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Partno	Mfg	Dc	Qty	Available	Descript
L5987	ST	N/a	830	avai	3 A step-down switching regulator
L5987A	ST	N/a	3	avai	3 A step-down switching regulator
L5987ATR	ST	N/a	35688	avai	3 A step-down switching regulator

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L5987-L5987A-L5987ATR
3 A step-down switching regulator
May 2014 DocID14972 Rev 4 1/40
L5987
3 A step-down switching regulator
Datasheet - production data
Features 3 A DC output current 2.9 V to 18 V input voltage Output voltage adjustable from 0.6 V 250 kHz switching frequency, programmable
up to 1 MHz Internal soft-start and inhibit Low dropout operation: 100% duty cycle Voltage feedforward Zero load current operation Overcurrent and thermal protection VFQFPN 3 x 3 -8L and HSOP8 package
Applications Consumer: STB, DVD, DVD recorder, car
audio, LCD TV and monitors Industrial: PLD, PLA, FPGA, chargers Networking: XDSL, modems, DC-DC modules Computer: optical storage, hard disk drive,
printers, audio/graphic cards LED driving
Description
The L5987 is a step-down switching regulator
with a 3.5 A (minimum) current limited embedded
Power MOSFET, so it is able to deliver an up to
3 A current to the load depending on the
application conditions.
The input voltage can range from 2.9 V to 18 V,
while the output voltage can be set starting from
0.6 V to VIN. Having a minimum input voltage of
2.9 V, the device is suitable also for a 3.3 V bus.
Requiring a minimum set of external components,
the device includes an internal 250 kHz switching
frequency oscillator that can be externally
adjusted up to 1 MHz.
The VFQFPN8 and the HSOP packages with an
exposed pad allow reducing the RthJA down to
60 °C/W and 40 °C/W respectively.

Figure 1. Application circuit
Contents L5987
2/40 DocID14972 Rev 4
Contents Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1 Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.3 Error amplifier and compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.4 Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.5 Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.6 Hysteretic thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.7 Maximum DC output current L5987A (HSOP8) . . . . . . . . . . . . . . . . . . . . 24
5.8 Maximum DC output current L5987 (VFQFPN) . . . . . . . . . . . . . . . . . . . . 24 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1 Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.4.1 Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.4.2 Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.5 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
6.6 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.7 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
DocID14972 Rev 4 3/40
L5987 Contents Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Pin settings L5987
4/40 DocID14972 Rev 4
1 Pin settings
1.1 Pin connection
1.2 Pin description

Table 1. Pin description
DocID14972 Rev 4 5/40
L5987 Maximum ratings
2 Maximum ratings

3 Thermal data

Table 2. Absolute maximum ratings
Table 3. Thermal data Package mounted on demonstration board.