DS6550A Datasheet, PDF (13/16 Pages) Richtek Technology Corporation – Synchronous DC-DC Step-Down Controller with 5V LDO

RT6550A
Table 1. Operation Mode Truth Table
Mode
LDO Over
Current Limit
Run
Over-Voltage
Protection
Under-Voltage
Protection
Discharge
Condition
Comment
LDO < UVLO threshold
Transitions to discharge mode after VIN POR. LDO5
remains active.
EN = high, VOUT is enabled
Normal Operation.
Either output >113% of the nominal level.
LGATE is forced high. LDO5 is active. Exit by VIN
POR or by toggling EN.
Either output < 52% of the nominal level Both UGATE and LGATE are forced low and enter
after 1.3ms time-out expires and output is discharge mode. LDO5 is active. Exit by VIN POR or
enabled
by toggling EN.
Either
mode
output
is
still
high
in shutdown
During discharge mode, there is one path to
discharge the output capacitors’ residual charge to
GND via an internal switch.
Shutdown
VIN > POR, VEN < 0.4V
LDO5 and VO_DIS discharge
Thermal
Shutdown
TJ > 150°C
All circuitries are off. Exit by VIN POR.
EN
OFF
ON
Table 2. Enabling State (RT6550A)
LDO5
OFF
PWM Controller (5VOUT)
OFF
ON
ON
VIN
EN
LDO5
5V VOUT
VIN POR threshold
EN threshold
VREG5 UVLO threshold
Start-Up Time
Soft-Start Time
Figure 4. Timing
Output Voltage Setting (FB)
Connect a resistive voltage divider at the FB pin between
V_OUT and GND to adjust the output voltage between 2V
and 5.5V (Figure 5). The recommended R2 is between
10kΩ to 20kΩ, and solve for R1 using the equation below:
V_{OUT (valley)}

V_FB



1
+
 R1
 _R2  
where V_FB is 2V (typ.).
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6550A-00 September 2016
V_IN
UGATE
PHASE
LGATE
FB
GND
VOUT
R1
R2
Figure 5. Setting V_OUT with a resistive voltage divider
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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