Applications Information: continued
5V
MMUN2111T1 (SOT-23)
5
8
SS
CS5150
V
FFB
IN4148
Shutdown
Input
Figure 14: Implementing shutdown with the CS5150.
Trace 3 = 12V Input (V
) and V
) (10V/div.)
CC1
CC2
Trace 4 = 5V Input (2V/div.)
Trace 1 = Regulator Output Voltage (1V/div.)
Trace 2 = Power Good Signal (2V/div.)
External Power Good Circuit
An optional Power Good signal can be generated through
the use of four additional external components (see Figure
15). The threshold voltage of the Power Good signal can be
adjusted per the following equation:
Figure 16: CS5150 demonstration board during power up. Power Good
signal is activated when output voltage reaches 1.70V.
Selecting External Components
The CS5150 can be used with a wide range of external
power components to optimize the cost and performance of
a particular design. The following information can be used
as general guidelines to assist in their selection.
(R1 + R2) × 0.65V
VPower Good
=
R2
This circuit provides an open collector output that drives
the Power Good output to ground for regulator voltages
less than VPower Good
.
NFET Power Transistors
Both logic level and standard MOSFETs can be used. The
reference designs derive gate drive from the 12V supply
which is generally available in most computer systems and
utilize logic level MOSFETs. A charge pump may be easily
implemented to support 5V only systems. Multiple
MOSFETs may be paralleled to reduce losses and improve
efficiency and thermal management.
5V
R3
Power Good
PN3904
10k
R1
10k
PN3904
V
OUT
Voltage applied to the MOSFET gates depends on the
application circuit used. Both upper and lower gate driver
outputs are specified to drive to within 1.5V of ground
when in the low state and to within 2V of their respective
bias supplies when in the high state. In practice, the MOS-
FET gates will be driven rail to rail due to overshoot caused
by the capacitive load they present to the controller IC. For
the typical application where VCC1 = VCC2 = 12V and 5V is
used as the source for the regulator output current, the fol-
lowing gate drive is provided;
CS5150
R2
6.2k
Figure 15: Implementing Power Good with the CS5150.
VGATE(H) = 12V - 5V = 7V, VGATE(L) = 12V (see Figure 17).
10
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
