L6738ATR STMicroelectronics, L6738ATR Datasheet - Page 17

• Manufacturer Part Number: L6738ATR
• Description: IC PWM CTLR 1PH STPDN 16-VFQFPN
• Manufacturer: STMicroelectronics

Specifications of L6738ATR

• Frequency - Max: 220kHz
• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Duty Cycle: 100%
• Voltage - Supply: 5 V ~ 12 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 32-VFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-11012-2

L6738A
6.1
For proper operations, VCC needs to be at least 1.5 V higher than the programmed output
voltage.
Table 6.
Overcurrent
The overcurrent function protects the converter from a shorted output or overload, by
sensing the output current information across the inductor DCR. This method reduces cost
and enhances converter efficiency by avoiding the use of expensive and space-consuming
sense resistors.
The inductor DCR current sense is implemented by comparing and monitoring the
difference between the CSP and CSN pins. If the monitored voltage is bigger than the
internal thresholds, an overcurrent event is detected.
DCR current sensing requires time constant matching between the inductor and the reading
network:
The L6738A monitors the voltage between CSP and CSN, when this voltage exceeds the
OC threshold, an overcurrent is detected. The IC works in constant current mode, turning on
the low-side MOSFET immediately while the OC persists and, in any case, until the next
clock cycle. After seven consecutive OC events, overcurrent protection is triggered and the
IC latches.
When overcurrent protection is triggered, the device turns off both LS and HS MOSFETs in
a latched condition.
To recover from an overcurrent protection triggered condition, VCC power supply or EN
must be cycled.
For proper current reading, the CSN pin must be filtered by 100 nF (Typ.) MLCC to GND.
Undervoltage (UV)
Overcurrent (OC)
Overvoltage
PGOOD
L6738A
(OV)
L6738A Protection at a glance.
VSEN = +12.5 % above reference.
Action: IC Latch; LS=ON until VSEN = 50 % of Vref; PGOOD = GND.
Action (EN=0): IC Latch; LS=ON; reset by EN rising edge (PreOVP).
VSEN = -25 % below reference.
Action: IC Latch; HiZ; PGOOD = GND.
Action (SS): SS reset (VIN Detection).
PGOOD is set to zero whenever VSEN falls outside the +12.5 % / -25 % of Vref.
Action: PGOOD transition coincides with OV/UV protection set.
Current Monitor across Inductor DCR.
Action: 1st Threshold (20 mV): IC latch after 7 consecutive constant current
events.
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DCR
L
=
Doc ID 18134 Rev 1
R
⋅
C
⇒
V
CSP-CSN
Comments
Output voltage setting and protections
=
DCR
⋅
I
OUT
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