,' ±
ID
3.6
RT (k:)
(4)
B. ID = Oscillator discharge current at 25°C is typically 7.5.
C. For large values of ⁹d ^{(µs)  145CT (µF)}
D. Oscillator frequency is approximated by the formula:
¦_T
N+]
|
RT
2.2
(k:) u CT
(µF)
(5)
Figure 8. Oscillator Circuit
8.2.1.1 Design Requirements
DESIGN PARAMETER
Oscillator frequency = 200 kHz
Dead time, Td = 75.8 ns
Table 1. Design Parameters
EXAMPLE VALUE
R_T = 10 kΩ, C_T = 1 nF
R_T = 10 kΩ C_T = 1 nF
REFERENCE
Equation 4, Figure 8
Equation 5, Figure 8
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